canada; stormwater management guidelines - halifax

Stormwater Management Guidelines March 2006

Halifax Regional Municipality

05-4680-0400

Submitted by:

Dillon Consulting Limited

Executive Summary The purpose of the Stormwater Management Guidelines is to describe a set of criteria for the design of stormwater management practices to protect the environment of the Halifax Regional Municipality from adverse impacts of urban storm water runoff. The Guidelines describe Best Management Practices (BMPs), techniques and methods of managing stormwater drainage for adequate control and pollutant reduction by using the most effective and practical means that are economically acceptable to the community. The ultimate selection of recommended stormwater BMPs is dependent on the tributary-specific and in some instances, the reach-specific characteristics, sensitivities and functionalities present within the watershed. Ideally, all BMP design criteria should be based on recommendations developed as part of a comprehensive watershed or subwatershed plan prepared for the subject location’s basin. These plans are produced through the study of the environmental and land use features of a watershed. The purpose of the plan is to identify those areas that should be protected and preserved as part of the land use planning process, to evaluate the impact of future land use changes and to develop criteria to mitigate potential cumulative impacts in the watershed. In the absence of watershed/subwatershed study recommendations, the Guidelines provide general design criteria that should be used in HRM for quantity, quality, erosion, and base flow control. The use of this unified approach should result in a design of stormwater management practices that would meet the flood, water quality, erosion control and groundwater recharge criteria adopted until the completion of the watershed and subwatershed studies. The overall objectives of introducing BMPs are to minimize the adverse effects on and off the development site. An important part of the selection of BMPs is to preserve the sensitive, natural features and to develop a new stormwater system that can reproduce, as closely as possible, the natural conditions of the undeveloped state. This approach stresses the importance of preserving natural storage, infiltration and pollutant filtering functions where feasible, thus reducing the lifecycle cost for stormwater management and minimizing the need for costly capital improvements to the existing system. There is no single BMP that suits every development, and a single BMP cannot satisfy all stormwater control objectives. Therefore, cost-effective combinations of BMPs may be required that will achieve the objectives. These Guidelines are intended to be a tool to be used by HRM to guide developers and their designers toward the selection and design of appropriate stormwater management facilities. It will also be used by HRM staff for the review and design of facilities. It is intended that it will be used in combination with the Regional Plan and other planning and design tools already in place to achieve HRM’s long-term goals and objectives.

Halifax Regional Municipality Stormwater Management Guidelines March 2006


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Table of Contents

1.0 Introduction .........................................................................................................1-1

2.0 Legislative Authority...........................................................................................2-1

3.0 Goals and Objectives...........................................................................................3-1

4.0 Alternative Best Management Practices ...........................................................4-1 4.1 Background.......................................................................................................... 4-1 4.2 Urban Stormwater Management Alternatives ..................................................... 4-2

4.2.1 Source Control Measures ........................................................................ 4-2 4.2.2 Conveyance Control Measures ................................................................ 4-5 4.2.3 End of Pipe Measures .............................................................................. 4-5 4.2.4 Municipal Measures................................................................................. 4-8

4.3 Summary of Rural Stormwater Management Practices..................................... 4-10 4.4 Emerging Technologies ..................................................................................... 4-13

5.0 Design Criteria For Best Management Practices .............................................5-1 5.1 Introduction.......................................................................................................... 5-1 5.2 Design Criteria for Water Quantity Control ........................................................ 5-1 5.3 Design Criteria for Water Quality Control .......................................................... 5-2 5.4 Design Criteria for Erosion Control..................................................................... 5-6 5.5 Recharge and Base Flow Maintenance ................................................................ 5-6 5.6 Municipal Infrastructure Criteria ......................................................................... 5-8 5.7 Pollutant Loads .................................................................................................. 5-10 5.8 Exemptions From Runoff Control ..................................................................... 5-12

6.0 Selection of Best Management Practices ...........................................................6-1 6.1 Introduction.......................................................................................................... 6-1 6.2 Treatment Train ................................................................................................... 6-9 6.3 Selection Process ............................................................................................... 6-10 6.4 Stormwater Management for Infill Developments ............................................ 6-15 6.5 Retrofitting......................................................................................................... 6-16 6.6 Example of Pre and Post Development Pollutant Load Water Quality

Computation....................................................................................................... 6-17

7.0 BMP Design Fact Sheets .....................................................................................7-1



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8.0 Operation and Maintenance of BMPs...............................................................8-1 8.1 Introduction.......................................................................................................... 8-1 8.2 Goal, Objectives and Policies .............................................................................. 8-1 8.3 Past Performances of Stormwater Management Facilities .................................. 8-2 8.4 Design Review of BMP Facilities........................................................................ 8-3 8.5 Inspection During Construction........................................................................... 8-6 8.6 Operation and Maintenance Tasks after Construction......................................... 8-8 8.7 Monitoring Prior to Accepting the BMP Facility .............................................. 8-13 8.8 Public Information ............................................................................................. 8-15

9.0 Erosion and Sediment Control at Construction Sites ......................................9-1 9.1 Background.......................................................................................................... 9-1 9.2 Legislative Framework for Erosion and Sediment Control ................................. 9-4 9.3 Nova Scotia Erosion and Sediment Control Requirements ................................. 9-5

10.0 Submissions by Developers...............................................................................10-1



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List of Figures: Figure 5-1 Example of Sizing Permanent Pool Storage for Water Quality Control ............. 5-5 Figure 8-1 Annual Sediment Deposition Estimates– m3/ha ................................................ 8-11 Figure 9-1 Observed Sediment Accumulation in Richmond Hill Wet Ponds ....................... 9-1 List of Tables: Table 4-1 Summary of Most Frequently Used BMPs.......................................................... 4-2 Table 4-2 Summary of Rural Stormwater Management Practices..................................... 4-10 Table 4-3 List of Stormwater Management Products ........................................................ 4-13 Table 5-1 Classification of Downstream Habitat ................................................................. 5-3 Table 5-2 Risk to Fish Habitat by Increase in TSS .............................................................. 5-3 Table 5-3 Summary of Design Criteria ................................................................................ 5-7 Table 5-4 Summary of Existing HRM Storm Drainage Design Guidelines ........................ 5-8 Table 5-5 Mean Pollutant Concentration Generated by Different Land Uses ................... 5-11 Table 6-1 Stormwater Management Best Management Practices........................................ 6-2 Table 6-2 Treatment Train Components .............................................................................. 6-9 Table 6-3 Examples of Treatment Train Alternatives........................................................ 6-10 Table 6-4 Selection of Design Criteria............................................................................... 6-11 Table 6-5 Stormwater Management BMPs – Initial Assessment Matrix........................... 6-12 Table 6-6 Capability Matrix for Selected BMPs................................................................ 6-14 Table 6-7 List of Alternative BMPs Suitable for Infill Development................................ 6-16 Table 6-8 Total Annual Pollutant Load Generated by the Site in kg/year ......................... 6-18 Table 6-9 Example of Pre and Post Development Wter Quality Estimates....................... 6-19 Table 7-1 List of BMP Fact Sheets Presented in Appendix I .............................................. 7-1 Table 8-1 Municipal Input to Stormwater Management ...................................................... 8-2 Table 8-2 Performance Statistics of Maryland BMPs.......................................................... 8-3 Table 8-3 Example of POperation and Maintenance Schedules for Stormwater

Management BMPs............................................................................................ 8-12 Table 8-4 Typical Stormwater BMPs Monitoring Functions............................................. 8-14 Table 9-1 Frequently Used Erosion and Control Measures ................................................. 9-4 Appendices: Appendix A Stormwater Management and Erosion Control Municipal By-law Example Appendix B International Stormwater Management Practices Appendix C Rural Stormwater Management Practices Appendix D Typical Watershed Study Terms of Reference Appendix E Rainfall Analyses Appendix F Probabilistic Model for Sizing Wetponds and Wetlands Appendix G HRM Municipal Services Systems Design Guidelines - Drainage Design Appendix H HRM Storm Sewer By-Law Appendix I Fact Sheets



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Acronyms BMP Best Management Practice HRM Halifax Regional Municipality MGA Municipal Government Act MSS Municipal Services System NP Not practical NSEL Nova Scotia Environment and Labour OP Operating Procedure SWM Stormwater Management SUDS Sustainable Urban Drainage Systems TN Total Nitrogen TP Total Phosphorus TSS Total Suspended Solids US United States USEPA United States Environmental Protection Agency


Dillon Consulting Limited - 1-1 -

1.0 Introduction

The Halifax Regional Municipality (HRM) spans a geographic area of 5,600 square kilometres and has a population of approximately 350,000. HRM was formed in 1996 through the amalgamation of four pre-existing municipalities. The amalgamation resulted in HRM inheriting various policies and procedures relating to stormwater management (SWM). In order to achieve consistency in its approach to SWM, HRM embarked on the development of the Stormwater Management Guidelines. Since the amalgamation of HRM, there has been an increased awareness of the potential negative environmental effects associated with the discharge of stormwater to watercourses. Due to the acknowledgement that SWM is becoming of increased importance to the protection of watercourses the Guidelines update HRMs approach to SWM as well as provide consistency. The purpose of the Stormwater Management Guidelines is to describe a set of criteria for the design of SWM practices to protect the environment of the Municipality from adverse impacts of urban storm water runoff. The Guidelines identify effective SWM practices for developments that: • will provide the required environmental protection; • will function appropriately over time; • are safe; • are easy to operate and maintain; and • will have public acceptance. The recommended guidelines are based on proven technology developed and used locally, across North America and Europe. It incorporates the latest practices presented in the Canadian InfraGuide developed by the Federation of Canadian Municipalities and the National Research Council. The Guidelines describe Best Management Practices (BMPs), techniques and methods of managing stormwater drainage for adequate control and pollutant reduction by using the most effective and practical means that are economically acceptable to the community. Generally, these are methods that attempt to replicate the natural runoff characteristics and infiltration components of an undeveloped system to the extent possible and reduce or prevent water quality degradation caused by urban development. The Guidelines are intended primarily for those professionals who are involved in the planning, design, review, operation and maintenance of SWM facilities. It is assumed that the readers have background knowledge in hydrology, drainage engineering, hydraulics, and flow and pollutant analyses.



2.0 Legislative Authority

One key to developing the Stormwater Management Guidelines is to understand the authority HRM has over stormwater management. The level of authority influences the extent to which a problem can be solved and the mechanisms that can be used to solve it. The Constitution Act, 1867, which allocates powers to the federal and provincial levels of government, has resulted in shared jurisdiction between Canada and the provinces over water, environmental protection and public health. However, the federal government has focused primarily on its constitutional responsibility for fisheries and navigation, and for waters that lie on or across international borders, while the provinces have assumed the primary responsibility for water management and drinking water safety. There is currently no federal legislation relating directly to stormwater. The Navigable Waters Protection Act, and the Fisheries Act are federal legislation related to infrastructure works where there is some potential for navigation or fisheries habitat impacts. The Navigable Waters Protection Act involves limiting actions that affect the ability to navigate a watercourse. Many of the watercourses within HRM could be considered navigable, but navigability is typically determined on a project basis. The Fisheries Act provides protection of fish and the natural environment systems that support fish. A municipal government could be charged under the Fisheries Act if it was found that stormwater-related discharges were deleterious to fish. The Constitution Act grants the provincial government jurisdiction over property and civil rights, and consequently over water and watercourses. Therefore the provinces have the most direct authority over environmental matters (with the exception of the Fisheries Act). The primary legislation enacted by the provincial government for the protection of the environment is the Environment Act. The Environment Act authorizes the Nova Scotia Environment and Labour (NSEL) to: • ensure the health and integrity of aquatic ecosystems, protect the habitat for animals and

plants, and provide for continued recreational benefits; • designate protected water areas to protect water supply sources; • approve, restrict or prohibit the alteration of watercourses; • make regulations respecting the uses of specified watercourses and the works which may

be permitted in or around watercourses; • administer an environmental assessment process, applicable to both public and private

projects. The Environment Act restricts HRM from discharging contaminants into the environment by requiring approvals for designated activities. The design, construction, operations and



maintenance of stormwater collection, pumping, storage and treatment systems are regulated through the Approvals required under the Environment Act. Construction of stormwater management facilities, as designated in the Environment Act under the Activities Designation Regulations, require approvals from NSEL under the Storm Drainage Works Approval Policy. This includes the construction, operation or reclamation of a storm drainage works including: i) storm collection systems and pumping stations; ii) retention or storage facilities; iii) treatment facilities; iv) outfalls. The Storm Drainage Works Approval Policy contains detailed requirements for the approval application. An approval is only granted if a number of criteria are met by the proposed facility, such as: • The owner ensures that the facility will be installed, used and operated to achieve compliance

with the approval; • The proposed works are acceptable to NSEL; • The owner will undertake all necessary investigations to ensure that the facility would not:

o create safety health hazards to the general public; o impair fish passage; o destroy aquatic habitat; or o degrade the water quality.

The authority of HRM for stormwater management is delegated from the Province under the Municipal Government Act (MGA). The MGA enables HRM to make by-laws for municipal purposes, and provides for authority to enforce those by-laws and charge offenders. The MGA further enables the Municipality with the primary responsibility for planning within its jurisdiction, through the use of municipal planning strategies and land use by-laws, consistent with interests and regulations of the Province. A municipal planning strategy may include land use planning restrictions to provide for stormwater management (e.g., by controlling development in flooding zones, in environmentally sensitive areas, on steep slopes, in wetlands, etc). Where a municipal planning strategy so provides, a land use by-law may also prescribe methods for controlling erosion and sedimentation during the construction of a development. HRM may also prescribe a subdivision by-law. Within the subdivision by-law the Municipality may provide minimum requirements for stormwater management. They may also require that the infrastructure be installed as part of the subdivision. The MGA further enables the Municipality to collect fees for stormwater management. The existing HRM by-laws and policies with respect to stormwater management are for the most part those of the four former Municipalities. The two main exceptions include the Municipal Services Systems (MSS) which detail the design requirements for stormwater infrastructure and the Wastewater Discharge By-law that regulates the quality of single point source discharges into



HRM sewers. The MSS specifies general guidelines for stormwater and erosion and sediment control, but the long-term quality of stormwater is not specified. The Wastewater Discharge Bylaw does specify quality limits, but there is no direction for how to achieve the limits. An example of a stormwater management and erosion control by-law is attached in Appendix A. These Guidelines are intended to be a tool that may be used by HRM to guide developers and their designers toward the appropriate management of stormwater. It is intended that it will be used in combination with the Regional Plan and other tools already in place to achieve the goals and objectives.



3.0 Goals and Objectives

Through various meetings with stakeholders during the Water Resource Management Study (Dillon 2002) and through ongoing communications with staff at HRM and the public, the Stormwater Management Guidelines have been developed to achieve the following goals: • To provide a consistency in standards by ensuring that the requirements for stormwater

management are the same for all areas within HRM; • Inclusion of stormwater management in planning so that proper resources are allocated

where necessary. For example, resources may involve allocating area for stormwater infrastructure or setting up cost sharing mechanisms to fund the infrastructure, testing and/or operation and maintenance;

• Installation of appropriate stormwater management infrastructure in all developments. This should also include a consideration of what may happen in the future within the watershed;

• Require that planning/design of developments is performed with environment sensitivity in mind to allow for the stormwater management to fit a given situation. This relates to the fact that there is no one solution for every situation. Ideally a watershed or sub watershed management plan will be prepared prior to any development so that the management can provide an adequate level of protection;

• Allowance for the use of new technologies in stormwater management as they are developed. It is understood that the technology must be proven to be effective in similar situations prior to being acceptable for HRM;

• Damage due to flooding must be minimized through stormwater management; • Combined with controlling the amount of water discharged, the nutrient (primarily

nitrogen and phosphorus) loading must be controlled where necessary; • Definition of the requirements for stormwater and erosion and sediment control for single

lot construction; and • Where possible, provide for the improvement of lake quality. This could involve

retrofitting existing developments and infrastructure to minimize the level of sedimentation or nutrient discharge into a watercourse;

In order to achieve these goals, the guidelines have the following basic objectives. The remainder of the document has been developed to meet these criteria. HRM should prepare watershed and sub watershed plans to identify sensitive watersheds and

apply an appropriate level of stormwater management; The Stormwater Management Guidelines must be implemented and enforced consistently

throughout HRM; The Stormwater Management Guidelines must require:

• pre-development hydrology and water quality be maintained or enhanced to the extent practical and that natural systems should be preserved and maintained;



• reduction in the concentration of sediments and contaminants being discharged into the storm sewer system and eventually into a receiving water to levels that are not harmful to the intended use of the receiving waters and shall not exceed current limits under the wastewater discharge by-law;

• reduction of peak storm discharges and volumes through a hierarchy of source, conveyance, and end-of-pipe control measures to reduce the risk of flooding and stream bank erosion in a watershed approach;

• consideration of emerging technologies for stormwater management with an emphasis on the importance of natural systems;

• require that developers investigate the cumulative effects of existing and future developments on the downstream environment;

• the institution of public education plan to inform storm sewer users of their potential effect on the environment.

• the application of erosion and sediment control measures to all development and construction approvals including lot level erosion and sediment control.

The stormwater management guidelines must direct design efforts to prevent future problems (i.e. promote prevention as opposed to remediation).

Since the submission of the 2002 report, a set of stormwater management policies have been incorporated in the Draft Regional Municipal Planning Strategy (May 2005). The Draft Regional Municipal Planning Strategy addresses the protection of watersheds that are designated for municipal water supply. It also addresses the issue of water quality monitoring for select lakes to detect change over time and other lakes under development pressure to track the progress of eutrophication.



4.0 Alternative Best Management Practices

4.1 Background

The following is a summary of alternative stormwater management practices used for controlling urban and rural runoff. The information presented is based on the latest technical literature and on experience in the planning, design, and construction of stormwater management facilities. Current practice with respect to operation and maintenance of facilities is also considered. A review of practices used in other jurisdictions is provided in Appendix B. In watersheds there is a limit to which urban development can proceed without causing severe damage to the natural systems. To limit the cumulative impact of urban development there may be a need to restrict the level of imperviousness in a watershed. Land use control measures could involve the control of the development type or a complete restriction of land use changes in a portion of the watershed. This chapter describes the current trend in urban developments which advocates the hierarchy of preferred alternatives: i) Source Controls. ii) Conveyance (system) Controls. iii) End of pipe Controls. iv) Miscellaneous Controls. Table 4-1 summarizes the latest techniques available to control urban runoff. The material contained in this section was developed for urban area development (residential/industrial/ commercial) with the philosophy that source controls be assessed first and end-of-pipe last. A separate rural stormwater management chapter is presented in Appendix C which describes the rural stormwater management alternatives. The Appendix first presents a general description followed by a table which summarizes the alternatives applicable for HRM sub-watersheds. It is important to note that the ultimate selection of recommended measures is dependent on the tributary-specific and in some instances, the reach-specific characteristics, sensitivities and functionalities present within the study area. Experience suggests that the best strategy in selecting suitable BMPs for a specific development is to avoid environmentally sensitive areas and consider the applicability of the site to accommodate the selected BMP. The selection of the appropriate alternative must be based not only on technical consideration such as applicability and cumulative effects, but also on acceptability by the public.



Table 4-1

Summary of Most Frequently Used BMPs

Urban Stormwater Management Alternatives

Source Control Conveyance Control End of Pipe Control Miscellaneous Housekeeping Controls

o Rooftop Runoff o Disconnection of

Foundation Drains o Catch Basin

Restrictors o Lot Control o Rooftop Detention o Porous Pavement o Permeable Pavers o Slope Stabilization

and Erosion Control Measures

o Compost Berm o Rain Garden

o Vegetated Swales o Channel/Outlet

Protection o Pervious Pipe

Systems o Pervious Catch Basins o Wet Swale o Permanent Check

Dams

o Detention/Retention Facilities

o Underground Tanks o Wetlands o Infiltration

Basins/Trenches o Filter/Buffer Strips o Sand Filters o Oil and Grit

Separators

o Public Education o Litter Control o Recycling Programs o Animal Waste Control o Spill Response Plans o Proper Storage and

Use of Chemicals, Fertilizers and Pesticides

o Vacant Lot Clean Up o Identification and

Prohibition of Illegal/Illicit Storm Drain Connections and Discharges

o Street Sweeping o Road Salt

Management o Land Use Restriction o Revision of

Development Standards

Note: The source, conveyance and end of pipe control measures listed above require operations and maintenance activities that vary depending on the type of stormwater management practice implemented.

4.2 Urban Stormwater Management Alternatives

The following pages describe various stormwater management practices that could protect and restore water resources within the study area. The BMPs reviewed consist of both well-established and new approaches. 4.2.1 Source Control Measures Source controls are on-site measures that control runoff at the source of generation. These include all measures that treat and/or control the runoff before it reaches the conveyance system (e.g. storm sewers, ditches or vegetated swales). In general, these involve ponding and/or infiltration on or into the developed area surfaces. The following provides a brief description of the source control measures.



Rooftop Runoff Discharge of the runoff from rooftops can be dealt with by using one or more of the following techniques: • Use of a splash pad at the outlet of the downspout to prevent erosion and to spread the runoff

over the immediate area, whereby the runoff then flows overland to the conveyance system. • Cisterns can be used to collect the discharge from roof leaders in an underground tank or rain

barrels for later use (e.g., watering of lawns and gardens) • Use of shallow ponding areas (maximum depth 10 cm) in rear yards or at the rear lot line to

detain water until it evaporates or infiltrates.. These ponds should be located at least 4 m from the building to prevent additional discharge into the foundation drainage. Ponding can be achieved in depressional areas and through the use of raised rear yard catch basins.

• Discharge of roof leaders into underground infiltration trenches or soakaway pits to facilitate the infiltration of rainwater into the groundwater system.

Foundation Drain Disconnection Discharging of foundation drains to the surface or into soakaway pits instead of discharging into storm sewers, reduces the risk of basement flooding due to sewer backup and reduces the downstream sewer discharge quantity while increasing infiltration. Catchbasin Restrictors The use of catchbasin restrictors/control orifices in urban storm sewer systems detains stormwater on parking lots or diverts flows onto road surfaces, thereby delaying the entry of stormwater into the conveyance system. Lot Control Typical lot grading standards require a minimum 2% grade away from the building to ensure adequate drainage. In naturally flat areas, new development lot grading can be reduced to 0.5% to promote recharge and evapo-transpiration. This effectively reduces runoff quantity, and with increased detainment and contact with the vegetated surface, provides some water quality benefits. Rooftop Detention Rooftop hoppers can be configured to provide rooftop detention of stormwater on flat commercial or industrial roofs to reduce the peak flow in the storm sewers. This alternative is more suitable to new developments rather than retrofits. The roof structure must be properly waterproofed and designed for the extra loading. A maximum ponding depth of 10 mm is permitted before water can flow into roof hoppers. Porous Paving Infiltration through road or parking area surfaces may occur through the use of porous pavements. The pavement consists of a thin layer of open-graded asphalt over a crushed-stone base. Since a key major roadway design consideration is maintenance of a dry sub-base for structural stability, porous pavement has no application on heavily traversed roads.



Although it has been applied in many Scandinavian countries, concerns have been raised on its suitability in our climate. A few municipalities in Ontario and BC are recommending the use of porous pavement as an alternative BMP. For example the Niagara Region Stormwater Management Guideline contains the following description on porous pavement:

Porous Pavement: A porous surface should be used where possible to enable stormwater to soak into the ground. Porous materials may be used for walkways, patios, plazas, driveways, parking lots, and some portions of streets. Pervious concrete in parking lots can be particularly useful because of its capacity to store a large volume of runoff for a period of time as well as catching oil and chemical pollutants. Permeable paving can be connected through attenuation/ infiltration basins to the wetland. In all instances, attention has to be paid that the quality of the ground water is not comprised and the material can withstand Canadian winters.

In Toronto, the Toronto and Region Conservation Authority has a demonstration project at the King Campus of Seneca College to assess the potential for using porous pavement to improve stormwater management. Use of this technology requires a pilot study. Permeable Pavers Infiltration through traditionally impermeable surfaces may also be achieved through the use of specially configured interlocking concrete pavers that incorporate gaps or voids between paving blocks, allowing infiltration into the base material. The base material must be graded with coarse material to avoid the build-up of pore pressures that would compromise the overall structural stability. Permeable pavers have been proposed for low traffic areas such as driveways, recognizing lower loads and the lower likelihood of infiltrating contaminants from the heavily travelled area. While there are several applications of this measure in Canada, concerns could be raised on its suitability to the local climate. Again, use of this technology requires a pilot study. Slope Stabilization Slope stabilization and erosion control measures, such as vegetating and benching, reduce sediment loading to storm drains, and downstream BMPs and receiving watercourses. Rain Gardens Rain gardens are landscaped areas planted with wild flowers and other native vegetation that soak up rainwater, mainly from the roof. The rain garden fills with a few centimeters of water after a storm and the water slowly filters into the ground rather than running off to a storm drain. Compared to a conventional patch of lawn, a rain garden allows about 30% more water to soak into the ground.



4.2.2 Conveyance Control Measures Conveyance control measures provide quantity and/or quality control of stormwater within the conveyance system between the source and outlet. Vegetated Swales Recent concerns about water quality of urban runoff have resulted in the use of vegetated swales instead of conventional curb and gutter, in urban areas. The use of vegetated swales detains runoff, reduces sediment and pollutant transport, and encourages infiltration. Outlet Protection Where there is a potential for erosion (e.g., outlets of pipes, steep channel segments, shorelines, etc.), installation of channel or outlet protection using materials such as riprap or gabions reduces the likelihood of erosion and thus the resulting downstream siltation. Pervious Pipe Systems Pervious (or perforated) pipe systems located below ground level can be used to convey runoff, allowing water to infiltrate through the pipe into the adjacent soils, thereby reducing the amount of storm runoff in the storm sewer system. 4.2.3 End of Pipe Measures End of pipe control measures provide quality and/or quantity mitigation at or near the downstream end of the stormwater conveyance system. Detention/Retention Facilities Detention and retention facilities, such as dry ponds and wet ponds (which have a permanent pool) can remove a large percentage of the coarse particulate pollutants carried by urban runoff. Soluble pollutants and trace metals are more difficult to remove without additional use of biological mechanisms. Dry ponds only contain water during runoff events and for a short time after. This type of storage facility was popular in the early 1970s and 80s. The primary reason for using dry ponds was to maximize land use through dual usage of land dedicated for recreational uses. Large grassed areas, such as football fields and ball diamonds could provide the needed storage capacities at relatively shallow depths. Some municipalities favoured dry ponds because they have less potential water quality and maintenance problems. However, in many cases it proved the cost of silt and debris removal and restoration to landscaping following a flood event were very high. Investigations in the U.S. also found that dry ponds can create a potential heath risk by forming small depressions at the pond bed that can turn into ideal mosquito breeding ground and thus potentially contribute to the spread of the West Nile Virus. Wet ponds are usually built for storage of stormwater to remove pollutants and to reduce hydrograph peaks. Storing the runoff provides attenuation. Physical, chemical and biological



processes, such as sedimentation, flocculation and metabolism by microorganisms and aquatic plants, accomplish removal of pollutants. An extended detention wet pond consists of a permanent pool which never drains, except during maintenance, and an extended detention storage component that drains slowly following a runoff event. Underground Tanks Underground tanks and large diameter pipes are another form of detention facility. The purpose of these structures is to store runoff temporarily and release it gradually after the peak has passed. Generally, tanks and “super pipes” are used in built-up areas requiring remedial works and where there is insufficient space available to control the runoff above ground. Construction and maintenance costs can be very high. Wetlands Over the past twenty years, the concept of using natural or constructed wetlands to improve the quality of stormwater effluents has generated significant discussion and research. It is now generally acknowledged that wetland ecosystems have an intrinsic ability to modify or trap and hold contaminants and pollutants. Thus, polluted water flowing through a wetland can be naturally cleansed by a combination of physical, chemical and biological activities. Wetlands, natural or artificial, are one of the most effective BMPs for water quality enhancement and generally are designed to provide extended runoff detention, which makes them effective in the treatment of highly contaminated waters (e.g. spills). When constructed with a sediment forebay, which facilitates maintenance, wetlands provide additional sediment removal, further enhancing the water quality benefits. Downstream flood and erosion control can also be provided. Maximum storage depths are generally limited to ensure the viability of vegetation and as a result wetlands are less efficient than wet ponds for quality control, i.e. they require more land to accommodate the active storage volumes at lower depths. Compared to conventional wet ponds, the potential benefits from increased nutrient removal makes the wetland alternative attractive. Infiltration Basins/Trenches Selection of the type and location for an infiltration facility requires a knowledge of soils and groundwater conditions in the sub-watershed. Standard infiltration basins and trenches reduce the amount of runoff entering the receiving system and increase recharge. Infiltration basins can also be designed with an underground perforated pipe collection network whereby the infiltrated runoff is collected and discharged to the local aquifer or to a receiving system. This type of BMP provides water quality benefits, but is ineffective for water quantity control and as such, is suggested as a secondary facility. The underlying soils should have a percolation rate not less than 15 mm/hr (60 mm/hr is recommended for infiltration basins) and the seasonally high groundwater table or underlying



bedrock should be at least 1 m below the bottom of the basin or trench. Depth of the active storage component should be sized to ensure a 24 to 48 hour drawdown. Pre-treatment of runoff should be mandatory (e.g., forebay, filter strips, oil and grit separators) to minimize the potential for clogging. Basins and trenches should not be located near septic fields or where infiltrated water may interfere with other groundwater uses. For example, stormwater facilities and infiltration basins have been identified as threats of provincial concern in some jurisdictions, recognizing the potential to contaminate sensitive aquifers and drinking water supplies. Filters and Buffer Strips Filter and buffer strips are constructed, natural areas that convey the runoff from small drainage areas (<5 ha) on the way to the receiving system. The vegetation filters pollutants, encourages evapo-transpiration and reduces the velocity of the flow. Buffer strips are a larger scale natural area as compared to a filter strip. Buffers provide increased filtering and some infiltration of runoff, thus reducing the amount of runoff and the pollutant concentration in runoff. Sand Filters Sand filters have been constructed in some jurisdictions in the U.S., where infiltration into the native soils was not possible. Sand filters can take numerous forms and can be constructed both above and below ground. Above ground, they can be incorporated into other BMPs, such as into swales enhanced with check dams comprised of rock fill; ideally, runoff would back up in the ditch behind the check dam and slowly flow through the self-contained sand filter, which comprises the core of the check dam. Alternatively, sand filters can be constructed below ground (i.e., beneath a ditch or swale invert). In general, the filter area would be excavated and backfilled with layers of sand and gravel. Within the lower gravel sub-layer, a perforated pipe collection system is required, along with a trunk storm sewer to convey filtered water to the surface water receiver. Oil and Grit Separators Oil and grit separators were developed for use with drainage areas of less than 5 ha such as, commercial/industrial areas, parking lots and transit stations. Grit and sediment in the runoff entering the separator are settled out and oil is removed through phase separation. Oil and grit separators provide some water quality control with no appreciable detention of stormwater runoff or quantity control. General designs include three chamber separators for areas <2 ha and manhole separators that treat low flows, allowing high flows to bypass the structure. While large and costly, some products can accommodate developed areas of over 30 ha with good treatment efficiency, and could be considered where limited land availability precludes the use of more conventional end of pipe measures.



4.2.4 Municipal Measures Public Education Stormwater management programs should be developed with the involvement of citizens of the watershed. Many jurisdictions involve young school children in the program, by providing educational trips in the watershed, or participating in a “blue fish” marking program of catch basins covers, to illustrate the path of urban runoff and the potential risk of killing the downstream fish habitat by polluted stormwater. Public education is essential in the promotion of efficient and safe housekeeping practices, when handling harmful materials such as fertilizers, pesticides, cleaning solutions, paint products, automotive products and swimming pool chemicals. Litter Control Litter control by-laws can be effective in reducing the amount of litter generated in the watershed. The by-law provides a uniform prohibition throughout the Municipality of any and all littering on public or private property; and prevent the desecration of the beauty and quality of life and prevent harm to the public health, safety, environment, and general welfare, including the degradation of water and aquatic resources caused by litter. A by-law can declare it to be unlawful to dump, deposit, throw or leave or to cause or permit the dumping, depositing, placing, throwing or leaving of litter on any public or private property or any waters. Public education is an essential part of a litter control program. Recycling Programs Most large municipalities in Canada offer residents curbside recycling, collection of yard trimmings, recycling drop off depots and community education programs. Animal Waste Control Animal waste collection as a pollution source control involves using a combination of educational outreach and enforcement to encourage residents to clean up after their pets. Animal waste collection programs use awareness and education, signs, and pet waste control by-laws to alert residents to the proper disposal techniques for pet droppings. Public education programs are another way to encourage pet waste removal. Often pet waste messages are incorporated into a larger non-point source message relaying the effects of pollution on local water quality. Brochures and public service announcements describe proper pet waste disposal techniques and try to create a storm drain-water quality link between pet waste and runoff. Signs in public parks and the provision of receptacles for pet waste also encourage cleanup.



Another option for pet waste management is the use of specially designated dog parks where pets are allowed off-leash. These parks typically include signs reminding pet owners to remove waste, as well as other disposal options for pet owners. The design of these dog parks should be done to mitigate stormwater impacts. The use of vegetated buffers, pooper-scooper stations, and the siting of parks out of drainage-ways, streams and steep slopes will help control the impacts of dog waste on receiving waters. Spill Response Plans A spill prevention plan should be prepared by businesses and public agencies that generate hazardous waste and/or produce, transport, or store petroleum products as part of the selection of BMPs. In addition to the prevention plans, structural methods used to control spills include: • Containment diking using temporary or permanent earth or concrete berms or retaining walls

that are designed to hold spills. • Curbing by constructing a barrier that surrounds an area of concern, usually implemented on

a small-scale basis. • Collection basins are permanent structures in which large spills or contaminated storm water

is contained and stored before cleanup or treatment. Collection basins are designed to receive spills, leaks, etc., and to prevent pollutants from being released into the environment.

Methods of cleanup, recovery, treatment, or disposal include: • Physical methods for the cleanup include the use of brooms, shovels, sweepers, or plows. • Mechanical methods include the use of vacuum cleaning systems and pumps. • Chemical cleanups of material can be achieved with the use of sorbents, gels, and foams. Storage of Chemicals Material storage control can prevent or reduce the discharge of pollutants to stormwater from storage areas. This can be done most efficiently by reducing the storage of hazardous materials on site, storing material inside or under cover on designated (paved) areas, installing secondary containment, conducting regular inspections and training employees and contractors. Illegal Connections Control procedures for the detection and removal of illegal connections from the storm drains should be implemented. Procedures include filed screening, sampling, smoke and dye testing, TV camera inspection, physical inspection, follow up of citizen’s complaints. Street Sweeping Some reduction in the discharge of pollutants to stormwater from street surfaces can be achieved by regular street cleaning. To achieve an effective street cleaning program areas with the highest pollutant loading should be swept at the highest frequency using the most advanced sweepers, optimizing the cleaning frequency based on storm inter-event times, introduce regular maintenance of sweepers. The general public should be educated to reduce street litter.



Road Salt There are many alternatives available to reduce the amount of salt that is needed to maintain a safe bare-pavement road. These involve: • Reducing the accumulation of snow and ice on the roads, therefore eliminating the need for

salt; • Better predicting when and where salt needs to be applied; • Improving the accuracy with which salt is placed on the road to achieve the best results; • Reducing the amount of salt lost to the roadside shoulders and ditches before it has had a

chance to work; and • Improving the storage and handling of salt at the maintenance yards. Land Use Restriction Part of land use planning, land use restriction is probably the most effective stormwater control. It represents the best opportunity to reduce the magnitude of runoff and the pollutants in stormwater runoff. It requires a comprehensive planning process to control or sometimes prevent certain land use activities in areas where water quantity and/or quality is sensitive to development. Revision of Development Standards The rapidly changing technology and data collected by local monitoring programs will necessitate the review of development standards at least every five years to determine the need to update and/or revise the development standards.

4.3 Summary of Rural Stormwater Management Practices

Table 4-2 summarizes the rural stormwater management alternatives applicable for the study area.

Table 4-2 Summary of Rural Stormwater Management Practices

BMP Benefit Suitability

Source Control

Disconnection of Tile Drains • decreased runoff quantity to receiving system; increased infiltration

• runoff detainment • decreased risk of surface water

contamination (i.e., bacteria, excess nutrients)

• retrofit applications may adversely affect drainage in top soils




Proper Manure Handling and Storage

• decreased runoff quantity to receiving system

• decreased risk of ground and surface water contamination (i.e., bacteria, excess nutrients)

• storage can be costly to construct and land consuming, depending on the size of the operation and method best suited to the farm

• depending on method used, can cause persistent odours

• liquid storage facilities can present health and safety hazards

• retrofit or new development

Proper Fertilizer Handling and Storage

• decreased risk of ground and surface water contamination

• retrofit or new development • requires dry, solid area for storage and

adequate spill containment

Effective Manure and Fertilizer Application


• requires organization, planning, and soil and manure testing

Prevention of Livestock Access to Surface Water Resources

• reduced stream erosion and sedimentation

• decreased risk of surface water contamination (i.e., bacteria, excess nutrients)

• very limited use in the study area • requires installation of some type of

watering device • may require construction of a stream

crossing to allow livestock access to lands on both sides of water


Water Well Protection • decreased risk of groundwater contamination (i.e., bacteria, excess nutrients)

• requires adequate location away from pollution sources and regular testing


Proper Disposal of Dead Animals and Hazardous Wastes

• decreased risk of ground and surface water contamination (i.e., bacteria, chemicals)

• decreased health risk

Proper Fuel Storage • decreased risk of ground and surface water contamination


• requires proper storage facilities with spill containment and regular inspections


Proper Pest Management • decreased risk of ground and surface water contamination

• requires organization, planning, and record keeping

Effective Tillage Strategies • decreased runoff quantity to receiving system; increased infiltration


contamination (i.e., chemicals, excess nutrients)

• reduced erosion and downstream sedimentation


• may require specialized or modified equipment

Proper Planning of Trips Over Fields

• decreased runoff quantity to receiving system; increased infiltration

• runoff detainment • reduced erosion and downstream

sedimentation

• requires organization and planning




Effective Planting Strategies • decreased runoff quantity to receiving system; increased infiltration


sedimentation; improved water quality


• depending on strategy implemented, can create some inconvenience in working fields due to trees between crops or alternating rows of different crops

Effective Field Surface Drainage


• runoff detainment • reduced flood risk • reduced erosion and downstream


• can be costly to construct, depending on method chosen, design and field area

• collection/outlet system components requires regular maintenance to prevent sediment accumulations

Windbreaks, Shelterbelts and Natural Fencerows

• reduced wind erosion and downstream sedimentation

• results in decreased acreage • may delay crop drying, harbour nuisance

animals and/or conflict with tile drains

Marginal/Fragile Land Retirement



sedimentation

• can involve moderate cost if reforestation is implemented, but water quantity and quality benefits will be increased, along with value as a forested natural area

Conveyance Control

Vegetated Swales/ Waterways and Roadside Ditches

• potential for decreased runoff quantity to receiving system; increased infiltration


sedimentation: improved water quality

• can increase mosquito breeding • results in decreased acreage • retrofit or new development

Drop Pipe Inlets/Rock Chute Spillways


• can involve moderate construction costs • retrofit or new development

Channel/Outlet Protection


• can involve moderate construction costs • retrofit or new development

End of Pipe Control

Sediment/Water Control Basins

• can provide water quantity control • potential for downstream erosion control • potential for spill control • improved water quality due to settling

• can involve moderate construction costs • potential for sediment re-suspension • can increase mosquito breeding • requires regular maintenance to prevent

sediment accumulation/clogging • results in decreased acreage • retrofit or new development

Filter/Buffer Strips • potential for decreased runoff quantity to receiving system; increased infiltration and evapo-transpiration

• runoff detainment • erosion protection and reduced

downstream sedimentation; improved water quality

• moderate cost to establish • results in decreased acreage • may require regular maintenance to

prevent sediment accumulation • retrofit or new development



4.4 Emerging Technologies

The field of stormwater management is constantly evolving and new technologies are continuously emerging. Most of the new BMP products such as media filters, catch basin inserts, separators, and sediment traps available on the market aim to provide some measure of water quality control. Generally, these products are made in the United States (US) and are designed to control water quality for small drainage areas. There is very little Canadian operational data available on the efficiency of these new products. Although the manufacturers provide limited specification data, the actual performance of the BMP depends on a number of site-specific factors. Most of the emerging technologies have not been evaluated in sufficient detail, especially in Canada and in the HRM region to be regarded as acceptable for general use for new developments. Preliminary data indicate that they may provide a desirable level of stormwater pollutant removal. Nevertheless, it is important to be cautious with the adoption of unproven technology. Before adopting any new technology, it is recommended the following criteria should be met: • Monitoring should be undertaken at a minimum of two different locations; • A minimum of five storms events, including at least one winter event and one event with

close to 25 mm precipitation must be sampled; • Groups independent from the supplier of the technology to be tested should undertake

sampling and analysis; and • Review of past performance at other jurisdiction. The stormwater management products presented in Table 4-3 and listed by the U.S. EPA are produced commercially, mainly in the U.S. Before adopting any of these alternatives, the designer should consult the manufacturer to establish applicability for the HRM area. It is recommended that if adopted, a pilot program should be established to determine the performance of the product before applying it in Nova Scotia.

Table 4-3 List of Stormwater Management Products

Product Name and Description Company

Aqua-Filter Stormwater Filtration System claiming high removal efficiency

Advanced Drainage Systems

Aqua-Guard Catch Basin Insert is used as first line of defense in a site’s stormwater treatment train.

Aquashield Inc

Aqua-Swirl A concentrator to remove sediment and free-floating oil and debris

Aquashield Inc

BaySaver A separation system removes suspended sediments, free oils, and floating debris from stormwater

BaySaver, Inc




Continuous Deflective Separation using fluid dynamics to separate solids from liquids

CDS Technologies

Cultec Contactor and Recharger are plastic leaching chambers for subsurface stormwater management, designed to replace conventional pipe and stone systems and retention ponds

Cultec, Inc

Downstream Defender A treatment device to capture settleable solids, floatables, oils and grease.

HIL Technology

Ecoberm One step pneumatic construction of filter berms made of compost and injected with a microbial food additive, vegetated or non-vegetated. Also has the ability to breakdown chlorinated and non-chlorinated hydrocarbons, pesticides and chemical fertilizers.

LandSource Organix

Filtrexx Ditch Checks made of composted materials contained in patented mesh tube(s) 300/400 mm diameter, filter water and settle solids from channelized flow of sediment laden waters.

Filtrexx Canada Inc.

HDPE Piping for subsurface retention/detention of urban runoff Advanced Drainage Systems Howland Swale Alternative detention structure to control flow and water quality

Environmental Research Corps

Inceptor Suspended from a catch basin, used in parking lots, and roads

Storm drain Solutions

Kleerwater Oil Water Separator, separates free-floating oils and greases from water

Modern Welding Company of Ohio

Microgen Stormwater Aeration System raises quickly Dissolved Oxygen in stormwater ponds, lakes after a rainstorm

Stamford Scientific

Netting TrashTrap captures floatables using passive energy of the flow

Fresh Creek Techn.

OARS Passive Skimmer to absorb and encapsulate hydrocarbons AbTech Industries Precast Stormvault captures and holds runoff to remove pollutants and it slowly releases the treated effluent

Jensen Precast

SNOUT Oil-Debris Separators, a high performance hood designed to aid in the removal of floatables, oil and grease and sediment in catch basins.

Best Management Products

Stormceptor. A precast modular structure to remove a high percentage of oil, sediment and other urban pollutants from stormwater

Stormceptor Canada

StormFilter is a passive, flow-through stormwater filtration system using rechargeable filter cartridges housed in a concrete vault.

Stormwater Management inc.

StormTreat. A system of six sedimentation chambers and a constructed wetland contained within a modular 9.5 ft diameter tank

StormTreat Systems

StreamGuard Exert II is a geotextile-covered, rigid plastic shell installed on top of a catch basin inlet to prevent sediment from entering during and after construction. Other catch basin inserts available for oil and sediment removal, or a passive skimmer for capturing hydrocarbons.

Bowhead Manufacturing Co

Turbotank Mobile Water Treatment Unit Transportable water treatment plant to remove suspended solids form groundwater at construction dewatering.

Turbotank Rental




Ultra-DrainGuard Oil and Sediment Model is a catch basin inlet to filter sediment, oil and debris from stormwater

UltraTech International Inc.

Ultra-Urban Filter to capture oil, grease, trash, and sediment form stormwater

AbTech Industries

V2B1 Stormwater Treatment System provides primary treatment using swirl sedimentation technology

Environment 21, LLC

Vortech Stormwater Treatment System is a below grade facility to remove and retain sand, hydrocarbon-laden sediments, metals, petroleum-based liquids, and other floatable and settleable debris from storm water

Vortechnics Inc.

Note. For more information see: http://www.epa.gov/ne/assistance/ceitts/stormwater/techs.html



5.0 Design Criteria For Best Management Practices

5.1 Introduction

Ideally all BMP design criteria should be based on recommendations developed as part of a comprehensive watershed or subwatershed plan prepared for the subject location’s basin. These plans are produced through the study of the environmental and land use features of a watershed. The purpose of the plan is to identify those areas that should be protected and preserved as part of the land use planning process, to evaluate the impact of future land use changes and to develop criteria to mitigate potential cumulative impacts in the watershed. A list of Watershed and Subwatershed Study components relevant to the selection and design of BMPs is presented in Appendix D. There is a degree of uncertainty associated with the prediction of pollutant retention, especially in parts of Canada where there is a lack of BMP performance monitoring data. The absence of local information on the pollutant retention process and inflow characteristics makes it difficult to verify criteria developed in other parts of the continent. This makes long–term performance monitoring in HRM essential to identify refinements, if needed, to improve design and construction techniques. In the absence of watershed/subwatershed study recommendations, the following set of design criteria should be used in HRM for quantity, quality, erosion, and base flow control. The use of this unified approach should result in a design of stormwater management practices that would meet the flood, water quality, erosion control and groundwater recharge criteria. The criteria developed in this chapter is partially based on the review of international practices provided in Appendix B. In the selection of design criteria, local rainfall characteristics should be taken into consideration. Appendix E presents the findings of the precipitation analysis undertaken for the study area. As a result of the analysis two factors have been incorporated in the selection of design rainfall events for HRM area: i) the unique rainfall pattern observed in the area which is different from other parts of Canada, and ii) the winter rainfall, or snowmelt and rain combination which could produce unique runoff conditions.

5.2 Design Criteria for Water Quantity Control

The intent of quantity control is to manage flood hazards by preventing or reducing damages associated with large, infrequent storm events. By controlling flood flow rates, flood plain and hazard limits in existing development areas can be maintained and the physical integrity of drainage infrastructure (e.g., bridges, culverts and stormwater management facilities) can be protected.



Ideally, watershed or subwatershed studies should evaluate requirements for post-development water quantity controls based on the potential cumulative impacts of development and potential flood hazards. Where such studies do not exist, requirements for water quantity control should be based on potential downstream flooding hazard. Generally, the criteria are to control post-development peak flows for the 2, 5, 25, 50 and 100–year storms to pre-development levels. If a proposed development is located in the lower reaches of a watershed or subwatershed discharging to coastal waters or large lakes with no downstream developments, quantity control may not be required. For sizing wet ponds and constructed wetlands, a 24-hour duration event should be selected, as shorter rainfall durations may under-estimate design runoff volumes and associated storage volume requirements. Hydrographs for the individual return period events should be generated by hydrologic models using the Shearwater gauge Intensity-Duration-Frequency data. A more detailed discussion on design storms is presented in Appendix E.

5.3 Design Criteria for Water Quality Control

Maintenance of healthy aquatic ecosystems requires that pre-development water quality be maintained and enhanced where feasible. The goal is to restore, protect and enhance water quality and associated aquatic resources and water supplies of the receiving watercourse. This goal mandates the prevention of contamination of streams and lakes from urban runoff containing nutrients, pathogenic organisms, organic substances, heavy metals and toxic substances. Similar to the quantity criteria, water quality criteria should be based on the premise that where feasible the post-development water quality should be similar to the pre-development water quality. The selection of water quality criteria is influenced to a great extent by the receiving system environment. Protection of receiving waters from impacts of sediments generated by urban development construction and post construction periods have been recommended by most provincial and municipal agencies across the North American continent. In Canada the Federal Government prepared guidelines on the potential impacts of sediment on aquatic organisms and their habitat. In controlling the pollutant efficiency of a BMP, it is recommended that Total Suspended Solids (TSS) be adopted as a primary indicator. As a rule of thumb, when rural land use becomes urbanized, the resulting runoff volume could double. At the same time the TSS loads from urban land uses are twice as high as from rural land uses. Therefore, the combined effect could be a fourfold increase in the TSS loads caused by urbanization. To match the pre-urbanized TSS loading, the selected BMP should reduce the post-development load by approximately 75%. Wet ponds and constructed wetlands are capable of removing 80% of TSS or higher.



The design criteria selection should start by assessing the state of the environment in the downstream receiving water bodies. There are two alternative indicators of the downstream water quality that could be considered in the selection of design criteria: 1) fish habitat, and/or 2) the nutrient concentration in the receiving system. For the first alternative indicator, consideration should be given to the selection of design criteria based on the potential effects of urban runoff on the aquatic habitats of the receiving system streams and lakes. A simple classification is presented in Table 5-1 to describe the downstream habitat:

Table 5-1 Classification of Downstream Habitat

Category Fishery Type of species Suggested TSS control

I Cold water fishery Salmonids, lobster fishery, aquaculture 80% II Warm water fishery Perch, minnows, suckers and urbanized lakes 70% III No existing or prospect of

future habitat Habitat in ditches, intermittent streams, stream with blockage

60%

The TSS indicator could also be used to assess receiving system impacts of the health on existing or potential future fish habitat. Impacts on this health can be measured by the relative changes in in-stream fish population or by the severity of impacts due to sediment concentration and duration of exposure. The following table compares the suspended solids concentration guidelines prepared by the European Inland Fisheries Advisory Commission and the Government of Canada, in the Yukon Placer Authorization 1993, document, based on suspended solids increases.

Table 5-2 Risk to Fish Habitat by Increase in TSS

European Commission Canada TSS – mg/L Risk Level TSS – mg/L Risk Level <25 Not harmful <25 Very low risk 25-80 Somewhat diminished yield 25-100 Low risk 80-400 Unlikely to support fisheries 100-200 Moderate risk >400 Only poor fisheries 200-400 High risk

Researchers on fish and exposure to increases in sediment concentration identified that most species of fish can withstand higher exposure of elevated levels of TSS, but impairment will occur when sediment exposure increases beyond threshold values which are a function of both the sediment concentration and its duration. According to Ward (1992) sediment concentration in the receiving stream below 25 mg/L would result in few ill effects regardless of the duration. For typical runoff events lasting less than 4 hours, moderate impacts would occur at about 200 mg/L. For duration of more than 10 hours, a concentration of 1,000 mg/L could result in major impacts.



Where body contact recreation, aesthetic or other uses require the control of nutrients entering the receiving system, it is recommended that Total Phosphorus (TP) removal be adopted as an alternative or as an additional primary design criterion. The following general relationship exists between TSS and TP removal rates: TSS % TP % 80 50

70 45 60 35

Based on estimated 50% higher TP concentration and 100% increase in runoff caused by urbanization, there could be an associated 150% increase in the TP loads. To match the pre-urbanized TP loads, the selected BMP should reduce the post-development load by approximately 67%. Wet ponds and constructed wetlands TP removal capability is limited to approximately 45% to 50%. Therefore, where the TP design criteria requires a reduction in excess of that range, additional BMPs would be required to meet the desired level of control. There is extensive background information available on the water quality of local lakes and rivers in the HRM area (http://lakes.chebucto.org), assembled by the Soil and Water Conservation Society of Metro Halifax. Just as comprehensive watershed studies may include flood control requirements based on cumulative effects of multiple developments, nutrient loading and trophic status modelling may be required to determine TP removal requirements. These studies may even identify linkages between nutrient levels and fish habitat as excessive algae and plant growth can result in the depletion of dissolved oxygen as plant material decomposes. The water quality criterion for sizing stormwater management facilities has two components: 1) for sizing storage facilities a volume criterion; and 2) for flow-through BMPs a peak flow criterion is recommended. Water quality control BMPs use primarily sedimentation processes to remove pollutants, through settling and/or filtering. Particulate pollutants such as sediment and metals are relatively easy to remove, while soluble pollutants such as nitrates and phosphates are more difficult to remove. A volume generated by a relatively low rainfall and runoff design event generally defines the detention volume requirement for water quality control with a storage facility. Design criteria for BMPs that permit runoff to a flow-through filtration or settling system are related to flow rates and velocities. When managing runoff for water quality impacts, the control of more frequent and smaller rainfall events are selected. This approach is based on the fact that the percentage of annual precipitation for very large events is relatively small, and the construction cost of storage facilities based on extreme rainfall events would be prohibitive. This approach can still provide partial benefit for larger storms as the BMP can continue to control pollutants from the first portion of the larger storm’s runoff.



The water quality volume criteria for sizing BMPs for the HRM area was determined from an analytical model as described in Appendix F. Long-term local rainfall data was analyzed to determine storage requirements for different impervious conditions and TSS removal efficiencies. The total storage volume in a wet pond or in a constructed wetland consisting of a permanent pool and an extended detention should generally be equivalent to the runoff volume generated by 90% of the long-term rainfall events observed in HRM. (For rainfall information see Appendix E) An example of the relationship between permanent pool storage and TSS removal efficiency as described in Appendix F is reproduced on Figure 5-1. Increasing the active storage over 40 m3/ha would only marginally increase the TSS removal. The peak flow water quality criterion is based on a statistical analysis of local precipitation data. It is recommended that a 25 mm winter rain event should be used to estimate the peak flow generated by the proposed land use.

Water Quality Control Sizing Criteria

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250

Permanent Pool Storage (m3/ha)

Ave

rage

Ann

ual T

SS

Rem

oval

(%)

0.350.550.70.85

Runoff Coefficient

Figure 5-1 Example of Sizing Permanent Pool Storage for Water Quality Control



5.4 Design Criteria for Erosion Control

The preferred approach for addressing erosion concerns is at the watershed/subwatershed planning level. During watershed/subwatershed planning, pre and post-development exceedance erosive index values are computed for a watercourse to determine the need for and the magnitude of erosion control measures. To select the erosion criterion when no such information is available, it is recommended to undertake an analysis of downstream channel conditions to assess the potential effects of post-development flows, water levels, and velocities on erosion. Such an analysis of erosion potential should extend downstream to a point where the runoff from the upstream drainage area controlled by the pond represents only 10% of the total drainage area. In the absence of information on downstream channel conditions, a 25 mm winter storm is recommended for the erosion control design event. This storm should be based on a 6 hour Chicago distribution event and should be routed through a storage facility assuming a gradual release rate with a drawdown time of 24-48 hours. For sensitive streams, the longer drawdown time should be used. The required storage is then compared to the extended quality control storage, and the greater of the two is used for design. For BMPs other than wetpond/wetland, the analysis of downstream channel conditions should determine the need for flow control or erosion protection requirements based on velocities and erosive forces generated by a 25 mm winter rain.

5.5 Recharge and Base Flow Maintenance

The need for providing groundwater recharge at a particular site will depend on the use of local aquifers. Where there is a potential risk of adversely affecting groundwater supply (quantity or quality) in the area, or the risk of reduction in base flow, the recharge from a proposed development should attempt to match the pre-development recharge. The pre- and post-development recharge can be estimated by a simple computation of the hydrologic cycle components. The local average annual precipitation and evaporation components of the hydrological cycle in the HRM area are: Precipitation 1421 mm Evapotranspiration 552 mm Surplus 869 mm (made up of recharge/base flow and surface runoff)



The recharge and base flow components of the surplus can be estimated by an infiltration factor determined by summing the following factors for topography, soils and cover (Ontario Ministry of the Environment, Stormwater Management Planning and Design Manual (2003)): Topography Factor Flat Land, average slope <0.6 m/km 0.3 Rolling Land, average slope 2.8 m to 3.8 m/km 0.2 Hilly Land, average slope 28 m to 47 m/km 0.1 Soils Tight impervious clay 0.1 Medium combinations of clay and loam 0.2 Open sandy loam 0.3 Cover Cultivated Land 0.1 Woodland 0.2 The range of infiltration factor to be applied is 0.3 to 0.8, therefore the minimum recharge and base flow component of the hydrological cycle could be 260 mm (= 0.3 x 869 mm). For post-development conditions when an area is paved and becomes impermeable, the infiltration/base flow and evapotranspiration components are removed from the hydrologic cycle. Infiltration through BMPs can provide groundwater recharge by diverting runoff from small and moderate storms into an infiltration facility. An additional benefit is achieved by providing opportunities for a number of physical, chemical and biological processes that remove pollutants from the recharge water. A general guideline for recharge and base flow maintenance is to capture where feasible the first 5 mm of rainfall. A summary of the recommended design criteria for BMPs is listed in Table 5-3.

Table 5-3 Summary of Design Criteria

Control Criteria Comments Flood and water quantity control

Control peak discharges from the 2, 5, 25, 50 and 100-year storms to pre-development rates

• Downstream system analysis may reveal that flood control criterion may not be required.

• Should consider the cumulative effects of development and controls.

Water quality Volume control for storage facilities, or control of peak flow from a 25 mm winter rainfall

• Compute storage from design graphs, or generate hydrographs for the single event design storm

Stream channel erosion

Control of peak flows • 24 hour-48 hour extended detention of post-development 25 mm winter storm event.

• Should consider the cumulative effects of development and controls.



Control Criteria Comments Baseflow Infiltrating the first 5 mm rainfall • Where feasible, the pre-development

hydrologic cycle components should be maintained.

5.6 Municipal Infrastructure Criteria

A set of storm drainage guidelines was released by HRM in 2005 as part of the Municipal Services Systems Design Guidelines. This municipal document describes the guidelines to be used in the design of municipal storm sewer pipes, ditches and other appurtenances. In particular, the document deals with the design of the major-minor drainage components of urban drainage systems, such as sewers, catch basins, and foundations drains. The stormwater sections of the Guideline document, reproduced in Appendix G, contains information on: • Design parameters for the Minor Drainage system; • Storm sewer system design: pipes, catchbasins, street drainage, ditches, culverts; • Minor drainage system connections, roof leaders, foundation drains; and • Erosion and sediment control. Table 5-4 summarizes the various guidelines listed in the Municipal document. It also details design requirements in addition to those outlined in the Municipal Services System Guidelines.

Table 5-4 Summary of Existing HRM Storm Drainage Design Guidelines

System Component Guideline Additional Requirements

Minor System Design flow • Larger of the winter or annual flow.

• Where time of concentration >6 hours use winter precipitation and ice/snowmelt.

• Where significant portion of area is underdeveloped use annual and winter data.

• Piped systems and driveway culverts: minor storm.

• Combined capacity of major and minor systems: major storm.

• Watercourses, culverts, roadside ditches, in absence of minor system: major system.

• Road culverts: 1:10 year storm.

• As recommended in watershed or subwatershed plans.

• In absence of such plans the sewer sizing should be based on 1 in 5 year storm without surcharge.

Downstream effects

• Have capacity to convey discharge from fully developed watershed.

Rainfall data • Historical data IDF curves for nearby station.

• Synthetic storms, Chicago distribution of 2 and 24 hours, r=0.5, discretization 5

• Storm discretization be selected considering basin size. Five minutes is less than the minimum Tc for




minutes and 1 hour for the two storms. • Historical storms used for verification of

storage pond performance.

most rational method design – it can lead to very high peaks in small basins.

Runoff computation

• Model must be calibrated and verified. • Rational method for preliminary design for

<20 ha, but not for storage.

Hydraulic design of sewer pipe

• Manning formula, based on published roughness coefficients.

• Minimum pipe size is 300 mm diameter. • No decrease in size in the downstream

direction, except at intakes.

Catch basins • Located in the gutter line, should minimize ice accumulation and ponding. Double catch basins may be required at locations to prevent by-pass of storm flows.

• Spacing not to exceed 120 m. • Interception capacity be compatible with the

storm drainage capacity. • Where potential for contamination inverted

siphons or separators may be required.

• For more details see Appendix G.

Catch basin leads • Minimum size 200 mm. • Minimum cover 1 m at construction and 1.2

m at completion of construction. • Minimum slope 1%. • Incorporate flexible joint. • Generally, catch basin connection to

another catch basin is not permitted.

• For more details see Appendix G

Storm sewer leads

• Connected from the building foundation should be PVC DR35, 150 mm diameter or less.

Foundation drains

• Normally drained by gravity to storm sewers and located above the hydraulic grade of major storms, or above the major storm flood if connected to a watercourse.

• No connection permitted to sanitary sewers. Basement floor >1m above 100 year hydraulic grade line.

Roof drains • May be connected to the storm sewer system if capacity available.

• Discharge to a dry well normally not permitted.

• Under the Lot Grading bylaw, roof drains are not permitted to be connected to the storm sewer except at discretion of HRM.

• Infiltration of roof runoff to be encouraged subject to soil conditions. Roof leaders should discharge to splash pads 4 m away from building.

Institutional, commercial and industrial connections

• Limit flow to 40% of uncontrolled fully developed flow.

Major System Street and overland flow routes

• Minor storms, depth of flow in gutters <50 mm.

• Major storms, depth of flows <50 mm at

• For major system use 100 year return storm event.




crown. • No overtopping of curbs and gutter enter

driveways, except where a major system is provided.

• Open ditches should not be overtopped and enter driveways.

Ditches and open channels

• Minimum grade 1%. • For rural roads ditch capacity based on

major storm. • Depth at bank full conditions <1.2 m, side

slopes not steeper than 2H:1V. • Wetted perimeter stabilized above 4%

grade. • Maximum velocity at unlined.

Culverts • Grade, obverts of outfalls <150 mm above minor storm level, above normal ice level, allowance for accumulation of debris at the outfall. Minimum grade 1%.

• Hydraulic capacity to determined by inlet and outlet control computation.

• Headwater depth <2 x diameter of pipe. No inundation of buildings.

• Grates if structure >30 m long. • Inlet and outlet structure if piped diameter

>375 mm extended >600 mm beyond toe of slope.

• Minimum diameter for driveway culvert diameter 450 mm, or not smaller than upstream culvert.

• Minimum diameter for roads 525 mm. • Culvert materials: reinforced concrete CSA

257.2 and STM C-76 or high-density polyethylene pipe CSA B182.6. ASTM F-667, and have a minimum stiffness of 320 kPa.

• Watercourses with drainage area > 40 ha to be maintained as open.

Culvert design capacities: • Urban arterial road, 50-100

year return frequency. • Rural arterial road, 25 – 50

year return frequency. • Local road, 10-25 year return

frequency.

5.7 Pollutant Loads

The goal in selecting the best BMP for a site is to minimize the adverse effects of the proposed development on the environment. The aim is to match predevelopment conditions in the receiving system. A list of pollutant loads generated by different land uses based on CH2M Hill is presented in Table 5-5 to assist the designer in estimating pre and post development pollutant



Table 5-5

Mean Pollutant Concentration Generated by Different Land Uses

Primary Indicators

Secondary Indicators Metals

Land Use TSS

(mg/L) TP

(mg/L) BOD

(mg/L) COD

(mg/L) TKN

(mg/L) TDS

(mg/L) TN

(mg/L) Cd

(ug/L)

Cr

(ug/L) Cu

(ug/L) Pb

(ug/L) Ni

(ugL)

Zn

(ug/L)

Forested wetland 19.0 0.2 4.1 29.4 0.6 52.0 1.1 0.5 2.8 5.3 3.0 4.7 22.9 Cropland and Pasture

19.2

0.2

4.2 29.7 0.6 52.0 1.1 0.5 2.9 5.4 3.1 4.7 23.5

Upland forest 19.7 0.2 4.3 30.4 0.7 52.0 1.1 0.5 2.9 5.6 3.2 4.7 24.8 Urban open 20.0 0.2 4.4 30.7 0.7 52.0 1.1 0.5 2.9 5.7 3.2 4.7 25.4 Communication and utilities

20.7

0.2

4.6 31.7 0.7 52.0 1.2 0.5 3.0 6.0 3.4 4.8 27.5

Low-density Residential

22.1

0.2

5.0 33.4 0.8 52.0 1.2 0.5 3.1 6.5 3.8 4.8 31.2

Medium-density residential

30.5

0.2

7.5 43.5 1.1 52.0 1.7 0.6 3.8 9.7 6.1 5.0 59.4

Institutional 41.9 0.3 11.3 56.7 1.5 52.0 2.4 0.6 4.5 14.7 9.9 5.3 112.9 High-density residential

47.7

0.3

13.3 63.1 1.7 52.0 2.7 0.7 4.9 17.3 12.0 5.4 145.9

Multifamily residential

47.7

0.3

13.3 63.1 1.7 52.0 2.7 0.7 4.9 17.3 12.0 5.4 145.9

Commercial 54.2 15.7 70.1 2.0 3.1 0.7 5.3 20.4 14.5 5.5 188.7 Highways 57.8 17.0 74.0 2.1 1.3 3.3 0.7 5.5 22.1 16.0 5.5 214.6 Industrial 57.8 17.0 74.0 2.1 1.3 3.3 0.7 5.5 22.1 16.0 5.5 214.6



loads for selected parameters. The data represents event mean concentrations monitored across North America. Generally, in the design of stormwater management facilities, only one or two key indicators, such as TSS and TP are considered. Runoff from impervious surfaces has a high potential for introducing pollutants to surface waters. Suspended solids, dissolved nutrients and oil/grease cause the most common water quality concerns. The existing and future pollutant loads could be estimated to provide an indication to the desired level of control. This early estimate will assist in the selection of the most appropriate alternative BMPs. The portion of the HRM Waste Water Discharge by-law related to stormwater is presented in Appendix H. This by-law describes limits for chemicals discharged to the municipal storm sewer system.

5.8 Exemptions From Runoff Control

Stormwater control would not normally be required for: • Single lot development of one family dwelling should apply, as a minimum, basic source

control measures, such as reduced lot grades and disconnection of roof leaders. Additional stormwater management measures may also be needed subject to local conditions;

• Addition to existing commercial buildings, provided the total impervious area is not increased, and the existing stormwater management facilities are adequate and are not altered; and

• Runoff from a development if it will be controlled by an external regional stormwater facility.

It is recommended that recognition should be given to any non-structural facility when selecting and sizing BMPs for a particular site. For example, appropriate reduction in the design volume or peak flow should be permitted for conservation of natural areas, disconnection of roof runoff if diverted to an infiltration facility, or use of vegetated swales with an infiltration function which will reduce the effective drainage area contributing to the BMP.



6.0 Selection of Best Management Practices

6.1 Introduction

The overall objectives of introducing BMPs are to minimize the adverse effects on and off the development site. An important part of the selection of BMPs is to preserve the sensitive, natural features and to develop a new stormwater system that can reproduce, as closely as possible, the natural conditions of the undeveloped state. This approach stresses the importance of preserving natural storage, infiltration and pollutant filtering functions where feasible, thus reducing the lifecycle cost for stormwater management and minimizing the need for costly capital improvements to the existing system. Runoff from impervious surfaces have high potential for carrying pollution, therefore it should be isolated from other types of runoff so the pollutants can be treated before mixing with less contaminated runoff. There is no single BMP that suits every development, and a single BMP cannot satisfy all stormwater control objectives. Therefore, cost-effective combinations of BMPs are required that will achieve the objectives. Some of the alternative BMPs can serve multi-purposes. In the HRM area, generally the most efficient site design would result when BMPs are selected in the following order: 1) water quality control, 2) runoff peak attenuation for flood and erosion control, and where required 3) groundwater recharge and base flow maintenance. Reducing the impervious cover at new developments, where feasible, could assist in achieving all three goals. In general, constructing end-of–pipe facilities is the least preferred approach, because of the relatively high construction and maintenance costs, the consumption of land area and the potential disruption of land features. Runoff from impervious surfaces have high potential for carrying pollution, therefore it should be isolated from other types of runoff so the pollutants can be treated before mixing with less contaminated runoff. When selecting BMPs, runoff may be conveyed through a series of connected BMPs, called a treatment train. Ideally, wetlands or buffers should be the last measure in the treatment of runoff in such treatment trains before the flow enters to the receiving system. A list of alternative BMPs are described in Table 6-1, which is an update of the alternative BMPs presented in the Water Resource Management Study (Dillon, 2002). It summarizes the most commonly used BMPs, and lists their applicability, advantages, disadvantages, effectiveness and operations and maintenance requirements.



Table 6-1 Stormwater Management Best Management Practices

BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Source Control Disconnection of Roof Leaders

• mostly for detached or semi-detached homes

• suitable outlet and soil conditions required

• requires cooperation of owners in existing homes

• By-law and/or public education required


• increased infiltration • runoff detainment • potential for some

water quality benefit

• potential for home owner inconvenience (i.e., ponding water, clogging of pond outlet/soakaway pit if implemented)

• difficult to implement in existing development or in poor soil conditions

• effective in reducing peak flow and volume of runoff in storm and combined sewers

• if combined with ponding or soakway, it will impact homeowner’s use of land

• roof leader filter cleaning and replacement and trash removal

• where constructed with soakway pits or ponding areas, it requires regular inspection.

Disconnection of Foundation Drains

• requires a potential outlet - often not available unless a clearwater sewer

• requires cooperation of owners in existing homes

• provide sump pump to discharge to surface


• increased infiltration

• may require sump pump • difficult to implement in

existing developments • if enforced may cause

unwanted discharge to sanitary sewer

• effective in reducing peak flow and volume of runoff in storm and combined sewers

• sump pumps not effective if high water table exists

• soakaway pits and sump pumps require regular maintenance

Catch Basin Restrictors/ Control Orifices

• Where temporary ponding will not create risk to safety

• runoff detainment • potential for limited

sediment removal

• potential for clogging inconvenience due to ponding water

• effective if regularly maintained

• Require regular inspection and cleanout.



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Reduced Lot Grading

• new developments


• increased infiltration and evapotranspiration

• runoff detainment • some water quality

benefit

• potential for home owner inconvenience (i.e., longer lot drainage time)

• vulnerable to alterations by home owner,

• difficult to regulate

• lack of monitoring data, little experience on efficiency of a subdivision scale

• could impact home owners use of the land

• homeowner’s responsibility to maintain

Rooftop Storage • new commercial, industrial and institutional building flat roofs

• runoff detainment • difficult to retrofit • only suitable for flat

industrial or commercial roofs

• effective in controlling peak flows, but no volume reduction

• regular inspection and roof hopper clean-out

Parking Lot Storage • mainly for new commercial, industrial or high rise residential development

• decreased peak flow to receiving system

• more suitable for commercial and industrial areas

• represents potential hazard to motorists and pedestrians

• effective in controlling peak flows, but no volume reduction

• require regular inspection and maintenance

Soakaway Pits • used in conjunction with other BMPs, such as roof leader or foundation drain discharge

• runoff detainment • flood control benefit • water quality

treatment • increased infiltration

• could interfere with sewage system leaching beds

• requires soils with minimum percolation rate of 15 mm/h

• high maintenance requirement

• uncertain longevity

• potential for clogging

• More effective if used for relatively clean runoff, such as roof runoff

• require regular inspection



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Porous Pavement • new technology

• requires testing before applying


• increased infiltration • traffic noise

reduction

• potential for groundwater contamination

• potential for clogging • not tried in Nova Scotia

• effectiveness is not known in Nova Scotia (some experience in Ontario)

• effectiveness affected by type of maintenance to keep pores clean

• require regular inspection and cleaning

Slope Stabilization and Erosion Control Measures

• mainly on construction sites

• reduced maintenance of BMPs

• improved water quality

• • effective if properly operated and maintained

• require regular inspection and replanting until established

Conveyance Control Road Drainage, curb and gutter

• built up areas where open ditches are not practical

• safety to pedestrians • protection from

erosion at the edge of road

• weeping tiles can be connected to deep storm sewers

• generally preferred by public in urban areas because of level of service and aesthetics

• limited quality treatment possibilities even when combined with oil/grit separators or sumps in cathcbasins

• no recharge to groundwater

• ice and debris blockage at catchbasins

• risk to cyclists

• only effective to convey runoff

• no peak or volume control or quality control

• require regular inspection, and removal of debris and sediment



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Road drainage, ditch and culverts

• where space available • soils are suitable • hydraulic losses at

driveway crossings manageable

• limited quantity control

• reduced risk of ponding on roads

• reduced risk to cyclists and motorists

• lack of sewer requires sump pump discharges from weeping tiles

• aesthetically not attractive

• frequent blockage of driveway culverts resulting in overflow

• not suitable for lots with narrow frontage

• only effective to convey runoff

• no peak or volume control or quality control

• require regular inspection, and removal of debris and sediment

Vegetated Swales • to filter and detain stormwater

• used where no hazard to pedestrians and cyclists

• potential for decreased runoff quantity to receiving system

• increased infiltration • runoff detainment • improved water

quality • generally preferred

over ditches by the public

• mosquito breeding ground

• require more land than conventional ditches

• contributing drainage area <2ha

• driveway connections by culverts

• effective for stormwater treatment and infiltration if length is at least 60 m and a minimum channel slope is maintained

• require regular inspection, grass cutting, weed control, removal of accumulated sediment and trash removal

Channel/Outlet Protection

• space permitting • not in sensitive areas

• decreased erosion • improved water

quality (i.e., decreased sediment loading)

• disruption of natural habitat

• effective for erosion control


Pervious Pipe System

• used for pre-treatment of road runoff

• requires soils with good infiltration potential and deep water table conditions

• combine with storage media



• requires porous soils • potential for

groundwater contamination

• potential for clogging • high cost of replacing

existing sewer

• little experience • effective in reducing

runoff and increasing infiltration

• expensive to maintain and repair

• require regular inspection, removal of accumulated sediment, trash removal and possible need to disconnect during winter if salting/sanding roads



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Pervious Catch Basin

• used for pre-treatment of road runoff

• requires soils with good infiltration potential and deep water table conditions

• combine with storage media



• requires porous soils • potential for

groundwater contamination

• potential for clogging • replacement filters are

expensive

• little experience • effective in reducing

runoff and increasing infiltration

• expensive to maintain and repair

• require regular inspection, frequent filter cleaning/ replacement, removal of accumulated sediment, and possible need to disconnect during winter if salting/ sanding roads

End of Pipe Control Detention/ Retention Facilities (Dry, Wet and Extended detention ponds)

• where adequate space available

• no adverse effects downstream

• water quantity control


• potential for downstream erosion control

• potential for spill control

• potential for sediment re-suspension (dry ponds)

• potential for thermal warming (extended detention)

• potential for odour, algae, debris and/or mosquitoes (wet ponds)

• potential for outlet clogging

• not suitable/economical for small areas, wet ponds require more land area than dry ponds, although both are land consumptive

• highly effective in reducing downstream flows, improving water quality and reducing erosion

• require regular inspection, grass cutting, weed control, replanting of vegetation as necessary, removal of accumulated sediments, trash removal and occasional outlet adjustment

Underground Storage

• no conflict in areas with underground services

• decreased runoff peak


• difficult to keep clean • effective in controlling peak flows

• require frequent and expensive cleanout

Artificial Wetlands • requires adequate • runoff detainment • potential for thermal • highly effective in • require regular



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance drainage area to provide runoff

• requires adequate space

• potential for water quantity control


• potential for downstream erosion control

• effective for spill treatment

warming • potential for outlet

clogging • potential for mosquitoes • not suitable/economical

for small areas • may have plant

sustainability problems where road salts are applied

• requires significant land area

reducing downstream flows, improving water quality and reducing erosion

inspection, grass cutting, weed control, replanting of vegetation as necessary, removal of accumulated sediments, trash removal and occasional outlet adjustment

Infiltration Basins/Trenches

• suitable soils • suitable groundwater

conditions


• increased infiltration if allowed to recharge groundwater system

• improved water quality if collected and discharged

• potential for clogging/ compaction

• potential for groundwater mounding

• potential for groundwater contamination

• oper./main. problems reported

• pre-treatment suggested

• effective if implemented as one of a series in a treatment train

• require regular inspection, grass cutting, weed control, replanting of vegetation as necessary, removal of accumulated sediments, trash removal, and possible need to disconnect during winter if salting/sanding roads.

• basin require periodic floor tilling



BMP Alternatives Applicability Advantage Disadvantage Effectiveness Operation/Maintenance Filter/Buffer Strips • requires adequate space

• mainly for low intensity residential developments

• potential for decreased runoff quantity to receiving system

• increased infiltration and evapo-transpiration

• runoff detainment • improved water

quality • erosion protection

• potential for clogging • effective if implemented as one of a series in a treatment train


• filter strips require weed control, replanting of vegetation as necessary, removal of accumulated sediments and trash removal

Sand Filters • mainly for low intensity residential developments

• runoff detainment • improved water

quality

• potential for clogging • potential for

unsightliness and odour • oper./main. problems

reported • may not be as cost-

effective as other BMPs

• effective if implemented as one of a series in a treatment train

• require regular inspection, grass cutting, removal of accumulated sediments, trash removal and possible need to disconnect during winter of salting/ sanding roads

• potential for regular replacement of filter media

Oil and Grit Separators

• for spill control • mandatory for certain

commercial sites • where only limited

water quality control is required

• limited runoff detainment


• spill control

• can only control limited areas

• not suitable for quantity control

• not suitable for soluble pollutants

• only effective for spill control or water quality control for low flows

• require frequent inspection, cleaning and removal of accumulated oil and sediment

Physical/chemical treatment

• for effluents to very sensitive receiving systems


• spill control

• not well tested for stormwater

• expensive

• little experience, effective for water quality control

• frequent inspection



6.2 Treatment Train

Frequently, one BMP cannot provide the required control capability. In some cases the type of land use or the sensitivity of the downstream receiving system may require an enhanced treatment. Certain developments, such as industrial and commercial uses, or high traffic areas can produce high concentration of oil, or metals, which may require enhanced treatment. Another scenario where enhanced treatment may be required is for developments discharging into highly sensitive streams with elevated phosphorus concentration threatening the existing fish population. To meet the required control and provide enhanced treatment for a pollutant of concern, two or more BMPs can be applied is series in a treatment train formation. The most common approach in selecting components for a treatment train is to start at the source where runoff volumes can most readily be controlled, followed by the conveyance system and then, if needed, at the end-of–pipe or outlet to receiving waters. End-of-pipe controls are typically required where 1) recharge requirements cannot be met with at-source BMPs due to soil conditions, or limited land availability; 2) where extended detention of increased runoff rates is required to meet erosion control requirements; or 3) where peak flow attenuation is required for flood control. Examples of water quality treatment train components are: Source controls; disconnecting roof leaders, use of sump pumps, construction of soakaway, rain garden; Conveyance controls; swales, separators; End-of-pipe controls; extended storage ponds with forebay The use of rain gardens are recommended by the Greater Vancouver Municipality, with a somewhat similar climate to HRM, as a source control component of the treatment train. Homeowners are encouraged to establish rain gardens on their properties. The treatment trains recommended for residential areas in the Vancouver area are shown in the Table 6-2 below:

Table 6-2 Treatment Train Components

Treatment train Order Treatment train Capture target % of rain

1st Runoff channeled to pervious paving, then 33% Runoff from pervious paving to infiltration swale

2nd Runoff from pervious paving to infiltration swale. 66%

1st Runoff from green roof to rain garden, then 33% Runoff from green roof to soakaway 2nd Runoff from rain garden to soakaways. 66% Table 6-3 illustrates examples of different combination of BMPs, which can provide enhanced treatment.



Table 6-3 Examples of Treatment Train Alternatives

Pollutant of Concern Basic BMP Treatment Train Alternatives

Oil Wet pond or wetland Separator Infiltration Pre-treatment settling Metals Wet pond Filter or swale Infiltration Pre-treatment settling Phosphorus Wet pond or wetland Filter or swale

Some of the most commonly used treatment train components include: • Rain gardens and bioretention • Rooftop gardens • Sidewalk storage • Vegetated swales, buffers, and strips; tree preservation • Roof leader disconnection • Parking lot storage • Permeable pavers • Impervious surface reduction and disconnection • Pollution prevention and good housekeeping. An example of a simple computation to determine the need and type of “treatment train” is presented at the end of Chapter 6.

6.3 Selection Process

A number of competing and conflicting factors have to be addressed when selecting the appropriate BMP for an area. Generally, all BMPs have limitations and therefore no single alternative will achieve the desired quantity and quality control. Instead, in most applications a train of BMPs will have to be applied. Physical constraints of the site, environmental conditions, construction, long term operation and maintenance costs, and aesthetics are all important considerations which will affect the design criteria selection process. The following four-step process could assist in the selection of the best BMP for a particular site: Step 1 – Select Design Criteria The first task in the design process is to establish the objectives of the BMPs and establish a set of design criteria applicable for a particular site. Ideally, a watershed or subwatershed report is available which analyzed the flooding, water quality, erosion and environmental conditions in the watershed and set out a clear set of design criteria. There is a concentrated effort by HRM to undertake a series of watershed or subwatershed studies for all major watersheds. Until that program is completed, in most cases a designer has to rely on a set of uniform design criteria developed for the entire HRM area, as described in Chapter 5. Table 6-4 summarizes the suggested criteria for the control of quantity, quality, erosion and base flow recharge for different site conditions.



Table 6-4 Selection of Design Criteria

Control Watershed Conditions Suggested Criteria

• Site close to lake or coastal waters with no existing or proposed development downstream.

• No peak flow control required for flood control

Flood and water quantity control

• All other locations. Should consider the cumulative effects of development and controls.

• Control peak discharges from the 2, 5, 25, 50 and 100-year storms to pre-development rates

Water quality • Identify downstream habitat, Category I, II or III, and determine suggested TSS % removal

• Identify need to control TP and determine suggested TP% removal

• Volume control for storage facilities, or control of peak flow from a 25 mm winter rainfall

Stream channel erosion

• Identify existing erosion sites, and establish need for erosion control. Should also consider the cumulative effects of development and controls.

• For storage facility, 24 hour-48 hour extended detention of post-development 25 mm winter storm event, or

• For other infiltration BMPs, infiltration from a 25 mm event

• Aquifer sensitive to impairment of drinking water use, also a high recharge area.

• The pre-development hydrologic cycle recharge component should be maintained by promoting infiltration from all impermeable surfaces with limited runoff contamination (such as rooftops) but excluding highly contaminated sources such as roadways or those with spill potential (industrial areas).

Baseflow

• Aquifer not sensitive to impairment of any drinking water use, also a high recharge area sustaining baseflows and fish habitat

• Where feasible, the pre-development hydrologic cycle recharge component should be maintained by promoting infiltration from all impermeable surfaces.



Table 6-5 Stormwater Management BMPs – Initial Assessment Matrix

Control of Slope Soils infiltration Bed rock Water table Drainage area Treatment TYPE OF BMP Quantity Quality Erosion Recharge Habitat 0-5% 6-10% >15mm/h <15mm/h <1m >1m <1m >1m <5ha >5ha train only*

SOURCE CONTROL Reduced lot grade Yes Roof leader disconnection Yes Roof storage N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A Yes Sump pump N/A N/A Yes CONVEYANCE CONTROL Vegetated swale Yes Perforated pipe END-OF-PIPE CONTROL Extended wet pond Extended dry pond Wetland Infiltration Yes Permeable pavement Yes Forested buffer Yes Filters strip Yes Sand filter Yes Separator Yes Bio-retention Yes

Legend Can be effective * BMPs used mainly as part of a treatment train Limited benefits Not recommended



Step 2 –Initial Assessment of BMP alternatives To aid the user in choosing the most suitable BMP for a site, a screening tool has been developed to compare the capabilities and limitations of each BMP. This initial assessment matrix is presented in Table 6-5. The designer can use this matrix, given the site limitations and design criteria, to develop a potential list of BMPs. In general the following group of factors should be considered when selecting an appropriate BMP or group of BMPs for a development: 1. BMPs control capability: water quantity, quality, and erosion control, recharge and habitat

protection capabilities 2. Site applicability: slope of land, local soils, location of bedrock and water table, size of

drainage area 3. Capability of the BMP to act as a stand alone control facility or to be used only as part of a

treatment train From the above analysis prepare a short list of alternative BMPs. Step 3 – Select a shortlist of alternative BMPs Refine list of alternatives derived from the initial assessment by considering additional constraints, such as: 1. Capability to remove pollutants: To assist in the selection of water quality control BMPs Table 6-6 provides an overview of a BMPs capability to remove the most common pollutants considered in stormwater management: • Total Suspended Solids (TSS) is the most common indicator and the BMP(s) should be

chosen to meet the water quality design criteria established in watershed or subwatershed studies. In absence of such studies, the design should meet the criteria established under the unified HRM Criteria. (Chapter 5).

• The nutrient treatment column indicates the TP and Total Nitrogen (TN) removal capabilities of each BMP.

• Metals include those observed in urban runoff: lead, copper, chromium, zinc and cadmium. • The bacterial removal column describes the capability to remove bacteria in urban runoff. 2. Space requirement: The space requirement for BMPs can range from 2%-5% of the drainage area for storage facilities, to 10% or more for swales. 3. Environmental considerations: The BMPs selection must also consider the implications of inhibiting the passage of aquatic fauna, potential for causing sediment build-up or starvation in downstream watercourse, loss of aquatic habitat and riparian vegetation, and increasing downstream water temperature. 4. Health and safety issues: In choosing BMPs the potential to cause injury due to climbing on structures, drowning, skin irritations and infections, mosquito borne diseases, odours, risk to maintenance staff must be considered.



Table 6-6 Capability Matrix for Selected BMPs

Removal rates (%) for water quality

parameters assuming ideal conditions1 BMPs TSS TP N Metals Bacteria

Habitat Flood

control

Channel protection potential

Drainage ha, and

Space in % of catchment

Relative maintenance

effort2

Construction cost per ha 4 Safety3

Wet pond 80 50 35 60 70 High Good Good >5, 2%-3% Medium Medium Low Wetland 80 50 30 40 80 High Good Good >5, 3%-5% Medium Medium High Infiltration 90 70 50 90 90 Low No No 2-5, 2%-3% High Medium High Filters 85 60 40 70 35 Low No No <2, 2%-3% High High High Swales 85 40 50 70 Negl. Low No No <2, 10%-20% Low Low High LIMITED APPLICATION CONTROL ALTERNATIVES Oil & Grit Separators

<40 <5 <5 No data No data Medium No No <2 High Low High

Porous pavement

Negl 80 80 No data 90 Medium No No <1 Medium Medium Medium

1 New York State Stormwater Management Design Manual 2 Effort is based on frequency of scheduled maintenance, chronic problems, and reported failures 3 Based on surveys, nuisance problems and visual exposure 4 Relative construction cost per impervious area



Once the above have been considered, the designer prepares a preliminary size of the alternative facilities and establishes the need for treatment trains. To assist in the selection of the BMPs, a preliminary estimate of the existing and future annual pollutant loads is prepared. The calculation should include the total annual rainfall, runoff coefficients for existing and future land uses, and the mean pollutant concentration values listed in Table 5-5. A comparison of the existing and future annual loads will provide an approximation of the required control, which in turn will assist in the selection of feasible alternative BMPs. An example of a spreadsheet computation of annual pollutant loads is attached at the end of Chapter 6. Step 4- Final selection of BMPs Review and analyze the short list developed in Step 3. Based on the above information estimate long-term operation/maintenance costs and select the most appropriate BMPs. Before the final selection is made, environmental regulations and permit requirements must be considered.

6.4 Stormwater Management for Infill Developments

Stormwater management in infill areas requires special consideration when selecting design criteria and suitable alternative BMPs. Generally, small infill areas provide limited opportunity to introduce many of the alternative BMPs reviewed. The focus of this section is on infill areas of less than 5 hectares in size where storm sewer infrastructure already exists. For infill areas in excess of 5 ha there should be more opportunity to introduce other alternative BMPs. Although the development of a relatively small infill area may not have a significant impact, the development of several individual sites can have a significant cumulative effect on the watershed. Infill developments with no stormwater management facility should be discouraged. As a minimum criterion a 5 mm rainfall event should be retained at the site (i.e., no runoff for the 5 mm rainfall event). Only where on-site control may be ineffective or impractical because of physical constraints, off-site control should be considered. An alternate solution could involve the Municipality requesting financial contribution from the infill developer toward the development of a stormwater management facility at another location, preferably in the same watershed. Only infill developments consisting of one residential lot discharging into an existing storm sewer (not combined) should be permitted to proceed without any BMPs, other than basic good housekeeping measures. When considering the need for stormwater management for infill areas, a number of factors have to be assessed: • Proposed land use;



• Infrastructure capacity; • Opportunities of retrofitting existing stormwater management systems; and • Site conditions, such as soil percolation level, slopes, vegetation, aquifer and bedrock

location. A list of alternative BMPs available for infill developments is listed in Table 6-7.

Table 6-7 List of Alternative BMPs Suitable for Infill Development

BMP Control Comment

Roof leader to pervious surface Peak flow Where physically feasible Rooftop storage Peak flow Flat roof only Parking lot Peak flow Dependent on site grades Underground storage/ Super pipes Peak flow Dependent on sewer invert levels Pervious pipe Quantity and quality Dependent on soils Swales Quality Dependent on soils Infiltration trench Quality Dependent on soils and water table Filters Quality Generally feasible Oil and grit separators Spills and some quality Generally feasible Storage ponds Quantity and quality Generally not feasible Wetlands Quantity and quality Generally not feasible

6.5 Retrofitting

Older runoff control structures constructed prior to the introduction of water quality control BMPs were designed to control flooding. Retrofitting is the process by which these existing structures are modified to serve a water quality improvement function as well. Retrofitting can improve the multi-use function (flood peaks, velocities, pollutant loadings) and appearance of existing facilities, enhance the useful life of the BMP, and reduce the operation and maintenance costs although in some instances the additional quality control and sediment removal may increase the maintenance cost. In some instances retrofitting could also be considered to improve an existing water quality BMP. Opportunities to retrofit may exist at the source, for example roof top storage on flat roofs, dry wells or below ground detention facilities. Detention basins provide another opportunity for retrofitting. Basins designed primarily for flood protection (e.g., dry ponds) can be retrofitted to provide additional benefits by providing extended detention and a permanent pool. Forebays at the inlet and outlet can be incorporated for enhanced settlement of suspended solids. Infiltration measures can be introduced where soil permeability and groundwater depth are sufficient at locations such as medians, parking areas and roadside swales.



6.6 Example of Pre and Post Development Pollutant Load Water Quality Computation

A 20 ha drainage area presently undeveloped is slated for development. The aim is to maintain as closely as possible the existing TSS and TP loads generated by the drainage area once a 7 ha portion of the land is developed. The following assumptions are made to compute annual TSS and TP loads (see Table 6-9 at the end of this section for the detailed calculations): • Annual rainfall, 1.25 m. • Adopt TSS and TP concentrations (mg/L) from Table 5-5 Runoff coefficients: • Wetland 0.1 • Agriculture 0.3 • Wooded area 0.15 • Residential/commercial 0.6 • Open space 0.3 1. Existing Land Use Runoff = 44,375 m3 per year TSS = 866 kg/year TP = 9 kg/year. Proposed development would have higher runoff coefficients for the urban area and higher pollutant concentration values. 2. Uncontrolled Post-Development Stormwater Runoff Runoff = 95,625 m3 per year TSS = 2,462 kg/year >866 kg/year TP = 19 kg/year >9 kg/year 3. Extended Wet Pond BMP Assume pollutant control capability of TSS = 80% and TP = 50%. The wet pond would capture the runoff from the urban area. The reduced pollutant loads in the pond outflow: TSS = 1,181 kg/year >866 kg/year. TP = 14 kg/year >9 kg/year.



As shown the annual pollutant loads were reduced by the pond, but did not match the pre-development values. If this small amount of increase is unacceptable, estimate the additional removal capability of a treatment train, consisting of a vegetated swale downstream of the pond. 4. For Vegetated Swale Assume a 50% TSS and TP removal in the vegetated swale. The residential/commercial runoff from the pond would reduce the total post-development loads TSS = 1021 kg/year TP = 11 kg/year The pollution loads for the different scenarios indicate that an extended wet pond could reduce the post-development pollutant loads but the pond alone could not match the pre-development TSS and TP values. By introducing a combined wet pond and vegetated swale treatment train arrangement the post-development pollutant loads could be further lowered but still could not match the pre-development values. Table 6-8 summarizes the computed pre and post-development TSS and TP loads.

Table 6-8 Total Annual Pollutant Load Generated by the Site in kg/year

Conditions TSS TP

Pre-development 866 9 Post-development, no stormwater management 2,462 19 Post-development with pond 1,181 14 Post-development with ponds and vegetated swale

1,021 11



Table 6-9 Example of Pre and Post Development Wter Quality Estimates

EXISTING LAND USE

Land use Area-ha Area m2 Rain Runoff C Total runoff TSS - mg/L TSS - kg No pond TP-mg/L TP-kg No pond Wetland 1 10000 1.25 0.1 1250 19 24 0.2 0

Agriculture 4 40000 1.25 0.3 15000 19.2 288 0.2 3 Wood 15 150000 1.25 0.15 28125 19.7 554 0.2 6 Total 20 200000 44375 866 9

FUTURE LAND USE

WITH POND Land use Area-ha Area m2 Rain Runoff C Total runoff TSS - mg/L TSS - kg TSS-kg TP-mg/L TP-kg TP-kg

Uncontrolled Pond effect Uncontrol Pond effect 80% capture 50% capture

Res/Com 7 70000 1.25 0.6 52500 30.5 1601 320 0.2 11 5 Wood 3 30000 1.25 0.15 5625 19.7 111 111 0.2 1 1

Open space 10 100000 1.25 0.3 37500 20 750 750 0.2 8 8 20 200000 95625 2462 1181 19 14

EFFECT OF URBANIZATION Runoff coefficients Existing land use Future Land use Change TSS 866 1181 kg/year Increase Assume Residential Imperv. 50% C= 0.9 TP 9 14 kg/year Increase Residential Pervious 50% C= 0.3

Average C= 0.6



Introduce additional BMP measures to reduce TP Investigate the additional effect of constructing a vegetated swale Assume that the outlet from the pond will be discharged via a long vegetated swale to the receiving system FUTURE LAND USE WITH POND AND VEGETATED CHANNEL

Land use Area-ha Area m2 Rain Runoff CTotal runoff

Res/Com 7 70000 1.25 0.6 52500 Wood 3 30000 1.25 0.15 5625

Open space 10 100000 1.25 0.3 37500 20 200000 95625

Vegetated swale: reduce TSS and TP in pond outflow by 50%

Land use TSS - mg/L TSS - kg TSS-kg TSS-kg TP-mg/L TP-kg TP-kg TP Uncontr. Pond Swale Uncontrol Pond effect Swale 50% 20% 50% 50% capture

Res/Com 30.5 1601 320 160 0.2 11 5 3 Wood 19.7 111 111 111 0.2 1 1 1

Open space 20 750 750 750 0.2 8 8 8 Total 70.2 2462 1181 1021 19 14 11

Effect of pond and vegetated swale

Existing land use

Future Land use

TSS 866 102 1 kg/year TP 9 11 kg/year



7.0 BMP Design Fact Sheets

A series of Fact Sheets are presented for the most common stormwater management BMPs in Appendix I. These sheets are applicable for HRM conditions and are based on a review of Canadian and International BMP practices. For each BMP a list of key considerations is summarized reflecting local conditions. In addition, a series of CMHC Fact Sheets are presented describing the acceptable designs for all Canadian users. Table 7-1 presents the list of BMP alternatives presented in Appendix I:

Table 7-1 List of BMP Fact Sheets Presented in Appendix I

BMP Type Fact Sheet

Source Control 1. Reduced lot grading - 2. Roof leader disconnection to soakaway or ponding area

CMHC

3. Roof storage CMHC 4. Sump pump - Conveyance Control 5. Vegetative practices, vegetated

swales CMHC

6. Perforated pipes/catch basins - End-of-Pipe Control 7. Wet ponds CMHC 8. Dry ponds - 9. Constructed wetlands CMHC 10. Infiltration trench/basin CMHC 11. Permeable pavement - 12. Forested buffers CMHC 13. Filter strips - 14. Sand filters CMHC 15. Oil and grit separators CMHC 16. Bio-retention/rain gardens - 17. Monitoring -



8.0 Operation and Maintenance of BMPs

8.1 Introduction

Stormwater management facilities designed for the control of flow, water quality and erosion/ sedimentation require a high level of maintenance. To assure effective operation, long life and compatibility with the local urban and natural environment stormwater control facilities must be monitored, inspected and maintained regularly. Public agencies responsible for stormwater management should continue taking great interest in these local facilities after the planning, design and construction stages. The lack of a regularly scheduled program of maintenance and operation reduces the effectiveness of a stormwater management system and often results in adverse environmental impacts that may be difficult and costly to correct. Without an assured source of funds, well-trained staff and suitable equipment required for operational activities in stormwater control, little can be achieved in developing an ongoing operation and maintenance program. The following describes the various operation and maintenance practices to achieve the storm water management goals and objectives established by the Province and HRM. Municipalities have a number of concerns with respect to operation and maintenance of storm water management facilities. These concerns are focussed in four different issues. • Safety and liability involved in the operation of various storm water management facilities, in

particular the liability involved in constructing extended wet ponds with steeper slopes than those recommended;

• Downstream environmental effects of quantity and quality control facilities; • Aesthetic considerations; and • Funding for future operation and maintenance activities.

8.2 Goal, Objectives and Policies

The goal of the operation and maintenance program is to ensure within an economic framework, an acceptable standard of stormwater management and BMP facilities in terms of structural and public safety, aesthetic effectiveness, and convenience. The main objectives are: • to protect and prolong the useful life of facilities; • to identify, repair and rehabilitate structures; and



• to provide a sound basis for a management system for the planning and funding of the operation, maintenance and rehabilitation of facilities.

All three aspects of a stormwater management facility: design, construction and long-term maintenance are equally important to insure a long useful life and high performance. The Municipality should have adequate opportunities to provide input into the design and construction phases, before undertaking the long-term maintenance program. Table 8-1 illustrates the various stages of development, where the Municipality should be given an opportunity to review and comment on the proposed SWM policies, design, or to carry out inspections and an efficient maintenance program.

Table 8-1 Municipal Input to Stormwater Management

Phase Municipal Input Output

Official Plan (O.P.) Formulation of SWM policy and land use plan

O.P. with generalized SWM policies

Secondary Plan SWM targets, goals, objectives, BMP requirements

Secondary plan with specific SWM policies

Draft Plan of Subdivision and Site Plan

Stormwater management plan, preliminary design review

Approved development plan with condition of draft plan approval, including SWM requirements

Final Design Design review of SWM facilities Certificate of Approval

Construction Inspection of SWM facilities Facility in place

Endorsement Clearing of deficiencies Municipal ownership

Post-Construction Operation and maintenance Annual programs

8.3 Past Performances of Stormwater Management Facilities

Design of SWM facilities must consider not only the hydraulic performance of the structure, but also the operation and maintenance aspects. There is only limited experience available in Canada on the performance of SWM facilities. Statistics from the State of Maryland, the first in the US to introduce stormwater management, show an alarming high number of failures of BMPs constructed prior to 1985, where the facility did not meet the criteria adopted at the design stage. (Maintenance of Stormwater Management Structures, Sediment and Stormwater Division, Water Resources Administration, Department of Natural Resources, July 1986). A summary of their findings is listed in Table 8-2.



Table 8-2 Performance Statistics of Maryland BMPs

Type of BMP Type of Failure % failed

Blocked outlet 46.5%

Sedimentation 13.4%

Aquatic vegetation 33.2%

Standing water 26.5%

Too wet to mow 54.2%

Soil erosion 42.7%

Dry ponds (389 surveyed)

% of dry ponds functioning 24.7%

Blocked outlet 22.2%

Sedimentation 4.4%

Soil erosion 2.2%

Wet ponds (34 surveyed)

% of wet ponds functioning 75.6%

8.4 Design Review of BMP Facilities

The first, and perhaps one of the most important opportunities by approval agencies to influence the effectiveness of a long-term operation and maintenance program is during the review stage of proposed stormwater management facilities. The following is a brief description of the operation/maintenance activities required for the most often used BMPs. The items to be considered during the design review have been highlighted. Designers of BMP facilities should address the issues related to operation/maintenance in their design reports. Wet Ponds (Retention Basins) Retention basins are often used where water quantity, quality, erosion and recreation or aesthetic objectives are included in the stormwater management program. The main areas of operation/maintenance are similar to dry ponds. One major difference is the multi-purpose nature of wet ponds, which may include extensive landscaping. However, it is important to emphasise that wet ponds are primarily storm water management facilities.

WET PONDS DESIGN REVIEW Safe access should be provided for maintenance equipment. Submerged inlets are preferred from the safety and vandalism point of view, but maintenance and cleaning could be more difficult to undertake. Where the intake pipe is at or close to the



bottom, protection of the bottom material against erosion and scour should be incorporated in the design. Outlet structures should be located to allow for suitable access by maintenance equipment. A low flow pipe capable of draining the pond should also be incorporated in the outlet structure. Sediment forebays should be equipped with a hard bottom capable of withstanding the weight of equipments used for operation/maintenance. As a minimum, hard surface protection should be provided at the inlet for scour protection. A low flow maintenance pipe should be provided to drain the forebay, if needed. The planting strategy should enhance the performance of the stormwater management facility, as well as provide safety and aesthetic benefits. Plants located in the area subject to inundation by infrequent storms, such as the 2 to 100 year events should be able to tolerate the inundation for several hours. Where landscape areas are incorporated around the pond facility for aesthetic functions, these plants should restrict access to steep areas or inlet/outlet structures and provide a wind barrier in order to protect the pond from wind-induced turbulence. Slopes requiring access by machinery should not be steeper than 3H: 1V. The design report should include estimates of annual sediment rates expected and an estimate of the maximum permissible sediment depth accumulation, when sediment removal is required. If possible, the design should incorporate a local sediment storage facility. Fencing along the pond may be necessary during construction period. However, once the construction in the development area serving the pond is complete and the Municipality has assumed responsibility for the pond, there is no need to leave permanent fencing around the pond, except around structures, such as inlets and outlets, provided the flat side slopes recommended are adopted.

(Extended) Dry Ponds The purpose of dry ponds (sometimes simply referred to as detention facilities) is to temporarily detain runoff and release the stored runoff at a specified reduced rate. Many of the aspects described under wet ponds also apply for dry ponds.

DRY PONDS DESIGN REVIEW One major difference between wet and dry ponds is the outlet of a dry pond, which is based on a perforated riser system. The risers are used to control the rate of outflow from a dry pond, these structures should be placed in a manhole located in the embankment where access during operation and maintenance is relatively easy. A low flow pipe with a minimum diameter of 250 mm should be provided in addition to the riser, and be capable of draining the pond. In case the riser becomes clogged, a by-pass system or a shut-off valve should be provided. If a shut-off valve is used adequate facilities should be provided for pumping the chamber until the riser is unclogged. Where a reverse slope outlet pipe is used, additional facilities such as under-drains should be provided to drain the portion of the pond located below the reverse sloped outlet pipe.



Constructed Wetlands The main purpose of a wetland is to provide stormwater management facilities and it should not be viewed as a significant natural area.

CONSTRUCTED WETLANDS DESIGN REVIEW The most important part of a constructed wetland area from the maintenance point of view is at the inlet forebay. Similar to the wet ponds, the forebay bottom should be able to withstand heavy machinery used for maintenance and have an adequate access for equipment used for cleaning. The constructed wetland design report should include sediment deposition rates and estimates for sediment removals. Side slopes generally less than 3V:1H (see design Fact Sheet) Have a micro-pool at the outlet to reduce risk of outlet clogging Have facility to drain the pool at the outlet Adequate allowance for future settlements in the embankment Sediment disposal arrangement

Infiltration Facilities Infiltration facilities are water impoundments constructed by excavation in a relatively permeable soil. The purpose is to temporarily store and infiltrate surface runoff through the bed and sides of the basin. From the operation and maintenance point of view, the design review should check that:

INFILTRATION FACILITIES DESIGN REVIEW Adequate access is provided for mowing and clean out equipment. Adequate pre-treatment of runoff is provided upstream of the facility to avoid premature clogging, by removing sediment, grit, oil, etc., before it enters the infiltration basin, or trench.Draining time should be not more than 72 hours after the design event, to free up storage for the next storm and to permit underlying soils to dry out. Adequate provisions for bypass for large flows Potential effects of inflow containing de-icing agents from road side winter runoff Risk of nitrate and chloride migration into groundwater Provision of test well adjacent to infiltration facility to monitor performance

Vegetated Swales Vegetated swales (grass-lined channels) with or without small (earth) check dams create a series of pools or very slow moving flow to induce infiltration. They can also be applied in development areas or highways as an alternative to curb and gutter drainage systems. Normally, swales are used in combination with other BMP systems.



VEGETATED SWALES DESIGN REVIEW

Diversion facilities, to prevent unprotected area runoff entering the swale during construction, or the construction of the swale after the site has been stabilized. Alignment of the swale should avoid wells or foundation walls. Design checks should include the outlet conditions leading into sewers or stream outfalls. Velocities below critical velocities Minimum bottom width for maintenance (<0.75 m) Side slopes not steeper that 3H:1V

8.5 Inspection During Construction

General The next opportunity for approval agencies to ensure an efficient long-term operation and maintenance program is during the construction phase. Regular on-site inspection is important, to ensure that the approved temporary and permanent stormwater management plan and designs are properly implemented. A pre-construction meeting with the developer and the consultant is recommended, to jointly review the project. Important elements of the inspection program are: • Inspection of sediment control, diversion and BMP structures during and following

installation. • Inspection following severe rainstorm or snow melts events. • Final inspection nearing completion, to ensure that temporary control measures have been

removed, stabilization of the site is complete, major-minor system is in proper condition and the grading agrees with the design.

All inspections should be documented in a report, listing the name of the inspector, date and time, and comments on compliance. Visual inspection of all BMP facilities will ensure that the facilities have been built according to approved design. The developer has the choice to build the final BMP first to also provide control during construction, or install a temporary facility for construction. An example of an Inspection Form is attached at the end of the Chapter.



Inspection of Storage Facilities (Ponds, Wetlands) Once the development is completed, and before a storage facility is handed over to the Municipality for future operation/maintenance, the storage facility should be cleaned and the accumulated construction sediment and debris should be removed from the storage pond. Construction fencing should be removed if approved by the Municipality. All signs should be in place, describing the purpose of the facility including any hazards, and identifying areas not open for the public. If monitoring is part of the project, the monitoring station should be operating, and the protocol for measuring, sampling and analyzing should be clearly established. Inspection of Infiltration Facilities Inspection at the excavation phase is important to ensure that the basin location and size is as specified on the approved drawings.

INFLITRATION FACILITIES INSPECTION Prior to the excavation of the infiltration facility, the basin area should be fenced or roped off to prevent construction equipment and construction traffic damaging the soil layer. It is premature to install infiltration before construction activities upstream have been completed. Sediment and organic material from construction activities will clog the soil pores; therefore all areas, which contribute stormwater runoff to an infiltration facility, must be stabilized before the facilities can receive surface runoff. Runoff should be diverted away from the infiltration site during construction. Excavation equipment should be lightweight to reduce compaction of the soils. Where the surface runoff enters the infiltration facility, soils should be protected to prevent erosion and sedimentation. Side slopes should be checked to ensure stability. Bottom of the infiltration facility should be inspected for removal of foreign objects such as tree roots, rocks, etc. These should be removed and replaced with permeable soils. If groundwater seepage is noticed, construction should be halted and the designer should be notified. Final inspection should be conducted before the infiltration facility goes into operation. Inlets should be free of erosion signs, outlets should be protected to prevent scour due to high velocities at the outflow channel. Permanent stabilization should be provided along the bottom and side slopes of an infiltration basin.

Inspection of Vegetated Swales Visual inspection of the swales will ensure that the facility has been built according to approved design. During the final inspection, the check dams should be checked for stability. The outlet should be stabilized to prevent erosion.



8.6 Operation and Maintenance Tasks after Construction

Stormwater management control facilities should be installed early during the construction phase (with the exception of infiltration facilities) to avoid any damage to the environment. Inspection of all BMP facilities will determine the type and frequency of maintenance required. Inspection should be undertaken more frequently during the first 2-3 years of operation. It is recommended that during this initial “phasing-in” period, the facilities should be inspected following each significant runoff event, (on the average 3-4 per year). Once the facility has proven to be functioning according to specifications, in most cases, only annual inspection will be required. One exception is the infiltration facilities, which should be inspected more often, at least three or four times per year, to identify potential clogging at an early stage. One maintenance activity, which may be common to most stormwater management facilities, is grass cutting that serves mainly aesthetic requirements, and is normally influenced by local residents. There are no, or very limited, water quality benefits derived from grass cutting. Where the land surrounding the BMP facility, especially around wet ponds or extended dry ponds, is used as public recreational land, or where private land abuts a public facility, the public may demand manicured lawns. However, these are expensive to maintain and do not serve stormwater management purposes. Dry Ponds (Detention Basins) The most important maintenance tasks to be considered are: • Sediment Removal; • Vegetation Maintenance; • Debris Removal; • Observance of Erosion; • Outlet Maintenance. Sedimentation rates in dry ponds will be affected by erosion/sedimentation control practised during construction activities. Where effective control was exercised, followed by an efficient removal of the sediment before the Municipality assumes the facility, removal of sediment can be expected every 5 to 15 years. If accumulated sediment is allowed to build up in the storage facility, the storage capacity will be reduced and potential for flooding will increase. Also, accumulated sediment could be re-suspended during high floods, which can create pollution problems downstream. Finally, local sediment deposits can prevent draining of the pond by gravity. Vegetation is used extensively in stormwater management facilities to prevent erosion, increase infiltration and improve water quality. Vegetation is also used to improve landscaping at and around the BMP facility. Maintenance of vegetation would include mowing and removal of debris. Mowing can only be done efficiently if slopes are 1V: 3H or flatter.



Debris and litter can block inlets and outlets, and can be very unsightly. Once debris and litter is trapped, it will attract more debris. The most cost effective maintenance practice is to remove the debris and litter during mowing. For outlets prone to be blocked by debris and litter, suitable trash racks will reduce the risk of clogging. Erosion can occur at unprotected embankments and at low flow channels carrying high velocity flow. Where velocities exceed the limit of safe vegetative channel design, stronger materials should be used to protect open channels from erosion. Repairs and replacements of various appurtenances are part of the operation/maintenance program. The frequency of the need for repairs or replacements is not known. Compared to the other operation/maintenance tasks, repairs or replacements are usually emergency tasks. Wet Ponds (Retention Basins) Regular maintenance activities are required to maintain aesthetic appearance, to ensure the proper functioning of control structures, to maintain acceptable water quality, undertake periodic weed control and sediment removal. Unscheduled maintenance may be required in response to extreme rainfall events. Access for maintenance equipment is important to provide rapid access to inlet and outlet structures. Frequent visits are needed to remove debris and litter. Blockages at inlets and outlets can occur frequently and require inspections after major storm events and at least 2-3 times a year. Mosquito control may be required depending on weather and local conditions. Some jurisdictions have used fish, pellets or chemical sprays to the pond surface to control mosquitoes. Grass cutting near the pond may also assist in reducing the mosquito population. Weed control around the pond could represent a substantial part of the operation and maintenance budget. Generally, weeding is done by hand to reduce the risk of destroying surrounding vegetation; the use of permitted herbicides could create subsequent water quality problems. Similarly, the use of fertilizers should be limited or eliminated to minimize the nutrient loadings downstream. Before using any chemical the municipality should check with provincial environment agency staff its permissibility. The following various control measures have been applied in the past to control weed or algae. • Control of nutrient input; • Use of fish and insects to control weed growth; • Algae control by zooplanktons; • Herbicides; • Mechanical harvesting; • Weed and algae control by shading;



• Bottom barriers to prevent root growth; • Control of water levels. During the early years of operation, the Municipality should develop a threshold level of weeds and algae with input from local residents. Such threshold values could be: • Rooted emergent macrophytes, not more than 5% over the lake area; • Algae control by keeping TP below 0.20 mg/L, and chlorophyll below 30 ug/L. The long-term performance of a storage facility depends on the rate of sediment accumulation. There is only limited data available on the required frequency of sediment removal, which depends on the type of BMP, available storage, drainage area and precipitation characteristics and municipal operation/maintenance practices. In absence of estimates of removal frequencies, usually required as part of the design submission, the following graph presented in Figure 8-1 provides an approximation on the total annual sediment deposits (m3/ha) generated by different catchment imperviousness expected in an extended wet pond designed for a 70% sediment removal rate. Generally, sediment accumulated in a wet pond is not contaminated and classified as hazardous waste. Testing of sediment samples will determine the disposal options. There are three ways sediment removed from ponds can be disposed, i) on-site, where a special area has been set aside for sediment disposal as part of the design, ii) off-site at an area undergoing filling or at a sanitary land fill, and ii) hazardous waste disposal site, if sediment contains hazardous material. Infiltration Facilities Infiltration facilities require more frequent inspection and cleaning than stormwater ponds. This is due to the fact that considerable amounts of sediment, organic matter, oils and grease and debris can accumulate in the soil pores, mainly on the surface of the infiltration facility. This in turn can reduce or totally eliminate infiltration.



Extended wet pond sediment deposition

0

0.5

1

1.5

2

2.5

3

30 40 50 60 70 80 90

Catchment imperviousness %

Ann

ual u

nit d

epos

ition

- m

3/ha

Figure 8-1 Annual Sediment Deposition Estimates– m3/ha

Constructed Wetland Facilities Wetlands used for stormwater management are not self-maintaining systems, therefore require extensive and continuous management, especially over the first five to seven years. The maintenance requirements can be grouped under: • Observation of the development of the wetland system; • Regulation and control of the upstream sediment supply; • Maintenance tasks to assist in maintaining the water balance; • Management of the wetland vegetation. Wetland inlets and outlets should be checked for blockage following the spring runoff and at least one other occasion in the summer season after a major runoff event. Any accumulation of debris and sediment should be removed by hand. Similarly the condition of aquatic vegetation and shoreline conditions should be checked to determine the need for maintenance work. Any presence of oil or other spill should be removed.



Vegetated Swales Vegetated swales should be inspected after the spring runoff. Debris should be removed, especially at check dams and at the outlet. This can be carried out during routine activities such as mowing. Where sediment accumulation is significant, especially if check dams are part of the vegetated swales, the sediment should be removed by hand. Vegetation should also be checked, such as the need for grass mowing, fertilizer application and re-seeding at eroded areas. Ponding after more than 24 hours in the swale indicates potential problem with natural recharge, caused by accumulated sediment and debris, requiring maintenance. Outlets should be free of obstruction. Side slopes showing signs of settlement, or slope failure should be repaired. Operation and Maintenance of Miscellaneous BMP Measures Porous pavements are very rare in Canada due to the severe winter conditions; the difficulty of rehabilitating clogged porous pavements; lack of experience in construction and operation; the highly skilled labour requirement; and the possibility of groundwater contamination. Oil and grit separators are designed to remove sediment and hydrocarbon loadings mainly from parking areas, before they enter the storm sewer system or one of the BMP facilities. They can only handle a small fraction of the minor system (2 or 5 year) flow. Only moderate removal of coarse sediment, oil/grease and debris can be expected from these facilities. Generally, these units are commercially available, and the design review should consider the oil/grit separators as part of the BMP system, providing some pre-treatment for the runoff. Frequent clean outs may be required therefore access is important. Scheduling Scheduling of Operation and Maintenance activities can be influenced by site-specific and weather conditions. Table 8-3 provides examples of scheduling to be used for long-term planning and budgeting.

Table 8-3 Example of POperation and Maintenance Schedules for Stormwater Management BMPs

Type of BMP Frequency O&M Activity

Semi-annual Inspect facility Clean and remove debris from inlet and outlet structures Control of invasive plants Mowing grass (Can be annual operation)

Annual Litter and debris removal Medium term (5-year or as needed)

Remove sediment from forebay Vegetation maintenance

Long term (10-year, or as needed)

Monitor sediment accumulation in pond and remove when needed

Wet pond

As needed Repair eroded areas and damaged structures



Type of BMP Frequency O&M Activity

Semi-annual Inspect facility Clean and remove debris from inlet and outlet structures Control of invasive plants Mowing grass

Annual Restore damaged areas in the pond bottom Medium term (5-year or as needed)

Remove sediment from forebay


Monitor sediment accumulation in pond and remove when needed

Dry pond

As needed Repair eroded areas and damaged structures Wetlands Semi-annual Inspect facility

Clean and remove debris from inlet and outlet structures Control of invasive plants Mowing grass (Can be annual operation

Annual Aquatic plant management Litter removal

Medium term (5-year or as needed)

Remove sediment from forebay


Monitor sediment accumulation in wetland and remove when needed

As needed Repair eroded areas and damaged structures Semi-annual Inspect facility Annual Mowing

Litter and debris removal Medium term (5-year or as needed)

Scrape swale bottom and remove sediment Restore original cross-section

Grassed swale

As needed Repair critically eroded areas, stabilize banks Semi-annual Inspect and monitor for sediment accumulation Annual Inspect appurtenances (separators, catch basins Medium term (2-5 year, or as needed)

Rehabilitation of trench to maintain design storage capacity

Filtration trench

As needed Remove sediment, debris Semi-annual Monitor for sediment accumulation

Remove leaves, litter and debris Oil/grit separator

Annual Remove sediment from separator sump

8.7 Monitoring Prior to Accepting the BMP Facility

The implementation of the BMP practices presented in the Guideline document will result in the construction of numerous stormwater management facilities that will become part of the HRM’s infrastructure. In the long-term HRM will have to assume, operate and maintain several dozen such facilities. These stormwater management facilities will require an ongoing operating and maintenance program in order to meet the intended flood protection, erosion and water quality control standards.



A monitoring program is essential for determining whether a BMP is functioning properly and to ensure that the facility operates in compliance with its intended design. Detecting any deficiencies before the Municipality assumes the facility and before any large-scale problems surface is the goal. The monitoring should address three basic questions: • Is the facility storing and releasing water at the approved rate; • Is the required treatment achievable and not reduced by sediment accumulation; and • Is there any release of excessive sediment or contaminants to the receiving watercourse.

Table 8-4 Typical Stormwater BMPs Monitoring Functions

Criteria Monitoring Purpose Data requirement Monitoring Frequency Elevation graph for non-winter period

Recorder with hourly readings Elevation of permanent pool

Does permanent elevation meet design

Staff gauge check After major rainfall Elevation of water quality and/or erosion control elevation

Does elevation exceed design elevation

Elevation graph for non-winter period

Recorder with hourly readings

Outflow and pond elevation

Does outflow meet design elevation-flow relationship

Flow and level recorder Recorder with hourly readings

Sediment accumulation Sediment accumulation significant (>5% reduction in storage?)

Estimate accumulation by survey

Subject to results of visual inspection, suggested every two year during the early life of facility

Sediment discharge Does it exceed acceptable rate?

Total sediment data Approximately 5 times per year after rainfall events, in the early life of facility

Contaminant discharge Does it exceed acceptable rate?

Determined after first few samples

Determined after first few samples

Monitoring of water quality is normally carried out for larger projects, near the receiving stream, or water body and in locations where there is lack of information on performance of various BMPs. Although some monitoring is required for research or for obtaining data for computer model calibration, the monitoring program a Municipality implements should concentrate on assessing the performance of their facilities. As part of the design documentation, the designer should describe the recommended location, frequency, parameters and type of monitoring. Generally, there is a need to monitor a number of parameters in order to understand the hydrologic, hydraulic and biological processes and the performance of the stormwater management facility. In addition to inflow volumes, the following quality data needs to be collected: • total suspended and dissolved solids; • heavy metals, lead, copper, chromium, zinc and cadmium;



• phosphorus and nitrogen parameters; • oil and grease; • chlorides. It is recommended that a four season monitoring program be established for large-scale facilities. If the four season results meet the design requirements, the monitoring should be suspended, until the operation/maintenance activities identify deterioration in the performance of the structure. The developer should cover the cost of the four season monitoring the same way as the cost of facility construction was allocated. Once the BMP facility has been accepted and taken over by the Municipality, the developer will also be required to cover the monitoring costs during the one-year maintenance period. Following the maintenance period the Municipality should cover the monitoring costs. The Municipality should assume responsibility for the operation and maintenance of a stormwater management facility when the development area draining into the facility has been substantially (in the order of 90%) developed.

8.8 Public Information

Consideration should be given to inform the public on stormwater management facilities. More particularly to their purpose, safety, cost of construction and operation/maintenance, on problems such as algae and weeds, future programs, contact names and telephone numbers.



INSPECTION FORM FOR STORMWATER MANAGEMENT SYSTEMS Operation and Maintenance Inspection Report for Stormwater Management Ponds

Inspector Name Location Inspection Date Type of Pond: Wet or Dry Name of Pond File Number Photo Numbers Overall conditions of facility:



Operation and Maintenance Inspection Report for Stormwater Management Ponds Pond Component Checked Maintenance Needed Remarks

Embankment

Vegetation and ground cover

Embankment upstream

Embankment downstream

Spillway

Intake

Trash rack

Erosion, rip rap protection

Endwall/Headwall

Sediment Forebay

Sediment depth



Pond Component Checked Maintenance Needed Remarks Pond

Debris

Sediment

Undesirable vegetative growth

Shoreline conditions

Odour

Mosquito problem

Outlet

Outlet pipe or riser

Maintenance outlet pipe



Miscellaneous

Grass mowing, graffiti

Maintenance access



9.0 Erosion and Sediment Control at Construction Sites

9.1 Background

The rapid increase in erosion and sedimentation caused by construction activities, if left uncontrolled, can result in serious damage to the environment. High erosion rates can result in loss of valuable topsoil, and the subsequent sedimentation of streams and lakes can affect water supplies, flood control, fishing, navigation and recreational activities. Measurements of erosion rates, taken from various land uses, show a wide range of values, however, representative erosion rates for construction sites with no erosion control measures are, on the average, 200-400 times higher than the natural erosion rate for rural land use. Experience across Canada identified that the most frequent loss of performance over time occurs at wet ponds and wetlands and is related to inadequate maintenance of accumulated sediment levels within the facility. Observations of annual sediment accumulation rates at wet ponds and wetlands showed that facilities located in drainage areas subject to active or recent construction activities accumulate sediment at very much higher rates than the assumed long-term rates. For example, extensive monitoring undertaken by the Town of Richmond Hill located north of Toronto showed that the long-term sediment accumulation rate of 2.0 m3/ha per annum observed at stabilized catchments could increase by close to ten fold during the early period of pond operation, in spite of active erosion and sediment control at the construction site. (See Figure 9-1) The relationship between sediment accumulation and age suggests that the first five years produce the highest rate of accumulation after the facility is constructed. This period coincides in most cases with active construction activities in the catchment.

Sediment accumulation rate in wet ponds

02468

101214

0 5 10 15 20 25 30 35

Mean annual sediment rate - m3/ha/year

Age

of f

acili

ty -

year

s

Figure 9-1 Observed Sediment Accumulation in Richmond Hill Wet Ponds

Local grain size observations of accumulated sediment could help to refine the design of wet pond and wetland forebays, and the municipal operation and maintenance program. Results of



grain size analysis at the Richmond Hill ponds showed that forebays contained the highest percent of coarse gravel and sand particles, especially once the catchment has been stabilized. Silts and clays dominated the accumulated sediments in ponds beyond the forebay. The lesson learned by Municipalities is not to assume new BMPs until construction in the catchments is complete, all accumulated sediment has been safely removed, and 100% of the designed storage capability becomes available for managing stormwater. Without such strict requirement the municipality’s financial liability could increase. For example a number of recent sediment removal costs at Ontario wet ponds ranged between $0.5 million to over $0.8 million. Strict erosion and sediment control at construction sites becomes an important component of a municipality’s operation and maintenance program. Assessing the characteristics of the sediments accumulated in stormwater management facilities is necessary to determine the means of safe disposal of the sediments after removal. Generally, it was found that sediment in facilities operating in residential areas can be considered uncontaminated for disposal purposes. In some locations where high level of road salt is being applied during the winter season, the electrical conductivity of sediment samples were excessive, but did not increase the disposal costs. The potential of the sediment removed to impair aquatic ecosystem health should also be assessed. Samples taken in Canada showed that chemical parameters such as TKN, TP, Chromium, heavy metals and oil and grease were found to exceed Sediment Quality Guidelines Lowest-Effect-Level criteria, but lower than the Severe-Effect- Level regarded as potentially detrimental to aquatic organisms. The purpose of the erosion guidelines for construction sites is to provide developers, contractors and review agencies with a set of practical methods for ensuring that urban construction is carried out in such a manner that a minimum amount of soil is eroded from the site and deposited in downstream watercourses. A review of erosion and sediment control practices across Canada identified a number of common features.

EROSION AND SEDIMENT CONTROL PRACTICES COMMON FEATURES There is still a lack of awareness by agency staff, engineers, developers, builders and contractors on the need to control erosion and sedimentation at constructions sites. Many agencies are organizing workshops and disseminating the knowledge required by studies and reports. There is a lack of formal reporting protocol to monitor the construction process and the lack of control by-laws to assist with the enforcement of policies. A number of municipalities established regulations and municipal by-laws on erosion and sediment control from existing statutory federal or provincial legislation. This gave the reviewing agency the mechanism for enforcement and in case of failure to comply with the appropriate legislation that can result in fines and/or jail time. In addition to municipal and provincial environmental protection acts, the federal Fisheries Act is used to enforce the erosion/sediment controls. The Fisheries Act prohibits the deposition of substances to water



that will degrade or alter fish and fish habitat. The possible fines are $300,000 - $1,000,000 and 6 months to 3 years prison term. There is a general lack of flexibility within the Erosion and Sedimentation Control Plan process. Once the Plan is approved, there is lack of opportunity to account for on-site changes during the construction activity. Ultimately, the developer, contractor and the consultant are liable for the proper implementation and use of erosion and sediment control measures. Municipal by-laws can effectively address the erosion and sediment control issues or the need for topsoil preservation. The by-laws regulate or prohibit the removal of topsoil and ensure that the work for which a permit is issued has no adverse environmental effects. Provisions are also provided depending whether the site is located next to a water body and on rehabilitation of lands where topsoil removal is permitted. To reduce the numbers of permit applications many jurisdictions established a minimum disturbed area for requiring a permit. All by-laws require the submission of Erosion and Sedimentation Control Plans. Municipalities charge a permit application fee to cover the administration of the permit process. A few municipalities require proponents to deposit securities with the Municipality for the erosion and sediment control works. Once the erosion and sediment control permit has been granted there is little input or control by the municipality once the building process begins until assumption of the works. Review agencies should take active role in inspecting the Erosion and Sedimentation Control works to ensure compliance. There is a lack of provisions in some municipal documents on accountability and on who is ultimately responsible for the implementation and maintenance of Erosion and Sedimentation Control. Erosion and Sediment Control Plans should be stamped by a professional engineer. The consultant should review the grain size distribution of the site soils prior to preparation of the Erosion and Sediment Control Plan. Sediment control works should be installed prior to the initiation of any earthworks. Where feasible, the ultimate stormwater management BMPs selected for the development should be used for sedimentation control during construction. Emergency overflow capacity should be incorporated into the design of a sediment control facility

A comprehensive Erosion and Sediment Control Plan should address all five stages of the development and construction process: 1) Stripping of topsoil 2) Earthwork and grading 3) Servicing 4) Construction 5) Assumption



Enforcement of the Erosion and Sediment Control Plan requirement can be challenging during the construction phase, especially where the design consultant no longer provides resident field inspection during the house construction. An approach Municipalities may take to resolve this issue includes requiring the builder to place securities to maintain the control measures stipulated in the plan and having the builder provide a street, catch basin, or pond cleaning program.

Table 9-1 Frequently Used Erosion and Control Measures

CONTROL MEASURE PURPOSE Flow spreader Filters and spreads flow prior to entering a watercourse to reduce erosion and

sedimentation Hydroseeding Provides temporary or permanent stabilization of disturbed area by application

of seeds, fertilizer, mulch, soil adhesives and water Interceptor swale Directs sediment-laden runoff to sediment control facility, by excavated swale. Matting with seeds Provides instant stabilization of disturbed soil until new vegetation is

established. Mud mats Prevents soil carried from off the site by installing a bed of gravel at the site

entrance and exit Sediment basins Intercepts sediment laden water and detains it to settle suspended sediment. Sediment control fence Acts as a barrier to the sediment laden flow and reduces flow velocity Sediment traps Intercepts sediment laden water and detains it to settle suspended sediment Sodding Establishes grass and provides quick and permanent stabilization Straw bales Intercepts, filters and traps overland flow of sediment-laden runoff. Temporary check dams Reduces velocity of concentrated flow in a channel to minimize erosion,

detain and trap small amount of sediment

9.2 Legislative Framework for Erosion and Sediment Control

Federal, Provincial and Municipal legislations may govern erosion and sediment removal at construction sites. The Federal legislation focuses on the Fisheries Act, which states: No person shall carry out any work on undertakings that result in the harmful alteration, disruption or destruction of fish habitat. {Section 35(1)}, and No person shall deposit or permit the deposit of a deleterious substance of any type in water frequented by fish. {Section 36(3)}. Guidance documents released by the Department of Fisheries and Oceans, such as Fish Habitat Compliance Protocol or Policy for the Management of Fish Habitat is available to assist in the interpretation of the Act. Under the Act, summary convictions up to $300,000 and/or 6 months imprisonment are possible. Indictable offences can be up to $1 million and/or 3 years imprisonment. As stated in Section 2.0 Provincial legislation is provided under the Environment Act. Provincial legislation covers approvals for stormwater management such as the design, construction, operations and maintenance of stormwater collection, pumping, storage and treatment systems.



The Act also regulates any other alteration of watercourses. Through the MGA, the Province allows Municipalities to enact planning policy and land use bylaws to deal with change in land use and erosion/sediment control provisions. Municipal by-laws usually require a permit to remove topsoil or undertake site alteration. Condition of approval requires erosion and sediment control. Enforcement powers could result in fines as much as $10,000, plus court order for rehabilitation. A number of municipalities provide exemptions to apply for erosion/sedimentation control permits. Categories for an exemption include: • Agricultural Land Management • Additions or Modifications to single family residence • Developments that disturb less than 500 square metres • Residential developments consisting of single residences on one lot

9.3 Nova Scotia Erosion and Sediment Control Requirements

The Nova Scotia Environment and Labour issued a comprehensive Handbook on Erosion and Sedimentation Control. The document is based on the following accepted principles and practices for reducing erosion and sedimentation: • Fit the activity to the topography, soils, waterways and natural vegetation of a site • Expose the smallest practical area of land for the shortest possible time • Apply soil erosion control practices as a first line of defence against on-site damage • Apply sediment control practices as a perimeter protection to prevent off-site damage • Implement a thorough maintenance and follow-up operation. The recommended steps to follow in preparing an erosion and sediment control program for construction project are reproduced from the Handbook in Figure 9-2 on the following page.



Figure 9-2 Steps to Follow to Prepare an Erosion and Sedimentation Control Program (NSEL Handbook)


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10.0 Submissions by Developers

Early consultation with municipal planners and engineers is essential for developers and/or their consultants to ensure a smooth implementation of the Stormwater Management approval process. The recommended procedure is based on a two-phased approach. A Stormwater Management Concept Plan should be first prepared for all developments greater than 5 ha to describe the effects of the proposed development on the existing drainage area and the environment, including proposed mitigating measures. Where watershed or subwatershed studies are available the Concept Plan should refer to the findings and recommendations of the Watershed/subwatershed Plan. A typical Stormwater Management Concept Plan includes: • Existing servicing constraints: hydrology, hydraulics, hydrogeological, and environmental; • Design criteria (quantity, quality, erosion and base flow control) adopted from Existing

Watershed/subwatershed Plan or from HRM Standard Criteria; • Layout of the proposed development; • Location of the major-minor system; • Location and approximate size of storage facilities; • Proposed channel works; • Erosion and sediment control activities; and • Location of environmentally sensitive areas. The second submission, a Final Stormwater Management Report should provide a more detailed description of the proposed Stormwater Management works: • Hydrologic and hydraulic parameters; • Major and minor system flows; • BMP facilities stage-storage-discharge relationship; • Lot and road grading; • Minor drainage system details; • Major drainage system details; • Outfalls; • BMP facilities, control structures, overflows, maintenance access, etc.; • Erosion and sediment control plans; • Planting and landscaping of BMP facilities; • Maintenance timing for BMP facilities; and • Monitoring plans.


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The Final report should include a number drawings/figures: • Location plan; • Drainage areas for existing and proposed land uses; • Overland flow routes; • Details of BMP facilities; • Details of erosion and sediment controls; • Computer outputs and schematics; and • Copies of approvals from federal and provincial agencies. It is not practical to require the above documentation for areas <5 ha. The minimum documentation required for a smaller development should include the following: • Description of the proposed development; • Proposed changes to drainage patterns; • Planned discharge location; • Potential changes to quantity/quality of stormwater; • Descriptions of proposed stormwater management techniques to minimize any changes to

quantity and quality of the stormwater; and, • Information on erosion and sedimentation.


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Glossary Base Flow – Flow in a stream during a sustained period between precipitation events. This flow is primarily sustained by groundwater. Best Management Practices (BMPs) – Activities, practices, products or devices or combinations thereof designed to prevent or reduce the release of excessive flows, sediment and other pollutants into receiving water bodies. Conveyance Control BMPs - Conveyance control measures provide quantity and/or quality control of stormwater within the conveyance system between the source and outlet. Design Storm – A rainfall event of specified size and return frequency which is used to calculate flow rates for selecting and/or sizing stormwater management measures. End of Pipe Control BMPs - End of pipe control measures provide quality and/or quantity mitigation at or near the downstream end of the stormwater conveyance system. Erosion and Sedimentation Control – Any temporary or permanent measure installed to reduce and/or prevent erosion and control siltation and sedimentation. The end result minimizes the amount of sediment entering a water body. Infiltration – The gradual downward flow of water from the surface through to groundwater. Quality Control Design – The design of BMPs to control the amount of pollutants within water flowing from a site. The design may require the removal of nutrients, metals and/or bacteria. Quantity Control Design – The design of BMPs to control the amount of water flowing from a site. Recharge – Amount of precipitation available to infiltrate into the surface to the groundwater. Source Control BMPs - Source control BMPs are on-site measures that control runoff at the source of generation. These include all measures that treat and/or control the runoff before it reaches the conveyance system. Storm Frequency – The expected period of time that will elapse between storm events, based on probability of storms within the area, of a given intensity and/or total volume will occur. Total Suspended Solids (TSS) – A measurement of the amount of sediment in water. Treatment Train – The use of multiple BMPs to achieve the required stormwater management control.


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Watershed/Subwatershed Plan - A watershed/subwatershed study should describe the components that would directly or indirectly determine the quantity and quality design criteria to be applied in the design of various BMPs. See Appendix D for further requirements.


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References General Stormwater Management Bibliography Caraco, D. and Claytor R. (1997) Stormwater BMP Design Supplement for Cold Climates. Center for Watershed Protection, Ellicott City, Maryland, USA. City of Calgary (2001) Guidelines for Erosion and Sediment Control. City of Calgary, Alberta. Claytor, R.A. and Scheuler, T.R. (1996) Design of stormwater filtering systems. Center for Watershed Protection, for the Chesapeake Research Consortium Inc. CH2M Hill, 2000. Technical Memorandum on Urban Stormwater Pollutant Assessment for North Carolina Department of Environment and Natural Resources. Droste, R.L., and Johnston, J.C., (1993) Urban snow dump quality and pollutant reduction in snowmelt by sedimentation, Canadian Journal of Civil Engineering, 20: 9-21. Finley, S.M. and Young, G.K. (1993) Grassy swales to control highway water quality runoff. Transportation Researrch Record, No. 1420, U.S. Transportation Research Board. Gibb, Allan et. al., (1999) Best Management Practices for Stormwater, Greater Vancouver Sewerage and Drainage District, GVRD, Burnaby, BC. Granger, R.J., Gray, D.M. and Dyck, G.E. (1984) Snowmelt infiltration to frozen prairie soils. Canadian Journal of Earth Science, 21(6): 669-677. Greenland International Consulting Inc. 1999. Storm Water Management Facility Sediment Maintenance Guide The Toronto and Region Conservation Authority, Ontario Ministry of the Environment SWAMP. Grizzard et al, 1983, Washington Metropolitan Area Nationwide Urban Runoff Project. Jokela, J.B. and Bacon T.R. (1990) Design of urban sediment basins in Anchorage. Cold regions Hydrology and Hydraulics, American Society of Civil Engineers, NY, pp.761-789. Kercher, W.C., Landon, J.C., and Massarelli, R., (1983). Grassy swales prove cost-effective for water pollution control. Public Works, USA, 1983, Vol. 114, No. 4, pp.53-54. Li, J., Orland, R., and Hogenbirk, T. (1998). Environmental road and lot drainage designs : alternatives to the curb-gutter-sewer system. Canadian Journal of Civil Engineering, 25, pp.



Livingstone, E., Cox, J., Sanzone, P. and Gourlie, N. (1984) The Florida Development Manual: A Guide to Sound Land and Water Management. Florida Department of Environmental Regulation, Tallahassee, Florida, USA. Marsalek, P.M. (1997) Special characteristics of an on-stream stormwater pond: winter regime and accumulation of sediment and associated contaminants. M.Sc. thesis, Dept. of Civil Engineering, Queen’s University, Kingston, Ontario, Canada. Middlesex University, Review of the use of Stormwater BMPs in Europe, 2003, under the EC Daywater program. Milne J. B., and Dickman M. (1977) Lead concentrations in algae and plants grown over lead contaminated sediments taken from snow dump in Ottawa, Canada, Journal Environmental Science Health, A12(4/5): 173-189. Montes, S. (1998) Hydraulics of open channel flow. American Society of Civil Engineers, USA, ISBN 0-7844-0357-0. Nova Scotia Environment and Labour (2002) Storm Drainage Works Approval Policy. Oberts, G.L. and Osgood, R.A. (1988) Lake McCarrons Wetland Treatment System: Final report on the function of the Wetland Treatment System and the impacts on lake McCarrons. Metropolitan Council, St. Paul, Minnesota, publication No. 590-88-095, 227pp. Oberts, G.L., Wotzka, P.J. and Hartsoe, J.A. (1989) The Water Quality Performance of Select Urban Runoff Treatment Systems. Metropolitan Council, St. Paul, Minnesota, publication No. 590-89-062a, 170pp. Ontario MOE, Stormwater Management Practices Planning and Design Manual, 2003. Pettersson, T.; German J.; Svensson, G. (1999) Pollutant removal efficiency in two stormwater ponds in Sweden. Proc. 8th Int. Conf. on Urban Storm Drainage, Sydney, Australia. Ryerson University, Clarifica Consulting, March 2004. “Assessment of Construction Sediment Control Ponds to Protect Receiving Waters. Schueler, T. (1987) Controlling urban runoff. Met Washington Council of Governments, Washigton DC. Schueler, T. (1992) Design of stormwater wetland systems: guidelines for creating diverse and effective stormwater wetland in the mid-Atlantic Region. Metropolitan Washington Council of Governments, Washington, DC. USA. Schueler, T.R. 1987, Controlling Urban Runoff practical Manual for Planning and Designing Urban BMPs, Publication No 87703, Metropolitan Washington Council of Governments.



Schueler, T.R. 1996, Design of Stormwater Wetland System Metropolitan Washington Council of Governments. Schueler, T.R. 1997. Comparative Pollutant removal Capability of Urban BMPs: A Reanalysis. Watershed Protection Techniques 2 (4): 515-520. Stahre and Urbonas, B. (1990) Stormwater detention for drainage, water quality and CSO management. Prentice-Hall, New Jersey, United States. Stahre and Urbonas, B. (1993). Stormwater. Best management practices and detention for water quality, drainage and CSO management. PTR Prentice Hall, Englewood Cliffs, New Jersey, USA. Stoneman, C. and M. L. Jones. 1996. A simple method to classify stream thermal status with single observations of daily maximum water and air temperature. North American Journal of Fisheries Management 16:728- 737. Stormwater BMP Designs and Performance to Receiving Water Impact Mitigation, Aug 19-24 2001, Snowmass Village, Colorado/USA, pp 354-368. American Society of Civil Engineers Thelen E., Fielding, and Howe L. (1978) Porous pavement, The Franklin Institution Press. Philadelphia, Pensylvania. Urbonas, B., Guo, and Tucker, (1990). Optimization of stormwater quality capture volume. Proceeding of an Engineering Foundation Conference, ASCE, October 1989 in Switzerland, Published in New York, Urban stormwater quality enhancement. Urban Drainage and Flood Control District (1999) Urban storm drainage. Criteria manual. Volume 3 – best management practices. Denver, Colorado. USA US EPA, (1974) Proposed guidelines for determining acceptability of dredged sediments disposal in EPA Region VI., Dallas, USA. US National Pollutant Removal Performance Data Base http://www.bmpdatabase.org/ Walsh, P.M., Barrett, M.E., Malina, J.F. and Charbeneau, R.J. (1997). Use of vegetative controls for treatment of highway runoff. Online report 97-5. Center for Research in Water Resources, The University of Texas at Austin, USA Wang, T., Spyridiakis, D.E., Mar, B.W., and Horner, R.R. (1981). Transport, deposition and control of heavy metals in highway runoff. Washington State Dept. of Transportation, Seattle, WA.



Watt, W.E., Marsalek, J. and Anderson, B.C. (1997) Stormwater pond perceptions vs.realities: a case study. Proc. Eng. Foundation Conference Sustaining urban water resources in the 21st century, September 7-12, 1997, Malmö, Sweden. WEF and ASCE, (1998) Urban runoff quality management. WEF manual of practice No. 23. ASCE manual and report on engineering practice No. 87. WEF, Water Environment Federation and ASCE, American Society of Civil Engineers. USA. Westerström, G. (1995) Chemistry of snow melt from an urban lysimeter, Water Quality Research Journal Canada, 30(2): 231-242. Yu, S. L., Norris, W. K. and Wyant, D. C. (1987) Urban BMP demonstration project in the Albemarle/Charlottesville area. Final Report to Virginia Department of Conservation and Historic Resources, University of Virginia, Charlottesville, Virginia. Yu, S. L., Kuo, J.T., Fassman EA, (2001) Field test of a grassed-swale performance in removing runoff pollution. Journal of Water Research PL-ASCE127 (3): 168-171.



Bibliography - Wet Ponds American Society of Civil Engineers (ASCE), 1998, “Urban Runoff Quality Management,” Manual and Report of Engineering Practice 87, Reston, VA. American Water Works Association (AWWA), 1990, Water Quality and Treatment, F.W. Pontius (ed), McGraw-Hill, New York, NY. Barrett, M., 1999, “Complying with the Edwards Aquifer Rules: Technical Guidance on Best Management Practices,” Texas Natural Resource Conservation Commission, Austin, TX. California Department of Transportation (Caltrans), 2004, “BMP Retrofit Pilot Program, Final Report,” CTSW-RT-01-050. California Stormwater Quality Association (CASQA), 2003, “Stormwater Best Management Practice Handbook,” New Development and Redevelopment. Dorman, M.E., M.E. Hartigan, J.P. Steg, and T.F. Quasebarth, 1996, “Retention, Detention, and Overland Flow for Pollutant Removal from Highway Stormwater Runoff,” FHWA-RD-095, US Federal Highway Administration, McLean, VA. Driscoll, E, G.E. Pelhegyi, E.W. Strecker, and P.E. Shelly, 1989, “Analysis of Storm Event Characteristics for Selected Rainfall Gauges Throughout the United States,” prepared for United States Environmental Protection Agency (USEPA). Engle, B.W., and A.R. Jarrett, 1995, “Sediment Retention Efficiencies of Sedimentation Filtered Outlets,” Trans. Amer. Soc. Agri. Engrs, 38, 2, 435. Fennessey, L.A., and A.R. Jarrett, 1997, “Influence of Principal Spillway Geometry and Permanent Pool Depth on Sediment Retention of Sedimentation Basins,” Trans. Amer. Soc. Agri. Engrs., 40, 1, 53. Goforth, G.F., J.P Heaney, and W.C. Huber, 1983, “Comparison of Basin performance Modeling Techniques,” J. Environ. Engr., 109, 5, 1082. Grizzard, T.J., 1987, “Final Report: London Commons Extended Detention Facility Urban BMP Research and Demonstration Project,” Virginia Tech University, Occoquan Watershed Monitoring Laboratory, Manassas, VA. Grizzard, T.J., C.W. Randall, B.L. Weand, and K.L. Ellis, 1986, “Effectiveness of Extended Detention Ponds in Urban Runoff Quality‹Impact and Quality Enhancement,” B. Urbonas and L.A. Roesner (eds), American Society of Civil Engineers, New York, NY.



Guo, J., and B. Urbonas, 1996, “Maximized Detention Volume Determined by Runoff Capture Ratio,” J. Water Res. Plan. and Manage., 122, 1, 33. Hazen, A., 1904, “On Sedimentation,” Trans. Amer. Soc. Civil Engr., 53, 45. Keblin, M.V., M.E. Barrett, J.F. Malina, and R.J. Charbeneau, 1998, “The Effectiveness of Permanent Highway Runoff Controls: Sedimentation/Filtration Systems,” Research Report 2954-1, Center for Transportation Research, University of Texas, Austin, TX. King County, 1998, Surface Water Design Manual, Department of Natural Resources, Seattle, WA. Mathews, R.R., W.E. Watt, J. Marsalek, A.A. Crowder, and B.V.C. Anderson, 1997, “Extending Retention Times in a Stormwater Pond with Retrofitted Baffles,” Water Qual. Res. J. Canada, 32, 1 73. McBean, E.A., and D.H. Burn, 1983, “Thermal Modeling In Urban Runoff and the Implications to Stormwater Pond Design,” in International Symposium on Urban Hydrology, Hydraulics and Sediment Control, University of Kentucky, Lexington, KY. Metcalf and Eddy Inc., 1991, Wastewater Engineering: Treatment, Disposal, Reuse, McGraw-Hill, New York, NY. Millen, J.A., A.R. Jarrett, and J.W. Faircloth, 1997, “Experimental Evaluation of Sedimentation Basin Performance for Alternative Dewatering Systems,” Trans. Amer. Soc. Ag. Engrs., 40, 1087 Minton, G.R., 2002, Stormwater Treatment: Biological, Chemical, and Engineering Principles, RPA Press, Seattle, WA, www.stormwaterbook.com. Nix, S.J., J.P. Heaney, and W.C. Huber, 1983, “Analysis of Storage/Release Systems in Urban Stormwater Quality Management: A Methodology,” 1983 International Symposium on Urban Hydrology, Hydraulics and Sediment Control, University of Kentucky, Lexington, KY. Oberts, G., 1997, Lake McCarrons Wetland Treatment System—Phase III Study Report,” Metropolitan Council of the Twin City Areas, St. Paul, MN. Persson, J., N.L. Somes, and T.H. Wong, 1999, “Hydraulic Efficiency of Constructed Wetlands and Ponds,” Water Sci. Tech., 40, 3, 291. Persson, J., 2000, The Hydraulic Performance of Ponds of Various Layouts, Urban Water, 2, 243.



Pitt, R., 2000, “The Design and Use of Detention Facilities for Stormwater Management Using DETPOND,” University of Alabama. Raasch, G.E., 1979, “Urban Stormwater Detention Sizing Technique, in International Symposium on Urban Storm Runoff,” University of Kentucky, Lexington, KY. Roesner, L.A., Burgess, E.H. and Aldrich, J.A., 1991, “Hydrology of Urban Runoff Quality Management,” Proceedings of the l8th National Conference on Water Resources Planning and Management, Symposium on Urban Water Resources, New Orleans, LA. Small, M.J., and D.M. Ditoro, 1979, “Stormwater Treatment Systems,” J. Environ. Engr., 105, 3, 557. Strecker, E., 2003, presentation to the Independent Science Panel regarding its review of the technical adequacy of the State of Washington Stormwater Management Manual for Western Washington. Timmins, K., T.L. Koob, M.E. Barber, and D. Yonge, 1999, “Thermal Stratification Impacts on Wetpond Performance,” International Water Resources Engineering Conference, ASCE, Seattle, WA. USEPA, 1986, “Methodology for Analysis of Detention Basin for Control of Urban Runoff Quality,” USEPA 440/5-87-001, Washington, D.C. Walker, D.J., 1998, “Modeling Residence Time in Stormwater Ponds,” Ecol. Engr., 10, 247. Ward, A.D., C.T. Haan, and B.J. Barfield, 1979, “Prediction of Sediment Basin Performance,” Trans. Amer. Soc. Ag. Engrs., 22,1, 126. Whipple Jr., William, Hunter, Joseph V., 1981, “Settleability of Urban Runoff Pollution,” J. Water Pollution Control Federation, Vol. 53, No. 12, pp. 1726 - 1731.



Bibliography – Swales Backstrom, M. 2002. Sediment transport in grass swales during simulated runoff events. Water Sci Tech 45: 7, 41. California Department of Transportation (Caltrans). 2004a. BMP retrofit pilot program, final feport, CTSW-RT-01-050. Caltrans. 2004b. Roadside vegetated treatment sites, final report, CTSW-RT-03-028. Colwell, S. 2001. Characterization of performance predictors and evaluation of mowing practices in biofiltration swales. MS thesis, University of Washington–Seattle. Fletcher, T.M., L. Peljo, J. Fielding, T. Wong, and T. Weber. 2001. The performance of vegetated swales for urban stormwater pollution control. Ninth International Drainage Conference on Urban Drainage. Portland, OR: American Society of Civil Engineers. Johnson, P.D, R. Pitt, S. Durrans, M. Urrutia, and S. Clark. 2003. Metals removal technology for urban stormwater, report 97-IRM-2. Water Environment Research Foundation. Kadlec, R. 2000. The inadequacy of first-order treatment wetland models. Eco Engr 15: 105. Kaighn, R.J., and S.L. Yu. 1996. Testing of roadside vegetation for highway runoff pollutant removal. Transportation Research Record 1523. Washington, DC: Transportation Research Board. Khan, Z., C. Thrush, P. Cohen, L. Kulzer, et al. 1992. Biofiltration swale performance, recommendations, and design considerations. Municipality of Metropolitan Seattle. Kuo, J., S.L. Yu, E.A. Fassman, and H. Pan. 1999. Field test of grassed swale performance in removing runoff pollution. 26th Annual Conference on Water Resources Planning & Management. Tempe, AZ: American Society of Civil Engineers. Mazer, G. 1998. Environmental limitations to vegetation establishment and growth in vegetated stormwater biofilters. MS thesis, University of Washington–Seattle. Minton, G.R. 2002. Stormwater Treatment: Biological, Chemical, and EngineeringPprinciples. Seattle: RPA Press. Ree, W.O. 1949. Hydraulic characteristics of vegetation for vegetated waterways. Agric Engr 30: 184. Samani, J. and N. Kouwen. 2002. Stability and erosion in grassed channels. J Hydr Engr 128: 1, 40.



Wang, T., D. Spyridakis, B.W. Mar, and R.R. Horner. 1982. Transport, deposition, and control of heavy metals in highway runoff, report 10. Seattle: Department of Civil Engineering. University of Washington. Washington State Department of Ecology. 1992. Stormwater management manual for the Puget Sound Basin. Olympia. Yousef, Y.A., M.P. Wanielista, and H.H. Harper. 1985. Removal of highway contaminants by roadside swales. Transportation Research Record 1017. Washington, DC: Transportation Research Board. Yu, S.L., J. Kuo, E. Fassman, H. Pan. 2001. Field test of a grass-swale performance removing runoff pollution. J Water Res Manage 127: 3, 168.



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Hsieh, Y., and C. Coultas. 1989. Nitrogen removal from freshwater wetlands: Nitrification-denitrification coupling potential. In Constructed wetlands for wastewater treatment, ed. D.A. Hammer. Boca Raton, FL: Lewis Publishers. Huneycutt, D. 2002. The demonstration project and stormwater management. Seventh Biennial Stormwater Research & Watershed Management Conference, Florida. Kadlec, R.H. 2000. The inadequacy of first-order treatment wetland models. Ecol Engr, 15, 105. Kadlec, R.H., and R.L. Knight. 1996. Treatment wetlands.Boca Raton, FL: Lewis Publishers. Kao, C.M., J.Y. Wang, and M.J. Wu. 2001. Evaluation of atrazine removal processes in a wetland. Wat Sci Tech, 44, 11, 539. Lawrence I., and P. Breen. 1998. Design guidelines: Stormwater pollution control ponds and wetlands. Canberra, Australia: Cooperative Research Center for Freshwater Ecology. Mckee, W.H., and M.R. McKevlin. 1993. Geochemical processes and nutrient uptake by plants in hydric soils. Environ Toxic and Chem, 12, 2,197. Minton, G.R. 2002. Stormwater treatment: Biological, chemical, and engineering principles.Seattle: RPA Press. www.stormwaterbook.com. Moustafa, M.Z., M.J. Chimney, T.D. Fontaine, G. Shih, and S. Davis. 1996. The response of a freshwater wetland to long-term ³low level² nutrient loads‹Marsh efficiency. Ecol Engr, 7, 15. Newman, J., and T. Lynch. 2001. The Everglades nutrient removal project test cells. Wat Sci Tech, 44, 11, 117. Newman, S., and K. Pietro. 2001. Phosphorus storage and release in response to flooding: Implications for Everglades stormwater treatment areas. Ecol Engr, 18, 23. Oberts, G. 1997. Lake McCarrons wetland treatment system—Phase III study report. St. Paul, MN: Metropolitan Council of the Twin City Areas. Olila, O.G., K.R. Reddy, and D.L. Stites. 1997. Influence of draining on soil phosphorus forms and distribution in a constructed wetland. Eco Engr, 9, 157. Pant, H.K., V.D. Nair, K.R. Reddy, D.A. Graetz, and R.R. Villapando. 2002. Influence of flooding on phosphorus mobility in manure-impacted soil. J Environ Qual, 31, 1,399. Pitt et al. 2004. Research project report, Findings from the National Stormwater Quality Data Base (NSQD). Tuscaloosa: University of Alabama.



Reddy, K.R., and W.F. DeBusk. 1987. Nutrient storage capabilities of aquatic and wetlands plants. In Aquatic plants for water technology and resource recovery, eds. K.R. Reddy and W.H. Smith. Orlando, FL: Magnolia Press. Reddy, K.R., and W.H. Patrick. 1983. Effects of aeration on reactivity and mobility of soil constituents. In Chemical mobility and reactivity in soil systems, ed. D.M. Kral. Special publication no. 11. Madison, WI: Soil Science Society of America. Richardson, C.I., and S.S. Qian. 1999. Long-term phosphorus assimilative capacity in freshwater wetlands: A new paradigm for sustaining ecosystem structure and function. Environ Sci and Tech, 33, 10, 1,545. Saeki, K., M. Okazaki, and S. Matsumoto. 1993. The chemical phase changes in heavy metals with drying and oxidation of the lake sediments. Wat Res, 27, 7, 1243. Stearman, G.K., D.B. George, K. Carlson, and S. Lansford. 2003. Pesticide removal from container nursery runoff in constructed wetland cells. J Environ Qual, 2, 1548. Thullen, J.S., J.J. Sartoris, and W.E. Walton. 2002. Effects of vegetation management in constructed wetland treatment cells on water quality and mosquito production. Eco Engr, 18, 441. Tidje, J.M., J.F. Quensen, J. Chee-Sanford, J. Schimel, and S.A. Boyd. 1993. Microbial reductive dechlorination of PCBs. Biodegradation, 4, 231. Toet, C, T. Hvitved-Jacobsen, and Y. Yousef. 1990. Pollutant removal and eutrophication in urban runoff detention ponds. Wat Sci Tech, 22, 10/11. US Environmental Protection Agency. 1986. Methodology for analysis of detention basin for control of urban runoff quality, USEPA 440/5-87-001. Washington, DC. USEPA. 1989. Analysis of storm event characteristics for selected rainfall gages throughout the United States: Draft. Washington, DC. Urbanc-Bercic, O., and A. Gaberscik. 1999. Seasonal changes of potential respiration of root system in common reed grown on the constructed wetland for leachate treatment. In Nutrient cycling and retention in natural and constructed wetlands. Leiden, Netherlands: Backhuys Publishers. Urbanc-Bercic, O., and A. Gaberscik. 2001. The influence of water table fluctuations on nutrient dynamics in the rhizosphere of common reed. Water Sci Tech, 44, 11, 245. Wetzel, R.G. 2001. Fundamental processes within natural and constructed wetland ecosystems. Wat Sci Tech, 44, 11, 1.



Wong, T., P.F Breen, N. Somes, and S. Lloyd. 1999. Managing urban stormwater using constructed wetlands, Report 98/7. Cooperative Research Center for Catchment Hydrology, Monash University.



Bibliography - Fisheries and Sedimentation Anderson, O.G., B.R. Taylor and G.C. Balck. 1995. “Quantifying the Effects of Sediment Release on Fish and their Habitats”. Submitted to the Department of Fisheries and Oceans, Eastern B.C. Unit, Habitat Management, Vancouver, B.C. & Alberta Area Habitat Management, Winnipeg, MB. ASCE, 1996. “Hydrology Handbook”. American Society of Civil Engineers. 2nd Edition. ISBN 0-7844-0138-1. Berkman, H.E. and C.F. Rabeni, 1987. “Effect of siltation on stream fish communities”. Environmental Biology of Fishes Vol. 18, No. 4. pp. 285-294, 1987. Birtwell, I.K., 1999. “The Effects of Sediment on Fish and their Habitat”. Fisheries and Oceans Canada, Science Branch, Marine Environment and Habitat Sciences Division, Freshwater Environment and Habitat Science Section, West Vancouver Laboratory. ISSN 1480-4883. Bodo, B.A., 1989. “Heavy metals in water and suspended particulates from an urban basin impacting Lake Ontario”. The Science of the Total Environment, 87/88 (1989) 329-344. Boyd, D., 1999. “Assessment of Six Tributary Discharges to the Toronto Area Waterfront. Volume 1: Project Synopsis and Selected Results”. Report prepared for: The Toronto and Region Remedial Action Plan. By: Water Monitoring Section, Environmental Monitoring & Reporting Branch, Ontario Ministry of the Environment. Clarifica Inc. 2001. “investigation to Develop an Improved Sizing Approach for Construction Sediment Control facilities, Prepared for Department of Fisheries and Oceans, Canada. Dodson, R. D. “Storm Water Pollution Control” McGraw-Hill, New York, 1998. Estrin, D. and J. Swaigen, 1978. “Environment on Trial – A Handbook of Ontario Environmental Law”. Canadian Environmental Law Foundation. Revised Edition. FAOC. 1999. “The Effects of Sediment on Fish and their Habitat”. Fisheries and Oceans Canada (FAOC). ISSN 1480-4883. Ottawa, 1999. GIC, 1999. “Storm Water Management Facility Sediment Maintenance Guide”. ‘DRAFT’. The Toronto and Region Conservation Authority, Ontario Ministry of the Environment SWAMP Program. By: Greenland International Consulting Inc. August 1999. GOC, 1993. “The Yukon Placer Authorization”. Government of Canada. Authorization and supporting documents applicable to placer mining in the Yukon Territory. Ottawa. 36 p. TRCA, 2001. “Urban Construction Sediment Control Study”. The Department of Fisheries and Oceans



Canada, Environment Canada and the Urban Development Institute. By: The Toronto and Region Conservation Authority and Greenland International Consulting Inc. February 2001. Graham, E.I. 1990. “An Urban Runoff Infiltration Basin Model”. M.A.Sc. Thesis. University of Waterloo. Waterloo, Ontario, Canada. Guther, R.T.. R.B. Scheckenberger and W.R. Blackport, 1997. “Use of Continuous Simulation for Evaluation of Stormwater Management Practices to Maintain Base Flow and Control Erosion”. Advances in Modeling the Management of Stormwater Impacts – Vol. 5. Published by CHI. ISBN 0-9697422-7-4 pp. 77-100. Hindley, B., 1992. “Setting Objectives for Urban Drainage Design to Ensure a Healthy Ecosystem and Recreational Opportunities”. Implementation of Pollution Control Measures for Urban Stormwater Runoff. U of T University Press, pp. 1-22. House, M.A.; J.B.Ellis; E.E.Herricks;T.Hvitved-Jacobsen; J.Seager; L.Lijklema; H.Aalderink and I.T. Clifforde, 1993. “Urban Drainage – Impacts on Receiving Water Quality”. Wat. Sci. Tech. Vol. 27, No. 12, pp. 117-158. IJC, 1978. “International Reference Group on Great Lakes Pollution from Land Use Activities”. International Joint Commission. Agricultural Watershed Studies in the Canadian Great Lakes Drainage Basin. Karr, J.R. and I.J. Schlosser, 1978. “Water Resources and the Land-Water Interface”. Science, Vol. 201, 21 July 1978. Copyright 1978 AAAS. Lloyd, D.S., 1987. “Turbidity as a Water Quality Standard for Salmonid Habitats in Alaska”. North American Journal of Fisheries Management 7:34-45. Lloyd, D.S.; J.P. Koenings and J.D. LaPerriere. 1987. “Effects of turbidity in fresh waters of Alaska”. North American Journal of Fisheries Management 7:18-33. Lord, B.N., 1986, “Effectiveness of Erosion Control”. Urban Runoff Quality – Impact and Quality Enhancement Technology. Proceedings of an Engineering Foundation Conference. June 23-27, 1986. American Society of Civil Engineers. Marsalek, J., (Date Unavail.). “Evaluation of Pollution Loads from Urban Nonpoint Sources”. River Research Branch, National Water Research Institute, Burlington, Ontario L7R 4A6. (Pub. Unavail.) Mathavan, G.N. and T. Viraghavan, 1987. “The Influence of Land-Use on Nonpoint Source Pollution”. New England Water Works Association Journal. Vol. 21, No. 2, pp. 175-191. MNR, 1987. ”Guidelines on Erosion and Sediment Control for Urban Construction Sites”. Ontario Ministry of Natural Resources. May 1987.



MNR, 1989. ”Technical Guidelines – Erosion and Sediment Control”. Ontario Ministry of Natural Resources. February 1989. MNR, 1992. “Northwester Ontario Boreal Forest Management Technical Notes”. Ontario Ministry of Natural Resources. North-western Ontario Forest Technology Development Unit. TN-21. MOE, 1994. “Stormwater Management Practices Planning and Design Manual”. Ontario Ministry of the Environment. 1994. MOE, 1994. “Evaluating Construction Activities Impacting on Water Resources – Part IIIB”. Handbook for Dredging and Dredged Material Disposal in Ontario – Legislation, Policies, Sediment Classification and Disposal Options. February 1991, Revised February 1994. ISBN 0-7729-4182-3. MOE, 1994. “Evaluating Construction Activities Impacting on Water Resources – Part IIIA”. Handbook for Dredging and Dredged Material Disposal in Ontario – Legislation, Policies, Sediment Classification and Disposal Options. February 1991, Revised February 1994. ISBN 0-7729-4181-5. MOE, 1994. “Evaluating Construction Activities Impacting on Water Resources – Part IIIC”. Handbook for Dredging and Dredged Material Disposal in Ontario – Legislation, Policies, Sediment Classification and Disposal Options. February 1991, Revised February 1994. ISBN 0-7729-4183-1. MOE, 1996. “An Integrated Approach to the Evaluation and Management of Contaminated Sediments”. Report Prepared by: R. Jaagumagi and D. Persaud, Environmental Standards Section, Standards Development Branch, Ontario Ministry of the Environment and Energy (MOE). ISBN 0-7778-3845-1 MTRCA, 1994. “Erosion and Sediment Control Guidelines for Construction”. The Metropolitan Toronto and Region Conservation Authority. April 1994. Murphy M.I.; C.P. Hawkins and N.H. Anderson, 1981. “Effects of Canopy Modifications and Accumulated Sediment on Stream Communities”. Transactions of the American Fisheries Society 110:468-478, 1981. Newcombe C.P. and D.D. MacDonald , 1991. “Effects of Suspended Sediments on Aquatic Ecosystems”. North American Journal of Fisheries Management 11:72-82, 1991. Overton, D.E. and M.E. Meadows, 1976. “Stormwater Modeling”. Academic Press Inc. New York. Papa, F.; B.J. Adams and G.J. Bryant, 1997. “Models for Water Quality Control by Stormwater



Ponds”. Advances in Modeling the Management of Stormwater Impacts – Vol. 5. Published by CHI. ISBN 0-9697422-7-4 pp. 1-22. Phillips, R.W. 1971. “Effects of sediment on the gravel environment and fish production”. Pages 64-74 in Krygier, J.T. and J.D. Hall (eds.) Proc. Symp. Forest Land Uses and Stream Environment. Oregon State University, Corvallis. Rowney, A.C. and C.R. MacRae, 1992. “QUALHYMO User Manual Release 2.2”. Redding, J.M.; C.B. Schreck and F.H. Everest, 1987. “Physiological Effects on Coho Salmon and Steelhead of Exposure to Suspended Solids”. Transactions of the American Fisheries Society 116:737-744. Richmond Hill Stormwater Management Background Studies - Final Reports, 1999-2002 Ryerson University, Clarifica Consulting, March 2004. “Assessment of Construction Sediment Control Ponds to Protect Receiving Waters. Schueller, T.R. and J. Lugbill, 1990. Performance of Current Sediment Control measures in Maryland Construction Sites. Prepared for Maryland Department of the Environment. Snodgrass, W.J., 1992. “Stormwater Quality and Quantity Management: Legal Considerations”. Implementation of Pollution Control Measures for Urban Stormwater Runoff. U of T University Press, pp. 1-22. Snodgrass, W.J.; B.W. Kilgour; M. Jones; J.Parish and K.Reid, 1997. “Can environmental impacts of watershed development be measured”. Effects of Watershed Development and Management on Aquatic Ecosystems. Edited by Larry A. Roesner. ASCE. SWMM4, 1992. “The USEPA SWMM4 Stormwater Management Model Version 4: Users Manual”. Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, Georgia. October 1992. Tchobanoglous, G. and E.D. Schroeder, 1985. “Water Quality – Characteristics – Modeling – Modification”. Addison-Wesley Publishing Company. ISBN 0-201-05433-7. Thomann, R.V. and J.A. Mueller, 1987.”Principles of Surface Water Quality Modelling and Control”. Harper Collins Publishers Inc. ISBN 0-06-046677-4. USDI, 1970. “Industrial Waste Guide on Logging Practices”. U.S. Department of the Interior. Federal Water Pollution Control Administration. Nortwestern Region, Portland, Oregon. Viessman, W.; J.W. Knapp; G.L. Lewis and T.E. Harbaugh, 1977. “Introduction to Hydrology”. Harper & Row. Second Edition.



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APPENDIX A

STORMWATER MANAGEMENT AND EROSION CONTROL BY-LAW

Halifax Regional Municipality Stormwater Management Guideline – Appendix A March 2006

Dillon Consulting Limited A-1

APPENDIX A STORMWATER MANAGEMENT AND EROSION CONTROL BY-LAW

The following is an example of a stormwater management and erosion control by-law. Before adopting it as a model for HRM it should be reviewed by planners, engineers and legal staff before completion. Title: Stormwater Management by-law for HRM Brief Summary of Background: The detrimental effects of uncontrolled runoff associated with land development could have significant effect upon the health, safety and welfare of the community. Objectives of the By-law: Prevent any increase in stormwater runoff peak and volume, prevent any increase in pollution in order to reduce flooding, sediment/erosion, and protect the water quality and the environment. Effective Date of the By-law Statutory Authority: Environment Act Jurisdiction: The by-law shall apply to all building, construction, land clearing and subdivision land within the Municipality. Permits and approvals required by this by-law may be incorporated into site plan, land use or zoning approvals documents. Prohibitions: • No person shall build, construct, erect, or enlarge any building or structure or place to

construct any impervious surface, such as pavement, road surfacing, crushed stone, packed earth without first receiving a stormwater management permit from the municipality unless otherwise exempted.

• No person shall create a subdivision of land subject to approval by the Municipality until first receiving a stormwater management permit from the Municipality for all buildings, structures and impervious surfaces proposed to be created.

• No property owner shall maintain a condition, which due to a human disturbance of land, vegetative cover or soil, results in the erosion of soil into any water body. The Municipality shall notify a property owner of such condition on his property and shall afford a reasonable time period to correct any such condition before a violation shall be deemed to exist.

• No person shall operate a land clearing machine such as a back hoe, grader or plough or similar device so as to clear or grade land or otherwise remove vegetative cover or soil or to



overlay natural vegetative cover with soil or other materials when such activities involves an area of land greater than X square metres without first having received a permit under this By-Law.

• No person shall create a condition of flooding, erosion, sedimentation or ponding resulting from failure to maintain previously approved stormwater control measures where such condition is injurious to the health, welfare or safety of individuals, or to the environment. The Municipality shall notify a property owner of such condition on his property and prescribe measures necessary to re-establish effective performance of the approved stormwater control measures. The Municipality shall afford such property owner a reasonable time period in which to correct any such condition, before a violation is deemed to exist.

• No person shall build, alter or modify a stormwater control measure without first receiving a permit from the Municipality. Such building, alteration and/or modification do not include the ordinary maintenance, cleaning and/or repair of stormwater control measures.

Exemptions: 1. Emergency repairs to any stormwater control measure. 2. Development involving land disturbance and land clearing of less than X square metre which

does not result in the creation of new impervious surfaces of more than … square metre. 3. Any logging and agricultural activity which is consistent with an approved soil conservation

plan. 4. Activities of an individual engaging in home gardening by growing flowers, vegetables and

other plants primarily for use by that person and his or her family. Design Requirements: • Stormwater volumes and rates of flow shall be calculated and control measures shall be

designed as described in the Halifax Regional Municipality Stormwater Management Guidelines document.

• Erosion control measures: temporary erosion and sediment control shall be provided for all disturbed areas in accordance with the Nova Scotia Department of Environment and Labour Handbook on Erosion and Sedimentation Control.

Compliance With the Following Restrictions Shall be Required: Any area of land from which the natural vegetative cover has been either partially or wholly cleared or removed by development activities shall be re-vegetated within X days from the substantial completion of such clearing and construction. Acceptable re-vegetation shall consist of the following: a) Reseeding with an annual or perennial cover crop b) Replanting with native woody and herbaceous vegetation. c) Any other recognized method which has been reviewed and approved by the municipality as

satisfying the intent of this requirement.



d) Any area of re-vegetation must exhibit survival of a minimum of X percent of the cover crop throughout the year immediately following re-vegetation. Re-vegetation must be repeated in successive years until the minimum survival for one (1) year is achieved.

e) Ground clearing or grading activities which occur during the period .. to …. during which germination of vegetation typically will not take place, shall be required to incorporate extra measures during re-vegetation in order to reduce erosion and maintain water quality. These extra measures include, but are not limited to, the use of screen mesh, netting, extra mulch, and sedimentation fences.

Permit Application Review Procedures: It is the responsibility of the applicant to provide a detailed plot plan showing the location and dimensions of all existing and proposed structures and impervious surfaces, water courses, water bodies, wetlands, wells, septic systems, and stormwater control measures on the site and within 50 metre of the site, and a location map of the site. Applications shall be submitted on forms prescribed by the municipality and shall require an application fee, and reference number of affected parcels, and names and addresses of adjacent parcel owners as required. 1. Preparation of a Stormwater Control Report in accordance with Schedule A is required. A

professional engineer licensed to practice under the laws of the Nova Scotia, who shall be employed by the applicant or developer to design and supervise the installation of all stormwater management facilities, shall prepare the report and accompanying plans. Stormwater management shall be within the area of expertise of the particular individual or firm performing the design and construction supervision, and if requested, that individual or firm shall furnish a listing and description of all stormwater management projects designed or supervised by them within the past five (5) years.

2. Approval of the Stormwater Concept Plan and stormwater control report may require a public hearing if the Z By-law requires such a hearing.

3. The Final Subdivision Plan shall contain stormwater control measures for all commonly owned roads, buildings, parking areas and impervious areas. Approved stormwater design plans shall be filed together with the Final Subdivision Plan with the municipality.

4. Prior to the approval of the Final Subdivision Plan it shall be first determined that there is sufficient information to support a finding that the stormwater measures subject to future approval can be designed and constructed in accordance with this by-law.

Criteria for Issuance of Stormwater Control Permits: An application for a stormwater control permit may be approved, denied, or approved with modifications or conditions, including modifications to non-stormwater aspects of the development necessary to achieve the required level of stormwater management. No stormwater management permit shall be issued unless the Municipality makes the following findings which shall be supported by substantial evidence. The facts supporting such findings shall be set forth in the decision document or permit. The issued permits shall set forth all



required conditions and incorporate all necessary documents and maps. The findings are as follows: 1. That the project meets the design requirements and performance standards set forth in this

by-law, HRM Municipal Services Systems Guidelines (Red Book) and NSEL Regulations. 2. That the project will not have an undue adverse impact on the health, safety and welfare of

the public or on the resources of the HRM and will not lead to a diminution of water quality, an increase in erosion, or an increase in stormwater runoff from the site either during or following construction.

3. That the stormwater control measures proposed for the proposed project will function as designed and that such measures represent the best possible methods and procedures for controlling stormwater runoff that is feasible and practicable at the particular project site.

4. That adequate and sufficient measures have been taken to ensure accountability and responsibility over the life of the project should the stormwater control measures not function as intended, fail, or suffer from inadequate maintenance to ensure its proper functioning.

5. That the proposed project will not contribute to flooding, sedimentation or stream bank erosion and will not result in any increase, directly or indirectly, in pollution to surface waters within the HRM jurisdictions from stormwater runoff.

Variances: A. If during the review of an application it is determined that the application of any design or dimensional requirement contained in this by-law result in the denial of the project, the applicant shall be afforded an opportunity to modify the project plans or in the alternative to make application for a variance. Upon denial of any permit application for a project for failure to conform with specific provisions of this by-law the applicant may make an application for a variance. B. If the applicant determines that any aspect of the project cannot meet any design or dimensional requirement contained in this by-law, the applicant may make direct application for a variance to the X Appeals. C. Variance applications shall be on such forms as may be prescribed and shall conform with and contain the permit application requirements set forth in this by-law. Enforcement and Penalties: Violations. Any development activity that is commenced or is conducted contrary to this by-law may be restrained by injunction or otherwise abated in a manner provided by law.



Civil and Criminal Penalties: In addition to or as an alternative to any penalty provided herein or by law, any person who violates the provisions of this by-law shall be punished by a fine of not less than X Dollars nor more than Y Dollars or by imprisonment for a period not to exceed Z days, or both such fine and imprisonment. Such person shall be guilty of a separate offence for each day during which the violation occurs or continues. Any violator may be required to restore land to its undisturbed condition. In the event that restoration is not undertaken within a reasonable time after notice, the Municipality may take necessary corrective action, the cost of which shall become a lien upon the property until paid. Notice of Violation. When the Municipality determines that an activity is not being carried out in accordance with the requirements of this by-law, it shall issue a written notice of violation to the owner of the property. The notice of violation shall contain: 1. the name and address of the owner or applicant; 2. the street address when available or a description of the building, structure or land upon

which the violation is occurring; 3. a statement specifying the nature of the violation; 4. a description of the remedial measures necessary to bring the development activity into

compliance with this by-law and a time schedule for the completion of such remedial action; 5. a statement of the penalty or penalties that shall or may be assessed against the person to

whom the notice of violation is directed; 6. a statement that the determination of violation may be appealed to the municipality by filing

a written notice of appeal within X days of service of notice of violation. The notice of violation shall be served upon the person(s) to whom it is directed either personally, in a manner provided for personal services of notices by the court of local jurisdiction, or by mailing a copy of the notice of violation by certified mail, postage prepaid, return receipt requested to such person at his or her last-known address. A notice of violation issued pursuant to this section constitutes a determination from which an administrative appeal may be taken to the Municipality.

APPENDIX B

REVIEW OF INTERNATIONAL STORMWATER MANAGEMENT PRACTICES


Dillon Consulting Limited B-1

APPENDIX B REVIEW OF INTERNATIONAL STORMWATER MANAGEMENT PRACTICES

The following is an update of the review of International Stormwater Management Practices undertaken as part of the Water Resource Management Study (Dillon, 2002). It presents a summary of recent information on design criteria and standards for BMPs. 1. Wet Ponds

1.1 Wet Pond Sizing Guidelines and Criteria for Water Quality Control Wet ponds and constructed wetlands can be very efficient in removing sediments and other pollutants by settling as well by biological processes, but they are the most complex BMPs to design, construct and maintain. These two alternatives are described in the majority of the technical literature on BMPs. Wet ponds are designed to maintain a permanent pool of water at all times, even between storms. This permanent pool helps to minimize turbulence and helps to prevent scour and resuspension of sediments. It also allows for the flocculation and settling of fine particles. Non-settleable and soluble contaminants can be removed from solution or converted to less harmful forms. Wet ponds can be multi-purpose and include flood control and stream bank erosion control in addition to water quality treatment. Wet ponds containing a permanent pond with an additional active storage zone, called extended wet ponds, detain water for extended periods. A sketch of an extended wet pond is shown on Figure 1. Some infiltration of water may also occur, depending on the type of underlying soil conditions. Ponds may also provide fish and wildlife habitat, recreational use and aesthetic enhancement, in addition to stormwater management. However, where contaminants in sediments are present, provision of fish and wildlife habitat should be discouraged. A review of North American and European BMP Manuals and technical background reports revealed a complex array of methodologies for establishing criteria for wet ponds and constructed wetlands. It is difficult to arrive at even general conclusions. Local observations taken over an extended period could provide the best basis for future design criteria. This is especially true for geographical areas, like HRM, with limited experience in the performance of BMPs. Many jurisdictions include safety factors in their designs to allow for uncertainty. Introducing safety factors not based on technical grounds and selecting larger ponds or wetlands than necessary could not only be costly, but it may not guarantee higher efficiency of pollutant removal.



Figure 1 Extended Wet Pond Plan and Profile (New York State Stormwater Manual)



Selection of Design Storm and Sizing of Basin Volume Early selection of design criteria for BMPs undertaken prior to the 1980s were based mainly on theoretical studies and/or laboratory tests. Most of these designs in the United States were based on the professional judgment of the designer. As more monitored performance data of the various BMP types are being collected, a number of jurisdictions are revising the early BMP Design Guidelines. The U.S. Environmental Protection Agency (USEPA) and American Society of Civil Engineers accumulated one of the best databanks of valuable information on the performance for different BMPs in a National Stormwater Database. The storage based BMPs built in the early years were designed to be empty following each storm. Subsequent tests on the performance of these ponds suggested that introducing a permanent wet pool at the bottom of the pond could enhance the efficiency of pollutant removals. Over time, agencies introduced the following dual criteria for sizing wet ponds and constructed wetlands: 1. a specified design depth of runoff over the drainage area to be captured in the storage facility

and then slowly released, and 2. storage volume of the pond, to normally exceed the specified captured design storm volume. Early designs of wet ponds were based on the assumption that if the first flush runoff could be captured, estimated to be in the order of 12.5 mm (0.5 inch), the majority of the pollutants would be retained. This runoff event was used to size the storage volume for wet ponds. However, it was soon realized that too many storms exceeded this volume and produced higher runoff, hence higher pollutant loads, than the first flush criteria. Subsequent designs increased the depth of runoff requirements from first flush to capturing approximately 80% to 90% of the total runoff over time. It became obvious that the size of the basin should be larger than the volume of the runoff produced by the design depth spread over the drainage area. This refinement improved the pollutant removal efficiency, especially when constructing a permanent pool at the bottom of a wet pond, or of a constructed wetland. This would also permit some stormwater to remain in the basin as a new storm arrives. The extra volume thus needed for storage depends on the drawdown time of the pond, and the inter-event time between consecutive events. The shorter the inter-event time, or the longer the drawdown time, the larger the required storage volume. To address the storage volume criteria, a number of agencies described the storage requirements for a wet pond as a function of the mean depth of the annual runoff. Since the development of continuous hydrological models, mean runoff generated by a proposed development can be simulated by using long-term (minimum 10–years) precipitation data. The currently available computing power enables designers to improve the accuracy of the rainfall-runoff analysis by adopting continuous modeling of long-term rainfall data. By using recorded data, the continuous modeling makes allowances for the antecedent and meteorological conditions. A simplified



approach of estimating the mean annual runoff was also accepted by approval agencies based on a ratio of total long-term annual runoff divided by the total number of runoff events. Gradually over the years, the volume-sizing criterion increased from one times the mean annual runoff to a ratio of 1.5 to 3.0 expressed as the size of basin volume to the runoff volume, based on a mean annual event. More recent U.S. data (Schueler, 1987) combined the required volume ratio to the total suspended solid (TSS) removal efficiency, and indicated the following ratios for a group of selected urban pollutants:

Table 1 Basin Volume and Mean Runoff Relationship

Basin Volume/Volume of Runoff from Mean Storm Pollutant Removal % TSS TP TN Lead Zinc, Copper, BOD

50 1.0 2.4 10 1.0 10 60 1.3 4.0 N. P. 1.5 N. P. 70 2.0 N. P. N. P. 2.4 N. P. 80 3.0 N. P. N. P. 4.0 N. P.

A ratio of over 4 was regarded as not practical (N.P.) Most of these data refer to wet ponds without an additional layer of extended wet pond. Unfortunately, there is insufficient field data available to determine the most appropriate ratio of permanent and extended detention volumes as this relationship is influenced by too many factors, such as local climate, soils, and development patterns. There is a lack of performance data on all aspects of extended detention ponds. A series of comprehensive analytical analyses of extended wet ponds by Adams and Papa (2000) provides good insight into the relationship between storage volume, TSS removal and detention times. The probabilistic modeling showed that as the total storage (permanent and extended) volume increases, the contribution of active extended detention storage toward the long-term removal of TSS is increased by a relatively small amount. This is especially the case as the detention time increases from 12 to 48 hours. According to the analytical results, a ratio of active and permanent pool between 0.3 and 0.5 would provide the best performance in a wet pond assuming a constant depth. Regarding the mean annual runoff for sizing, recent opinions expressed in the literature suggests that if capturing TSS is the only criterion with no extended detention facility, the permanent pool volume and mean annual runoff ratio of 1.5 should provide ample storage. Wet ponds with extended detention require larger storage, but the ratio of total storage and mean annual event could be less. When splitting the design volume derived by the ratio described above, most Manuals suggest that approximately half of the computed volume should be taken up by the extended detention portion of the pond, the other half by the permanent pool.



The Ontario approach in sizing the permanent and extended detention storage volumes is unique (Ontario BMP Manual). For the extended detention storage, a uniform 40 m3/ha storage (4 mm runoff) is required, regardless of the percent of urbanization or the sensitivity of the downstream receiving system. The size of the permanent volume is a function of TSS% removal dictated by the downstream aquatic environment and the percent of impermeable area, as shown on Figure 2.

Ontario Criteria for Permanent Pool Storage

0

2

4

6

8

10

12

14

16

18

20

30% 40% 50% 60% 70% 80% 90%

Impermeable area - %

Run

off v

olum

e - m

m 60% TSS

70% TSS

80% TSS

Figure 2 Impermeable Area and Runoff Relationship for Ontario Wet Ponds

Field monitoring of a limited number of Ontario ponds designed according to above criteria showed favourable sediment removal results. For example, at the Ballymore pond (Ryerson University and Clarifica), the 14 runoff events sampled showed a TSS removal efficiency of 82% and an average drawdown time of 46 hours. These results match the design estimate of 80% removal and a drawdown time of 48 hours. A summary of design criteria for sizing water quality control facilities adopted by various jurisdictions across North America and overseas is presented in Table 2.



Table 2 Summary of Wet Pond Design Criteria Recommended by Agencies

Jurisdiction Design Criteria

California Stormwater BMP Handbook

Capture volume to treat 85% of the annual runoff.

Canada, Fisheries and Oceans

Retain the 6 months 24-hour post-development volume from impervious area.

Canada, National Guide to Sustainable Municipal Infrastructure

Volumetric criteria, ranging from 12.5 mm to 25 mm, or capture of 80 to 90 percent of events.

City of Columbus Water quality volume (WQv) to be sized for runoff from a 0.75 inches (19 mm) rain. Additional 20% allowance for sediment storage. Each permanent pool and extended detention storage sized at 0.75 x WQv.

Coquitlam 90 % of the runoff volume in an average year to be determined by continuous modeling.

Denver 0.4 inch (10 mm) runoff. Georgia Treat the water quality volume generated by the first 1.2 inches (30.5

mm) of rainfall. Idaho Permanent pond volume equal to the runoff volume of 1/3 of the 2 year,

24-hour design storm. Malaysian Stormwater Management Manual

6 month, 24 hour rain.

Maryland Storage needed to capture and treat the runoff from 90% of average annual rainfall, derived from 1 inch (25 mm) of rainfall multiplied by the volumetric runoff coefficient (Rv) and site area. The runoff coefficient Rv is calculated Rv=0.05+0.0009 x % impervious cover.

Massachusetts Must provide 80% TSS removal. Critical areas = treat volume generated by 1 inch of runoff times the total impervious area of the post-development project. For other sites 50% of above criteria.

Michigan No recommendation on water quality design storm, or volume. Alternatives given: 0.5 inch (12.5 mm) over impervious area, 0.5 inch (12.5 mm) over the entire drainage area, 1 year, 24 hour storm and mean storm over impervious area.

New Jersey Stormwater Quality Design Storm should be based to treat the runoff volume generated by a 1.25 inch (31 mm) 2-hour storm. The actual storage required is selected depending on the required TSS removal. Curves provide information on different TSS ratios and ratios of permanent and extended detention volumes. This ratio can vary from 1 to 3.

New York Capture and treat 90% of average annual stormwater runoff volume. To compute this value, apply the 90% rainfall and a factor representing percentage of impervious cover.

New Jersey Runoff generated by a 1.25 inches (32 mm) 2-hour storm. Curves are provided for ratio of permanent pool and design storm runoff volumes.

North Carolina Capture and treat one inch (25 mm) of runoff will result in the removal of 85% of TSS.

North Vancouver Retain the 24-hour, 6-month event (59 mm). It could be derived from 72% of the 24-hour, 2-year event rainfall.

Ontario Tables for storage in m3/ha for different impervious % and receiving



Jurisdiction Design Criteria

water quality. Portland Treatment of runoff generated by 0.83 inches (21 mm) of rainfall over 24

hours. With a basin volume and runoff volume ratio of 2, the wet pool should treat roughly 90% of the average annual runoff. It is estimated that this criteria will result in the removal of 70% of TSS from 90% of the average annual runoff.

Texas Volume of storm depth 1-2 inches (25 to50 mm). Virginia 1 inch (25 mm) runoff from impervious area. Washington Volume of runoff predicted from a 6-month, 24-hour storm ranging from

0.8 inches (20 mm) to 2.25 inches (57 mm) depending on the region. Or if not known, the 91st percentile, 24-hour runoff volume derived from a continuous runoff model. The wet pool volume should be at least 1.5 times larger than the total volume of runoff from a 6 month, 24-hour storm, or a 91st percentile (continuous modeling) 24-hour runoff event.

Wisconsin Stormwater Manual

Route hydrograph from a 1.5 inch (37.5 mm) 4 hour storm through the pond.

The wet pond-sizing criteria selected by various approval agencies are mostly based on a runoff volume generated by a specified rainfall event. This is defined as the runoff volume generated by the first 12.5 mm to 25 mm (0.5 inch to 1 inch) rainfall from impervious surfaces, or based on the concept of capturing the runoff from a 25 mm (1 inch) rainfall and thereby treating at least 90% of the annual runoff. One jurisdiction, the State of Michigan, describes four alternative design storms in the Stormwater Management Guidebook: • First flush, 12.5 mm runoff over impervious drainage area • Runoff method, 12.5 mm runoff for the entire drainage area • Design storm, 1 year, 24 hour storm • Mean Storm, 3 x Runoff by the mean rainfall After presenting the four design criteria options the Guidebook concludes, “It is not the purpose of this Guidebook to provide a method that should be used in all communities, but to present methods that are currently in use throughout the United States. Actual criteria should be established at the local level.” To underscore this point the document provides the following example (Table 3) of detention pond volumes (m3) for the four alternative design criteria draining a 40 ha development. Storage volumes are shown as ratios to the lowest volume corresponding to the 25% impervious area and a 12.5 mm design storm applied only to the impervious area.



Table 3 Variation in Detention Storage Volumes for Different Design Criteria

% Impervious Area

12.5 mm, Imperv. Area

12.5 mm, Entire Drainage Area

1 year, 24-hour Storm Runoff

3x Mean Storm Runoff

85 3.4 4.2 6.1 13.2 72 3.0 4.2 5.1 11.2 38 1,6 4,2 2.7 4.5 25 1.0 4.2 1.8 2.1

Some jurisdictions provide guidance on pond surface area/drainage area ratio to assist in the sizing of a wet pond. Generally, the permanent pond surface area is within a range of 1 to 5 percent of the drainage area. An area ratio recommended in the North Carolina Manual is reproduced on Figure 3. For example, a 50% impervious drainage area would require a pond surface area between 2% to 4% of the drainage area, depending on the depth of the pond.

Permanent pond area/drainage area ratioDesign storm = 25 mm

01234567

0 10 20 30 40 50 60 70 80

% impervious area

Rat

io -

%

1 m deep

1.3 m deep

1.6 m deep

2 m deep

Figure 3 Permanent Pond Surface Area Graph as % of Catchments

There is a lack of information in the literature on the selection of design storm duration. It is believed that the pollution control efficiency of a wet pond is sensitive to the runoff volume produced by the design storm but relatively unaffected by the duration of the storm. Analyzing the cost effectiveness of different runoff volumes and storages showed, for example, that by increasing the annual treated volume from 91st to 95th percentile, the resulting pond had to be increased by 34% in volume. In the past, design criteria for sizing storage facilities were normally based on single event modeling. Past monitoring data showed that this approach may result in overestimates of pre-development peak flows with the result that post-development flows and detention release rates



are overestimated and storage requirements are underestimated. This is particularly the case if the single event modeling assumes that the detention facility is empty when the storm begins, as in some geographic areas a series of sequential storms could occur. In more recently released manuals some jurisdictions are asking for continuous modeling, or where a single event is used, safety factors are required (20% to 50% increase) in the sizing of storage volumes. There are only a few European Guidelines available for sizing water quality design storms and sizing storage volumes. The general indication of European BMP practices, also known as Sustainable Urban Drainage Systems (SUDS) a term adopted by the British, is primarily focused on flood control, rather than pollution control. However, constructed wetlands are becoming popular, especially in Scotland, comprising now approximately 30% of the structural BMPs. The most common types of SUDS used in Germany are swales and infiltration trenches. The increased occurrence of flooding in France over the last decade resulted in the construction of a number of retention basins to control runoff quantity. The use of porous paving is popular in France. In colder climate countries, such as Sweden and Denmark, ponds, swales and infiltration facilities are used. In the southern part of Europe, Greece, Spain and Italy, there is limited interest in adopting stormwater management facilities. One guideline suggests sizing wet ponds, a rather conservative value, based on winter soil conditions, percent of impervious area and rainfall. Typical values given in United Kingdom design manuals for the water quality storage design for an average residential development is 70-100 m3/ha. Other guidelines suggest i) a 12 mm-15 mm effective runoff distributed over the drainage area, or ii) the adoption of a larger volume, such as all runoff from 90% of storm events, or iii) runoff volume generated by a 25 mm of rainfall over the drainage area. Some European regulatory agencies, for example in the U.K., require that new developments limit stormwater discharges to 5 L/s/ha, but in some special cases the limit was 1 or 2 L/s/ha during peak river flow periods. However, the question of appropriate design treatment volume required for pollutant removal is still unresolved. European countries are wrestling with the dilemma of selecting the best design criteria event(s) for wet ponds and constructed wetlands. The larger return period events used for quantity control were judged to be unsuitable for water quality control, as any outlet controls sized for large runoff events could result in fast emptying during smaller runoff events, thereby preventing desired sedimentation effects. Generally, it was found that a pond designed to maintain a 1-year rain has a larger volume than the volume required to capture and treat 90% of the stormwater runoff reaching the pond in a year. To overcome this effect, ponds are designed with several outlet pipes of increasing dimensions, the smallest placed at the permanent pool water level and the larger ones placed above this level. In this way the flows from smaller runoff events can be emptied during a 12 to 24 hour period.



Research in Sweden concluded that wet ponds could effectively control pollution and that removal efficiencies increased with the size of storage volume of a pond up to approximately 250 m3/impervious ha. However, sediments in some ponds were found to be highly polluted and required disposal at a controlled landfill site. For this reason, generally ponds are regarded primarily as treatment facilities and not as habitat for wildlife. In cold weather countries experience shows that formation of an ice-layer in a retention pond forces inflowing melt water under the ice which can result in the scouring of fine bottom material. The ice can also restrict the air-water exchange, limiting the oxygen to the water column that is being progressively depleted through the winter due to organic decomposition. Field studies showed that settling velocities are 50% faster at a water temperature of 20 C compared to 4 C, resulting in decreased sedimentation during the winter period. For cold climates, guidelines recommend increasing the storage and treatment capacity of BMPs to cope with large volumes of potential runoff generated in the spring from a combination of snow melt and rain water. A rule-of- thumb used to decide whether over-sizing is required is when the average annual snowfall depth is greater than the annual precipitation depth. For the HRM region the 30-year normal for the Shearwater gauge is: rain 1,254 mm and snow 176.4 cm. Snowmelt occurs throughout the winter and spring in small, low flow events. These events can have high concentrations of soluble pollutants such as chlorides and metals. Although these events have significant pollutant loads, generally the flow volume is small and would not affect sizing decisions. Spring snowmelt can result in higher suspended solids, which can be stored in the snow pack until the last 10% of water leaves the snow pack. A large volume of runoff can occur over a relatively short time period. During spring melt season, rain on snow events may create significant runoff volume frequently close to 100% of the precipitation. Studies showed that in geographical areas with significant snowfall, the contribution of snowmelt in conveying pollutant loads could be grouped into four different categories:

Table 4 Pollutant Contributions by Snowmelt

Runoff Volume Snowmelt Area Duration Frequency Pollutants

Low Pavement melt Short Often Total load small, mainly soluble pollutants

Moderate Roadside Moderate Moderate Moderate concentration of soluble and particulate pollutants

High Pervious area Long End of season

Moderate to high concentrations of particulate pollutants

Highest Rain on snow melt Short Moderate High total loads In summary, guidelines for sizing wet ponds and constructed wetlands are based mainly on rainfall events in moderate climates. Designers in colder climates should consider increasing the



water quality volume requirement to account for conditions in colder climates, particularly when the spring snowmelt represents a significant portion of the total rainfall. Spring snowmelt, rain on snow and rain on frozen ground may warrant higher treatment volumes. Where snowfall represents more than 10% of the total annual precipitation the wet pond or constructed wetland should be oversized to account for these situations. 1.2 Selection of Detention and Drawdown Time The efficiency of a wet pond or constructed wetland is strongly influenced by the time the stormwater runoff is detained in the facility. Detention time is a function of the water volume in the pond and the outflow rate which can vary by storage elevation or stage. Increase in pollutant removal efficiency requires larger detention times as shown on Figure 4, based on work by Grizzard 1983 and Schueler 1996. While sediment removal efficiency could achieve 50% or higher values in wet ponds, the nutrient efficiencies, such as total phosphorus (TP) and total nitrogen (TN) generally are less than 50%. .

Figure 4 Detention Time vs. Pollutant Removal

The analysis of a wet pond requires the definition of the settling behaviour of the suspended particles on a real time basis. Laboratory tests of sediment settling columns, which showed very little additional removal of TSS beyond a settling time of 24 hours, depending on the TSS concentration. This was



confirmed by field monitoring of inflow and outflow TSS concentrations. In areas where the major issue was settling of winter de-icing sand, the detention time requirement was less than 24 hours. Where the sediment particles were finer, or where other pollutants had to be considered, such as metals or phosphorus a longer detention time was suggested. Drawdown time refers to the time required to lower the water levels in the active storage component of the extended wet pond from a maximum to a minimum storage. Drawdown times can range from 24 to 72 hours depending on the sediment particle distribution, pollutant concentration and downstream watercourse sensitivity. It is important to note that recent investigations of pond performance data indicated that in addition to the drawdown time the design criterion should include the drawdown rate. Observations at a number of wet ponds indicated that a drawdown rate of 45 mm per hour is adequate to settle particles, down to 5 microns. This value represents the average drawdown rate from full condition. For clay particles that are smaller than 5 microns, part of the clay suspension might not reach the pond bottom before the pool empties. Data monitored at ponds with influents high in clay content, showed that the percent removal after 48 hours was the equivalent to a 2 hour detention for larger sediment particles, illustrating the significance of taking into consideration local conditions when selecting the sizing criteria. 1.3 Removal Efficiencies Review of the pollutant removal rates achieved at different sites can assist in the selection of BMPs best suited for a particular geographical location. An example of observed efficiencies reproduced from the New York State BMP Manual is shown in Table 5.

Table 5 Summary of Observed Removal Efficiencies

BMPs Removal Rates (%) for Water Quality Parameters Assuming Ideal Conditions

TSS TP N Metals Bacteria Wet pond 80 50 35 60 70 Wetland 80 50 30 40 80 Infiltration 90 70 50 90 90 Filters 85 60 40 70 35 Swales 85 40 50 70 Negl. Oil & Grit Separators <40 <5 <5 No data No data Porous pavement Negl 80 80 No data 90

As Table 5 indicates, wet ponds and wetlands are among the most effective stormwater treatment practices for removing stormwater pollutants. Median contaminant removal efficiencies for wet ponds and wetlands based on 35 monitoring studies assembled by Schueler, (1997) are illustrated in Table 6:



Table 6 Wet Pond and Wetland Pollutant Removal Capabilities

Parameter Wet Pond Wetland

TSS 77% 78% Organic carbon 45% 28% TP 47% 51% Soluble phosphorus 51% 39% Total nitrogen 30% 21% Nitrate 24% 67% Lead 73% 63% Copper 57% 39% Zinc 51% 54% Cadmium 24% 69% Hydrocarbon 83% 90% Bacteria 65% 77%

Generally, ponds with 80% TSS removal efficiency are also able to reach close to 50% TP removal efficiency, as 75% to 90% of the phosphorus is typically bound to sediments. As nitrogen is more soluble than phosphorus, even a moderate nitrogen removal is more difficult to achieve. BMP Manuals from other jurisdictions do not distinguish between the removal of total sediments and dissolved sediments, which represent dissolved minerals in solution in the water. Removal efficiency of dissolved particles is not well known. Generally, laboratory analyses of urban runoff showed that 50% or more of the dissolved pollutants are made up of metals (zinc, copper, cadmium), nitrogen and phosphorus. Typically, urban runoff contains the following dissolved concentrations: Metals 45-130 ug/L Phosphorus 110-170 ug/L Nitrogen 90-140 ug/L Wet ponds and wetlands remove dissolved pollutants by adsorption/precipitation in the soil and by plant uptake. Fine colloid particles do not settle well but can attach to plants. Constructed wetlands are believed to be more efficient in the removal of pollutants, due to the presence of vegetation. However, it has not been proven that wetlands are more efficient at removing dissolved pollutants. To remove soluble phosphorus in constructed wetlands and to transform organic nitrogen and ammonia to nitrate, a thin layer (>25 mm) of aerobic soils is required. Research shows that the majority of the metals removed can be found in the soil, while bacteria remove most of the nitrogen.



Removal of dissolved pollutants can occur in the water as well, where algae consume pollutants and then sink to the bottom. Consequently, drying out the pond or wetland bottom can be damaging to the anaerobic soil. It has been found that after an initial period of plant growth, most of the pollutants in a wet pond are stored in the soil or are transformed by bacteria. There is an indirect benefit achieved by plant roots, when the plant dies it produces organic matter to which pollutants tend to absorb, in particular metals. It is noted that effluents from a wet pond or a constructed wetland will contain not only pollutants from the recent storm but also pollutants from previous runoff events. The most recent and most comprehensive assessment of stormwater management facilities was published in the US National Pollutant Removal Performance Data Base for Stormwater Treatment Practices. This joint effort by the US EPA, and the American Society of Civil Engineers analysed the performance of approximately 200 facilities, and concluded the following: • Effluent quality is much less variable than percent pollutant removed. This may be due to the

fact that the percent removal in a BMP depends on the pollutant concentration in the runoff. For example, while the median wet pond TSS removal ranged from 50% to 90%, the effluent quality ranged between 11 to 18 mg/L.

• The lowest effluent quality achieved for phosphorus was in the range of 50 to 60 ug/L, higher than originally assumed.

• Wet ponds showed a significant reduction in fecal coliform, from an inflow concentration of 2,400 counts to 491.5, however, in some cases heavy wildlife use could increase the concentration.

• Wet pool volumes greater than the mean monitored storm volumes performed better than those with smaller storage volumes.

• In future, more effort should be spent in applying continuous simulation techniques to assess potential sizing of BMPs and to ascertain the hydraulic performance over a longer period. Selecting a single 24-hour rainfall event for water quality volume sizing can be problematic.

• Using a single treatment BMP to do all the controls is not feasible in most cases, only well designed treatment trains can provide satisfactory results.

• The use of statistical tools is becoming more prominent in sizing and characterising BMPs. • It is now apparent that detention basins and biofilters can contribute significantly to runoff

volume reduction (depending on local soil and water table conditions), and there should be recognition of this volume reduction when assessing BMPs.



1.4 Wet Pond Sizing Guidelines and Criteria for Flooding, Erosion and Recharge Control

Flood Control Flood control and stream bank erosion protection generally require larger storage volumes than the criteria for water quality or groundwater recharge control. Flood control criteria are typically based on the concept: to restrict the post-development peak flow to that of the pre-development peak flow for selected design storms. Detention storage only affects the magnitude of peak flow and timing, it cannot affect the volume of runoff. In most of Canada the 5 or 10-year storm is used for design purposes in sizing of the minor (storm sewer) system for individual subdivisions, and the 100-year event is used for sizing the major system. The duration of the design storm is usually set which produces the highest peak flow. In watersheds with little habitat value or where downstream channels are not sensitive to erosion the post development peak flow may not have to meet the pre-development peak flow for the 2 and 10-year events. Where residential or commercial buildings or roadways may be affected by the 100-year event, additional flood control is required. In Canada and most parts of the U.S. the 100-year event is used to protect development within the 100-year flood plain. According to the Ontario approach, in the absence of watershed/subwatershed studies, the location of the downstream potential flood hazards will determine the requirements for flood control. If the potential flood hazard site is located downstream and close to the pond, quantity control must be implemented. If the proposed development is located at or close to the headwater areas, the post-development peak flow rates should be controlled to pre-development levels. If the proposed development is located in the lower reaches of the watershed, quantity control may not be required. Typically, for developments with no watershed/subwatershed plans, the quantity requirements include controlling the post development peak flows to pre-development levels for the 2, 5, 25, and 50-year storms. Municipalities require the modeling of the 100-year storm in addition to these storms, since their major (overland flow) system is designed to accommodate this storm. In some cases where over-control is required, because of downstream flood or erosion hazards, the 2, and 5-year post-development peak flows are typically controlled to 50% of their pre-development levels. A typical storm distribution used in Ontario for quantity control in urbanized areas is the Chicago distribution storm. This distribution relies on local intensity-duration-frequency information to derive rainfall hyetograph. The Chicago distribution was found to be more representative for small urban areas <100 ha. The longer distributions, such as 6, 12 and 24-hour storms are generally representative of larger areas and areas with low imperviousness. The time step taken for the modelling should be representative of the time of concentration. Sediment Control Wet ponds can also be used to control sediment load from construction sites. This would require the construction of the pond at the early stage of the construction program. It is estimated that during construction, even with erosion/sedimentation control measures at the site, the annual



sediment load could increase from a stable post-development rate of 1.9 m3/ha to 3.2 m3/ha. (Greenland, 1999). Generally, it would require an assessment of the pond storage lost due to sediment at the end of the construction periods. If necessary, the sediment in the pond would have to be removed before the Municipality takes possession. Stream Bank Erosion Control Past stormwater management measures developed to control stream erosion potential were based on the control of a peak flow rate, generally based on the reduction of the post-development peak flow for a specified design storm, to the pre-development flow rate for the same storm. The two-year storm is frequently adopted as the design event because it is believed to correspond to the bankfull flow stage, and it performs the most work in terms of sediment movement. The weakness of this approach is that an active channel is not formed by any single event, but a sum of forces exerted on the channel boundary by a range of events. The second weakness of this approach is that it does not address the resistance of boundary materials. Extended wet ponds are used to control the erosion potential of downstream flows entering a receiving system. The general criteria for stream bank control are similar to the flood control criteria, based on comparison of pre and post-development hydrographs. To achieve this, a 24-hour detention is required for a selected event, such as the 1or 2 year or a 25 mm storm event. Some municipalities require a more stringent criterion for streams with erosion-prone channels or for sensitive habitats. For example Washington State municipalities may ask for the control of flow duration to match the pre-development levels for all flows between the 2-year and 50-year peak flows. However, experience shows that stream bank erosion control by detention and subsequent slow release of a single design storm has only limited success in controlling downstream erosion and sedimentation. The limited storage provided is usually unable to control the higher flows, which are the major causes of erosion. Where extended detention time is provided the peak flows can be further reduced, when compared to conventional storage pond design, but the runoff volume would not be controlled. For example, to meet the erosion control criteria in Ontario the 25 mm storm had to be detained for a 24-hour to 48-hour period. This applies in most areas where no watershed-specific studies have been conducted to establish control volumes and release rates based on geomorphologic characteristics and sensitivities of individual streams. The current Ontario design approach recognizes the limitations of the traditional single event approach and requires a more comprehensive characterization of the fluvial system before the selection of the design alternative. Two different approaches are recommended, a simple or a detailed design approach depending on the extent of the development area and on receiving channel characteristics. The simple approach involves the analyses of two components: i) a geomorphic survey of the stream channel, and ii) determination of the volume of source control



and the active storage volume flow rate. This simple approach is applicable for development areas less than 20 ha and for relatively shallow bankfull flow channels (<0.75m). The ten step detailed design approach is based on the assessment of the channel system, stream stability and sensitivity, constraints and opportunity mapping, design targets, criteria for control of volume and flow rate, before the selection of an appropriate BMP for stream restoration. Groundwater Recharge Control Similar to flood control the objective is to maintain the post-development recharge rate at least at that of the pre-development recharge rate. As the site conditions can vary considerably, there are few generalized criteria available. Maryland provides an approach to estimate the recharge requirements subject to local soils, percent of impervious cover and size of drainage area. Ontario specifies the minimum criteria that no runoff should occur from a 5 mm rainfall for any new developments, except roads. Special Considerations Construction of new developments can frequently result in the removal of riparian cover, and vegetative canopy which moderate water temperature during the summer period. Temperature tolerances vary from fish species to fish species. There is evidence that a daily maximum mid-summer water temperature of 18 C to 20C is desirable for the more sensitive streams (Stoneman C. and Jones M, 1999) To mitigate the changes created by new development, stream corridor management plans should be prepared to ensure the protection of the stream and the vegetative buffer along the corridors. There is no acceptable and affordable technology available for the removal of dissolved salts in runoff using stormwater treatment facilities. 1.5 Design Features of Wet Ponds The following design guidelines were extracted from various design manuals. Length-to-Width Ratio Length to width ratio can influence the hydraulic efficiency of a BMP by encouraging exchanges of the stormwater entering the pond with the older water stored in the basin. Generally, ponds with extended detention facilities equipped with sufficient outlet control tend to spread the incoming flow into all areas of the pond. There is insufficient knowledge on how to select the optimum length-width ratio. Performance monitoring of ponds with different length to width ratios found that for ratios between 3 to 10, performance of the facility was unaffected by the ratio. Adoption of a high ratio may also create a geometry that could be difficult to fit into a proposed development layout.



Sediment Allowance in Storage Calculations Sediment accumulation in a pond, if left in place, could seriously affect the efficiency of a pond. Once the construction period is over, the sediment load entering a pond is substantially reduced. At that time the major portion of the incoming sediment could be trapped in the forebay. Typical accumulation of sediment ranges between 5 mm/year to 10 mm/year. Inlet and Outlet Structure Performance Pollutant removal efficiency of a pond can be affected by adverse inlet and outlet conditions, where re-suspension of previously deposited sediment could occur. At inlets, especially during high flows, scour could occur where energy dissipation is inadequate. Where approach velocities to the outlet are high relative to the settling velocities sediments are “lost” through the outlet. Riser type outlets have the advantage of reducing the velocities at the outlet. A core of gravel bottom at the outlets could reduce the risk of erosion. Selection of Minimum Drainage Area Most BMP Manuals describe a minimum drainage area needed for wet ponds and wetlands. This is based on the theory that a minimum base flow is required to sustain the permanent pool. The minimum requirements range from 5 to 10 ha based on the climate of the region. There is a concern that wet basins will not be efficient without some stored water, although there is a school of thought that there is no need for the basin to settle sediments between storm runoff events. In areas where mosquito problem is prevalent, allowing a pond to dry out may be preferable to wet ponds. However, sampling of mosquito larvae in parts of the U.S. indicated that dry ponds with small wet pockets at the bottom could be the ideal breeding environments for larvae. Storage For water quality control with no extended detention the typical criteria for sizing a permanent wet pond is a 6 month 24 hour storm, or a storage volume and long-term average storm runoff volume ratio of 3 to 4.5. For estimates of the 6 month 24 hour storm and average storm runoff in the HRM area see Appendix E. Pool depth should be sufficiently shallow to avoid thermal stratification and deep enough to minimize algal blooms and re-suspension of previously deposited materials. Prevention of thermal stratification will maintain an aerobic bottom layer, maximize pollutant uptake and minimize the potential release of nutrients. Average depth of permanent pool should be limited to 1-2 m. A shallow depth near the inlet structure is preferred to concentrate sediment deposition. The outlet pipe should be located in a deeper area to facilitate withdrawal of relatively cold bottom water for the mitigation of downstream thermal impacts. Design Parameters • Total land area: 2% to 3% of watershed area. • Pond area 1% to 2% of watershed area. • Average pond depth 1m to 2 m, maximum depth 2.5 m.



• Freeboard >0.3 m. • Include cells and baffles to minimize short-circuiting. • Length width ratio 3:1 to 5:1. • Maximum side slope 3:1. • Maintenance access maximum grade 8% to 10%. • Inlet velocity to be kept low. • Protect orifice from clogging, use submerged reverse-slope pipe. • Use anti-seep collar around outlet pipe. • Provide drain to empty pond for maintenance purposes. • Safety bench >4.5 m around pond perimeter, maximum slope 6%. • Aquatic bench 3 m to 4.5 m wide around pool perimeter, maximum water depth 0.6 m. • Provide emergency spillway to pass storms larger than the design event. • Minimize the thermal effect by providing shading vegetation, and avoid excessive concrete

and riprap. • Require adequate base flow to maintain permanent pool. • Preferred drainage area 10 ha, maximum drainage area 25 km2. • Maximum side slope 15%. • May require liner to sustain permanent pool. Forebay Sizing • Volume 10% of total pond volume. • Depth 1.2 m to 1.8 m. • Hard bottom for access of heavy machinery. • Inlet to dissipate flow energy. • Reduce velocities at outlet by stilling basin. Operation and Maintenance • Operation and maintenance cost per year 3%-6% of construction cost. • Inspect periodically during wet weather. • Clean sediment forebay every 5-7 years or when 50% of capacity has been filled. • Remove sediments from pond bottom when 10% to 15% of pool volume is filled. • Typical sediment filling 1% of storage per year. • Inspect structures annually. • Remove floatables at the beginning of the rainy season. • Mow grass areas, a minimum, annually. • Control nuisance insects and weeds as required.



2. Constructed Wetlands

Constructed, or engineered wetlands are very similar to wet ponds. For a typical design see Figure 5. Wetlands maintain a permanent pool of water for contaminant removal, and can be designed to include live storage for flood control and stream bank control. Water quality control wetlands should be constructed off-line. Contaminant removal in wetlands includes gravity settling of particulates, filtration of solids by roots and soils, adsorption to soil particles, chemical transformation, and uptake or conversion to less harmful forms by plants and bacteria. Wetlands can be used for peak flow control and stream bank erosion protection, water quality enhancement, recreation and aesthetic values. Design Parameters • Design permanent pool volume according to procedures described under wet ponds. This will

result in larger surface area than wet ponds, as wetland depths are shallow. • Recommended minimum wetland surface area 1% to 2% of contributing area. Depths: • Minimum 25% of the total permanent pool volume should have depth greater than 1.2 m. • Minimum 35% of total surface area should have depth of 15 cm or less; minimum 65% of

total surface area should have depth of 45 cm or less. • Minimum freeboard 30 cm. • Minimum length to width ratio 3:1, but 5:1 preferred. • Longitudinal slope parallel to flows path less than 1%. • Recommended side slopes 5:1 to 12: 1, maximum 3:1. • Inlet should be wide to distribute flow. • Provide shallow safety bench 5 m wide where toe of side slope meets any deep pool. • Provide multiple meandering channels, baffle islands may be included to prevent short-

circuiting. • Provide minimum 8 m wide buffer zone. Inlet/Outlet • Provide micro-pool at outlet 1.2 m to 1.8 m deep to protect low flow pipe and limit sediment

re-suspension. • Place anti-seep collar around outlet pipe. • Provide drain capable of dewatering wetland for maintenance if possible. • Protect low-flow orifice from clogging, use submerged reverse-slope pipe, trash rack, or if

perforated pipe is used for outlet, protect with wire cloth and stone jacket. • Provide emergency spillway. • Orifice outlet may not be practical for small drainage area, as the perforation required may be

smaller than the minimum size of perforation required to keep the outlet free from clogging.



Figure 5 Extended Wetland Plan and Profile (New York State Stormwater Manual)



Forebay • Requires forebay to provide sedimentation, volume 10% of permanent pool storage, 1.2 m to

1.8 m deep. Operation and Maintenance • Inspect at least twice per year during the first three years after construction during growing

and non-growing season, and inspect at least annually thereafter and after each major storm event.

• Inspect during wet weather to observe function. • Remove trash at outset of rainy season and after each significant storm. • Inspect hydraulic and structural facilities annually. • Note whether design elevation is maintained. • Clean sediment forebay every 5-7 years, or when 50% of capacity has been lost. • Vegetation maintenance and harvesting

• soils to be tested every second year and if necessary adjustments should be made to sustain plant growth

• vegetation that poses threats to safety, buildings, fences and other structures should be removed

• Vegetation maintenance during establishment phase • dead plants should be replaced, • growth should be promoted by the use of fertilizer, irrigation, mulching and

eliminating unwanted plants • plants should be protected by pruning, staking, fencing

3. Dry Ponds

Dry ponds are designed to control downstream flooding and limit the peak flow for post-development conditions to that of pre-development. Typically, they empty within a few hours following an event. Detention starts when the inflow rate exceeds the outlet capacity, beyond a certain flow event they do not reduce the frequency or duration of more significant flows, or the total mass loading of contaminants. Where extended storage is provided the drawdown time could be extended to 72 hours, thus providing additional benefits by reducing the duration and frequency of the bank full flows, and by reducing sediment loads by providing a longer settling time. Multiple outlet designs, consisting of weirs, orifices and spillways are capable of controlling the more frequent and less frequent events thus enabling the designer to meet two or more objectives in one facility. Removal Efficiency Performance data shows that dry ponds could be effective in controlling peak flows, but, unless an extended storage is provided, remove negligible amounts of pollutants. Extended detention dry ponds could remove approximately:



• 50% of TSS; • 20%-40% of TP and TN; • 75%-90% of lead; • 30%-60% of zinc; • 50%-70% of hydrocarbons; and • 50%-90% of bacteria. Typical Detention Times • Conventional dry ponds for flood control 1-2 hours. • Extended detention dry ponds for stream bank control – 24 hours. • Extended detention dry ponds for water quality control – 24–72 hours. • Additional storage allowance for sediment accumulation 20%. • Drawdown requirement for maintenance purposes, ½ of the total storage volume to be

emptied not longer than 1/3 of the total emptying period. Size • Area requirement, rule of thumb, 0.5% to 2% of the total contributing drainage area • Length to width ratio of pond 2:1 to 4:1. • Extended dry ponds contain storage in two parts, the lower part to store 15%-25% of total

design volume with depth 1.0 m to 3.0 m, the upper part hold the remainder of the storage with a depth 0.5 m to 2.0 m.

• Bottom slope 2% towards the low point, with no pockets to trap water. • Side slopes 3:1 to 4:1. • Freeboard >0.3 m. • Low flow channel from forebay to outlet. • Emergency spillway to pass storms > design event. • Trash rack protection at outlet. • Any recreational activities limited to the upper part of the storage area. • Orifice outlet may not be practical for small drainage area, as the perforation required may be

smaller than the minimum size of perforation required to keep the outlet free from clogging. • Sediment forebay volumes should be approximately 10% of the total volume of the pond. Operation and Maintenance • Approximate annual maintenance cost 1% of construction cost. • Inspect at the start of the rainy season and after each significant storm. • Remove sediment from the lower part every 5-15 years. • Routine mowing.



4. Flow-Through Type BMPs

4.1 Vegetated Swales and Flow-through Filter Strips This group of BMPs are designed to allow the majority of the urban runoff to flow through. Filter strips are used mainly along roads without curbs to treat runoff discharged along the length of the road. These control measures are sometimes described as biofilters, although sedimentation is the main component in the pollutant removal process. Research found sedimentation is the main process in removing particles, but grass swales are not efficient in filtering out particulates. Consequently, vegetated swales are acting only as very shallow settling basins. There is a wide range of design criteria recommended for vegetated swales in different Manuals. One approach in the selection of design criteria is to specify a design volume to be captured and retained along the swale. The recommended range of design volumes is 80% to 90% of the mean annual event. Some Manuals require the use of peak flow rates as a design event; others specify an infiltration rate, such as 12.5 mm per hour as a criterion. The removal efficiency of vegetated swales depends on the condition of the grass; efficiency is greatest when the grass stays upright during the entire flow, and the water depth stays below the top of grass. In such cases settling of sediments and attached pollutants are the most efficient. When designing a vegetated swale it is important to consider the following design components. The typical ranges of design parameter values are shown in brackets. • Selection of % of stormwater runoff to be treated, (80% to 90%). • Selection of depth of flow dictated by the condition of the grass; (10 cm – 15 cm). • Selection of Manning’s n; (0.3–0.4 during low flows, grass erect, 0.03–0.04 when grass

submerged). • Selection of longitudinal slope, (1% - 5%). • Determining the required length of the channel, (60 m – 100 m), or detention time (5 minute-

9 minute). Efficiency of vegetated swales can vary considerably. In a few cases it could achieve an 80% removal of TSS for low and medium flows. For this reason some manuals recommend that vegetated swales should be constructed with bypasses for large flows, when the swale is inefficient. One major item found in the review of vegetated swale performance is the need for frequent maintenance. Without effective infiltration the vegetated swale would not perform efficiently in removing dissolved pollutants. Filter strip design criteria vary considerably in different BMP manuals. Some manuals do not recommend filters be used as a stand alone BMP, although tests showed high TSS removal by filter strips. The main issue in achieving a high efficiency is the difficulty of maintaining sheet



flow into the strips and along the strips. Curbs, or even curb cuts can significantly reduce the treatment efficiency by concentrating flow. Roadside and median grass-lined channels are commonly used in Europe and Australia. In general, good removal rates were achieved, but there was quite a considerable variability in performance. Very little removal is achieved for soluble metals, nutrients and bacteria. Better performance was recorded for solids, oils, and heavy organics and solids removal increased as flow TSS concentration increased. The following event mean concentrations (EMC) and range of values (shown in bracket), loading and removal efficiencies were reported in swales in Europe (Middlesex University, DayWater 2003):

Table 7 Swale Pollutant Removal Performances

Parameter EMC and Range (mg/L)

Load (kg/ha/yr)

% Removal Efficiency

TSS 25 (7.0 – 47.0)

- 86 (55 – 91)

Total Zinc 0.032 (0.011 – 0.143)

7.05 (1.85-9.2)

83 (63-93)

Total Lead 0.079 (0.014-0.144)

0.78 (0.25-2.61)

54 (17-76)

In cold climates, such as Sweden, swales are also used as snow deposit areas and were found to have good capacity to convey melt water during the snowmelt period. However, some conveyance problems were noted due to ice at inlets, outlets and in culverts. The positive effects of vegetation, such as flow attenuation and pollutant removal are less apparent during the snowmelt period, and this may result in some erosion damage. One test site in Sweden produced 30% TSS removal during the snowmelt period compared to 75% TSS removal during rainfall events. Typical layouts of different swale types are shown in Figures 6, 7 and 8.

Figure 6 Infiltration Swale Section (Vancouver Stormwater Design Guidelines)



Figure 7 Infiltration Swale with Ponding and Subdrain (Vancouver Stormwater Design Guidelines)

Figure 8 Swale with Check Dam (Schuler 1987)

4.2 Fine Media (Sand) Filters Fine media filters, most commonly made up of sand material, can be efficient in the removal of suspended sediment. Generally, these filters are less sensitive to variation in flow rate than vegetated swales. The major disadvantage is the size of filter and the rigorous maintenance practices required. Frequently, BMP manuals required a pre-treatment facility to be constructed



before the stormwater enters the filter to reduce solids loading. The most commonly used pre-treatment is a wet pond or wetland. Fine media filters are more often selected in regions with low annual rainfall to replace wet ponds with unattractive low water or dry conditions. Other types of filters and their main advantage include:

Table 8 Alternative Filters

Filter Main Advantage Peat Removing Metals Activated carbon Removing organics Calcite Removing phosphorus Iron filings Removing phosphorus

Media depth selection is influenced by the recognition that the majority of the removal of TSS and attached pollutants takes place near the surface of the filter bed. A media depth of 50 cm is regarded as sufficient for the removal of TSS. The hydraulic conductivity of filter media refers to the ability of the stormwater to move through the media, and is influenced by the make up of the media, its size distribution and sediment accumulation. BMP manuals specify a range of hydraulic conductivities, between 50 to 100 cm per day. The greater the hydraulic conductivity the smaller the required filter area. Examples of filters are shown in Figures 9 and 10.

Figure 9 Sand Filter Profile and Section (New York State Stormwater Manual)



Figure 10 Organic Filter Profile and Sections (New York State Stormwater Manual)

Water Depth Available depth of water at the filter affects the surface area of the filter, the higher the depth, the smaller the filter area required. The maximum water depth available over the top of the filter is usually dictated by the stormwater system. Detention Time Detention time, similar to wet pond operations, is subject to the removal objective, the time needed for the filter to dry. The most frequently recommended drawdown time is 40 hours, but can range from 24 hours to 72 hours. 4.3 Infiltration Systems Soakaways have been widely used in the U.K. for treating runoff from impervious surfaces and for the disposal of highway drainage. Soakaway fields have also been used to increase the storage and infiltration capacity for highway runoff, but it was found that this practice could result in downstream build-up of pollutants. Infiltration trenches have been reported to perform well with regard to the removal of heavy metals, SS and BOD levels. Examples of infiltration systems are shown on Figures 11 and 12.



Figure 11 Bioretention Plan and Profile (New York State Stormwater Manual)

Figure 12 Infiltration Basin (Schueler 1987)

A summary of the various filtration and infiltration BMPs is shown in the attached table.



Table 9 Summary of Bioretention BMP Features

Design Consideration

Buffer Filter strip Swales Infiltration Basin

Infiltration Trench

Suitable location

Adjacent to receiving water

Small drainage area, low velocity flow

1 m above water table and bedrock



Pre-treatment Sheet flow Sheet flow Sediment trap Sediment and debris removal

Sediment and debris removal

Water quality and erosion control criteria

N/A Runoff from 25 mm rain, velocity <0.2 m/s, minimum 10 minute flow

Runoff from 25 mm rain, velocity <0.5 m/s,

Runoff from 25 mm rain, drain through to soil in 24-48 hours

Runoff from 25 mm rain, drain through to soil in 24-48 hours

Runoff from a 2 year event

N/A Velocity <1.0 m/s Velocity <1.0 m/s, check tractive force

Runoff to drain in 72 hours, or provide bypass

Runoff to drain in 72 hours, or provide bypass

Runoff from a 100-year event

N/A Velocity <2.0 m/s Velocity <2.0 m/s

Provide bypass Provide bypass



List of Stormwater Management Manual web sites (accessed in August 2005). Jurisdiction References

Calgary http://www.urbanswm.ab.ca/sag-4.1.8.asp California http://www.cabmphandbooks.com/Development.asp Canada, Fisheries and Oceans http://66.102.7.104/search?q=cache:52ZHSYtZgYwJ:www.mapleridge.org/municipal/departments/environment/

stormwater_BMP_guidelines41.pdf+canada+fisheries+and+oceans+stormwater&hl=en National Infrastructure http://www.infraguide.ca/ Coquitlam www.coquitlam.ca/.../33844/ StormwaterManagementPolicyandDesignManual.pdf Denver www.udfcd.org/usdcm/vol1/Chapter%2000%20Preface.pdf Florida http://www.dep.state.fl.us/water/nonpoint/ero_man.htm Georgia www.georgiastormwater.com/vol2/3-2-5.pdf Idaho http://www.deq.state.id.us/ City of Knoxville http://www.ci.knoxville.tn.us/engineering/bmp_manual/ Malaysian Stormwater Management Manual agrolink.moa.my/did/river/stormwater Maryland http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.asp Massachusetts http://www.mass.gov/dep/brp/stormwtr/stormpub.htm Michigan http://www.michigan.gov/stormwatermgt/0,1607,7-205--93193--,00.html Minnesota http://www.pca.state.mn.us/water/pubs/sw-bmpmanual.html

http://www.metrocouncil.org/environment/watershed/bmp/manual.htm New Hampshire http://www.des.state.nh.us/desguid.htm New Jersey http://www.state.nj.us/dep/stormwater/bmp_manual2.htm New York www.dec.state.ny.us/website/ dow/toolbox/swmanual/references.pdf North Carolina http://h2o.enr.state.nc.us/su/Manuals_Factsheets.htm Ohio http://www.epa.state.oh.us/dsw/storm/ Ontario http://www.ene.gov.on.ca/envision/gp/4329eindex.htm Oregon http://www.deq.state.or.us/wq/wqpermit/wqpermit.htm Pennsylvania http://www.pacd.org/products/bmp/bmp_handbook.htm Portland http://www.portlandonline.com/bes/index.cfm?c=35117 Texas http://www.ci.arlington.tx.us/publicworks/env_SWMSP.html Vancouver http://www.gvrd.bc.ca/sewerage/pdf/Storm_Source_Control_PartII.pdf Virginia www.dcr.virginia.gov/sw/docs/swm/Chapter_3-10.pdf Washington http://www.ecy.wa.gov/programs/wq/stormwater/manual.html Wisconsin cecommerce.uwex.edu/pdfs/G3691_P.PDF

APPENDIX C

OVERVIEW OF RURAL STORMWATER MANAGEMENT ALTERNATIVES

Halifax Regional Municipality Stormwater Management Guidelines – Appendix C March 2006

Dillon Consulting Limited C-1

APPENDIX C OVERVIEW OF RURAL STORMWATER MANAGEMENT ALTERNATIVES

There are a number of isolated agricultural resource and general rural resource areas located within the HRM subwatersheds. The following is a description of the various rural stormwater management practices applicable for the study area. The alternatives are presented under the source, conveyance and end-of-pipe headings. Source Control Measures In rural areas the primary concern in controlling stormwater runoff is to protect water quality in downstream receiving systems and groundwater systems. This is often achieved in rural settings through source control measures which are implemented/practiced on-site at the source of discharge. Source controls include all measures which treat the runoff prior to it reaching the conveyance system (i.e., ditch, swale or tile drain) or the receiving watercourse. Disconnection of Illegal Tile Drains If there are any illegal tile drains located within the study area, disconnecting those illegal tile drains decreases the amount of runoff/waste water entering the receiving system and prevents contamination (i.e., bacteria, high nutrient loading). Various alternatives to direct tile drainage, discussed in the following sections, exist to prevent contamination of stormwater and to contain, treat and/or dispose of contaminated runoff and wastewater. Proper Manure Handling and Storage There are some annual operations in the study area, but most agriculture is cash crops or pasture. Where manure is handled, steps must be taken to avoid the contamination of surface and groundwater systems through runoff, infiltration, storage overflows and spills adding bacteria and excessive nutrients to the systems. Proper manure handling and storage prevents such occurrences and can improve/ protect water quality, along with providing a number of other benefits. Effective handling and storage systems: $ Prevent surface water contamination and excessive nutrient loading; $ Prevent groundwater/water supply contamination; and $ Provide a valuable source of fertilizer and organic material for soil to improve soil

quality, crop yield and reduce erosion. Manure can be stored and handled as a solid or as a liquid. Common solid manure storage systems and the advantages/disadvantages of each method are:



$ Manure storage with bedding material (manure pack barn): prevents runoff contact, cost-effective (same building used to house livestock), contains odour and bedding promotes composting, but this method requires sufficient headroom in the barn to provide 200 or more days of pack storage without removal.

$ Manure moved to covered storage: suitable when existing housing barn does not have pack storage capacity or if it is not practical to pack store with livestock type; prevents runoff contact and contains odour, but is costly (separate structure from housing barn).

$ Manure moved to open manure stack: less costly than covered storage, but requires contaminated runoff storage (larger land area), has high odours from open liquid storage of runoff, requires enclosure (lockable gates/fencing) for safety and can attract flies, other insects, birds and rodents. This method, with the runoff storage area, may be particularly suitable and cost effective when storage of other contaminated waters (i.e., wash waters, silo leachate) is necessary.

Liquid manure storage systems are rare in the study area. Like the open manure stack (solid), liquid manure has the advantage of being able to store wash waters and other contaminated waters (additional liquid necessary for liquid storage systems). Liquid storages structures may be open or covered. Open storages can be constructed as a lined earthen pond, an in-ground concrete tank or an aboveground glass lined steel tank. Open storages must be sized to accommodate the manure/contaminated water and precipitation, and thus, require more land than a covered storage, but are usually about half the cost of a cover storage or less. The main disadvantage of open storage is the persistent odour. Covered storages may be in the form of a concrete tank, usually with a reinforced concrete top, or a concrete tank under a slatted barn floor (normally extends outside barn for agitation and manure removal). Covered storages are usually twice the cost of open storages, but have reduced odours during the storage period and require less space. Caution must be used with tanks directly below a barn as toxic and explosive gases may be produced, particularly when manure is agitated for removal. Both types of liquid storage facilities must be enclosed (i.e. fenced, locked) for safety. Stored liquid or solid manure may be use as a fertilizer and organic soil additive. Solid manure, unlike liquid manure, may be composted to produce a more stable material. Proper Fertilizer Handling and Storage Proper fertilizer handling and storage can prevent groundwater contamination through leaching and surface water nutrient loading. Practices to prevent water quality impacts are as follows: $ Only store small amounts of fertilizer for short periods; $ Store in a restricted area in an orderly fashion (clearly labelled to prevent accidents) and

maintain storage containers (i.e., no holes, punctures or tears); $ Protect dry fertilizer from weather and store on a solid surface (i.e. sealed concrete); $ Contain and store liquid fertilizer on a solid surface with an adequately sized spill

containment area;



$ Store away from wells (at least 90 m suggested); $ Mix and load on a solid surface with spill containment measures. Effective Manure and Fertilizer Application Manure and fertilizers can provide organic matter, nitrogen, phosphorus, potassium and numerous micronutrients for crops when properly handled and applied. Mismanaged manure and fertilizer applications can pollute surface and groundwater systems while providing little or no benefit to the soil or crops. Important considerations in the application of manure and fertilizers are the amount to apply, the method of application and the time of year. The amount of manure and/or fertilizer required should be determined based on soil tests, manure tests and determination of the nutrient needs of the crop. Excess components of manure or fertilizer can leach into the groundwater system. Liquid manure applied at a rate in excess of the soils infiltration rate or amounts beyond the storage capacity of the soil can runoff and enters surface water systems. Manure and/or fertilizers should be applied in a manner that provides even distribution and minimal compaction. On bare soil prior to planting, it should be worked into the soil immediately to prevent nutrient losses and removal with runoff. Liquid manure should not be applied to dry, cracked fields without tillage to prevent seepage into drainage systems. As well, cultivation is suggested where preferential flow paths have developed. Manure and/or fertilizers should not be applied closer than 9 m from a surface water source or tile drain inlet. Timing of manure/fertilizer application can greatly affect the benefits to the crop/soil and the risk to water resources. Practices to prevent water quality deterioration are: $ Apply to fields immediately prior to or at time of seeding and/or early in growing season

- do not apply after the main growing season when there is no growth to absorb it; $ Do not apply manure/fertilizer when soils are saturated (i.e., immediately after spring

thaw) or to flood prone and high runoff areas; $ Do not spread manure/fertilizer onto frozen, bare or snow-covered ground during winter; $ Reduce soil erosion to minimize phosphorus and organic matter loss; and $ Implement cover crops and residue management practices to cycle nutrients. Prevention of Livestock Access to Surface Water Resources Livestock operations are located mainly in or near streams and wetlands. Unrestricted livestock can destroy shoreline plantings along waterways which protect the banks from erosive forces. Prevention of direct livestock access to surface water resources (i.e., ditches, watercourses, wetlands, etc.) will reduce stream bank/shoreline erosion, allowing establishment of vegetation, and decrease downstream sedimentation. In addition, water quality will also be



protected/improved by prevention of animal wastes directly entering waterways which can result in nutrient loading and faecal coliform pollution. To prevent livestock access to surface water resources, fencing is the most economical Practice; for streams, livestock crossings allow access to lands on both sides. Livestock watering devices, many of which are available at a moderate cost, must be implemented. Proper Milkhouse Waste Management There is very little if any dairy operation within the study area. Milkhouse wastes produced at dairy operations include detergents and phosphoric acid used for equipment cleaning, and waste milk (i.e., in pipeline system). These wastes, improperly disposed of, can result in downstream nutrient loading, and decomposing milk can result in bacteria which can transmit diseases, decreasing the water quality in the system. Methods to prevent deterioration of water resources due to milkhouse wastes include: $ Addition of milkhouse waste to manure storage system can be cost-effective, but

increases volumes of liquid to be applied to fields (though it may be needed to dilute liquid manure systems); suitable for farms with excess existing storage capacity or farms looking at new facilities.

$ Exclusive storage of milkhouse waste in a covered tank, a fenced open tank or a fenced earthen pond; relatively high cost (separate structure from manure storage) and increase application costs; suitable for farms where combination with existing manure storage is not feasible.

$ Treatment of milkhouse waste in a trench and tank system: for small to average operations, less costly than exclusive storage, but may fail if not properly operated; requires suitable soils.

Water Well Protection Water wells in rural areas should be suitably located away from septic beds and runoff contamination sources (i.e., manure storage area, livestock pens, etc.) to prevent groundwater contamination. Measures to maintain water quality include having an adequate cover on the well, regular testing and using caution with potential pollutants in the vicinity of the well. Proper Disposal of Dead Animals and Hazardous Wastes A decomposing dead animal carcass can contaminate people directly, surface waters receiving runoff in contact with the carcass and by leaching to surface or groundwater systems. Proper disposal prevents degradation of ground and surface water quality.



Options for disposal are pickup by a licensed collector (preferred) or burying of the dead animal within 48 hours. For proper burial, the carcass must be placed under 0.6 m of earth away from any wells or surface water sources in soils with low permeability (restrict seepage). Hazardous wastes should be taken to hazardous waste disposal sites as opposed to disposal in on-farm dumpsites to prevent water quality impacts. On-farm dumpsites can be leaching contaminants to the groundwater system and/or surface systems via runoff. Proper Fuel Storage Many rural properties have motor and/or heating fuel storage facilities. Leaking tanks and fuel spills can be a great threat to ground and surface water systems. The potential for fuel leaks can be decreased with the following measures: $ Have all storage tanks installed and serviced annually by a registered professional; $ Locate tanks at least 90 m away from wells; $ Inspect all related equipment regularly and maintain inventory control to help determine

if the system is leaking; $ With above ground tanks, dike the area around the tank to contain spills (at least 110 %

of tank volume) and regularly remove rainwater to maintain capacity; $ With above ground tanks, pump fuel from top of tank; gravity fed tanks are illegal and

are prone to leaks around hoses and nozzles; and $ Have unused underground tanks removed according to regulations. Poper Silage Storage Only a few silage storage areas are located in the study area. Under good storage conditions silage poses little threat to ground and surface water resources. Poor storage conditions (i.e., poor containment, excess moisture or pressure in the silo) can result in contamination of ground and surface water systems from nutrient rich silage leachate. To prevent silage leachate contamination of water resources, the following SWMPs should be followed: $ Store silage at least 90 m from any well and at least 150 m from surface water resources; $ Have silage storage on impermeable soils (heavy clay) to prevent seepage to the

groundwater system; $ Perform regular inspections of silage storage structure and reline if any cracks are

present; $ Cover storage to prevent excess precipitation; and $ Have a seepage collection system to contain and prevent spreading of leaks.



Proper Pest Management Proper pest management to control weeds, insects and diseases can prevent ground and surface water contamination. Strategies to minimize the risk of water quality impacts include: $ Use of biodegradable pesticides, (herbicides are counted as pesticides); $ Reduction in the use of pesticides through:

-aggressive crop growth to compete with weeds -use of cover crops as biological weed control -crop rotation -rotation of pesticides -selective area applications and maintenance of accurate records -use of tillage to control weeds -herbicide application after crop emergence (rather than soil applied) -avoidance of application of herbicides late in season when crop yields will not be affected;

$ Reduce pesticide losses: -avoid chemical sprayer loading near wells and surface water -do not fill sprayer directly from well or surface water source -protect surface water from spraying (i.e., maintain a buffer strip between field and surface water resource) -avoid spraying prior to heavy rains -monitor application rates (follow directions closely) and accurately calibrate sprayer -reduce chemical drift by avoiding spraying if winds are higher than 8 km/h and by using a low spray pressure to produce larger drops or high water volumes (170 l/ha or more)

Effective Tillage Strategies Although most farming practices involve hay and pasture, various tillage strategies could be applicable to conserve soil and improve production while addressing environmental concerns. Strategies range from "no tillage" techniques to carefully planned tilling/ploughing methods, described below, combined with proper residue management and timing to minimize impacts and maximize benefits. Timing Ploughing in the spring instead of fall minimizes the time the field is uncovered, thereby reducing runoff and erosion. Also ploughing during wet periods when the soil is saturated can result in soil compaction which also has water quantity and quality impacts.



Residue Management Residue management is an important part of any tillage strategy to be used. Leaving a portion of the previous year's crop residue on the surface of the field after planting provides numerous water quantity and water quality benefits. These include: $ reduced chemical loss to water; $ reduced soil compaction and improved soil conditions; $ increased infiltration; $ reduced runoff amounts and velocities; and $ decreased erosion and downstream sedimentation. Effective residue management can be achieved through mulch tillage practices and may be employed with conventional tillage (to a degree), conservation tillage, and contour ploughing. Care should be taken to determine the residue levels desired, the appropriate crops and the handling methods to prevent planting delays or reduced crop yields due to poor residue management. No Tillage/Ridge Tillage No tillage techniques include any system where the soil is not disturbed between harvesting and planting. An example is ridge tillage where crops are planted on pre-formed ridges with minimal soil disturbance. Inter-row cultivation is done after the crops emerge to control weeds and maintain ridges. No-tillage techniques are best applied where lighter textured soils exist (i.e., sands and sandy loams) that tend to be well structured and drained, though it is reported that ridge tillage allows soils to dry quickly and therefore, can be an option for more poorly drained soils. High levels of residue that accumulate with no-tillage techniques dramatically decrease erosion and improve soil structure, improving infiltration ability and reducing runoff quantity. Disadvantages are that the success of such methods depends on soil characteristics and high residue levels can slow soil drying and warm-up. In addition, no-tillage offers fewer options for using manure produced on the farm. Conventional Tillage Conventional tillage is any system that ploughs most of the crop residue into the soil, leaving less than 30% of the crop remains on top after planting. This type of tillage is often used where heavy, poorly drained soils exist (i.e., clays and clay loams) that need sufficient tillage to allow the soil to dry and warm for planting. Advantages of conventional tillage are that manure can be incorporated easily and specialized or modified machinery is not required.



Unfortunately, the low crop residue levels maintain with this method makes soil vulnerable to crusting and erosion, and numerous trips on the fields and working with wet soil can cause compaction. These problems can increase runoff volumes and sediment transport, as well increasing sediment and nutrient loading downstream. Various field drainage, planting and residue management practices can be incorporated into a conventional tillage system to decrease runoff and erosion, and improve water quality. The following measures are examples of SWMPs, discussed in other sections of this document, that can be employed: $ Reduce trips over the field; $ Vary tillage patterns; $ Use crop rotation techniques and use forages in the rotation or cover crops between

regular crops; $ Reduce tillage intensity and increase residue cover through plough modifications; $ Implement contour ploughing and contour planting; $ Use strip crop or buffer strip cropping; $ Terrace the field to control runoff; and/or $ Retire areas where there is severe erosion. Mulch Tillage (Conservation or Reduced Tillage) Mulch tillage leaves at least 30 % or more of the crop residue on the surface. This is often achieved by methods such as chisel ploughing or discing, which breaks up the soil without completely turning it over. Mulch tillage provides all the residue management benefits for water quality and quantity, and provides opportunity for manure usage with fewer trips over the field. This method is compatible with most soils with the exception of poorly drained clays and clay loams (i.e., suitable for light to medium texture soils). This method may also be combined with other field drainage and planting strategies to maximize benefits. Disadvantages, as mentioned previously under "Residue Management", are that planting delays or reduced crop yields can result if crop residue is not managed properly. In addition, high residue levels may require planter attachments. Conservation tillage or reduced tillage are other terms often used for mulch tillage, being that fewer trips are made over the field. Contour Ploughing Contour ploughing can be incorporated into any tillage strategy and involves ploughing perpendicular to the slope of the land. This creates a series of dams that retain the water until it can infiltrate into the ground, reducing erosion by up to half during severe storms and decreasing



runoff quantities. Combined with contour cropping, vegetation perpendicular to the natural flow path also acts as a filter to remove sediment and trap nutrients further protecting downstream water quality. Proper Planning of Trips Over Fields Increased mechanization has resulted in larger and heavier farm equipment. Large, heavy equipment run excessively over fields, especially during wet conditions, can cause soil compaction. This condition reduces the soils ability to hold water and creates numerous other problems. As a result, water quantity and quality control impacted as infiltration is decreased, runoff amounts and velocities are increased, and the erosion potential is greatly increased. To prevent soil compaction, the following measures should be employed: $ Avoid working on wet soils; $ Reduce the number of trips over a field; $ Keep the weight on individual axles to below five tonnes; $ Use radial tires for traction (increase surface contact); $ Use four-wheel drive tractors (better weight distribution between axles); $ Use good crop rotation practices (include deep rooted plants or cover crops); and $ Limit traffic to certain areas (i.e., use same travel lanes each year). Effective Planting Strategies Crop Rotation Crop rotation is the changing of the crops grown in a given field on an annual basis. This practice preserves soil structure and quality, as tillage depths vary with the crop being planted and different crops return and derive varying nutrients in the soil. This maintenance of the soil reduces erosion potential and improves infiltration ability, reducing the amount of runoff and sediment delivered to the receiving system. Cover Crops Cover crops are planted to protect the soil surface and maintain soil structure. These include a variety of grasses, legumes, brassicas and other plants such as buckwheat. Cover crops planted following the annual crop, prior to winter or when an annual crop doesn't cover sufficiently, protect the soil from erosive forces that can result in rill and gully formation and soil loss. Cover crops also reduce runoff velocity and improve infiltration ability, reducing the amount of runoff and sediment delivered to the receiving system. Contour Cropping Contour cropping is the practice of planting crops across the slope of the land and usually includes grass field borders. Contour cropping can be combined with other planting and storm water management techniques (i.e., strip cropping) to maximize production and environmental benefits.



This method of planting slows and diverts runoff moving down the slope, increasing infiltration, and reducing erosion and runoff quantities. The vegetation perpendicular to the natural flow path also acts as a filter to remove sediment and trap nutrients improving downstream water quality. Contour cropping can cut typical erosion rates in half and increase yields by 5 to 10 %. Combined with other strategies (i.e., no till system) can reduce erosion up to 90 %. Strip Cropping Strip cropping uses alternating strips or sections of varying widths planted with crops that have different growth habits (i.e., combination of row crops, small grains and forages). This method of planting with the close growing rows of different crops acts as a vegetative filter that traps sediment, reduces runoff amounts, runoff velocities, erosion, soil loss and downstream sedimentation, and results in increased infiltration. Types of strip cropping include: $ Contour strip cropping; $ Field strip cropping; $ Buffer strip cropping; and $ Wind strip cropping; Contour strip cropping combines contour cropping and strip cropping so that the alternating strips of different crops are arranged in bands at right angles to the natural slope of the land. This combination of strategies can increase the allowable slope length guidelines and can greatly reduce erosion rates. Field strip cropping is normally implemented across the slope of the land in uniform strips with grassed field borders to protect against erosion and provide access. This method provides similar benefits to contour strip cropping. Buffer strip cropping is useful on longer slopes and combines permanent strips of grass or forage to break up the slope. Benefits include reduced soil transport and loss through the increased filtering action of the grass or forage, reduced runoff velocities, erosion and downstream sedimentation, and increased infiltration. Wind strip cropping is implemented on flatter lands where wind erosion can result in soil movement and increased sediment transport in runoff. Crops are planted in a similar method to field strip cropping, but are laid out cross-wise to the prevailing wind. Intercropping Intercropping is the practice of growing field crops and tree crops at the same time, on the same land, in alternating rows. This method can be used to farm fragile or marginal land. Benefits include improvement soil, decreased runoff velocities and erosion, and increased infiltration.



The main disadvantage of the practices mentioned above, with the exception of crop rotation, is the inconvenience of working fields with varying crops (i.e., rows of trees or cover crops between other crops). Effective Irrigation An effective and well-managed irrigation system must consider: $ the water holding capacity of the soil; $ effects on water tables; $ the amount of water needed by the crop; $ the irrigation method best suited to the crop; $ natural forces including forecasted rain and evapotranspiration expectations; and $ impacts on the water-taking source (may require permit). Such measures to properly manage farm irrigation minimize excess water application which can result in increased runoff, field erosion, downstream erosion and sedimentation. Effective Field Surface Drainage Good land drainage is necessary for all farm operations and can reduce the amount of surface runoff by allowing more water to soak into the soil. This subsequently reduces erosion and downstream sedimentation, increase infiltration and prevent flooding; sedimentation due to excessive field erosion can clog drains and ditches resulting in an increase in risk and severity of flooding. Various methods that can provide effective field drainage are discussed in the following sections. Tile Drainage and Water Table Management Underground tile drains are perforated pipes that remove excess water from the soil providing the benefits of good soil drainage. Modern systems have outlet regulated to maintain groundwater levels near the bottom of the crop root zone, providing irrigation and reducing the amount runoff and nutrients/chemicals discharged at the outlet of the tile drain to the receiving system. As indicated above, tile drains (especially unregulated drains) can increase chemical and nutrient loading in the downstream receiving system, disrupt groundwater systems, and increase the risk of groundwater contamination. In addition, tile drains can increase springtime flooding downstream which can consequently increase in stream erosion and sedimentation, and pose a threat to life and property. Collection/outlet system components must be inspected regularly and kept clear of debris for efficient operation.



Terraces/Berms (Contour Farming) Terraces and berms break up long slopes into a series of short slopes through the use of collection system, and often a berm, constructed across slope to collect and remove excess water safely from the field. Collection systems at the base of each short slope may consist of vertical pipe inlets and tile drains or grassed waterways. Spacing depends on slope, soil type, crop types, and management and rainfall characteristics. This type of system allows water on the field to be retained longer, allowing for increased infiltration and decreased runoff, nutrient/chemical loss, erosion and downstream sedimentation. The main disadvantage is that the initial construction costs are quite high, although crop yields are shown to increase 10 to 15 % and cost recovery can occur in as little as three years. Collection/outlet system components must be inspected regularly, maintained and kept clear of debris for efficient operation. Diversions A diversion is a grassed channel with a supporting ridge on the lower side that is constructed across the slope at the bottom of a field to intercept drainage. This technique can be consider as a combined source/conveyance control and is particularly useful where terraces cannot be implemented due to the topography or because the land upslope is owned by someone else. This type of structure diverts runoff to where it can be safely conveyed to the outlet. This prevents additional runoff and erosion on downslope fields, and provides some water quality and quantity benefits to the runoff in the system through detainment and filtering of runoff which encourages infiltration and sediment removal. Windbreaks, Shelterbelts and Natural Fencerows Windbreaks and shelterbelts are bands of trees and shrubs established to shelter crops, livestock, buildings and soil, and to control snow accumulation. Natural fencerows are the volunteer growth of trees and shrubs around old fences and field borders. These SWMPs reduce wind speeds near the ground, preventing wind erosion and soil loss. This in turn, reduces particle transport in runoff and the subsequent sediment loading of receiving systems. Windbreaks and shelterbelts should extend beyond what is being protected and are often established in a series at right angles to the prevailing or troublesome winds. A rule of thumb is to place these bands of trees every 100 to 200 m depending on the height of the trees. More details on suitable tree species and design can be obtained from local Conservation Authorities, the Ministry of Natural Resources, and OMAF Best Management Practices publications. Disadvantages of windbreaks, shelterbelts and natural fencerows are lost acreage, maintenance requirements, potential for delayed crop drying, potential for harbouring nuisance animals and weeds near fields or pastures, and that they may conflict with tile drains.



Marginal/Fragile Land Retirement Marginal and fragile lands are often composed of steep slopes, knolls, and/or floodplains. Fragile lands are easily damaged by traditional farming methods which result in excessive erosion, loss of productivity and downstream water quality impacts due to sedimentation. Marginal lands may be poorly drained, extremely stony, or steep and are not profitable to farm. Reforestation of marginal or fragile lands protects and improves the soil, and reduces runoff velocities resulting in increased infiltration and decreased erosion. As well, it may produce valuable forests and natural areas. Retirement of marginal or fragile lands to reforestation has no land use or environmental disadvantages, but can present a moderate establishment cost if not subsidized. Conveyance Controls Conveyance control measures provide quantity and/or quality control of stormwater within the conveyance system between the source and outlet. Potential methods are described in the following sections. Grassed Swales/Waterways and Roadside Ditches Grassed swales and waterways are broad, shallow channels protected from erosion by grass cover. They may serve to convey water for farm terraces and diversions, between contour rows or entering a rural area from other lands. As well, grassed swales and waterways may be constructed with tile drains along the sides to improve drainage. The use of grassed swales and waterways detains runoff, reduces sediment and pollutant transport, and encourages infiltration, decreasing runoff volumes. To provide measurable water quality benefits, the contact between the runoff and the grassed surfaces should be maximized. Therefore, grassed swales should be shallow (0.5 m), with flat side slopes (2.5:1) and a wide bottom (0.75 m or greater). Velocities should be kept below 0.5 m/s. On farms, these waterways must be shaped to allow easy crossing by farm machinery, while being large enough to handle heavy rains without damage. Crop rows should enter the waterway at right angles. In areas with access or driveway culverts, the culvert can be raised to act like a check dam. This allows for increased infiltration and settling of sediment and pollutants in the ponded area created by the check dam. This also minimizes velocities within the waterway, thereby preventing scour and erosion. Such culverts should be under drained when raised to prevent a permanent pool from developing in the waterway over time. Drop Pipe Inlets/Rock Chute Spillways Drop pipe inlets (large pipes) and rock chute spillways (channel constructed of rock underlain with filter cloth) can be used to safely convey water down steep slopes or drops. Such structures prevent erosion of the steep area and provide rapid drainage without backwater accumulation and flooding of upstream fields or rural areas.



These types of structures do not reduce or detain runoff entering downstream systems and do not provide additional water quality benefits. Channel/Outlet Protection Where there is a potential for erosion (i.e., outlets of pipes, chutes or tile drains, steep swale/channel segments, shorelines, etc.), installation of channel or outlet protection using materials such as riprap reduces the likelihood of erosion and the resulting downstream sedimentation. End of Pipe Controls Sediment/Water Control Basins Control basins allow water to pond and are released slowly. This allows for particle settling and reduced downstream erosion, flooding and water quality impacts. Control basins for rural use are generally quite small and can be simply constructed by building short earthen embankments across the drainage path to detain the water. They are useful where other runoff and sediment control measures are not practical. The outlet may consist of a perforated riser pipe structure (if there is sufficient runoff volumes) or an overflow. Size is determined based on the area being drained and the runoff characteristics. The basin and the outlet must be inspected regular and cleaned out periodically to prevent sediment accumulation and re-suspension. The disadvantages are that control basins do not prevent erosion and soil loss in the field at the source or prevent effective nutrient/chemical loading of the receiving system. Filter and Buffer Strips Filter and buffer strips, often considered as a combination end of pipe/conveyance system, are natural areas (often engineered) protecting the receiving system from surrounding land uses. The vegetation filters pollutants, encourages evapo-transpiration and reduces the velocity of the flow. Buffer strips, which are a larger scale natural area compared to a filter strip provide increased filtering and some infiltration of runoff, thus reducing the amount of runoff and the pollutant concentration in runoff. These strips are useful around ponds and wetlands, and along ditches/swales, watercourses and shorelines to intercept overland sheet flow. Generally, the vegetated strip filters the sheet flow prior to it being discharged to the receiving stream or drainage swale. They also serve as an erosion protection measure to prevent loss of the slope upon which they are located. A filter strip is often combined with a level spreader which is placed perpendicular to the flow and acts like a weir. The spreader may be engineered using such a material as concrete or it may take the form of an earth berm over which the water is conveyed as sheet flow to maximize the contact area with the vegetation. The spreader and filter strip should be designed to result in a 50



to 100 mm flow depth through the vegetation during a 4 hour, 10 mm storm. Storage behind the spreader is determined based on the level of control desired. Vegetative strips should be at least 10 to 20 m wide with a 1 to 5 % slope, the flatter the better. Wider filter strips are required where slopes exceed 5 %. Disadvantages are lost acreage, potential for harbouring nuisance animals and weeds near fields or pastures, and that they may conflict with tile drains. Summary of Rural Stormwater Management Practices The following Table summarizes the rural stormwater management alternatives applicable for the study area.

BMP Benefit Suitability Source Control Disconnection of Tile Drains



contamination (ie., bacteria, excess nutrients)

• retrofit applications only applicable in one area

Proper Manure Handling and Storage


• decreased risk of ground and surface water contamination (ie., bacteria, excess nutrients)

• storage can be costly to construct and land consuming, depending on the size of the operation and method best suited to the farm

• depending on method used, can cause persistent odours

• liquid storage facilities can present health and safety hazards

• retrofit or new development Proper Fertilizer Handling and Storage


• retrofit or new development • requires dry, solid area for storage

and adequate spill containment Effective Manure and Fertilizer Application


• requires organization, planning, and soil and manure testing

Prevention of Livestock Access to Surface Water Resources

• reduced stream erosion and sedimentation

• decreased risk of surface water contamination (i.e., bacteria, excess nutrients)

• very limited use in the study area • requires installation of some type

of watering device • may require construction of a

stream crossing to allow livestock access to lands on both sides of water




BMP Benefit Suitability Water Well Protection • decreased risk of groundwater

contamination (i.e., bacteria, excess nutrients)

• requires adequate location away from pollution sources and regular testing

• retrofit or new development Proper Disposal of Dead Animals and Hazardous Wastes

• decreased risk of ground and surface water contamination (ie., bacteria, chemicals)


Proper Fuel Storage • decreased risk of ground and surface water contamination


• requires proper storage facilities with spill containment and regular inspections

• retrofit or new development Proper Pest Management



Effective Tillage Strategies



contamination (i.e., chemicals, excess nutrients)



• may require specialized or modified equipment

Proper Planning of Trips Over Fields



sedimentation

• requires organization and planning

Effective Planting Strategies





• depending on strategy implemented, can create some inconvenience in working fields due to trees between crops or alternating rows of different crops

Effective Field Surface Drainage


• runoff detainment • reduced flood risk • reduced erosion and downstream


• can be costly to construct, depending on method chosen, design and field area

• collection/outlet system components requires regular maintenance to prevent sediment accumulations

Windbreaks, Shelterbelts and Natural Fencerows

• reduced wind erosion and downstream sedimentation

• results in decreased acreage • may delay crop drying, harbour

nuisance animals and/or conflict with tile drains



BMP Benefit Suitability Marginal/Fragile Land Retirement



sedimentation

• can involve moderate cost if reforestation is implemented, but water quantity and quality benefits will be increased, along with value as a forested natural area

Conveyance Control Grassed Swales/ Waterways and Roadside Ditches

• potential for decreased runoff quantity to receiving system; increased infiltration


sedimentation: improved water quality

• can increase mosquito breeding • results in decreased acreage • retrofit or new development

Drop Pipe Inlets/Rock Chute Spillways


• can involve moderate construction costs

• retrofit or new development Channel/Outlet Protection



• retrofit or new development End of Pipe Control Sediment/Water Control Basins

• can provide water quantity control • potential for downstream erosion

control • potential for spill control • improved water quality due to

settling


• potential for sediment re-suspension

• can increase mosquito breeding • requires regular maintenance to

prevent sediment accumulation/clogging

• results in decreased acreage • retrofit or new development

Filter/Buffer Strips • potential for decreased runoff quantity to receiving system; increased infiltration and evapo-transpiration

• runoff detainment • erosion protection and reduced

downstream sedimentation; improved water quality

• moderate cost to establish • results in decreased acreage • may require regular maintenance

to prevent sediment accumulation • retrofit or new development

APPENDIX D

WATERSHED/SUBWATERSHED STUDY CONTENTS

Halifax Regional Municipality Stormwater Management Guidelines - Appendix D March 2006

Dillon Consulting Limited D-1

APPENDIX D WATERSHED/SUBWATERSHED STUDY CONTENTS

All land uses generate runoff within a watershed/subwatershed to an outfall location. Preventing the pollutants from entering the stream upstream can most effectively control the amount of pollutant carried by sediment or the water that accumulates at the outfall. The control of surface water quality by managing the source of runoff within a watershed is the goal of watershed-based approach. A watershed/subwatershed study should describe the following components that would directly or indirectly determine the quantity and quality design criteria to be applied in the design of various BMPs. I INVENTORIES

• Watershed/subwatershed boundaries • Watershed/subwatershed inventories of natural resources • Stream inventories, flow regimes, water quality, flood plain • Identify significant environmental features • Identify quantity and quality of existing point and on-point pollutant sources • Model the existing hydrology and hydraulics of the streams to understand the impact of

land use II PLANNING

• Define the future goals of the watershed/subwatershed Plan • Identify future quantity and quality of point and on-point pollutant sources • Model the future hydrology and hydraulics of the streams to understand the impact of

future land uses • Develop and evaluate alternatives to meet the goals and manage quantity and quality • Develop the watershed/subwatershed plan and include recommendations on BMPs

III IMPLEMENTATION

• Define implementation costs • Establish a schedule and requirements for implementation • Begin demonstration projects • Develop and initiate monitoring programs

APPENDIX E

PRECIPITATION ANALYSES

Halifax Regional Municipality Stormwater Management Guidelines – Appendix E March 2006

Dillon Consulting Limited E-1

APPENDIX E PRECIPITATION ANALYSES

1 Introduction

Setting design criteria for BMPs requires the understanding of the frequency and magnitude of flows and runoff volumes generated by local precipitation. For this reason the analyses of local climatic characteristics becomes an integral part of the stormwater management investigation. As rainfall is one of the major generators of runoff, an extensive study was undertaken to establish the rainfall characteristics in HRM, as part of the Manual preparation. After consultation with Environment Canada meteorological staff, the Shearwater rainfall gauge was selected as the most representative station for the study area. The main purpose of the analyses of local precipitation data is to understand the rainfall characteristics of the HRM area and to assist in the selection of the following design events: • storm to be detained in a wet pond/constructed wetland and released over a specified period; • runoff used for sizing the storage volume of a wet pond/constructed wetland; • 2, 5, 10, 25, 50 and 100-year rainfall events required for the pre and post-development peak

runoff computations; and • estimates of components of the hydrological cycle.

2 Frequency of High Rainfall Events

An important aspect of the rainfall characteristics, which has a direct influence on stormwater flow, is the frequency of high rainfall events in a year. For BMP designs, all North American jurisdictions adopted a rainfall event which can occur only a few times per year as the basis for the water quality criteria. Any increase in the severity of the design event, such as a 1 in 2 –year or 1 in 10-year rainfall would require the construction of extensive and costly BMPs. A reduction in the design criteria to an event which could occur frequently would increase the impact on the downstream environment. Consequently, water quality design criteria for most North American jurisdictions were selected based on a daily rainfall event which is exceeded only a few times in an average year. Some jurisdictions selected the 90 percentile of an average year; others selected the design storm of a 6 month, 24-hour rainfall. Early BMP manuals identified this event to be approximately a 1-inch (25 mm) rainfall for their geographical area and many other jurisdictions adopted the same 1-inch (25 mm) criteria, as it seemed to be an easy to use, round figure. To understand the implication of adopting the 25 mm criteria an analysis of daily rainfall events recorded across Canada was undertaken. Results plotted on Figure 1 showed that HRM is unique in Canada, as it recorded the highest number of daily totals equal to or in excess of 25 mm. The Halifax total of 13.3 events per year of rainfall 25 mm or greater is by far the highest



number observed at the gauge even when compared to the east and west coast area gauges analyzed.

Figure 1, Daily Rainfall > 25 mm Occurences in Canada (1971-2000)

0

2

4

6

8

10

12

14

Vanco

uver

Edmonton

Regina

Winnipeg

Toronto

Montreal

Frederi

cton

Halifax

St. Johns

City

Day

s of

pre

cipi

tatio

n >

25

mm

Figure 1. Daily Rainfall >25 mm Occurrences in Canada (1971-2000)

This prompted a more detailed analysis of the HRM rainfall characteristics, as the results could directly influence the selection of the water quality design criteria for the Region. Although extreme rainfall data developed by Environment Canada is available for the Shearwater gauge, the published data only covers the 1:2 to 1:100-year frequency events. For the water quality criteria, there is a need for a statistical analysis of events which can occur more frequently (several times in an average year) as most of the water quality design criteria are based on more frequently occurring storms, generally an event is selected which would capture 90% of the events and would be exceeded by only 10% of the storms in a year. The results of the Shearwater rain data analysis is presented on Figure 2:



Shearwater gauge data - storm occurence

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Figure 2 Shearwater Data Analysis

The data shows that if a 25 mm rainfall were selected for the water quality criterion, 90% of the events would be captured. As explained below it is recommended that this rainfall should be assumed to occur in winter, when used for generating runoff.

3 Winter Rainfall Analysis

Another important aspect of the HRM rainfall characteristics is the effect of winter storms on the urban runoff. Previous work done by Waller (1983), as part of the Porter Dillon City of Halifax Storm Drainage Criteria Manual, identified the need for investigating the winter versus non-winter runoff. Results of cold season precipitation analysis at the Shearwater gauge reported by Waller indicated that the 2-year 24-hour cold season rainfall is only 77% of the annual 24-hour rainfall. Similar results showed a ratio of 47% in Edmonton and 66% in Toronto. Another project by Hogg as part of the National Research Council Canada 1980 Hydrology Symposium analyzed the Shearwater rainfall data and found the 24-hour snowmelt and rain total was 69% of the annual rainfall for a 25-year event. Rain and snowmelt intensity data analysis in Ontario suggest that winter rainfall and snowmelt only exceed maximum rainfall intensities for durations of two days or more. Waller reported that for the Shearwater gauge data the 5–year and 100-year winter rainfall plus snow curves exceed the non-winter values for longer durations, those exceeding the 12 to 24 hour values. When considering the influence of winter and non-winter precipitations, the runoff analysis should include the effect of seasonal differences in runoff coefficients. It is well known that for paved surfaces, the summer precipitation could create higher runoff than winter values. For undeveloped areas, winter rainfall on frozen ground can produce runoff conditions which exceed the non-winter rainfall events.



4 Estimate of the 6 Month, 24-hour Event

Some jurisdictions base the design of a wet pond on a storm that could occur on the average every 6 months. By definition this event must be more severe than the 90% alternative event. Daily rainfalls observed at the Shearwater gauge over the 30-year period were ranked in two groups: winter (December to March), and non-winter events for the rest of the eight months. To derive an estimate of the 6-month, 24-hour runoff event, first the 30-year rainfall data was ordered and the four highest events expected in an average year were selected: Order Total Rain Season 1st 56.6 mm Non-winter 2nd 47.6 mm Non-winter 3rd 42.4 mm Winter 4th 35 mm Winter The potential effect of the seasons on the runoff is illustrated on Table 1 in a simple spreadsheet calculation done for the four highest rainfall events:

Table 1 Estimate of the 6 Month, 24-Hour Runoff

Season 24-hour Rain Order of Rain % Imperm. Runoff

Co-efficient Mean

Runoff Runoff

Occurrence Winter 42.4 mm Highest winter 30% - 70% 0.8 33.9 mm Highest Winter 35.0 mm 2nd high winter 30% - 70% 0.8 28.0 mm 2nd highest*

Highest annual 30% 0.39 22.1 mm - 50% 0.45 25.4 mm -

Non-winter

56.6 mm

70% 0.51 28.9 mm 2nd highest* Non-winter

47.6 mm 2nd high annual

30% 0.39 18.6 mm -

50% 0.45 21.4 mm - 70% 0.51 24.3 mm

*Indicate alternate runoff values influenced by % of impermeable area The above example showed that if the 6-month, 24-hour winter or non-winter event is selected as a water quality sizing criterion the runoff would be approximately 28 mm, for developments with less than 70% impervious area. For developments with higher impermeable percentages the 6 months, 24-hour runoff event would be approximately the same (28.9 mm). To compare the 6-month 24-hour 28 mm estimate to the previously computed runoff generated by the 90% capture event, and if we assume the same winter runoff coefficient of 0.8, the 90% runoff value would be 0.8 x 25 mm = 20 mm which is less than 28 mm.



5 Selection of the Mean Runoff Event for Storage Volume Design

The Shearwater rainfall data set was analyzed for winter and non-winter events to determine the 24-hour mean rainfall and mean runoff values. The mean winter rainfall was estimated from the total rainfall recorded in the four months of December, January, February and March, divided by the total number of rainy days. The non-winter mean rainfall was estimated the same way using the rest of the eight months of data. To convert the rainfall data to runoff, winter and non-winter runoff coefficients have to be selected for a range of impermeable areas expressed as a percent of the total area. To illustrate the difference between winter and non-winter season runoffs, a set of calculations are presented in Table 2 for impermeable areas ranging from 30% to 70%. In the calculations, for the winter runoff conditions a volume coefficient of 0.8 was assumed for both permeable and impermeable areas. For the non-winter season the runoff coefficients assumed were 0.3 for permeable areas and 0.6 for impermeable areas.

Table 2a Winter Months Runoff

Total Rain Number of Days

Mean Rainfall % Impermeable Runoff Co-efficient

Mean Runoff

mm 379.4 37.7 10.1 30% - 70% 0.8 8

Table 2b

Non-Winter Months Runoff

Total Rain Number of Days

Mean Rainfall % Impermeable Runoff Co-efficient

Mean Runoff

mm 30% 0.39 3.4 50% 0.45 3.9

874.8 101 8.7

70% 0.51 4.4 The above mean rainfall estimates can be compared to the analysis by Adams and Papa of the Halifax March to December rainfall data (for AES gauge #8202200) for the period 1960-74, with inter-event time of 6 hours which resulted in a long term mean rainfall of 8.25 mm.

6 Rainfall Intensity-Duration-Frequency Data

To estimate peak flows required for the quantity and erosion control criteria, the Shearwater rainfall intensity-duration-frequency data prepared by Environment Canada from long-term records should be used. Values for the 2–100 year events for duration 1 to 24 hours are attached. The analysis for the data did not separate winter and non-winter precipitation, however, for the



infrequent events listed, usually the non-winter season would be applicable. Therefore, to generate the 2 to 100-year peak flows the published rainfall-intensity-duration data is acceptable. The duration of the design event should be selected from time of concentration analysis for the site in question.

7 Water Balance Data

To assist in estimating recharge, long-term monthly precipitation and evaporation data is presented for the HRM region in Table 3.

Table - 3 HRM Region Water Balance Data - mm

Month Precipitation Evaporation Surplus Jan 134.7 0 134.7 Feb 107.4 0 107.4 March 127.3 0 127.3 April 114.3 0 114.3 May 113.5 96.1 17.4 June 107.8 108 -0.2 July 107.4 120.9 -13.5 Aug 96.9 105.4 -8.5 Sept 100.1 75 25.1 Oct 126.6 46.5 80.1 Nov 137.1 0 137.1 Dec 148.3 0 148.3 Total 1421.4 551.9 869.5

8 Summary

To obtain input for the design of stormwater BMPs in the HRM area, 30 years of rainfall data at the Shearwater gauge was collected and analyzed. The analysis of seasonal variations in rainfall and runoff produced two different rainfall values to assist in the analysis of BMPs. In summary, Table 4 presents the rainfall/runoff data that could be used for sizing BMPs:



Table -4 Summary of Rainfall and Runoff Data

Event Rainfall Runoff

90% event 25 mm 20 mm (assumed runoff coefficient 0.8) 6 months 24-hour event 35 mm winter 28 mm 47.6 mm non-winter 22 –29 mm (function of runoff coefficient) Mean event 10.1 winter 8 mm 8.7 mm non-winter 3 mm – 4 mm (function of runoff coefficient)

APPENDIX F

PROBABILISTIC MODELING OF WET PONDS

Halifax Regional Municipality Stormwater Management Guidelines – Appendix F March 2006

Dillon Consulting Limited F-1

APPENDIX F PROBABILISTIC MODELING OF WET PONDS

For sizing extended wet ponds an Analytical Probabilistic Modeling was adopted, originally developed at the University of Toronto and well tested by the practices in Canada1. The method assesses the long-term TSS removal efficiency of a wet pond. The model assumes that the incoming runoff is captured in the permanent pool and treated in the inter-event period by quiescent settling. Dynamic settling treats the volume of runoff processed in the active storage. When the volume of incoming runoff has both displaced the contents of the permanent pool and filled the active storage, and the incoming rate of runoff exceeds the controlled release rate from active storage, spills occur and are assumed to receive no treatment. Input parameters to the model Rainfall, parameters obtained from 14 years of record at the Halifax gauge (#8202200) were analyzed and were used in the analysis of wet ponds. The rainfall parameters are shown in Table 1 and represent observed data processed for inter-event time of 6 hours.

Table 1 - Rainfall Parameters Used in the Analysis Halifax Rainfall Parameters IETD = 6h IETD = 9h

Average event duration, t (h) 8.25 λ 0.121 10.1

Average interevent time, b (h) 74.9 y 0.0134 83.4

Average event volume, v (mm) 9.01 ζ 0.111 10.1

Average event intensity, i (mm/h) 0.994 β 1.01 0.973

Average annual rainfall event number 88.6 Average annual rainfall volume (mm) 798

Particle settling velocity distribution, another important input parameter was based on US EPA and Canadian research in absence of local data. Table 2 shows the particle settling velocity distribution assumed for urban runoff.

Table 2 - Particle Settling Velocity Distribution in Urban Runoff2

Size Fraction Particle Size Range

Fraction of Total Mass Contained in Size Fraction Fi

Average Settling Velocity of Particles in Size Fraction, Vsi

(m/h) 1 x<=20um 0.2 0.00914 2 20um<x<=60um 0.1 0.0468 3 40um<x<=60um 0.1 0.0914 4 60um<x<=0.13mm 0.2 0.457 5 0.13mm<x<=0.4mm 0.2 2.13 6 0.4mm<x<=4mm 0.2 19.8

1 Urban Stormwater Management Planning with Analytical Probabilistic Models by Adams and Papa, 2000 2 Stormwater Management Practices Planning and Design Manual, Ministry of Environment and Energy, 1994



Other input parameters assumed were: catchment depression storage = 1.5 mm., detention time was set at 24 hours. The initial analyses were based on a permanent pool depth of 1.5 m. Model Output The initial model runs identified the permanent pool volumes required to meet removal efficiencies. In the analysis storage volumes are expressed as a unit catchment area in ha. To convert this storage volume to equivalent runoff depth over the catchment, use a ratio of 1 mm runoff = 10 m3/ha.

Water Quality Control Sizing Criteria

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Figure 1 Wet Pond Sizing Criteria on Runoff Quality Control



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TSS Removal

Figure 2 TSS Removal Isoquants Figure 1 shows the average annual TSS removal rate versus permanent pool storage at different runoff coefficient values, while Figure 2 shows isoquants of TSS removal rate. Both graphs can be used in wet pond sizing on runoff quality control. The curves in both figures are based on a permanent pool depth of 1.5 m, which is viewed as a typical value. Variation in the permanent pool depth within the generally accepted range of 1.0 m to 2.0 m results only in small changes in the required pond volumes. The next step is to select the active storage volume. Model runs were aimed at finding the relationship between permanent and active storage volumes. According to the literature permanent pool performs more efficiently in pollutant (TSS) removal than active pool, therefore a sensitivity analysis was conducted to establish TSS removal efficiency versus active storage volume for different permanent pool storage volumes. Figure 3 shows for an average runoff condition (coefficient of 0.55) that beyond a certain storage point, increasing the active storage volume would only marginally increase the TSS removal efficiency. Thus, choosing a high active storage volume may not be cost-effective in TSS removal. Curves for runoff coefficients of 0.35, 0.7, and 0.85 were also analyzed and showed similar trends to Figure 3. Continuous modelling done in Ontario3 and from a visual inspection of Figure 3, a value of 40 m3/ha of active storage was selected as a reasonable volume for HRM. 3 Stormwater Management Practices Planning and Design Manual, Ministry of Environment and Energy, 1994.



TSS Removal with Respect to Different Permanent Pool Storage

(Runoff Coefficient 0.55)

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Permanent Pool Storage

Figure 3 Sensitivity of TSS Removals to Changes in Active Pool Storage at Runoff Coefficient 0.55 The permanent pool volume controls the wet pond’s pollutant removal efficiency. The model uses inter-event time instead of detention time. A sensitivity analysis of TSS removal to the detention time is conducted and the results are shown in Figure 4. Curves in Figure 4 indicate that the TSS removal is not sensitive to the detention time when fixing the other input parameters. In the other words, from the runoff quality point of view, longer detention time does not improve the pollutant removal from the wet pond. Thus, flexibility is introduced in sizing the outlet orifice from the pond.



TSS Removal Versus Detention Time(hp=1.5m, Sp=10mm, SA=4mm)

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0.350.550.70.85

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Figure 4 Sensitivity of TSS Removals to Changes in Detention Time at Constant Permanent and Active Pool Storage Figure 5 illustrates the TSS removal versus permanent pool storage at different depth of the pool for the catchment runoff coefficient 0.55. Same curves for runoff coefficient 0.35, 0.7, 0.85 are also plotted and the maximum variation is within ±3%.



TSS Removal with Respect to Different Permanent Pool Depth (Runoff Coefficient 0.55)

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Figure 5 Sensitivity of TSS Removals to Changes in Permanent Pool Depth The active storage outlet should not be finalized until the erosion control volume is determined. Then it should be confirmed that the outlet provides a maximum drawdown time of 48 hr – 72 hr to ensure that the active storage can accommodate a possible incoming runoff event. Sensitivity of Inter-event Time in Computing TSS Removal In the analytical model, the IETD (Inter-event Time Definition) has to be selected to separate individual events in the long-term rainfall record. Different IETDs can result in different rainfall parameters; a longer IETD would increase the rainfall event volume and rainfall duration and reduce the average rainfall event intensity. Results plotted in Figures 1 to 5 are based on IETD = 6 hr. In order to understand the performance of the extended detention wet pond with respect to different IETD (i.e., different input rainfall parameters) a sensitivity analysis was conducted and the results are presented in Figure 6. Within a small permanent pool storage range (less than 60 m3/ha), the pond performs better at a smaller IETD. When permanent pool storage volume is greater than 60 m3/ha, the pond performs better at a longer IETD.



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Figure 6 Sensitivity Analysis of TSS Removal to IETD Erosion Control Criteria The design criteria for the control of downstream erosion is a controlled release of pond flow over a 48 hour period generated by a 25 mm 6 hour winter storm. Using a hydrologic model a runoff hydrograph should be generated based on the 25 mm winter storm to determine the inflow into the pond. For the discharge capacity at the controlled outlet an orifice or a weir formula should be used to estimate the outflow depending on the pond depth in the active storage facility. To accommodate the erosion control criteria additional flow controls may be required above the range of pond depths controlled by the water quality orifice outlet. A cumulative distribution analysis was undertaken to review the occurrence of a 25 mm rainfall event. In the analysis, it was assumed that the rainfall events are adequately represented by an exponential distribution4 and is given by the following expression: PDF (Probability Density Function) of rainfall volume, v

vV evf ζζ −=)( , 0≥v where

v1

=ζ (mm-1)

4, Adams, B. J., and Papa, F., Urban Stormwater Management Planning with Analytical Probabilistic Models, John Wiley & Sons, Inc., New York, 2000.



CDF (Cumulative Distribution Function) of rainfall volume, v

vV evF ζ−−= 1)(

According to the analytical model for the HRM rainfall data, ζ = 0.111 for IETD = 6 h. As shown in Figure 7, 93.8% of rainfall events have volumes less than 25 mm in Halifax. This analysis confirmed the findings of the 30-year daily rainfall data analysis presented in Appendix F, that capturing of runoff from a 25 mm winter rain would include approximately 90% of events in a year.

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Figure 7 Cumulative Distribution Function of Halifax Local Rainfall Volume

APPENDIX G

HRM MUNICIPAL SERVICES SYSTEMS DESIGN GUIDELINES – DRAINAGE DESIGN

APPENDIX H

HRM STORM SEWER BY-LAW

APPENDIX I

FACT SHEETS

Halifax Regional Municipality Stormwater Management Guidelines – Appendix I March 2006

Dillon Consulting Limited I-1

APPENDIX I BMP DESIGN GUIDELINES AND FACT SHEETS

This appendix provides design guidelines for the most common BMPs utilized for stormwater management. The attached design guideline sheets applicable to HRM are based on a review of Canadian and International BMP practices. For each BMP a list of key considerations is presented reflecting local conditions. A series of CMHC Fact Sheets are presented with these guidelines that provide a general description of acceptable designs for all Canadian users. The following is a list of BMP alternatives presented:

BMP Type Fact Sheet

Source Control 1. Reduced lot grading - 2. Roof leader disconnection to soakaway or ponding area

CMHC

3. Roof storage CMHC 4. Sump pump - Conveyance Control 5. Vegetative practices, grassed

swales CMHC

6. Perforated pipes/catch basins - End-of-Pipe Control 7. Wet ponds CMHC 8. Dry ponds - 9. Constructed wetlands CMHC 10. Infiltration trench/basin CMHC 11. Permeable pavement - 12. Forested buffers CMHC 13. Filter strips - 14. Sand filters CMHC 15. Oil and grit separators CMHC 16. Bioretention/rain garden - 17. Monitoring -



1. Reduced Lot Grading

Key Considerations • Little evidence on effectiveness at a subdivision scale. • Difficult to apply to existing developments. • Can be interfered with by homeowners. • Very little water quality benefits, as roof runoff is relatively clean. • Can promote infiltration and recharge of groundwater. • Limited flooding and erosion control benefits. • Gradient within 4 m of the building should not be reduced below 2%. Recommended design features • Minimum lot grade 0.5%, except within a 4 m distance from the building. • Roof leaders should not discharge closer than 2 m from the building. • Tilling the surface to a depth of 30 cm before sod is applied could enhance infiltration to the

ground. A sketch of typical lot grading reproduced from the Ontario BMP Manual is shown below. Figure 1 Sketch Showing Reduced Lot Grades



2. Disconnection of Roof Leaders

Disconnected roof leaders can discharge to the surface or to a soakaway. The advantages of overland ponding and overland flow compared to the soakway alternative are longevity and little or no maintenance requirement. The disadvantages are: less recharge due to evaporation and inconvenience to homeowners. Key considerations • Difficult to apply to existing developments • Roof leaders should not be connected to sanitary sewers • Reduces flow in storm sewers • Can be interfered with by homeowners • Very little water quality benefits, as roof runoff is relatively clean • Can promote infiltration and recharge of groundwater • Limited flooding and erosion control benefits • Gradient within 4 m of the building should not be reduced below 2% • Discharges relatively clean water, provides recharge, and quantity control benefits, but very

little water quality benefits • Requires suitable outlet at a backyard, if not feasible, the outlet should not interfere with the

use of a foot path, or sidewalk in the winter season • May not be suitable for townhouse development with small permeable surfaces • Outlets should be protected from blockage in winter by ice and snow • Soakaway pits should not interfere with septic system operations • Soakways may not be feasible where:

o groundwater levels are high, within 1 m of the building foundations o bedrock is within 1 m of the foundation drain elevation

• Requires periodic inspection and maintenance • Located on private property, access by municipal staff in case of emergency is restricted Design Guidelines - Discharging to ponding area • Use overland flow route to rear yard pond • Roof leader to discharge more than 2 m from building • Ponding area >4 m away from the building • Till pond area to a depth of 0.3 m before sod is laid Design Guidelines - Discharging to soakaway • Bottom of soakway pit >1 m from high water table or bedrock • Soakaway pit >4 m away from the building • Storage media: clear stone, approx. 50 mm diameter • Intake to soakway pit from roof leader by perforated pipe, diameter >100 mm • Perforated pipe located approximately 100 mm from top of pit.



• Depth of soil cover over pit to be sized to take into account frost heave. • Storage volume of pit >5 mm over roof top area • Drawdown time 24-48 h • Soakaway pit not to be located close to septic systems • Soil minimum percolation rate 15 mm/h • Install overflow pipe to discharge roof leader to splash pad if pit clogged



Canada Mortgage and Housing Corporation Fact Sheet Downspout Disconnection Description Downspout disconnection (sometimes called roof leader disconnection) represents a cost-effective onsite alternative for reducing the volume and cost of stormwater that requires public management. Runoff from residential rooftops is collected by eaves troughs, which are installed along the edge of the roofline. Water collected in the eaves trough is conveyed to ground level by one or more downspouts. Downspouts may then connect directly into the storm sewer system or in older neighbourhoods into a combined storm and sanitary sewer system. Disconnecting downspouts brings a number of economic and environmental benefits to the municipality and the homeowner: • in combined sewer areas, disconnection reduces the amount of combined flow requiring

treatment and reduces the threat of CSOs; • in separated sewer areas, the diverted stormwater reduces volumes of flows conveyed and

resulting loads to watercourses; • downspout disconnection can reduce basement flooding from sanitary sewer backups and

leaking downspout connections; and • environmental benefits can result in terms of cleaner watercourses, groundwater recharge,

and availability of "recycled" rainwater. Source: http://www.cityfarmer.org/downspout96.html Some Canadian municipalities already have voluntary, incentive-driven, or mandatory downspout disconnection programs in place. In these cases, downspouts on existing homes are disconnected from the sewer system, and downspouts on new homes are built without connections to the system. Effectiveness Analysis Downspout disconnection is focused on stormwater quantity management. By disconnecting downspouts, less conveyance and treatment infrastructure is needed. In addition, major environmental benefits emerge as the volume of stormwater direct discharged to watercourses is reduced, and the frequency and severity of combined sewer overflows (CSOs) can be reduced. Downspout disconnection reduces the amount of stormwater that is either: • conveyed along a public separated storm sewer system, and ultimately direct discharged to a

watercourse; or • conveyed along a public combined sanitary/storm sewer system, and ultimately treated at a

treatment plant.



The amount of stormwater runoff diverted depends on the amount of rainwater intercepted by rooftops (annual rainfall and roof area) as well as the number of downspouts that can be disconnected. The City of Toronto investigated the effectiveness of a residential rooftop downspout disconnection program. Evidence from a primarily residential area of the City of Toronto suggests that rooftops cover approximately 20% of surface area, indicating the amount of rainwater that could be diverted [J.F. Sabourin and Associates Inc. (1999), Implementation Plan Overview Moore Park/North Rosedale Demonstration Area]. Assuming an annual rainfall of about 700 mm (typical of Toronto, excluding snowfall), disconnection of an average home with a roof area of 140 m2 would result in diversion of nearly 100,000 litres of stormwater from the sewer system each year. In reality, downspout disconnection usually can be done on about 3/4 of a property's downspouts (without resorting to more complex and costly disconnection schemes) in average density urban areas. Disconnection is expected to have a small impact on the quality of stormwater runoff conveyed through a combined or separate sewer system. A major quality benefit, however, results to receiving watercourses through avoided CSO incidents. The Toronto study indicates that some parts of the combined sewer system overflowed as many as 15 times per year, resulting in a discharge of stormwater and wastewater to receiving watercourses. It was estimated that disconnecting one quarter of the downspouts in the study area would result in a 50% decrease in the number of CSOs. Disconnecting two thirds of the downspouts would nearly eliminate CSOs. The number of CSOs avoided elsewhere depends on specific features of the sewer system. Economic Analysis The costs of downspout disconnection vary depending on whether a simple or complex disconnection occurs. The costs of a simple disconnection are quite small relative to other lot-level stormwater management alternatives. If a connection already exists, the costs of disconnection have been shown to be as low as: • labour cost (per house) $4.00 • material cost (per house) $6.00 • total cost (per house) $10.00 At the high-end, some municipal governments have made available a subsidy of about $100 to homeowners to disconnect downspouts. This subsidy was estimated to be sufficient to cover the full time and materials costs of a complete disconnection. Materials costs are for downspout extensions, elbows, splash pads, and possibly rain barrels. Note that it may be necessary to deploy rain barrels to manage runoff at some properties, which will cost homeowners about $100 - $200 per barrel depending on volume and make.



For some properties, notably those in high density neighbourhoods or with low soil permeability, more complex disconnection techniques may be required, for example using soakaway pits. These alternatives would have additional construction and on-going maintenance costs. For new home builders, cost savings may actually result from not initially connecting downspouts to the sewer system. Additional savings may be realized because the reduced flows may allow smaller sewers to be built. No estimates of these cost savings are available. Implementation Issues A great deal of experience exists with downspout disconnection programs. However, no firm technical guidelines exist identifying when a disconnection can or cannot be attempted. Rather, a range of property characteristics must be assessed subjectively. The three most important considerations are: • Lot Size - The lot size should be sufficient to provide an area for the diverted runoff to

infiltrate. Runoff should not pool significantly, or run across the surface onto a neighbour's property. Pooling and cross-property runoff raise a number of safety and legal issues.

• Soil Perviousness - Runoff should be redirected to soft landscaped surfaces such as lawns, gardens, or swales to allow infiltration. If directed to hard landscaped surfaces such as driveways, runoff will flow to the street and sewer system, eliminating potential benefits.

• Property Grade - Downspout disconnection works well on properties with small grades. The grades help avoid significant pooling of runoff. Higher grades (for example greater than a few degrees) are too steep to allow infiltration.

• Proximity to Buildings - Runoff should not be discharged immediately beside buildings or on a grade which would direct flows to buildings. Runoff reaching a building could cause foundation damage or basement flooding.

As such, a number of safety and legal concerns can arise in consideration of downspout disconnection programs. Safety concerns relate primarily to the threats posed by pooled runoff and ice formation on walkways in the winter months. Legal concerns may arise in respect of either of these, or from foundation damage or basement flooding. Discussions with managers of municipal downspout disconnection programs indicate that these concerns can be mitigated through the use of prudent planning (i.e., ensuring that the disconnection is performed properly, and only disconnecting downspouts where the right lot conditions exist).



3. Roof Storage

Alternative BMP: Wet pond, Infiltration trench or basin, Swales. Advantages • Lightweight; roof generally does not require reinforcement. • Suitable for large areas. • Suitable for roofs with 0 - 30° (slope). • Low maintenance and long life. • Often no need for irrigation and specialized drainage systems. • Less technical expertise needed. • Often suitable for retrofit projects. • Can leave vegetation to grow spontaneously. • Relatively inexpensive. • Looks more natural. • Easier for planning authority to demand as a condition of planning approvals. Disadvantages • Less energy efficiency and stormwater retention benefits. • Limited choice of plants. • No access for recreation or other uses. • May be unattractive in the winter. • May interfere with other uses such as solar panels.



Photo of Ducks Unlimited Winnipeg Office Building



Canada Mortgage and Housing Corporation Fact Sheet Greenbacks from Green Roofs Introduction Finding practical and effective ways to implement sustainable development remains a significant challenge in Canada. One approach involves using green roof and vertical garden technologies on residential, institutional, industrial and commercial buildings. These technologies address a number of economic and environmental challenges facing Canadian cities. They provide such benefits as better air quality, reduced greenhouse gas emissions, improved stormwater management and long-term economic advantages, plus social benefits. Green roof installations are different from freestanding planters in that they are applied as part of the roofing system. This green roof technology includes the following components: • roof structure, and possibly some insulation • waterproofing membrane, often with root repellent insertion • drainage system, sometimes with built-in water reservoirs • landscape or filter cloth to contain the roots and the soil • specialized growing medium • plants. The barrier between the plants and any roof penetrations, parapet walls or flashing is crucial to prevent roof penetration and allow excess water to run off the roof. There are basically two types of green roof systems: extensive and intensive. Extensive green roofs are characterized by their low weight, low capital cost and minimal maintenance. Intensive green roofs have a greater soil depth and more plantings with higher maintenance requirements. Further differences between the two systems are outlined in Figure 1 on the following page.



Figure 1. Comparison of Extensive and Intensive Green Roof Systems Extensive Green Roof Intensive Green Roof • thin soil, little or not irrigation, stressful conditions

for plants • deep soil, irrigation system, more favourable

conditions for plants Advantages: Advantages: • lightweight – roof generally does not require

strengthening • suitable for large areas • suitable for roofs with 0-30’ (slope) • low maintenance • often no need for irrigation and drainage systems • relatively little technical expertise needed • often suitable for retrofit projects • can leave vegetation to develop spontaneously • relatively inexpensive • looks more natural • easier for planning, authority to demand green roof

as a condition of planning approvals

• allows greater diversity of plants and habitats • good insulation properties • can stimulate a wildlife garden on the ground; can

be made very attractive; visually often accessible, with more diverse utilization of the roof, i.e., for recreation, growing food, as open space.

Disadvantages: Disadvantages: • more limited choice of plants • usually no access for recreation or use • unattractive to some, especially in winter

• greater weight loading on roof • need for irrigation and drainage systems (greater

need for energy, water, materials, etc.) • higher cost • more complex systems and expertise required

A vertical garden is essentially a living cladding system with many of the benefits of a green roof. With these gardens, plants grow on, up or against a building’s façade. Suitable plants include a wide variety of perennial and annual vines as well as espaliered trees. Vertical greening has more potential impact, with greening of a building’s façade often encompassing four times the area of the roof and even more for a highrise building. Green roofs and vertical gardens are a well-established feature in many European countries, with policy makers having put in place various measures to support the application of these technologies. This has resulted, for example, in 10 million square metres of green roofs being developed in Germany alone in 1996. While these technologies are not totally unfamiliar in Canada, they are used only to a very limited extent. Canada Mortgage and Housing Corporation funded research, with in-kind support from Environment Canada, to gain a better understanding of the benefits of green roofs and vertical garden technologies and barriers that prevent more widespread adoption in Canada. Research Objectives and Methodology The research had four objectives: • Review the status, quantitative and qualitative benefits and opportunities associated with

green roof and vertical garden technologies. • Identify barriers to more rapid implementation of these technologies in Canada.



• Engage a variety of public and private stakeholders in a workshop to familiarize them with the concept and benefits of this form of greening, and obtain their input.

• Develop recommendations to overcome the most significant barriers to adopting these technologies in Canada.

The research included a literature review, interviews with 10 individuals involved in green roof and vertical garden projects in Canada and a workshop with industry and government representatives. An advisory team provided strategic advice and technical information. Benefits Green roof and vertical garden technologies offer a wide range of public-private, environmental, economic, and social benefits. Finding new ways of using roof and wall space can generate added economic impetus and make cities more liveable by providing significant amounts of accessible outdoor recreation or amenity space close to work and home. Vertical gardens block movement of dust, while green roofs have a moderating effect on thermal air movement and trap airborne particulates. Studies have shown that treed urban streets have substantially less dust compared to those without trees. Both green roofs and vertical gardens further contribute to reducing pollution by absorbing gaseous pollutants. These systems have a beneficial impact on moderating the heat gain and loss of buildings, as well as on humidity, air quality and reflected heat. In conjunction with other green installations, these technologies can play a role in altering the climate of a city as a whole. A German source remarked that a healthy urban climate could be achieved by greening only 5% of all roofs and walls within a city. Widely implemented, these technologies can provide effective methods for reducing greenhouse gas emissions by shading buildings, improving insulation values and reducing higher urban temperatures caused by the expanse of reflective surfaces in urban areas, known as the “Urban Heat Island Effect”. Higher temperatures increase atmospheric instability, which in turn can increase the chance of rainfall and severe thunderstorms. They also affect air quality, as heated air stirs up dust. Strategically placed vertical gardens can help cool air and slow it down, by creating turbulence in vertical airflow. Another significant benefit of green roofs is their ability to retain stormwater. Typical stormwater systems in urban areas have resulted in a number of problems, such as water contamination, sewage overflows, drops in local water tables, water temperature increases, severe flooding and erosion. Green roofs and vertical gardens provide viable alternatives for environmentally appropriate stormwater management. Studies in Berlin show that green roofs absorb 75% of the precipitation that falls on them. Runoff occurs over several hours, thereby reducing the risk of sewage overflows and flash floods. There are economic cost benefits for building owners. The green roof and vertical garden systems provide energy cost savings due to increased insulation, extend the life span of roof



membranes and vertical surfaces due to improved protection, provide sound insulation, increase aesthetic appeal and, potentially, improve property values. Green roofs protect roofing membranes against ultraviolet radiation, extreme temperature fluctuations and puncture or physical damage from recreation or maintenance. Vertical gardens likewise provide protection from ultraviolet radiation, driving rain and wear and tear caused by moisture and temperature differentials. They also decrease the effect of wind pressure, which can improve the airtightness of doors, windows and cladding. Green roofs can be used for other advantages, such as recycling wastewater and in water-based heat exchange systems. Recommendations The research project identified a number of steps to overcome barriers to greater diffusion of green roof and vertical garden technologies in Canada. The major types of barriers identified were a lack of knowledge and awareness of the systems and associated cost benefits, a lack of incentives to facilitate implementation, a lack of specialized products, few Canadian installations and no technical standards. The following steps were recommended to overcome these barriers: 1. Address knowledge and awareness limitations by compiling a repository of green roof and

vertical garden knowledge on the Internet, and promoting its availability. 2. Generate awareness through high-profile demonstration projects, such as design and

implementation competitions in major cities across Canada. 3. All levels of government should actively support green roof and vertical garden technologies,

by introducing relevant procurement policies, implementing aggressive plans for installations and making it mandatory to include these technologies in new buildings.

4. Introduce grants or indirect subsidies to reduce payback periods and associated economic uncertainties to encourage private owner installations.

5. Encourage insurance companies to investigate benefits that would reduce premiums, such as increased building envelope life span and energy efficiency, and facilitate performance-based contracting installation through industry-government partnerships.

6. Reduce technical issues and uncertainty by providing financial support for increased research and creating high standards for both retrofitted and new installations.

Housing Research at CMHC Under Part IX of the National Housing Act, the Government of Canada provides funds to CMHC to conduct research into the social, economic and technical aspects of housing and related fields, and to undertake the publishing and distribution of the results of this research. This fact sheet is one of a series intended to inform you of the nature and scope of CMHC’s research. The Research Highlights fact sheet is one of a wide variety of housing-related publications produced by CMHC. For a complete list of Research Highlights, or for more information on CMHC housing research and information, please contact:



The Canadian Housing Information Centre Canada Mortgage and Housing Corporation 700 Montreal Road Ottawa, ON K1A 0P7 Telephone: 1 800 668-2642 FAX: 1 800 245-9274 Although this information product reflects housing experts' current knowledge, it is provided for general information purposes only. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. Readers are advised to consult appropriate professional resources to determine what is safe and suitable in their particular case. CMHC assumes no responsibility for any consequence arising from use of the information, materials and techniques described.



4. Sump Pumps

Key Considerations • Sump pumps can discharge to the surface or to a soakaway. • The advantages of overland ponding and overland flow compared to the soakway alternative

are longevity and little or no maintenance requirement. • The disadvantages of overland ponding are: less recharge due to evaporation and

inconvenience to homeowners. • Discharges relatively clean water, provides recharge, and quantity control benefits, but very

little water quality benefits. • Reduces flow in storm sewers. • Applied where foundation drain connection to storm sewers is not permitted. Foundation

drains should not be permitted to be connected to sanitary sewers. • Soakaway pits should not interfere with septic system operations. • Sump pumps may not be feasible where:

o groundwater levels are high, within 1 m of the building foundations; o bedrock is within 1 m of the foundation drain elevation.

• Requires suitable outlet at a backyard, if not feasible, the outlet should not interfere with the use of foot path, or sidewalk in the winter season.

• Outlets should be protected from blockage in winter by ice and snow. • Outlets can be directed to the surface or to a soakway. • If not provided with alternative power supply, it will not function during power cuts, which

usually coincide with heavy storms. • Requires periodic inspection and maintenance. • Located on private property, access by municipal staff in case of emergency is restricted. Design Guidelines for Soakaways • Storage media clear stone, approx. 50 mm diameter. • Intake to soakway pit from roof leader by perforated pipe, diameter >100 mm. • Perforated pipe located approximately 100 mm from top of pit. • Depth of soil cover over pit to be sized to take into account frost heave. • Drawdown time 24-48 h. • Soakaway pit not to be located close to septic systems. • Soil minimum percolation rate 15 mm/h. • Install overflow pipe to discharge roof leader to splash pad if pit clogged. • Soakaway pit depth can be computed from the percolation rate x drawdown time (24–48

hour). • Maximum depth of soakaway pit is 1.5 m. • Make allowance for decrease in percolation rates over time. • Overflow bypass pipe should be installed to divert excess flow from the roof leader to a

splash pad.



• Below the overflow pipe a filter should be installed, equipped with a screened bottom to prevent leaves and debris entering the soakway.

A sketch of a sump pump and soakaway arrangement reproduced from the Ontario BMP Manual is shown in Figure 3.

Sketch Showing Sump Pump and Soakaway Arrangement



5. Grassed Swales

Alternative BMP: Bioretention Key Considerations • In most cases it cannot achieve the TSS target removal rate on its own, will require additional

BMPs. • Can provide pre-treatment. • Requires suitable underlying soils to permit infiltration. • Requires flat side slope. • Only effective if velocities are low <0.5 m/s. • Aim for retaining the design runoff volume in the system for at least 10 minutes. • Sizing of the channel capacity should be dictated by the major-minor system criteria. • Choose the Manning’s n to reflect the condition of the grass. Design Recommendations • Maximum drainage area, depending on the % of imperviousness. • For 35% imperviousness, drainage area <2 ha. • For 75%, imperviousness, drainage area <1.5 ha. • Shallow and wide cross sections are more effective for pollutant removal. • Swale to be designed to carry both major and minor system events. • Typical dimensions:

o Bottom width 0.75 m o Side slopes 2.5:1 o Longitudinal slope <1% o Depth 0.5 m o Velocity < 0.5 m/s.

• To enhance performance apply check dam: height 0.3 m, spacing >30 m. • At culvert crossings provide adequate opening under driveway to prevent backwater

occurring or clogging.



Canada Mortgage and Housing Corporation Fact Sheet Vegetative Practices Description Vegetation is often employed as part of a BMP system to slow runoff and help stormwater infiltrate the soil and settle particulates before entering another treatment device. Two frequently used vegetative measures, filter strips and grassed swales, are described below. Filter strips provide stormwater quality controls. They are bands of close-growing vegetation, usually grass, planted between a source area and receiving water or channel. Filter strips can include shrubs or woody plants that help stabilize the grass strip. They are often used as pre-treatment devices for other stormwater control practices such as infiltration basins and trenches. Such strips are used primarily in residential areas around streams or ponds, where runoff does not tend to be heavily polluted and an additional level of quality control is desired. Grassed swales are shallow earthen channels covered with a dense growth of a hardy grass. In a residential setting, swales look like an extension of a front lawn, and can be used as alternatives to curb and gutter stormwater systems. This method is again usually used to provide pre-treatment before runoff is discharged to treatment systems, providing initial water quality improvements. Swales provide some reduction in stormwater pollution by filtering sediment and other matter. They also slow runoff and reduce peak flows. The following exhibit provides a view of vegetated filter strips and grassed swales. A grassed swale and perforated storm sewer system is a related stormwater conveyance system that may be used in areas where the streets are constructed without curbs. The system consists of a shallow grassed ditch that is underlain by a gravel trench. A continuous length of perforated pipe is located in the gravel trench. A layer of grass and sod filters the stormwater by removing suspended sediment and trash before it enters the gravel trench. In addition, a layer of synthetic fabric surrounds the gravel trench, providing additional filtration. Once the trench is at capacity, stormwater is conveyed by the perforated sewer system to an outlet such as a traditional closed storm sewer system.



Effectiveness Analysis Both filter strips and grassed swales serve to reduce the quantity of stormwater runoff by slowing flows and providing an area for increased infiltration. In addition, these vegetative practices provide a means for increased groundwater re-charge, an important consideration in urban areas facing groundwater supply concerns. The extent that stormwater quantity benefits are achieved depends primarily on the volume and timing of stormwater, the size of the device, vegetative cover, ground slope, and soil porosity. Filter strips reduce pollutants such as sediment, organic matter, and trace metals by the filtering action of the vegetation, infiltration of pollutant-carrying water, and sediment deposition. They are less effective at removing soluble pollutants. Although studies indicate highly varied effectiveness, treed filter strips can be more effective than grass strips alone because of the trees' greater uptake and long-term retention of plant nutrients. Properly constructed treed and grassed filter strips can be expected to remove more than 60% of the particulates and perhaps as much as 40% of the plant nutrients in urban runoff. Grassed swales prevent erosion, filter sediment, and provide some nutrient uptake. Pollutants such as suspended solids and trace metals are removed from surface flow by the filtering action of the grass, sediment deposition, and infiltration into the soil. The efficiency of swales in removing pollutants is moderate to low depending on the quantity of flow, the slope of the swale, the density and height of the grass, and the permeability of the underlying soil. Research on



grassed swales has found 30% - 90% reductions in solids and 0% - 40% reductions in total phosphorus loads. Typical pollutant removal efficiencies for filter strips and grassed swales are shown below.

Pollutant Removal Efficiency Plant Nutrients Low Sediment Moderate Trace Metals Moderate Organic Matter Low Oil and Grease Moderate Bacteria Low

Source: Compiled from Schueler 1987; Schueler, et al. 1992; US EPA 1990; Phillips 1992; Birch, et al. 1992 and others.

Two monitoring studies for grassed swales and perforated storm sewer systems - one in Ottawa and one in Toronto - find that the systems are relatively efficient in managing stormwater quality. Results from these studies are shown below. These pollutant removal efficiencies highlight differences that can be achieved across different sites, land uses, soils, and drainage areas.

Study Suspended Solids Heavy Metals Phosphorus Nitrogen Ottawa 90% 75%-93% 75% 70% Toronto 75% 25%-90% - -

Economic and Financial Analysis Vegetative BMPs are relatively inexpensive to establish and maintain. Grassed swales are even described as being more economical than curb and gutter drainage systems from a capital and operations cost perspective. A description of costs of vegetative BMPs is provided below. These costs include any necessary earth moving and shaping. Costs of vegetative practices excluding earth moving and shaping are much smaller.

Device Type Cost Unit Filter Strips Topsoil, Grading, Sodding (Turf) $6 m2 Hydroseeding (Turf), Grading, Mulch $3 m2 Tree and Shrub Planting, Grading $18 m2 Grassed Swales Sodded Swale $36 m Source: Ontario Ministry of the Environment (1991), "Stormwater Quality Best Management Practices".



Implementation Issues Grassed swales should be constructed in consideration of the following realities: • Applications - Swales can provide runoff control for single-family residential lots. They are

inappropriate for controlling runoff from larger facilities, and are usually insufficient to manage runoff from substantial rainfall events.

• Design (Soils) - Swales are less effective in regions with sandy soils, as sandy soils contribute to collapse of swale walls. Furthermore, sandy soil conditions influence the extent that alternative species of vegetation can grasp hold and flourish.

• Design (Flows) - Swales operate efficiently under conditions when maximum flow rates do not exceed 0.5 m/s. Therefore, the suitability of a swale depends on its area, slope, and imperviousness of the contributing watershed.

• Maintenance - Swales require maintenance including periodic inspection, mowing at least twice each year, fertilizer application, and repair and reseeding of washed out areas and bare spots. Higher runoff velocities increase the frequency of required maintenance.

Filter strips should be constructed in consideration of the following realities. • Applications - Filter strips can be utilized in urban settings for treating rooftop runoff and

runoff from lawns and other pervious areas from small properties. They are not suitable to control runoff from large parking lots or commercial/industrial establishments.

• Design (Soils) - The ability of filter strips to remove nutrients from runoff improves where clay soils or organic matter are present. Filter strips work best when established with a minimum width of 15-20 m, and having a relatively low slope.

• Design (Flows) - Filter strips have limited effectiveness when runoff velocities approach 0.75 m/s. Because their ability to effectively filter stormwater is limited, contributing areas should be less than 2 hectares in size.

• Maintenance - Filter strips require periodic repair, re-grading, and sediment removal as well as re-seeding and re-planting. Inspections may also show the importance of removing dead vegetation. Inadequate maintenance will cause filter strips to be non-functional.



6. Pervious Pipes And Catch Basins

Alternative BMPs: Grassed swales Key Considerations • Long-term performance unknown. • Often clogged, especially if no pre-treatment is applied. • Construction timing is important, should be installed after the entire upstream area is

developed. • In sensitive groundwater areas it could elevate metal, oil/grease and chloride levels in

groundwater. • Pervious catch basins require more frequent maintenance and some jurisdictions will not

accept it.

Design Feature Objective Recommendations

Pervious Pipes Pre-treatment To reduce suspended

solids in runoff and to extend longevity of the pervious pipe system

• Pre-treatment by grassed swale to discharge runoff into pipes.

• Perforated pipe system to be protected from sediment during road construction.

Perforated pipes to convey street runoff.

To convey and exfiltrate runoff

• Runoff collected in surface catch basins to be connected to the pervious pipes.

• Pipe diameter >200 mm. • Slope of pipe <0.5% to encourage infiltration.

Bedding and storage

To exfiltrate storm flow below ground, increase infiltration, reduce quantity and improve quality of flow downstream, without creating groundwater pollution hazard

• Implemented in soils >15 mm/h percolation rate. • High water table or bedrock >1 m below pipe. • Non-woven fabric placed at the interface between

pipe bedding and the native soil. • Pipe bedding using clear stone 50 mm diameter. • Anti-seepage collars to be fitted. Spacing to be

determined subject to local soil conditions. • Storage volume in pipe bedding runoff from a

minimum 5 mm storm to a maximum 15 mm storm with 4 hours duration from the contributing drainage area.

• Bedding layer approximately 100 mm above the top of pipe. Depth and width of bedding below pipe invert dependent on the storm event to be exfiltrated.

• Non-woven fabric to be installed at the interface between pipe bedding and the native soil.

Pervious Catch Basins Pre-treatment To reduce suspended

solids in runoff and to extend longevity of the pervious pipe system

• Grassed swale to discharge runoff into catch basin • Over sizing catch basin storage capacity. • Perforated catch basin system to be protected from

sediment during road construction. • Optional use of catch basin filters sold commercially

to reduce TSS entering the system.




Catch basin To convey and exfiltrate runoff through a large sump connected to an exfiltration storage media

• Standard catch basin with minimum 1 m deep sump.

Bedding and storage

To exfiltrate storm flow below ground, increase infiltration, reduce quantity and improve quality of flow downstream, without creating groundwater pollution hazard

• Perforated pipe 200 mm diameter to connect catch basin with storage media.

• Implemented in soils >15 mm/h percolation rate. • High water table or bedrock >1 m below pipe. • Non-woven fabric placed at the interface between

pipe bedding and the native soil. • Bedding using clear stone 50 mm diameter. • Storage volume in bedding from a minimum 5 mm

storm to a maximum 15 mm storm with 4 hours duration from the contributing drainage area.

• Bedding layer approximately 100 mm above the top of pipe. Depth and width of bedding below pipe invert dependent on the storm to be exfiltrated.

• Non-woven fabric to be installed at the interface between pipe bedding and the native soil.

The attached sketches on perforated pipes and pervious catch basins shown on Figure 4 were reproduced from the Ontario BMP Manual. Figure 1 Perforated Pipe and Pervious Catchbasins



7. Wet Ponds

Source: New York State Stormwater Manual Alternative BMP: Constructed wetland Caution: any wet pond facility which creates a dam is required to meet the Canadian Dam Safety Guidelines. Design Guidelines for sizing wet ponds are presented in the attached Design Sheets.




Drainage area Sufficient runoff volume to sustain permanent pool

• Minimum 5 ha, preferred minimum 10 ha.

Pond surface area Sufficient pond area to provide required control

• Approximately 1% of drainage area.

Permanent pool Trap pollutants, only to be drained for maintenance purposes

• Max depth at outlet = 2.5 m. • Generally, 1- 2 m.

Water quality extended detention storage

Capture and treat more frequent smaller storms

• Maximum depth = 1.0 m.

Erosion Control storage Reduce rate of flow to reduce risk of erosion


Flood control storage Reduce peak flow to reduce risk of flooding


Maximum Pond Depth Reduce risk of injury • Maximum depth = 3.0 m with 0.3 m freeboard

Forebay Initial settling of particles. • Volume appr. 10% of total pond volume.

• To be separated from the wet pond by a berm, 3 m top width, with top level <0.3 m above permanent pool level, maximum slope 3:1.

• Length to width ratio minimum 2:1. • Bottom lined crusher run limestone or

similar. Geotextile lining below invert may be required. (Provide Geotechnical Consultant report).

• Forebay length L=[rQ/V]0.5. • Dispersion length= 8Q/dV. • Bottom width= Disp/8. • Minimum depth 1m.

Freeboard Provide safety against overtopping

• 0. 3 m above design high water level (100-yrear).

Length to width ratio Maximize flow path and minimize short circuiting

• 3:1 to 5:1.

Pond berming Separate pond from surrounding area

• Around perimeter of pond, minimum top width 3 m.

Side slopes Safety. Flat slopes to reduce risk of slipping to pool

• Slope not steeper than 5:1 extended to the top of the extended detention storage elevation. Above permanent pool elevation 3:1

Inlet Convey flow to pond,

avoid clogging and freezing

• Non-submerged inlets preferred. Inlet pipe with slope <1% could create backwater

• Provide erosion protection between inlet and forebay




Outlet Reduce erosion downstream, avoid clogging and freezing

• Channel downstream be protected from erosion.

• Reversed slope pipe. - diameter >75 mm to reduce risk of clogging and freezing - pond depth >1m at reverse slope outlet - gate valve preferred • Perforated riser pipe - hole diameters 12 mm-25 mm - orifice diameter >50 mm - stone around riser >75 mm diam.

Maintenance pipe outlet Drain permanent pool • Capacity to drain the pond in 6 hours. Do not drain during spring season, high chloride contents. Requires gate valve.

Maintenance Access Access for backhoes or dredging equipment

• To be provided to inlet and outlet and to base of forebay.

• Roadway width 4 m. • Max cross fall 2%. • Max gradient 10%. • Minimum centreline radius 12 m. • Geotextile under granular B. • Access between private lots for sole

purpose of maintenance access shall have a minimum easement of 6 m.

Emergency overflow To allow runoff safely to exit should the outfall structure fail, or should the storm event exceed the 100 –year event

• Provide erosion protection.

Fencing and warning signage

Fencing not essential, except at structures. Temporary fencing after initial construction until vegetation is established

• Place signs around facility indicating its purpose and function, with warning of potential fluctuating water levels.

• If residential areas are located adjacent to facility consider using 1.5 m high, black vinyl chain link fence.

• Also place warning signage adjacent to pedestrian traffic routes.

Setback • Minimum setback 5 m from facility to property line.

Sediment drying area Reduce water content of dredged material before carting away

• To be provided close to the maintenance access.

• Minimum surface area to match forebay pool area.

• Maximum depth 1 m. • Provide drainage back from drying area

to forebay. • Use same granular material as for

access road.




Access restriction Reduce risk of accidents • Planting of thorn bearing vegetation preferred to fencing, except at high risk areas such as headwalls, inlets and outlets.

The following additional design features are recommended to reduce the risk of injury, while maintaining the stormwater management function. These recommended measures are intended to restrain access to deep standing water through a series of physical, natural and aesthetic barriers. This approach is intended as a deterrent to accidents and to replace fencing - if preferred by the municipality - with an appropriate alternative, while maintaining the stormwater management function and public safety. 1. The preferred pond depth is 1.5-2.0 m. Shallow ponds of less than 1.0 m are likely to be

ineffective, and should be discouraged due to the possible re-suspension of sediment and greater land requirements.

2. The maximum depth shall not exceed 3.0 m with a maximum 0.3 m freeboard. 3. For extended wet ponds side slopes should be maximum 5:1 or flatter, for dry ponds

maximum 4:1 side slopes are to be applied around the perimeter of the sediment forebay and rest of the facility. Steeper slopes (maximum 3:1) may be allowed to be used when these slopes are representing only less than 20 % from the total area and are combined with a minimum buffer of 5.0 m above the 100 year storm event (plus 0.3 m freeboard) elevation to the property line; and are combined with unfriendly vegetation.

4. SWM facilities should be located above the 25-50 year storm flood line 5. Unmowed vegetated buffers will be required around the perimeter to act as a natural

barrier. This buffer should be comprised of tall grasses and wild flowers, trees and densely planted shrubs. A densely vegetated margin on the aquatic safety bench would serve as an aesthetic amenity and an additional natural barrier.

6. An aquatic safety bench must be constructed around the forebay and the main treatment

cells with the lower edge to be located 0.9 m above the pond bottom with a minimum 2 m width and incorporate a minimum slope of 10:1 or flatter.

7. Pedestrian and cycle paths must always be located no lower than the 5-year storm event

water elevation and used in conjunction with the preferred slopes to further maximize recreational user safety and minimize public risk and liability. Paths below this point and leading to the lower portions of a facility should be posted to warn the public of potential safety hazards during pond operation.



8. Restricted area signage will be necessary to warn the adult public to avoid areas or activities under certain conditions.

7.1 Extended Wet Pond Design An extended wet pond may have to provide a variety of functions including water quality, erosion and flood control for the downstream environment, depending on the specific sensitivities and requirements of the receiving watercourse. Step 1, Sizing for Water Quality Control The following design approach is based on Analytical Probabilistic Modeling developed at the University of Toronto and applied in numerous areas across Canada1. Specifically, this method assesses the long term TSS removal efficiency of the pond. There are numerous variables, (permanent and active storage volume, pond depth, detention time, runoff ratio, inflow and outflow characteristics) which can influence the design of the quality control component of a wet pond. Two storage volumes are of interest, the permanent pool volume (SP) and the active pool volume (SA), however the permanent pool is considered to be the principle component affecting pollutant removal efficiency. The main input parameters in the design are the drainage area, catchment depression storage, and runoff coefficient. The Analytical Probabilistic Methods predict TSS removal efficiency considering theses variables and long-term rainfall characteristics. Removal rates for TP can be estimated considering the following observed relationship between TSS and TP: TSS Removal Rate TP Removal Rate 80% 50% 70% 45% 60% 35% The first task is to size the permanent pool. Figure 5 shows the relationship between TSS removal rates and permanent pool storage for different runoff coefficients2. The graph assumes a permanent pool depth of 1.5 m, which is regarded as typical. Variation in the permanent pool depth within the generally accepted range of 1.0 m to 2.0 m results only in small changes in the required pond volumes as shown on Figure 6. Once the storage volume and depth is selected the average area of the permanent pool can be estimated.

1 Urban Stormwater Management Planning with Analytical Probabilistic Models by Adams and Papa, 2000 2 Note: storage volumes are expressed on a unit catchment area basis. A storage volume of 10 m3/ha,is equivalent to a runoff depth of 1 mm from the contributing catchment.



0

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TSS Removal 84% TSS Removal 80% TSS Removal 75% TSS Removal 70% TSS Removal 65% TSS Removal 60% Figure 1 Permanent Pool Depth 1.5 m

TSS Removal with Respect to Different Permanent Pool Depth (Runoff Coefficient 0.55)

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Figure 2 Sensitivity of Permanent Pool Depth in Sizing Permanent Pool Storage



The next step in the wet pond quality treatment design is the selection of the active storage volume, i.e., the component of the pond that undergoes filling and extended period drawdown following runoff events. The analytical model and past monitoring of extended wet ponds confirm that the volume allocated to the permanent pool provides greater water quality benefits than the equivalent volume in active storage – this is due the the effectiveness of quiescent particle settling in the permanent pool between rainfall events. Figure 7 shows the relationship between TSS removal and active storage for a range of permanent pool volumes considering an average runoff coefficient of 0.55. According to the graph, increasing active pool storage beyond a certain point only marginally increases or even decreases TSS removal efficiency. Similar curves for runoff coefficients of 0.35, 0.70, 0.85 have been developed and showed similar trends to Figure 7. To optimize performance, the analysis suggests that in most instances a higher efficiency can be achieved by allocating storage to the permanent pool instead of the active pool3. Analysis by others using continuous simulation suggests an optimal value of 40 m3/ha.4 This value can be considered for HRM meteorological conditions as well.

TSS Removal with Respect to Different Permanent Pool Storage(Runoff Coefficient 0.55)

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Active pool storage (m3/ha)

TSS

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Figure 3 Different Active Pool Storage Volumes

Designers should review the volumes, depths and the surface area of the permanent and active pools obtained from Step 1, to optimize the design for the site. For example, to meet site 3 For example, a higher efficiency is achieved with a storage allocation of 60 m3/ha permanent and 40 m3/ha active, than 40 m3/ha permanent and 60 m3/ha active. 4 Stormwater Management Practices Planning and Design Manual, Ministry of Environment and Energy, 1994



constraints the permanent pool depth may have to be altered to change the pool surface area, or to meet outlet elevation constraints. Step 2. Erosion Control The suggested design criteria for downstream erosion control are the active storage and controlled release of runoff over a 48-hour period, based on runoff generated by a 25 mm 6 hour winter storm. Using a hydrologic model a runoff hydrograph should be generated based on a 25 mm winter storm to determine the inflow into the pond. For the discharge capacity at the controlled outlet, an orifice or a weir formula should be used to estimate the outflow depending on the selected outlet and pond depth in the active storage facility. Generally, the erosion control storage requirement will exceed the previously computed water quality storage requirement (i.e., 40 m3/ha or 4 mm of runoff), and should be the governing criterion in sizing the active storage component of a wet pond. Step 3. Flood Control To provide control for high peak flows generated by the proposed land use, the flood control criterion requires that post-development peak flows for the 2-year to 100-year return periods be reduced to the pre-development peak flows. Using a hydrologic model a series of runoff hydrographs should be generated and routed through the pond. These high flows would require additional outlet controls above the active storage controls previously designed for lower release rates under water quality and erosion control. Usually, a single weir or a series of stepped weirs may be required. The control elevation for these outfall components is generally located at or above the maximum extended water quality and erosion control water levels. To prevent overtopping of the facility by extreme floods or malfunctioning of the outlets, an emergency spillway should be sized and located, to provide a safe outlet and to minimize the risk of upstream impacts Extended Wet Pond Design Assume the following input parameters: Total drainage area 20 ha Runoff coefficient 85% (winter conditions) TSS removal rate 80%



Step 1. Water Quality Control To size permanent pool, assume:

• permanent pool depth 1.5 m • detention time 24 hours

From Figure 5, permanent pool volume 186 m3/ha = 3,720 m3. The permanent pool average surface area 3,720/1.5 = 2,480 m2. The permanent pool side slope is 5:1; the length to width ratio is 3:1. The permanent pool average width = 29 m; average length = 86 m. To size active pool: Select a constant value, 40 m3/ha = 800 m3 Active storage depth 800/2,480 = 0.32 m Step 2. Erosion Control Use 25 mm 6 hour winter storm to estimate erosion control requirements. The Hydrological model, XPSWMM for example is used to simulate the 25 mm Chicago design storm through the pond. XPSWMM simulation results show that for erosion control an active storage of 3,207 m3 is required using a 100 mm orifice as the extended detention outlet control. This value exceeds the water quality volume requirement of 800 m3, and will be used for sizing the active pool. The side slope of the extended detention storage is 5:1. According to the side slope and the previously determined permanent pool geometry, the maximum depth of the extended detention pool is 0.81 m. The average extended detention pool width = 41 m, average length = 98 m. A 100 mm release orifice with the discharge coefficient 0.6 can draw down the extended detention storage volume around 48 hours. Step 3. Flood Control Estimate the flood control storage requirements for the 100-year event. From the Halifax IDF curve, the 100-year 24- hour storm is selected (155 mm depth). Use a hydrologic model to compute both pre-and post-development hydrographs. Pre-development imperviousness: 20%, post-development imperviousness: 80%. XPSWMM results: Pre-development peak rate: 2.36 cms Post-development peak rate: 3.35 cms In order to reduce the post-development peak discharge rate to the pre-development peak rate, a broad crested weir with a length of 1.0 m (discharge coefficient 1.5) is required with the crest elevation set at the top of the extended detention storage volume.



Storage volume for quantity control is 6850 m3. The side slopes above the extended detention level are set at 3:1. The average flood control storage width = 49 m, average length = 106 m. The total depth of the flood control component is 1.33 m. Summary of Wet Pond Configuration: The permanent pool volume is 3,720 m3with a depth of 1.5 m. The extended detention storage volume is 3,207 m3 (erosion control governs), with a depth of 0.81 m above the permanent pool water surface. The flood control storage volume is 6850 m3, with a depth of 1.33 m above the permanent pool water surface (includes extended detention volume). Orifice size for runoff quality control and erosion control is 100 mm with the discharge coefficient of 0.6. Weir length for runoff quantity control (100 year storm): 1.0 with the discharge coefficient of 1.5.



Canada Mortgage and Housing Corporation Fact Sheet Retention Ponds Description Retention ponds, also called wet ponds, maintain a permanent pool of water in addition to temporarily detaining stormwater. This permanent pool of water is the principal distinguishing feature between retention ponds and detention ponds. One example of a wet pond, known as an enhanced wet pond, is illustrated below. An enhanced wet pond is distinguished from a simple wet pond by the existence of a forebay designed as an additional trap to incoming sediment. Effectiveness Analysis Retention ponds bring both stormwater quantity and quality benefits. These ponds fill with stormwater and release most of it over a period of a few days, slowly returning to its normal depth of water. Some stormwater infiltrates underlying soils, and some is evaporated. This process marks a small reduction in stormwater quantity. Wet ponds help reduce frequent peak stormwater discharges which, in turn, controls downstream flooding and reduces scouring and erosion of streambanks. Because these ponds tend to have a large amount of storage, peak flows are delayed. The extent of these stormwater quantity benefits depends on the size of the pond, volume of inflow, and rate of release, among other factors. These peak flow benefits require detailed stormwater management models to estimate. Retention ponds provide stormwater quality benefits through several mechanisms, including: • gravitational settling of suspended particulates; • biological uptake of pollutants by plants, algae, and bacteria; and • decomposition of some pollutants. The exhibit below describes pollutant removal levels for nutrients, sediment, metals, organic matter, oil and grease, and bacteria. In general, retention ponds provide more effective pollutant removal than other stormwater management devices. Negligible removal of soluble pollutants (such as salt) is provided.

Pollutant Removal Efficiency Plant Nutrients Total Phosphorus Moderate to High Total Nitrogen Moderate Sediment Total Suspended Solids High Metals Lead High Zinc Moderate Organic Matter Biomedical and Chemical Oxygen Demand Moderate



Pollutant Removal Efficiency Oil and Grease High Bacteria High Source: Compiled from Schueler 1987; Schueler, et al. 1992; US EPA 1990; Phillips 1992; Birch, et al. 1992 and others. The following exhibit is a tabulation of percent removal in two retention ponds that were monitored in Southern Ontario. It is important to note that these removal efficiencies will be slightly lower during the winter/spring season since the permanent pool will be completely or partly frozen.

Percent Removal (Summer/Fall Season) Pollutant Wetland (Retrofit)1 Wet Pond2 Total Suspended Solids 80% 87% Total Phosphorus 41% 79% Oil and Grease - 79% E-coli 53% - Source 1: SWAMP (1998), Performance Assessment of a Retrofit Stormwater Quality Detention Pond, Harding Park, Richmond Hill. Source 2: SWAMP (1998), Performance Assessment of a Highway Stormwater Quality Retention Pond, Rouge River, Toronto. As an alternative cost measure, a 2,000 m3 wet pond is expected to have construction costs of about $50,000. Annual maintenance of the pond could be expected to be about $2,000. Implementation Issues • Design (Shape) - Improper design shape can result in "short-circuiting" and a reduction in

pollutant removal efficiency. To maximize pollutant removal benefits, a long distance between inlet and outlet is needed (a 3:1 or greater ratio of length to width is appropriate). Where the pond shape is not ideal this can be achieved by a system of low berms that force stormwater to travel longer distances to the outlet.

• Design (Size and Depth) - A traditional wet pond requires a minimum area of 2,500 m2 and is about 1-2 metres deep. Wet ponds are not well suited to very small developments because of their size, but are appropriate for a cluster of houses. The development site should be a minimum of five hectares in area in order to sustain the permanent pool in the retention pond. In a retention pond the design volume and depth of the permanent pool is critical for the efficient removal of pollutants.

• Design (Soil) - Where soils are permeable it may not be possible to maintain a permanent pool. In areas with permeable soils, a pond liner is recommended. The liner can be a layer of impermeable clay soil or a synthetic (plastic) liner. Alternatively it may be possible to compact underlying soils.

• Design (Slopes) - The side slopes of a retention pond should be no steeper than 3:1 to avoid excessive erosion, and not flatter than 20:1 to provide a permanent pool of sufficient volume and depth that is capable of efficient pollutant removal.



• Design (Area) - A buffer strip, about 10 metres wide, should surround a retention pond. The buffer strip should be planted with a mix of low maintenance vegetation, and should be tolerant to changes in the depth of water in the pond.

• Design (Site) - Because many people find retention ponds to be aesthetically pleasing, they can be sited in both low and high visibility areas. The pool of water can enhance property values as well as the aesthetic and recreational value of the area.

• Routine Maintenance - Retention ponds require regular inspection, landscaping (mowing), and cleaning of inlets and outlets. Care must be taken to control nuisance insects (especially mosquitoes), weeds, algae, and odours.

• Periodic Maintenance - Structural repairs and sediment removal will be required, the extent depending on the design and operation of the retention pond. Sediment removal every 10 years is frequently recommended, sometimes with costs reaching $100,000.

• Safety - The pond is a potential hazard for nearby residents due to the presence of standing water. The inclusion of a shallow safety bench around the permanent pool of the pond may reduce the hazards. Additionally, growth of dense vegetation will limit immediate access to residents.



8. Dry Ponds

Alternative BMPs: Wet ponds, Constructed wetlands, Roof top storage. Caution: any pond facility which creates a dam is required to meet the Canadian Dam Safety Guidelines. Key Considerations: • Can be effective to control erosion and flooding, as it has no permanent pool of water to

control water quality. • The minimum size of drainage area is influenced by the outlet capacity. Generally, the

minimum drainage area should be 5 ha-8 ha. For very small flows the outlet can be easily clogged.

• Grading of dry ponds is less critical than for wet ponds. • Many of the design parameters are the same as for wet pond.

Design Feature Objective Recommended Criteria Drainage area Sufficient runoff to require

an outlet diameter not subject to clogging

>5 ha

Storage pond Quantity and erosion control. Quality control subject to drawdown time generally not effective, particles subject to re-suspension

Control of peak flows up to 100-year event, For erosion control 25 mm storm over the drainage area with detention >24 hours

Freeboard 0. 3m above design high water level Length to width ratio Maximize flow path and

minimize short circuiting 4:1 to 5:1

Permanent pool depth 2 m – 3m Active storage depth Settle suspended solids Maximum depth 1 m for storms <10 year

event Side slopes Safety. Flat slopes to reduce

risk of slipping to pool Minimum slope 4:1

Inlet Convey flow to pond, avoid clogging and freezing

Non-submerged inlets preferred. Inlet pipe minimum diameter 450 mm. Slope <1% could create backwater

Outlet Reduce erosion downstream, avoid clogging and freezing

Reversed slope pipe Diameter >75 mm to reduce risk of clogging and freezing Pond depth >1m at reverse slope outlet Gate valve preferred A portable pump may be required to drain pond if the invert of reversed sloped pipe is above the pond bottom Perforated riser pipe hole diameters 12 mm-25 mm orifice diameter >50 mm



Design Feature Objective Recommended Criteria stone around riser >75 mm diam.

Maintenance pipe outlet Capacity to drain the pond in 6 hours. Requires gate valve


To be provided to inlet and outlet and to base of forebay. Roadway width 4 m Max cross fall 2% Max gradient 10% Minimum centreline radius 12 m Geotextile under granular B Access between private lots for sole purpose of maintenance access shall have a minimum easement of 6 m.

Fencing Temporary fencing during construction until vegetation established

Grading and planting to replace the need for permanent fencing

Forebay Pre-treatment to settle larger particles and ensure exit velocities are non-erosive. Also to facilitate maintenance.

• Length to width 2:1 • Minimum depth 1.0 m • Surface area <1/3 pool area • Forebay length, L=[rQ/V]0.5 • Dispersion length, Disp = 8Q/dVF • Hard bottom width= Disp/8 • Minimum depth 1m

Volume = estimated 10 year sediment accumulation

• Berm to separate forebay from pond to be designed as a dam. A weir located at the top of berm to convey flows to pond. A maintenance pipe to be installed to drain forebay

Access restriction Planting of thorn bearing vegetation preferred to fencing, except at high risk areas such as headwalls, inlets and outlets

Forebay formula L, Forebay length in m R, Forebay length to width ratio Q, Peak flow from pond V, Settling velocity (suggested value 0.0003 m/s) Dispersion formula D, Depth of permanent pool in forebay, m VF, Forebay velocity, m/s



9. Constructed Wetlands

Alternative BMPs: Extended wet ponds, bio-retention

Source: New York State Stormwater Manual Caution: Any design of a constructed wetland with an embankment may have to meet the Canadian Dam Safety Guidelines.



Key Considerations • Removes multiple pollutants generated in urban areas • Could provide limited peak flow attenuation. Control of high peak flows by the active

storage is limited due to the maximum allowable active storage depth • Provides habitat for wildlife and waterfowl • Requires more land than any other BMP • Requires adequate and reliable flow from upstream • Must be kept free of invasive plant species • Pollutants from industrial and commercial land uses may eventually create environmental

risk to wildlife • Can lead to over-population of waterfowl • Highly variable water levels and high hydraulic loading rates can adversely affect the

survival of wetlands • Generally, pre-treatment of runoff is recommended • Planting should be done early in the season to ensure the plants survive the winter season. • If a combined wet pond/wetland system is used, the wet pond should be sized to

accommodate 50% of the total required permanent pool volume.

Design Feature Objective Recommendations Drainage area Sufficient runoff to

sustain a permanent pool

• Area >5 ha. Constructed wetlands should not be completely empty following a 30-day summer drought.

Surface area Quantity quality and erosion control

• Surface area of the entire wetland >1.5% of the drainage area

• 35% of surface area less than 0.15 m deep • 65% of surface area less than 0.5 m deep.

Freeboard Safety • 0. 3 m above design high water level Length to width ratio Maximize flow path

and minimize short circuiting

• 3:1. Length measured along the flow path

Permanent pool depth • Average depth 0.15 m – 0.3 m. Deep areas to be limited to<25% of surface area

Permanent and active storage volumes

• See water quality and erosion control criteria.

Active storage depth Settle suspended solids • Maximum depth 1 m Side slopes Safety. Flat slopes to

reduce risk of slipping to pool

• Near permanent pool 5:1 or flatter In the extended detention portion 3:1. Terraced grading 7:1 to minimize risk of public to fall into the wetland.

Inlet Convey flow to pond, avoid clogging and freezing

• Minimum diameter 0.45 m. Non-submerged inlets preferred. Inlet pipe with slope <1% could create backwater

• If submerged obvert below expected ice depth Outlet Reduce erosion

downstream, avoid clogging and freezing

• Use a micro pool at the outlet 1-2 m deep to protect the pipe from clogging and prevent sediment re-suspension.

• Reversed slope pipe



Design Feature Objective Recommendations • Diameter >75 mm to reduce risk of clogging and

freezing - Pond depth >1m at reverse slope outlet - Gate valve preferred - A portable pump may be required to drain pond if the invert of reversed sloped pipe is above the pond bottom

• Perforated riser pipe - hole diameters 12 mm-25 mm - orifice diameter >50 mm - stone around riser >75 mm diam.

Maintenance pipe outlet

Drain wetland • Capacity to drain the wetland in 6 hours. Requires gate valve

Forebay Improves pollutant removal and facilitate maintenance

• Hold approximately 10% of total pond volume • Length to width 2:1 • Surface area <1/3 pool area • Forebay length L=[rQ/V]0.5 • Dispersion length= 8Q/dV • Hard bottomed width= Disp/8 • Minimum depth 1m • Berm to separate forebay from pond to be

designed as a dam. A weir located at the top of berm to convey flows to pond. A maintenance pipe to be installed to drain forebay


• To be provided to inlet and outlet and to base of forebay.

• Roadway width 4 m • Max cross fall 2% • Max gradient 10% • Minimum centreline radius 12 m • Geotextile under granular B • Access between private lots for sole purpose of

maintenance access shall have a minimum easement of 6 m.

Fencing Temporary fencing during construction until vegetation established

• Grading and planting to replace the need for permanent fencing

Planting. For more detail see attached plant list at the end of the Appendix.

Plants absorb nutrients, filtrate stormwater, enhance aesthetics, and assist in safety, prevention of resuspension of bottom sediments, and in the reduction of flow velocities.

• Planting should be done early in the season • Deep water area at inlet and outlet, planting

limited to submergent vegetation • Shallow depth area, and permanent pool < 0.5 m

deep, planting include both submergent and emergent vegetation

• Shoreline fringe located between permanent pool and erosion and water quality control high water level, planting similar to shallow marsh area.

• Flood fringe subject to infrequent flooding, grass, shrub and trees



Design Feature Objective Recommendations Access restriction • Planting of thorn bearing vegetation preferred to

fencing, except at high risk areas such as headwalls, inlets and outlets

Constructed Wetland Design The design approach is very similar to the one described under wet ponds. The only difference is the changes in the permanent pool due to the shallow depth required for a wetland. The commonly applied water depth in a wetland is between 0.15 m to 0.3 m. Figures 8 and 9 show the relationship between TSS removal and permanent pool storage requirement the two most commonly used permanent pool depth of 0.15 m and 0.3 m, respectively. For the active storage 40 m3/ha was selected using the same methodology as in the wet pond sizing process.

0

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TSS Removal

Figure 1 Wetland Sizing Criteria at Permanent Pool Depth 0.3m, Active Pool Storage 40 m3/ha



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Figure 2 Wetland Sizing Criteria at Permanent Pool Depth 0.15 m, Active Pool Storage 40 m3/ha

As shown by the graphs, constructed wetlands require much smaller permanent pool storage than wet ponds, but spread over a larger area.



Canada Mortgage and Housing Corporation Fact Sheet Constructed Wetlands Description Constructed wetlands are shallow pools developed specifically for storm or waste water treatment that create growing conditions suitable for wetland plants. Constructed wetlands differ from other artificial wetlands in that they are not typically intended to replace all of the functions of natural wetlands. Rather, they are designed to provide water quality benefits by minimizing point source and non-point source pollution prior to its entry into streams, natural wetlands, and other receiving waters. They can also play a water quantity management role. There are two basic types of constructed wetlands: • subsurface systems have no visible standing water, and are designed so that the

wastewater flows through a gravel substrate beneath the surface vegetation; and • surface flow systems have standing water at the surface and are more suited to larger

constructed wetland systems such as those designed for municipal wastewater treatment. The following exhibit illustrates a "two-cell" constructed wetland involving an impermeable cell and permeable cell.

Source: Revised from http://www.marshlands.com/ Enhanced constructed wetlands can also be designed for more effective pollutant removal. They include design elements such as a forebay, complex microtopography, and pondscaping with multiple species of wetland trees, shrubs and plants.



Effectiveness Analysis Constructed wetlands can be used to manage stormwater runoff peak discharges and make modest reductions in overall runoff quantity. Quantity reductions can be achieved through infiltration of stormwater to the water table, and some delays in peak flows. Stormwater quality management is typically the reason why constructed wetlands are considered as a stormwater management facility. Properly constructed and maintained wetlands can provide very high removal rates of pollutants from stormwater. Removal of pollutants is accomplished through adsorption, wetland plant uptake, retention, gravitational settling, physical filtration and microbial decomposition, thus improving runoff quality. Among the most important pollutant removal processes are the purely physical processes of sedimentation and filtration by aquatic vegetation. These processes account for the strong removal rates for suspended solids, organic matter (particulate BOD), and sediment-attached nutrients and metals. Similarly, pathogens show good removal rates in constructed wetlands through sedimentation and filtration, natural die-off, and UV degradation. Dissolved pollutants such as soluble organic matter, ammonia and ortho-phosphorus tend to have lower removal rates. Removal rates for metals are variable, but are consistently high for lead, which is often associated with particulate matter. Constructed wetlands can be expected to achieve or exceed the pollutant removal rates estimated for wet pond detention basins and dry detention ponds.

Pollutant Removal Efficiency Plant Nutrients Total Phosphorus Total Nitrogen

High Moderate

Sediment Total Suspended Solids Very High Metals Lead Zinc

High High

Organic Matter Biomedical and Chemical Oxygen Demand

Moderate

Oil and Grease Very High Bacteria High

Source: Compiled from Schueler 1987; Schueler, et al. 1992; US EPA 1990; Phillips 1992; Birch, et al. 1992 and others.

Actual pollutant removal rates depend on the aquatic treatment volume, the surface area to volume ratio, the ratio of wetland surface area to watershed area, and plant types. Additionally, longer stormwater flow paths through the wetland and longer detention times within the wetland are expected to improve pollutant removal rates. Economic and Financial Analysis The cost of establishing a constructed wetland varies depending on size and site conditions. In general, larger constructed wetlands involve higher construction, installation, maintenance, and waste disposal costs. Some sources suggest that constructed wetlands, for the storm and/or waste



water they treat are relatively inexpensive, with the costs of a constructed wetland intended to serve a cluster of houses similar to installing a conventional septic system. Several estimates of the costs of constructed wetlands have been published: • Construction Costs - Using data from municipal systems, Kadlec (1995) cites

construction costs from 18 North American surface flow wetlands ranging from $6,000 to $300,000 per hectare (1994), with a mean of $100,000. Reed et al. (1994) cited a range of $100,000 to $240,000 per hectare for the same type of system.

• Operations and Maintenance Costs - Once established, the operation and maintenance costs for constructed wetlands can be lower than for alternative treatment options, generally less than $1,500/ha/year (Kadlec, 1995), including the cost of pumping, mechanical maintenance, and pest control.

Details on the size and features of these constructed wetlands are unavailable. Implementation Issues Wetlands may be highly valued by homeowners, and can therefore be serve as centerpieces to developments and recreational areas. • Site - Constructed wetlands can be applied to most development situations where

sufficient baseflow is available to maintain water elevations. To maintain a constant water level, it is often necessary to have a reliable dry-weather baseflow source or groundwater supply.

• Soils - It is difficult to establish wetlands at sites with sandy soils or other soils with high infiltration rates. A careful review of local climate and water table conditions should be conducted before choosing this BMP.

• Climate - Constructed wetlands can be adapted for most regions of the country that are not excessively arid. Constructed wetlands have been effective in treating wastewater as far north as the N.W.T. and the Yukon.

• Thermal Pollution - The standing water in constructed wetlands may contribute to thermal pollution and contribute to downstream warming. This may preclude the use of this BMP in areas where sensitive aquatic species live.

• Safety - Both natural and constructed ponds are attractive play areas for children. A shallow "safety bench" around the edge of a wetland and/or dense vegetative growth around the perimeter to limit access may ease some safety concerns in urban areas.

Maintenance - Constructed wetlands have an establishment period during which they require regular inspection to monitor hydrologic conditions and ensure aquatic, shoreline, and upland plants are surviving. Wetland operators may need to control nuisance insects, odours, and algae.

Wetland Plantings Form Botanical Name Common Name Indicator

Status

Maximum Rate or

Minimum Spacing

Light Conditions

Soil Conditions Ponding Salt Oil/Grease Metals Insects Root System: Surface

(S) or Tap (T) Height/Diameter Propagules Benefits

Deciduous Tree Acer rubrum Red Maple 30’ min. Sun Moist or Dry Tap/S 1’ to 2’ 60’ to 90’/2.5’ Seedings or Container (3-15 gal Acer saccharinum Silver Maple 12’ Full Sun/Part Shade Wet or Moist S 1’ to 2’ 50’ to 80’/3’ Live stake or joint planting; fragile limbs Softwood cuttings in July & Oct. hardwood

cuttings in winter with rooting hormone Fagus grandifolia American Beech 30’ FS, P, Shade Moist, Dry T, S 1’ to 6’ 70’/2.5’ Seeds, seedlings, containers 3 to 15 gal.

(cuttings appear favourable) Understory species, shade tolerant, favour food for many wildlife

Amelanchier arborea Downy Serviceberry, Shadbush, Juneberry, Shadblow, Sarvis

20’ Full Sun Moist T, S 13 40’/1’ Seeds, seedlings, containers 3 to 15 gal. Understory species, prefers moist soils in hardwood forests, streambanks, etc. Star shaped white flowers, wildlife beneficial.

Acer negunda Box eider Full Sun Freshwater, resistant to salt water Container Songbirds; waterbirds, small mammals Betula populifolia Gray birch FAC 10’ O.C. Sun to Partial Sun 4-6 High High Moderate High Shallow to deep 35’ to 50’ High Gleditsia triacanthos Honeylocust FAC 15’ O.C. Sun 2-4 High Moderate Moderate Shallow to deep 50’ to 75’ Low Juniperus virginiana Eastern red cedar FACU 10’ O.C. Sun 2-4 High High High Taproot 50’ to 75’ Very High Quercus rubra FAC 20’ O.C. Sun to Partial Sun 2-4 Moderate High Moderate Moderate Deep taproot 60’ to 80’ High Deciduous Shrub Sambucus Canadensis Elderberry 3’ min. Full Sun/ Part Shade Wet or Moist 10’ x 10’ Live stake or joint planting Fast growing prolific berries Corylus Americana Wait. American hazelnut 10’ Sun Moist 15’ x 10’ Seedlings or Container (1-3 gal) Fast growing Viburnum dentatum Southern arrowwood viburnum 6’ min. Sun Moist or Dry 10’ x 6’ Seeds, seeding, container (1 gal.) or fascine Deep rooted; prolific berrier; Viburmum

nudum had very poor survirorshop in test plots using live stakes.

Myrica pennsylvanica Bayberry FAC 6’ O.C. Sun to Partial Sun 2-4 High Moderate Moderate High Shallow 6’ to 8’ High Evergreen Shrub Llex deciduas/verticillata Possumhaw 8’ min. Sun Moist or Dry Seedlings or Container (3-5 gal.) Turf Grass Agrostis alba Red Top 15% of mix Sun Danthonia spicata Poverty Oatgrass 10% of mix Sun or Shade Dry 12” Perennial; dry woods and roadsides Prairie Grasses Panicum virgatum Switch Grass 40% of mix Sun erosion tolerant, flood tolerant Wildflower Myosotis sylvatica Forget-Me-Not 10% of mix Full Sun/Part Shade Dry to Moist Blue, wildlife food source, delicate Rudbeckia hirta Black-Eyed Susan 10% of mix Sun Prairie Water, plants require ½ inch equivalent

rainfall per week. Orange/Yellow, Butterfly and bird food

Deciduous Tree Acer rubrum Red Maple 30’ min. Sun Moist or Dry Tap/S 1’-2’ 60’ to 90’/2.5’ Seedlings or container (3015 gal.) Fraxinus americana White Ash, Biltmore Ash 30’ Full Sun/Part Shade/Shade Moist or Dry Dominant tap root 80’-2’ Seeds, seedlings, containers 3 to 15 gal.

(cuttings appear favourable) Understory and overstory species, shade tolerant when younger, sensitive to ozone pollution, wildlife food – many species.

Acer negunda Box elder Full Sun Freshwater, resistant to salt water Container Songbirds; waterbirds; small mammals. Betula populifolia Gray birch FAC 10’ O.C. Partial Sun 4-6 High High Moderate High Shallow to deep 35-50’ High Gleditsia triacanthos Honeylocust FAC 15’ O.C. Sun 2-4 High Moderate Moderate Shallow to deep taproot 50-75’ Low Deciduous Shrub Comus Stolonifera Red Osier Dogwood 3’ min. Full Sun/Part Shade Wet or Moist 10’ x 10’ Best as a fascine; can be live stake or joint

planting Fast growing prolific berries

Alnus serrulata Alder 2’ min. Full Sun/Part Shade Wet or Moist Live staking NOT recommended Nitrogen FIXER; plant min. 20’ away from top of bank.

Viburnum dentatum Southern arrowwood viburnum 6’ min. Sun Moist or Dry 10’ x 6’ Seeds, seedling, container (1 gal.) or cuttings

Deep rooted; prolific berries; Viburnum nudum had very poor survivorship in test plot using live stakes.

Hammamelis virginia Witch hazel FAC 4’ O.C. Sun or Shade Moderate Moderate Moderate Moderate Moderate Shallow 4’-6’ Low wildlife benefit Myrica pennsylvanica bayberry FAC 6’ O.C. Sun to Partial Sun 2-4 High Moderate Moderate High Shallow 6’-8’ High Viburnum cassinoides northern wild raisin FACW 6’ O.C. Sun to Partial Sun 2-4 High High High High Shallow 6’-8’ High Evergreen Shrub Ilex decidua/verticillata Possumhaw 8’ min. Sun Moist or Dry Seedlings or Container (3-5 gal) Ilex glabra inkberry FACW 6’ O.C. Sun to Partial Sun 2-4 Low Moderate High Shallow 6’-12’ High Ilex verticillata winterberry FACW 6’ O.C. Sun to Partial Sun 2-4 Low Moderate High Shallow 6’-12’ High Herbaceous Bunch Grass Hystrix patula Bottlebrush Grass 10% of mix Full Sun Moist 2 to 5’ Perennial; rich or low woods. Turf Grass Secale cereale Rye (Ky-31) 30% of mix Sun Dry 18” Dominant in Summer; Sow in winter only. Excellent starter species (“nurse” seed). Agrostis alba Red Top 15% of mix Sun Danthonia spicata Poverty Oatgrass 10% of mix Sun or Shade Dry 12” Perennial; open woods, balds and

roadsides.

Prairie Grasses Panicum virgatum Switch Grass 40% of mix Sun erosion tolerant; flood tolerant. Wildflower Myosotis sylvatica Forget-Me-Not 10% of mix Full Sun/Part Shade Dry or Moist Blue, wildlife food source; delicate Rudbeckia hirta Black-Eyed Susan 10% of mix Sun Prairie Water; Plants require ½ inch equivalent

rainfall per week Orange/Yellow, Butterfly and bird food.

Deciduous Tree Fraxinus pennsylvania Swamp Ash 30’ Full Sun/Part Shade Wet or Moist Tap/S 1’-6’ 60’/ 1’-2’ Seedlings or container (3-15 gal) Can withstand continued flooding, transplants

easily. Deciduous Shrub Cephalanthus occidentalis Buttonbush 4’ min. Full Sun/Part Shade Moist, Wet 20’ x 12’ Live stake or joint planting. Fast growing, button like balls of fruit; plant on

lower creek bank where moisture is abundant and inundation is frequent.

Hammamelis virginia Witch hazel FAC 4’ O.C. Sun or Shade Moderate Moderate Moderate Moderate Moderate Shallow 4’-6’ Low wildlife benefit Rosa palustris Swamp rose Full Sun Freshwater Container Songbirds; gamebirds Viburnum cassinoides northern wilde raisin FACW 6’ O.C. Sun to Partial Sun 2-4 High High High High Shallow 6’-8’ Height High Evergreen Shrub Ilex glabra inkberry FACW 6’ O.C. Sun to Partial Sun 2-4 Low Moderate High Shallow 6’-12’ High Scripus cyperinus Wool grass 0.3 to 0.9 m O.C. Fun Sun Freshwater Rhizome; bare root plant Ducks; geese; swans; cranes; shorebirds; rails;

snipe, muskrats; fish Turf Grass Secale cereale Rye (KY-31) 30% of mix Sun Dry 18” Dormant in Summer; Sow in winter only. Excellent starter species (“nurse” seed). Agrostis alba Red Top 15% of mix Sun Danthonia spicata Poverty Oatgrass 10% of mix Sun or Shade Dry 12” Perennial; open woods, balds and

roadsides.

Aquatic Plants Acorus clamus Sweetflag Varies Sun Wet or Moist Can tolerate flooding Juncus effusus Soft Rush 12” O.C. Sun Wet or Moist Can tolerate floooding clumpy Emergent Herbacious Acorus calmus Sweetflag 0.3 to 0.8 m O.C. Partial shade Fresh to brackish Rhizome; bare root plant Waterfowl; muskrat

Form Botanical Name Common Name Indicator Status

Maximum Rate or

Minimum Spacing

Light Conditions

Soil Conditions Ponding Salt Oil/Grease Metals Insects Root System: Surface

(S) or Tap (T) Height/Diameter Propagules Benefits

Iris versicolor Blue flag 0.15 to 0.45 m O.C.

Partial shade Fresh to moderately brackish Seed; bulb; bare root plant Muskrat; wildfowl; marsh birds

Juncus effusus Soft rush 0.15 to 0.45 m O.C.

Full sun Freshwater Seed; rhizome; bare root plant Wildfowl; marshbirds; songbirds; waterfowl.

Sparganium eurycarpum Giant bur-reed 0.6 to 1.8 m O.C. Partial Shade Freshwater Seed, rhizome; bare root plant Ducks; swan; geese; beaver; muskrat. Herbaceous Bunch Grass Agrostis perennans Bentgrass 10% of mix Full Sun Dry 12” Perennial; wet to moist soil in marshes, ditches

and roadsides wildlife habitat Carex crinita Long Hair Sedge 10% of mix Full Sun/Part Shade Moist 12% Perennial; moist soils in ditches, low woods,

meadows, streambanks. Carex lurida Sallow Sedge 10% of mix Full Sun Moist 12” Perennial; moist soils in ditches, marshes,

meadows, streambanks. Aquatic Plants Carex stricta Tussock Sedge 12” O.C. Sun Wet or Moist Can tolerate flooding clumpy Sagittaria latifolia Duck Potato 24” O.C. Full Sun/Part Shade Wet Plant in first 6” of normal water level Scripus americanus Three-square Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Scirpus validus Softstem Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Typha latifolia Common Cattail, Broad-leaved

Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ excellent toxin uptake Helps stop washout caused by muskrat.

Typha angustifolia Narrow-leaved Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ excellent toxin uptake Helps stop washouts caused by muskrat. Emergent Herbaceous Hydrocotyle umbellata Water-pennywort Partial Shade Freshwater Bare Root plant; whole plant Wildfowl; waterfowl. Acorus calamus Sweet flag 0.3 to 0.9 m O.C. Partial Shade Fresh to brackish Rhizome; bare root plant Waterfowl; muskrat. Iris versicolor Blue flag 0.5 to 0.45 m

O.C. Partial Shade Fresh to moderately brackish Seed; bulb; bare root plant Muskrat; wildfowl; marsh birds.

Juncus effusus Soft rush 0.15 to 0.45 m O. C.

Full Sun Freshwater Seed, rhizome; bare root plant Wildfowl; marshbirds; songbirds; waterfowl.

Scirpus acutus Hardstem bulrush 0.9 to 1.8 m O.C. Full sun Fresh to brackish Seed; rhizome Ducks; geese; swans; cranes; shorebirds; rails, snipe; muskrats; fish

Sparganium eurycarpum Giant bur-reed 0.6 to 1.8 m O. C. Partial Shade Freshwater Seed; rhizome; bare rootplant Ducks; swan; geese; beaver; muskrak. Aquatic Plants Carex stricta Tussock Sedge 12” O.C. Sun Wet or Moist Can tolerate flooding clumpy Sagittaria latifolia Duck Potato 24” O. C. Full Sun/Part Shade Wet Plant in first 6” of normal water level Scripus americanus Three-square Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Scirpus validus Softstem Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Typha latifolia Common Cattail, Broad-leaved

Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ excellent toxin uptake Helps stop washout caused by muskrat.

Typha angustifolia Narrow-leaved Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ excellent toxin uptake Helps stop washouts caused by muskrat. Emergent Herbaceous Scirpus americanus Olney’s bulrush 0.9 to 1.8 m O.C. Full Sun Wet or Moist Can tolerate flooding clumpy Aquatic Plants Carex stricta Tussock Sedge 12” O.C. Sun Wet or Moist Can tolerate flooding clumpy Sagittaria latifolia Duck Potato 24” O. C. Full Sun/Part Shade Wet Plant in first 6” of normal water level Scripus americanus Three-square Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Scirpus validus Softstem Bulrush 18” O.C. Sun Wet Plant in first 6” of normal water level Typha latifolia Common Cattail, Broad-leaved

Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ Excellent toxin uptake Helps stop washout caused by muskrat.

Typha angustifolia Narrow-leaved Cattail 18” O.C. Full Sun Wet one container per 50’ 3’-9’ Excellent toxin uptake Helps stop washouts caused by muskrat. Lemna minor Common duckweed Partial shade Freshwater Whole plant Ducks; gallinules; coots; rails; geese; beaver;

muskrat; small mammals. Nymphea odorata Fragrant water lily Partial shade Freshwater Bare root seeding Cranes; ducks; beaver; muskrat; moose. Ceratophyllum demersum Coontail Freshwater Whole Plant Ducks; coots; geese; grebes; swans;

marshbirds; muskrats.



10. Infiltration Trench and Basin

Alternative BMPs: Key Considerations: • Suitable for residential land uses. • Requires pre-treatment to protect groundwater quality, recommended volume of pre-

treatment 25% of the design runoff volume. • Suitable pre-treatment facilities: grassed channels, sedimentation basins. • Not to be used during construction activities. • Soils to have clay content <20%, and silt/clay content <40%. • Slopes less than 15%. • To be located minimum 10 m downgradient from septic systems. • The velocity of the surface runoff collected by the infiltration facility should below the

erosive velocities. • Capable to dewater the design runoff volume within 48 hours. • Must have safe overflow facility designed to take flows in excess of the design event. • Requires an observation well. • Provide facility to dewater. • Winter operation concerns:

o Draining the ground beneath an infiltration system with an under drain can increase cold weather soil infiltration

o Alternative for winter operation is to provide some alternative treatment during the winter season.

o Consider diverting snowmelt runoff from infiltration facility in locations where chloride concentration is a concern

o Place filter beds below the frost line o Do not use organic filters, such as peat or compost media o Increase under drain pipe diameter to 200 mm o Carry out inspection following the spring snowmelt season.

Infiltration Trench

Design Feature Objective Recommendations Drainage area Limit infiltration to

capacity of trench • Maximum 2 ha

Pre-treatment To remove parts of the suspended solids from storm runoff

• Use wet or dry ponds, wetlands, or filters. For surface trench use a minimum 20 m wide filter strip

• For sub-surface trench use filter strip, grassed swale, oil and grit separator.

Trench Provide storage to treat stormwater for residential areas

• Not to be located close to sewer leaching beds, water wells

• Soil percolation rate >15 mm/h • High water table level and bedrock > 1m



Design Feature Objective Recommendations below trench bottom

• Storage media 50 mm diameter clear stone, or manufactured precast infiltration storage media

• Non-woven filter fabric at the interface of the trench and the surrounding native material and150 mm-300 mm below the ground.

• Filter layer such as a 30 cm thick sand layer (effective size 0.25 mm) to be provided below storage media for additional treatment. A mix of peat and sand would enhance the pollutant removal characteristics

• Depth of storage layer to ensure a 24 to 48 hour drawdown for stored water.

• Maximum storage volume equal runoff from a 4 hour 15 mm storm

• Water to be conveyed in a sub-surface trench via a pipe, in a surface trench water should be conveyed by a uniform distribution.*

• Check for potential groundwater mounding. Distribution pipe Distribution pipe to

evenly distribute flow in a sub-surface trench

• Use perforated pipes >100 mm diameter for sub-surface trenches, spaced 1.2 m apart, located 100 mm from top of storage layer

Bypass/overflow pipe To be used as the normal outlet until the site is stabilized, during routine maintenance, during severe cold weather conditions

• Bypass can be used during periods of heavy sanding or salting of roads, or local excavation works to prevent overloading of infiltration media

Basin • Equation to calculate bottom area • A=[1000 V]/[P n dt] • A= bottom area m2 • V = runoff volume • P = percolation rate of native soil (mm/h) • n = porosity of storage media, 0.4 for clear

stone • dt = detention time (24 to 48 hour)

Fencing/safety Not essential. Temporary fencing after initial construction until vegetation is established

• Place signs around facility indicating its purpose and function, with warning of potential fluctuating water levels



Infiltration Basin Design Feature Objective Recommendations

Contributing area To match runoff generation of drainage area with capacity of filters

• Drainage area <2 ha. For high impervious areas maximum contributing area to be reduced

• Provide a healthy vegetative cover over the contributing pervious area before permitting flow to enter the infiltration facility

Pre-treatment Prolong life and enhance performance

• Treat at least 25% of design volume • Use sedimentation basin for pre-

treatment and assume sediment rap efficiency of 90%

• Or use grass filter strip Infiltration Basin Provide above ground

infiltration facility for residential land use areas

• Drainage area <5 ha • Highly pervious soils >60 mm/h • High water table and bedrock > 1m

below bottom • Depth <0.6 m • Length and width ratio 3:1 • Check for potential groundwater

mounding. Treatment in Infiltration Media

• To hold 75% of design runoff volume • Typical depth of filter bed is

minimum 50 cm • Media should be medium sand,

meeting concrete sand specification. For organic filters use a peat/sand mix

• Typical coefficient of permeabilities: Sand 1 m/day Peat 0.75 m/day Leaf compost 3 m/day Bioretention soil 0.15 m/day

• Bio-retention systems should have at least a 1 m deep planting soil bed, a surface mulch layer and a 15 cm deep surface ponding area.

Flow conveyance • Provide a flow regulator to diver flows to the filtering system and allow larger flows to bypass

• Provide overflow to a receiving system capable to receive flow

• Install a perforated pipe, minimum diameter 150 mm, under-drain in a gravel layer

• Install a permeable filter fabric between the gravel layer and the filter media



Design Feature Objective Recommendations Landscape • Provide grass cover to assist

adsorption with grass capable to withstand frequent inundation and drought.

• Trees should be planted only along the perimeter of the facility

Maintenance • Sediment should be removed when it accumulates in the sediment chamber to a depth of 15 cm.

• Trash and debris should be removed as necessary

• Sediment in the filter bed area should be removed when the accumulation exceeds 3 cm.

• When the filtering capacity is diminished the top few cm of discoloured material shall be removed and replaced with fresh material



Canada Mortgage and Housing Corporation Fact Sheet Infiltration Trenches Description A conventional infiltration trench is a shallow, excavated trench that has been backfilled with stone to create a narrow underground reservoir. Stormwater runoff diverted into the trench drains from the bottom of the trench into the subsoil and eventually to the water table. A design variation from the conventional trench includes a dry well to control small volumes of runoff. Enhanced infiltration trenches also include pre-treatment systems to remove additional sediment and oil.

Effectiveness Analysis Infiltration trenches are primarily designed for stormwater quality management, and generally provide little or no stormwater quantity management. Stormwater Quality Infiltration trenches can improve the quality of stormwater runoff. A properly maintained trench can remove both particulate and soluble pollutants. Effective removal of sediment, phosphorus, nitrogen, trace metals, coliforms, and organic matter is accomplished through adsorption by soil particles, and biological and chemical conversion in the soil. Rates of pollutant removal are contingent on the type of soil (sandy soils are less effective at removing nitrates and trace metals than less porous soils). Particulates may also be trapped when an infiltration trench is used as part of a treatment train with other stormwater BMPs (i.e., filter strips, urban forestry, etc.).



Pollutant removal capabilities for infiltration basins that filter the entire amount of captured stormwater are shown below.

Pollutant Removal Efficiency Plant Nutrients Total Phosphorus High Total Nitrogen Sediment

High

Total Suspended Solids Metals

Very High

Trace Metals (Sediment-Bound) Organic Matter

Very High

Biochemical and Chemical Oxygen Demand (BOD) Oil and Grease Bacteria

Very High High Very High

Compiled from Schueler 1987; Schueler, et al. 1992; US EPA 1990; Phillips 1992; Birch, et al. 1992 and others Stormwater Quantity Most infiltration trenches have a minimal impact on stormwater runoff quantity. They can, however, help provide ground water recharge, control peak stormwater flows, and protect against erosion. A significant advantage of infiltration is that in areas with a high percentage of impervious surface, infiltration is one of the few means to provide significant groundwater recharge. Economic and Financial Analysis Infiltration trenches bring both one-time capital costs and recurring maintenance costs. Costs tend to vary according to the size of the trench, with the following table illustrating existing construction cost experiences. Following the estimates in the table, an infiltration trench (400 m2) would have construction costs of $38,200. It is expected that reconstruction would be required after about 15 years. Note that this infiltration trench is considerably larger than would be constructed on a single residential property, and would rather be used for a cluster of properties or non-residential property. Schueler provides an alternative formula for estimating trench capital costs. Using this formula, the same 400 metres2 infiltration trench would have capital costs of about $36,000. In addition, two types of maintenance costs would be incurred. Sediment/oil removal would cost about $4,500 per year, and grass cutting would cost about $150 per year.



Capital Costs Amount Unit Cost Cost

Filter Cloth 400 m2 $12/ m2 $4,800 Pervious Pipes 16 (20 m) pipes $20/ m2 $6,400 Sand Filter 80 m3 $50/ m3 $4,000 Gravel Storage 160 m3 $50/ m3 $8,000 Excavation 720 m3 $12/ m3 $8,640 Overflow Pipe 20 m $240/m $4,800 Seed and Topsoil 400 m2 $3/ m2 $1,200 Observation Wells 2 m $180/m $360 Total $38,200 Implementation Issues Although infiltration is a simple concept, infiltration devices must be carefully designed and maintained if they are to work properly. Poorly installed or improperly located devices fail easily, and do not achieve the stormwater quality efficiencies noted above. Furthermore, and depending on the quality of the runoff, pre-treatment will generally be necessary to lower the failure rate of the trench. • Applications - Infiltration trenches take up little land and can be located on or close to

residential sites or clusters of sites. Smaller infiltration devices such as infiltration basins and dry wells are aptly suited to manage stormwater quantity from roofs or other surfaces.

• Sites - Siting considerations are extremely important in the construction of an infiltration trench. The user of trenches is restricted by soil type, depth of water table, slope, and contributing area conditions, and requires professional assessment.

• Soils - It is critical that infiltration devices only be used where the soil is porous and can absorb the required quality of stormwater. In areas where runoff is polluted, about 1 metre of clearance above the water table is recommended to help prevent groundwater pollution.

• Drainage - Infiltration basins should drain within 72 hours to maintain aerobic conditions (which favour bacteria that aid in pollutant removal) and to ensure that the basin is ready to receive the next storm.

• Climate - Trenches may not perform well in regions with long, cold winters and deep freeze-thaw levels. Likewise, trenches may not be appropriate in areas with sparse vegetative cover that would have significant sediment levels in runoff.

• Maintenance - Maintenance requirements include regular inspections, cleaning of inlets to prevent clogging, mowing and inspection of observation wells to maintain proper operation. Insect, odours, and soggy ground can arise as nuisances.



11. Permeable (Porous) Pavement

Alternatives: Infiltration basin or trench, filter strips Key Considerations • Very limited experience in Canada • Use only in low vehicle traffic areas • Permits water to flow through and reduce the imperviousness of walkways, sidewalks, and

driveways. • Requires moderately permeable soils, with depth at least 1 m above high water table or

bedrock. • Only effective for small drainage areas. • Can be combined with conventional paving for heavy traffic areas. • Where pre-treatment not available, efficiency is unknown • Should not be applied in parking areas where sanding or salting is used in the winter • Can reduce peak flows and improve groundwater recharge • Soil permeability >16 mm/hour • Not to be located on recent fills • Longitudinal slopes <15% • Site must be at least 1 m above high groundwater table or bedrock • Preferably divert runoff from permeable areas and only collect runoff from paved areas • Do not collect runoff with high sediment content on porous pavement • Provide conveyance for large storms • Do not compact subsoil during construction • Require frequent inspection and maintenance Advantages are: • Can be effective in sandy soils • Can reduce loads of some pollutants in surface runoff • Can improve groundwater recharge • Suitable for parking areas at condominiums, institutional buildings, office buildings, and

commercial facilities. Disadvantages are: • Limited pollutant removal efficiency, estimated to be 25% of TSS removal. Cannot achieve

80% TSS removal efficiency on its own. • Prone to clogging by suspended solids • Should not be installed until the upstream disturbed areas have been stabilized • Not recommended for slopes greater than 2 %. Before undertaking the design of a permeable pavement, detailed geotechnical tests should be carried out to determine the soil properties and location of the water table, which should be at



least 1 m below the bottom of the pavement. Also, sub-grade specifications should be prepared to ensure it conforms to the engineering requirements for accommodating design loads. The design must ensure that the permeable pavement functions both hydraulically and structurally. To ensure the structural performance the design must follow accepted criteria, such as the AASHTO. Types of permeable paving: Perforated brick and concrete grid pavers, most suitable for areas carrying pedestrian or light vehicular traffic. Can be damaged by snowploughs. Require sand for bedding. The open cells could be filled with topsoil or vegetation. Permeable interlocking concrete paving blocks, suitable for areas with more constant traffic and higher tire loads than other types of porous pavers. Maintenance is relatively easy and the paver has long service life. Requires coarse aggregate bedding. The open cells can be infilled with decorative pea gravel. Vegetation on the open cells should be discouraged, and semi-annual maintenance should ensure the removal of vegetation. Compacted gravel, suited for areas with light vehicular traffic, should not be used for pedestrian path frequented by older persons. The fine particles in the mix will greatly influence the effectiveness; therefore only open graded mixtures that contain very few fines should b used, instead of dense graded road aggregates. As sweeping or washing of gravelled surfaces is not practical these surfaces are more prone to clogging by sediment. Separating the surface course and base layers with a geotextile can reduce the risk of penetration of fine materials. To refresh the upper surface it should be scraped off and replaced with fresh material. The longevity of gravel is shorter than for the other alternatives. Porous bituminous asphalt or concrete can withstand low to moderate traffic, such as parking areas and driveways. Also, can be combined with traditional pavement under layer for additional strength. It is less prone to damage by snowploughs. Records in the U.S. show that this type of pavement can function effectively for 20 years or more. Maintenance involves semi-annual vacuum sweeping. NO pressure washing is recommended. Runoff collection is controlled by the infiltration potential of surface layer and by the storage capacity of the base. Long-term infiltration rates are lower than initial rates. Typical long-term infiltration rates: Porous concrete and asphalt 6 cm/hr Permeable interlocking concrete paving blocks 4 – 25 cm/hr Concrete grid pavers bedded in sand 2 – 5 cm/hr Compacted aggregate 5 – 15 cm/hr



Permeable pavements require porous base, usually uniform, clean-washed, crushed stone is used. Water will infiltrate through the pavement until the voids are filled in the base media. After that the infiltration rate will depend on the permeability of the underlying soil sub-grade. Design should aim to store 100 percent of the volume of water that will infiltrate. This will determine the depth of the base layer. To preserve the storage potential of the base, a geotextile should be installed between the base and sub-grade to minimize the migration of the soil to the base. For sizing the peak flow a 2-year storm should be used to estimate the post-development runoff in mm over the drainage area. The infiltrated water volume is computed from the area of the permeable pavement multiplied by the runoff (mm) to be infiltrated. The required thickness of the base is computed from the infiltrated water volume, divided by the area over which the base will be installed, times the porosity of the base. If needed, interconnecting the base with infiltration trenches can use additional storage capacity. The base should be capable to dewater within a 48 to 72 hour period by exfiltration to the underlying soil. The dewatering time can be calculated from the infiltrated water volume divided by the surface area, times the percolation rate for the underlying soil layer.

Design Feature Objective Recommendations Drainage area • Only for small areas, due to limit of

infiltration Base and sub grade

Assist in infiltration • Typical depth of stone bed, 15 cm - 45 cm. Subject to frost consideration, laid over a permeable geotextile fabric

• Uniformly graded 4 cm – 6 cm clean washed angular, hard, durable stone, free from organic material, dust and dirt.

Placing of material • Base material should be spread in lifts on top of the geotextile with minimum compaction.

• No vibrator should be used. • Joints should be infilled with aggregate or

with pea gravel. • Porous concrete and asphalt should be

placed in a single lift and compacted not more than two passes of a 10 t roller.

• High traffic areas should be paved with conventional pavement.

• Surfaces draining to the pavement should be stabilized first.

Permeable interlocking concrete paving blocks

Support loads and permit infiltration

• To be placed in 5 cm concrete sand

Compacted gravel Pavement


• Could be similar to the base material. Geotextile should be used to separate the surface course from the underlying base material



Design Feature Objective Recommendations Porous bituminous asphalt and concrete pavement


• Standard bituminous asphalt with aggregate fines (smaller than No. 30 sieve) to be screened out Asphalt grade to meet AASHTO specification M_20 for 65 to 80 penetration road asphalt. The binder should be approximately 6 % by weight of the final mixture. Anti striping agent is needed if the estimated coating area is not above 95%. Also, a polymer additive may be used to improve stiffness and to minimize drain down in the binder.

Periodic inspections are an essential part of the long –term operation and maintenance program, at least one inspection per year shortly after a heavy storm is recommended. Construction costs can vary. Porous concrete, including excavation, filter fabric, and the base costs approximately $200 per square metre. Porous asphalt costs less, approximately $50 per square metre.



12. Forested Buffers

Alternative BMPs: Bio-retention, Filter Strips Buffers are ecosystems constructed adjacent to streams and lakes consisting of, trees, grasses, shrubs and other vegetation types which function as filters to remove urban pollutants from overland urban runoff, prior to discharge to receiving systems. Key Considerations • Buffers can filter pollutants through infiltration, filtration, deposition, adsorption, plant

uptake and biodegradation. • Pollutant removal, up to 85% of TSS and 30% of Nitrogen where sheet flow is maintained. • Buffers alone cannot treat surface runoff but be part of a treatment train • Capable to attenuate the rate of flow, increase infiltration, base flow, groundwater levels,

reduce erosion, improve aquatic habitat and reduce sedimentation and pollutants in the receiving streams.

• No concentrated flow, such as ditch, stream, and pipe flow should be permitted in the buffer, unless first re-directed to a flow spreader.

• Additional BMPs should be used where necessary to create sheet flow before the urban runoff enters the buffers.

• No heavy maintenance vehicles should be used in the buffer zone. • Removal of natural leaf litter is discouraged. • No impervious surfaces such as trails should be constructed in the buffer zone. • Livestock should be excluded. Advantages • Provides water quality treatment. • Provides erosion control. • Provides limited flow control. • Increases groundwater recharge. • Provides canopy to moderate summer water temperatures, and minimize soil disturbance

under the canopy. • Offers aesthetic and passive recreational benefits. • Relative low construction and operation/maintenance costs. • Once well established, it could be self-perpetuating, requiring no fertilizers or pesticides. Disadvantages • If not accompanied by public education, can be used as an illegal dumping ground for litter

and trash. • Its use is limited. Only effective for sheet flow, therefore not feasible where urban runoff

reaches a well-defined watercourse.



The buffer width required to achieve a specific level of effectiveness should be evaluated on a site-specific basis. The best opportunity to provide effective buffers is to protect existing vegetation where feasible. Buffer width is a useful measure to assess the effectiveness of the BMP. The optimum width will depend on the desired control function. The following guidelines are provided to assist planners and designers of buffers: Design Objectives Minimum buffer width - m Bank stabilization 13 Water temperature moderation 20 Nitrogen removal 40 Sediment removal 50 The selection of width should take into consideration the drainage area, and slope of the land. To increase the effectiveness gentle slopes should be used. The slope of the elevation difference across the buffer should be under 2 metres. Native plants should be used, sufficiently dense to filter sediment and provide nutrients for aquatic organisms. Ideally, a tree density of 12 trees per 100 m2 buffer areas should be maintained Implementation tasks: 1. Stabilization of channel banks. 2. Site preparation. 3. Planting. 4. Monitoring, operation/maintenance. Stabilization of channel banks requires vegetative and some limited structural techniques. The vegetative practices could include live stakes, tree revetments, live fascines, and brush mattresses. Structural measures, such as boulders, logs, and sandbags can be combined for additional stability, but riprap, gabion baskets, or concrete structures are discouraged. Site preparation needs are strongly influenced by conditions of the existing vegetation. Invasive species and livestock access should be removed. If needed supplementary watering should be applied. After weed removal the ground should be ploughed and disked to prepare for tree planting. Planting will stabilize the soil. In the flood plain only trees, which can tolerate flooded conditions, should be planted. Best choices are fast growing native species. Further away from the stream banks more diverse tree species can be planted. Best season for planting is the spring or fall season. Planting should be 5 m-7 m apart, while shrubs should be planted closer 2 m- 3m apart, followed by a through watering. Native grasses are recommended for the grassed portion



of the buffer. The grassed areas should be established by ploughing and disking or by broadcasting. Monitoring is important to assess the success of the buffer construction. Plants should be replaced if necessary. Maintenance requirements include: • Initial watering • Repairing • Fences • Bank erosion • Wild life damage • Removing • Weeds • Gullies • Thinning of trees after well established • Cutting • Replanting • Weed control • Mowing The cost of implementing a buffer BMP can very according to site conditions. Where the land is owned privately additional costs may be involved. Generally, the lowest costs are involved to enhance existing forested buffers. Generally the cost of creating a forested buffer consisting of mixed hardwoods, shrubs, and grasses ranges from $3,000 to $4,000 per hectare. Maintenance costs are relatively low, annual inspection, mowing and unwanted litter removal $100 per hectare.



Canada Mortgage and Housing Corporation Fact Sheet Urban Forestry Description Urban forestry refers to post-development planting or pre-development preservation of trees, shrubs and other ground covers in an urban context. This lot-level BMP is a functional and attractive supplement to residential lawns and has positive implications for property values particularly once trees and shrubs mature. Studies have been conducted that look at the impact of natural forests on hydrology. These studies demonstrate that urban forests can: • help reduce the quantity of stormwater flows; and • help improve the quality of stormwater runoff. In addition, urban forests convey a number of environmental benefits through air pollutant uptake and greenhouse gas reduction functions. These functions will make urban forestry an increasingly valuable BMP from an environmental and economic perspective. Effectiveness Analysis Stormwater Quantity Studies show that urban forests help detain stormwater runoff and reduce stormwater quantity. Some rainfall that is intercepted by tree leaves or needles evaporates or evapotranspirates. Rainfall that passes through the canopy may fall on soil that is more pervious than it otherwise would be because of the influence of tree roots on soil. The actual runoff quantity benefits are dependent on the species, canopy density, level of maintenance, and time of year. One Canadian study measured the amount of rain intercepted, retained in the mulch layer, and running off or infiltrated based on a 25 mm rainfall. At a minimum, the results show that a considerable portion, about 25%, is intercepted.

Species Interception mm

Water Retained in Mulch Layer

(mm)

Runoff/Infiltration to Soil (mm)

White Spruce 5 7 13 Red Pine 8 8 9 Balsam Fir 8 10 7 Sugar Maple 5 6 14 Aspen 4 19 2 Source: Mahendrappa, M.K.,(1982) Effects of Forest Cover Type and Organic Horizons on Potential Water Yield. A second study of interest was completed in Toronto that illustrates the effects of urban forests at a higher level. The study considered the potential effects of increasing the percentage of tree cover in five defined residential blocks. Their analysis, based on a review of other studies, that the interception capability of trees is about 2 mm, or about 40% of an average rainfall event. The



study also shows that increasing the amount of tree cover will reduce the amount of stormwater runoff. For an increase in tree cover from about 25% to 50%, the results indicated that the average potential reduction in annual runoff ranged from about 10%-20%. Stormwater Quality Urban forestry can provide limited improvements to runoff quality. Pollutants are removed by plant uptake and storage, preventing soil erosion, and by reducing the overall quantity of stormwater (thereby reducing associated pollutants). Reliable estimates of the stormwater quality benefits of urban forests were not found. Economic and Financial Analysis Costs of urban forestry depend on whether activity is pre-or post-development. Pre-development urban forestry is quite inexpensive, as existing trees are preserved. Some costs may be associated with using special heavy machinery to keep from damaging the trunks and roots of the selected trees. Costs of post-development urban forestry involve purchasing seedlings and manual planting labour (based on a rough transferal of U.S. experience): • seedlings cost about $50 -$500 per thousand; and • manual planting labour may cost about $400 -$800 per hectare. Purchasing and planting of mature trees from a nursery is a more expensive alternative. Full costs in the range of $3,000 -$15,000 might be incurred. Canada's Urban Forests Centre surveyed 600 municipalities across the country to gather information on urban forestry activities. The survey uncovered average costs for establishing trees of between $20 and $150 per tree. The average annual maintenance costs ranged between about $3 and $12 per tree. Costs to developers may be considerably less, since development activities may provide a cost-effective avenue for tree planting activities. At the highest level, benefit-cost studies have shown a high return to urban forests. For example, one study in California describes the benefits of municipally owned and managed forests as being at least twice as much as the costs. Benefits included air pollutant uptake, aesthetics, temperature moderation, reductions in atmospheric carbon dioxide, and reductions in stormwater runoff. Implementation Issues Urban forestry is a stormwater BMP with virtually limitless application that can be scaled to suit any size requirements. Trees make an attractive addition to residential landscaping, and produce between 30%-50% less runoff than lawns, and provide food, cover, and nesting sites for wildlife. Some of the related benefits of urban forests include noise absorption, shade, privacy screening, moderation of local temperatures, and provision of a wind barrier. These all serve to increase property values.



A number of implementation issues are important. • Site - Considerations Areas expected to have significant foot traffic are not suitable for urban

forestry, as natural ground covers will compact and eventually erode. Urban forests have the greatest quantity impacts where they are planted in a continuous dense stand that is allowed to naturalize. Trees should not be planted where branches will encroach upon overhead wires or roots will damage building foundations (or driveways and sidewalks).

• Species - Consideration should be given to the types of species that best flourish in a particular region. In addition, care should be taken in selecting a species appropriate to the individual site (ex., moisture, winds, and soil pH and fertility).

• Planting the tree - The ideal time to plant trees and shrubs is during the fall after leafdrop or early spring before budbreak. This period of cool weather allows plants to establish roots in their new location before spring rains and summer heat stimulate new growth.

• Maintenance - Some maintenance is required for urban forestry. In the first few years after planting, seedlings require watering, weed and rodent control, and staking. Furthermore, if mulch is allowed to develop under the tree canopy, more rainfall will be detained since the mulch layer tends to have a relatively high water holding capacity.

• Energy Considerations - The east, west, and south walls of your house receive the most sun. Deciduous trees around a house will provide shade, reducing cooling bills in summer. Trees can also save energy in winter. A row of evergreen trees on the north side of a house (or the side with prevailing winter winds) will serve as a windbreak and lower heating costs.



13. Filter Strips

Alternative BMPs: Forested buffer, permeable pavement. Similar to the forested buffer, filter strips are vegetated strips of land formed along the perimeter of a stream of a lake, or areas that need protection from upstream development. Vegetated surfaces with dense foliage and thick root mat, such as grass, grassy meadows, and shrubs could be used as filter strip. The purpose is to trap sediment and sediment bound pollutants. In addition filter strips help to reduce peak flow, increase time of concentration and infiltration. Most common forms are the grass filter strips, which can be effective in spreading the runoff as sheet flow. Used for treating runoff from highways, roofs, downspouts, parking areas and where development density is low. Also useful for providing pre-treatment for other infiltration based BMPs. Advantages: • effective in reducing particulate pollutants such as sediment, trace metals • slows runoff and enhance infiltration • reduces stream bank erosion • can be combined with landscaping feature, open space for recreation Disadvantages: • Can only accommodate flow from small areas, (<2 ha) with low flow velocity • Could be prone to erosion if flow is concentrated, it requires sheet flow • Not efficient to control peak flow or flow quantity, therefore it is mainly used as part of a

treatment train. Typical TSS removal efficiencies of filter strips 25% for grassed areas, 30% for planted woody vegetation. The estimated nutrient removal efficiency is 20%.


Drainage area Limit flow and velocity • Maximum 2 ha Level spreader Encourage sheet flow • Gravel-filled trench at

least 1 m deep and 0.3 m wide, lined with filter geotextile

Length-width ratio Maximize efficiency • Width: 75 m for every ha of drainage area, minimum length 20 m.

Slope Minimize erosion, increase

infiltration • Slope <5%




Flow velocity Minimize erosion, increase infiltration

• Velocity <0.5 m/s for peak design flow. Highest sediment trap efficiency <0.1 m/s

Vegetation Increase efficiency of filter strip • Local plants: - deep-rooted - dense, well-branched top growth - resistant to damage from saturation or drought, de- icing chemicals and heavy metals

Soils Ensure infiltration • Use well drained soils and

minimize compacting during construction

Berms Direct flow to strip • If needed, use berms 20 m-30 m intervals perpendicular to the strip

Inspection of filter strips during and after major storms is important during the first 2 years after construction. After that initial period, the strip should be inspected annually. If erosion is evident, the damaged areas should be filled and re-seeded. Filter strips can stay effective with very little maintenance. Maintenance involves mowing, trimming, and replanting, periodic re-grading and re-seeding. The following are the typical maintenance tasks: • Remove sediment annually • Repair when needed gullies and rills and re-grade the filter strip • Repair the level spreader to prevent the formation of channels in the strip • Re-seed if needed to maintain a dense growth • Mowed grassed surfaces 2-3 times a year and harvest the clippings to promote growth • Keep strip free of litter • Check for need to irrigate or fertilize the strip • Perform aeration of soil, if needed Cost Estimates To establish a filter strip requires low capital expenditure. Planting $5 per m2 for grass seed or $10 m2 for sod. There are no costs reported on constructing a level spreader. Routine maintenance costs, including inspection, mowing, sediment removal, re-seeding, debris removal and repair of gullies is estimated to be $1,500 per ha.



The Figure 10, shows a sketch of a filter strip, based on Schueler (1987), constructed in a residential development.

Figure 10 Sketch of Filter Strip



14. Sand Filters

Alternative BMP: Bio-retention Key considerations: Very effective in filtering TSS Require minimum 1 m head Where space is limited, it can be constructed underground Prone to failure without frequent maintenance Require suitable trash screens Not effective in controlling higher peak flows Where local soils have low permeability pipes can be used to collect flow from the sand area and direct it to a storm drain or a stream Construction costs range from $150 to $350 per m3 of stormwater treated Design Guidelines


Drainage area Limit flow and velocity • Maximum 5 ha Water quality design Remove pollutants • Runoff from a 25 mm winter

rainfall • Overflow or bypass for excess

flows • Sand filter drawdown time not

more than 48 hours Filter chamber Capture runoff • Volume 40 m3/ha

• Surface area 80 m2/ha • Minimum depth 0.5 m

Sand filter material Filters runoff • Average diameter 2 mm Under drain Collects runoff • Minimum diameter 15 cm

• Capacity to discharge maximum flow from filter

Filter fabric Prevent clogging • Geotextile fabric Inspection • After major storms, minimum

twice a year Maintenance • Must have maintenance

access • Remove visible surface

sediment accumulation, trash, debris and leaf litter.

• The top layer of the filter may need to be removed and replaced if monitoring shows a decrease in capacity.

• If hydrocarbons are contained in the runoff the top 5-10 cm of sand must be replaced every 3 to 5 years




• Vegetation in the chamber must be removed



Canada Mortgage and Housing Corporation Fact Sheet Sand Filters Description Sand filters are a stormwater management device used to treat stormwater runoff from residential and commercial buildings, parking lots, and roads. Sand filters generally function only as a storm water quality BMP and do not provide runoff significant quantity reductions. As the name implies, sand filters work by filtering stormwater through beds of sand and other filtering materials. Sand filters may be range from being small or large, and can be relatively complex as the example below illustrates.

Source: http://www.epa.gov/owowwtr1/watershed/Proceed/botts.html

In a sand filter such as the above, stormwater is collected in a ponding area and is allowed to filter through a layer of aggregate and a filter cloth to remove sediment. The water then filters through a sand layer that is at least 0.5 m deep. As stormwater filters through these layers, pollutants such as heavy metals, sediment, E. coli, and phosphorus are removed. The runoff is then collected in underground pipes and conveyed. Effectiveness Analysis The Regional Municipality of Ottawa-Carleton constructed a large sand filter to treat approximately 44 ha of contributing area in 1990. The facility was constructed to provide treatment of stormwater to help improve surface waters in the Rideau River during the swimming season. The land uses contributing runoff to the sand filter are mainly commercial and industrial, and significant amounts of additional development are expected to take place in the future. The sand filter facility itself consists of: • a 0.30 m layer of gravel and stone; • a 1.55 m layer of sand; and • a series of gravel-filled trenches.



The layer of gravel and stone is capable of supporting maintenance vehicles. Geotechnical fabric is located between the upper layers and the native soils to prevent migration of soil into the filter material. Perforated pipes in the gravel trenches convey the filtered stormwater to a storm sewer, which ultimately outlets to the Rideau River. Performance monitoring of the facility has been ongoing since 1992. Monitoring results indicate that the facility has exceeded expectations for the removal of heavy metals, sediment, E. coli bacteria, and phosphorus. Pollutant removal rates have consistently exceeded 95% on a loading basis1. It is important to note that the facility is currently performing at approximately 45% of its maximum capacity since the upstream drainage area is only partially developed. It is expected that pollutant removal rates will change when higher capacities are reached. At a more general level, pollutant removal for sand filters varies depending on the site, runoff, and climate. Overall removal of sediment and trace metals is better than removal of more soluble pollutants because the filter functions by straining particles out of the stormwater. The following table lists some published removal efficiencies for various pollutants.

Pollutant Removal Efficiency Plant Nutrients Total Phosphorus High Total Nitrogen High Sediment Very High Trace Metals (Sediment-Bound) Very High Organic Matter Biochemical Oxygen Demand (BOD)

Moderate

Oil and Grease High Bacteria Moderate Source: Compiled from Schueler 1987; Schueler, et al. 1992; US EPA 1990; Phillips 1992; Birch, et al. 1992 and others. Economic and Financial Analysis Construction and maintenance costs of sand filters vary according to the type of sand filter (i.e., design complexity), size of the filter, whether the filter is above or below ground, and the quantity and quality of stormwater treated. This variability is reflected in the relative unavailability and range of existing cost assessments. Several estimates were found of the costs per unit of stormwater treated by sand filters. One cost estimate suggests that the total cost of the installation of such a system in Canada may be in the range of $5,000 to $10,0003. An alternative estimate from the U.S. Environmental Protection Agency suggests construction costs of about $70-$555 m3 of runoff treated. Annual maintenance costs of about 5% of the initial construction cost are predicted2.



One drawback that has limited the widespread use of sand filters is that they often require a relatively large area. For example, in the U.S., by-laws governing buried sand filters require one square foot of sand filter for every 1 or 2 gallons of wastewater. This means that a homeowner would have to set aside up to 200 square feet (~20 square metres) for such a filter at a cost of roughly $4,0004. Implementation Issues • Site Considerations -Sand filters are readily adapted to fit space and runoff volume needs.

They are particularly appropriate for townhouses or clustered housing, and in ultra-urban areas where space limitations may prohibit the use of other stormwater management methods

5.

• Aesthetic Considerations -Larger above ground sand filter designs without grass covers may not be attractive in residential areas, and may have undesirable odours. Creative landscaping with hedges and other natural barriers can improve the appearance of an above ground sand filter. Restricting activities or access to the portion of a property occupied by a sand filter may be objectionable to a homeowner.

• Climate Considerations -The effectiveness of both above and below ground sand filters will be diminished during winter months when inflow and outflow pipes may freeze. With the spring thaw, the filter will return the filter to its normal functioning.

• Maintenance-Sand filters have long lifetimes and consistent pollutant removal when properly and frequently maintained. Normal maintenance includes raking the sand surface and disposing of accumulated litter. The upper few inches of dirty sand must be removed and replaced with clean sand when the filter clogs.

1

Lynch, D., R.G. Rooke, C. Melanson, S. Short, M. Trudeau (1998), Stormwater Infiltration That Works, Regional Municipality of Ottawa-Carleton. 2 Drawn from http://www.dal.ca/~cwrs/altern/intfilt.htm.

3 From Tull (1990) and Schueler et al (1992)

[http://www.epa.gov/owowwtr1/NPS/MMGI/Chapter5/ch5/2e.html]. 4 Drawn from http://twri.tamu.edu/twripubs/Insights/v2n3/article-5.html.

5 See US Environmental Protection Agency (1994) Developments in Sand Filter Technology to

Improve Runoff Quality, Http://www.epa.gov/owowwtr1/NPS/wpt/wpt02/wpt02fa2.html].



15. Oil and Grit Separators

Alternative BMPs: Sand filter, Bio-retention Oil and grit separators are manufactured BMPs, designed to remove sediments, oil and grease and other hydrocarbons, debris and floating substances. This type of BMP is mainly suitable for spill control, or in paved areas frequently used by motor vehicles. All separators are based on a proprietary design and sold by Canadian, U.S. Australian and European manufactures as prefabricated units. The advantages of separators are: • Can be effective if used as part of a treatment train, as a first stage of treatment • Useful where space is restricted • Underground facility reduces the visual impacts The disadvantages area: • Can only serve a small drainage area <2-5 ha • Only effective for low flows, medium and high flows are bypassed • Removal efficiency is low for other pollutants • Require frequent cleanout • Clogging can occur unnoticed Oil and grit separators should be selected and installed according to the manufacturer’s specification. Generally, specifications describe the minimum head required to drive flow though the separators, size and storage capacity of the structure and expected efficiency of TSS removal, for specified flows. The cost of separators can vary anywhere from $10,000 to $75,000, depending on site conditions, type of unit and manufacturer. When calculating the costs, the frequent maintenance costs should be added.



Canada Mortgage and Housing Corporation Fact Sheet Oil and Grit Separators Description Oil and grit separators are structures consisting of one or more chambers that remove sediment, screen debris, and separate oil from stormwater. These structures are also known as oil and water separators or water quality inlets. Their major environmental benefit comes in the form of improved downstream water quality as part of a treatment train. Runoff quantity management is not directly afforded. Oil and grit separators are particularly well suited to capture particulates and hydrocarbons from small, highly impervious areas such as residential townhouse/apartment parking lots, loading/parking areas at commercial facilities, and gas stations. Two basic types of oil and grit separators are available: the three chamber OGS; and the manhole OGS. A typical model is shown below. Typical OGS Profile Source: U.S. Environmental Protection Agency (1996), Structural Best Management Practices for Storm Water Pollution Control at Industrial Facilities, at http://www.epa.gov/owowwtr1/watershed/Proceed/botts.html. Effectiveness Analysis Both the three chamber OGS and the manhole OGS operate under the same general principles. Particulate matter and oil are washed from the ground surface by stormwater runoff and transported to an oil and grit separator. The sediment and oil laden stormwater runoff enters the oil and grit separator and flows into a water-filled chamber. The water-filled chamber has the effect of slowing the velocity of stormwater runoff, allowing some of the particulate matter to settle and allowing suspended oil to rise. Oil and grit separators are installed underground and are integrated into the storm sewer system. Some OGS have a flow bypass as part of their design. This means that only low flows enter the OGS, and more significant flows from infrequent rainfall events bypass the facility. This bypass reduces the potential for contaminants to be re-suspended and to re-enter the storm sewer system. Alternatively the OGS may be constructed off-line from the main storm sewer system with a pipe from the main storm sewer line to divert only low flows to the OGS. In many circumstances, stormwater quantity controls are used in conjunction with oil and grit separators. In such cases peak inflows may be reduced so that bypass is not necessary. Designers, however, must recognize the link between the OGS design runoff volume and the volume of storage provided in the OGS. The effectiveness of the OGS is largely dependent on the relative amount of impervious drainage and the size of the OGS, and whether bypass or flushing occurs during a particular event.



The Ontario Ministry of the Environment carried out a comparison study for two types of oil and grit separators. The sites were located in southern Ontario and were of similar land use and drainage area. The results are shown for an average removal rate during 60 runoff events for the three chamber OGS. Oil and Grit Separators - Canada Mortgage and Housing Corporation (CMHC) Page 2 of 3 and 43 runoff events for the manhole OGS. The three chamber OGS is larger in size, however, the unit did not include a bypass for large storm events. The manhole OGS design includes a bypass for larger storm events. Efficiency of Oil and Grit Separators

Percent Removal Type of OGS Chamber Size TSS Heavy Metals Oil/Grease Three Chamber OGS 52 m3 48% 21-36% 42% Manhole OGS with Bypass 35 m3 61% 42-52% 50% Source: Henry, D., W. Liang, and S. Ristic (1999), Comparison of Year-Round Performance for Two Types of Oil and Grit Separators, Presented at the International Congress on Local Government Engineering and Public Works, Sydney, Australia, August 22 – 26, 1999. These results should be taken as "ballpark", given that effectiveness varies depending on a number of parameters --for example site characteristics, the ratio of flow to capacity, flow velocity, the OGS manufacturer, and even frequency of OGS maintenance. Economic Analysis Four main cost categories are associated with the acquisition and operation of an oil and grit separator: [i] one-time capital costs; [ii] one-time installation costs; [iii] recurring maintenance costs; and [iv] recurring waste disposal costs. The capital costs depend primarily on the model and size of the OGS purchased. Installation costs vary significantly depending upon whether the OGS is placed in a greenfield or brownfield development. Maintenance costs vary by device, site, and practice, while waste disposal costs are location-specific. A summary of the annualized costs associated with oil and grit separators is shown below. In general, a typical OGS system can be expected to cost about $2,000 or more (undiscounted) per year over a 30-year lifetime. Again, these costs are "ballpark", given their variability by site and application. Higher costs would result for large models, for brownfield retrofits, and in areas with more frequent maintenance requirements.



Life Cycle Costs of Oil and Grit Separators (1999 $C) Cost Category A B C D

Annualized Purchase Cost $480 $1,260 $560 Annualized Installation Cost $1,880 $120 $320 Unknown Annual Maintenance Cost $6,640 Annual Disposal Cost $620 $1,400 $600 Unknown Total Annual Cost $2,500 $2,000 $2,180 $7,200

A: Case study of a OGS purchase and operation from Edmonton, AB.1

B: Data provided by an un-named OGS manufacturer, based on a medium-sized system. C: Data provided by an un-named OGS manufacturer, based on a medium-sized system. D: Information from an Ontario Ministry of Environment publication.

2

Implementation Issues Applications -Oil and grit separators can operate as a pre-treatment device in a train of BMPs, or as a stand-alone water quality (not water quantity) BMP in situations were a lower level of protection is needed. They provide relatively efficient removal of debris, sediment, and hydrocarbons, sometimes trap trash, debris, and other floatables, but have minimal effects on nutrients and organic matter. Design Considerations – Inlets typically serve small, highly impervious areas, typically less than 4,000 square metres (about 1 acre). Because several small catch basins can be distributed over a large drainage area, they may prove advantageous over constructing a single large structure downstream. Land Uses – OGS systems can be used in urban areas where land use constraints prohibit the use of other BMPs. They can be installed in almost any soil or terrain, which allows their use near or at the impervious surfaces contributing heavily to the stormwater runoff. Since these devices are underground, appearance is not an issue and public safety risks are low. Maintenance – Oil and grit separators require regular inspection and cleaning to remove sediment, accumulated oils and grease, floatables, and other pollutants (at least twice annually and after major storm events). Some concern exists over the toxicity of trapped residuals, which may require disposal as a hazardous waste. Odours are sometimes a problem. 1. See Labatiuk, C., V. Nataly, and V. Bhardwaj (1997), Field Evaluation of a Pollution

Abatement Device for Stormwater Quality Improvement, Presented at the 1997 CSCE Environmental Engineering Conference.

2. See Ontario Ministry of Environment (1991), Stormwater Quality Best Management Practices.



16. Bioretention and Rain Gardens

Alternative BMPs: Infiltration trench or basin, Extended wet detention pond, or constructed wetland. Bioretention facilities rely on plants and soils for the removal of pollutants from urban runoff, through a range of processes, such as sedimentation, filtration, adsorption and biological decomposition. Key Consideration: • Provides landscaping and habitat enhancement • Capable to remove a variety of pollutants,

o efficient in removal of suspended solids and heavy metals o moderately efficient in removal of phosphorus

• Other beneficial effects are reduction in runoff rates, runoff volumes and recharging groundwater through infiltration.

• Suitable for use in small highly developed urban areas • Require overflow facility to cope with higher runoff • Can be used in low infiltration soils with under drains • Require pre-treatment, such as grassed buffer, or grassed swale. • Can be enhance landscaping and habitat • Require careful maintenance and trash removal • Not to be used where high water table or bedrock is within 1 m below the bottom of the

facility, or where the available depth for the facility is less than 0.5 m • Most frequently used adjacent to parking areas • Traffic consideration are important in the location and plant selection


Design criteria Sizing of facility • Control the 25 mm post-development peak flow to pre-development level if possible use a series of bioretention facilities, or other BMPs

Depth of facility Storage • Minimum 0.5m, maximum 1.5 m

Inlet Sheet flow to reduce erosion risk

• Curb openings, or small drainage pipe

Under drain • Gravel layer surrounding a horizontal perforated pipe 10 cm 15 cm diameter. Filter fabric can be used to protect the under drain from blockage.

Planting medium Support plant life • A mix of 85% construction sand, 10% of silt and clay, and 5%




organic matter such as peat moss. For removal of N use higher fines.

Plant material Provide bioretention • A diverse native plant community should be used, tolerant to stormwater.

• Aesthetics and visual characteristics should be considered in the selection

Mulch selection Performance enhancer • Use at least 6 months old standard landscaping coarse shredded hardwood mulch or chips. Do not use grass clippings, or pine bark

• Place uniformly maximum 2 cm deep

Ponding Added flow control • Allow ponding depth of 15 cm to 30 cm for the “first flush” runoff

Construction Guide Improve performance • Only collect runoff once the vegetation in the drainage area is established

• Minimize compaction and use tilling operation

• Backfilling in 0.3 m lifts, do not use heavy equipment

• Plants should be set and kept upright. Grasses should be drilled into the soil

• Under drains must be placed on filter cloth, followed by grave bedding, ends must be capped.

• Collector pipe under the drain should have a slope >0.5%. Size collector pipe to carry maximum exfiltrating flow

Maintenance Ensure high performance • Inspect and clean up trash monthly.

• Add mulch 1-2 times a year, • Change mulch every 2 years • Plant maintenance twice a year • Water 14 days after planting

completed Construction costs: simple residential area facility $50 m2, with construction of curbing and storm drains is $500 m2.



Rain gardens Rain gardens are landscaped areas planted with wild flowers and other native vegetation that soak up rain water, mainly from roof of a house or other building. The rain garden fills with a few centimetre of water after a storm and water slowly filters into the ground. Compared to conventional lawn, a rain garden allows about 30% more water to soak into the ground. The advantages of rain gardens are:

• Increased infiltration to recharge the aquifer • Reduced flows downstream • Reduced pollutant loads entering the receiving system • Enhanced landscaping • Provision of habitat for birds, butterflies and many other beneficial insects

Rain gardens should be located at least 4 m from the house so infiltrating water will not seep into the foundation, away from septic systems, or wet patches, or large trees. Rain garden surface area can be estimated by using the roof area that provides the runoff as the base, by knowing the maximum depth of the rain garden and the type of surface soils, as shown in the table below:

Rain gardens < 10 m from downspouts

Rain gardens > 10 m from downspouts

Depth of rain garden

Soil type

7-15 cm 16-19 cm 20 cm For all depths

Sandy soil 0.19 0.15 0.08 0.03 Silty soil 0.34 0.25 0.16 0.06 Clayey soils 0.43 0.32 0.20 0.10

For example, a 200 m2 roof draining to rain garden, 15 cm deep, located in silty soils would require a rain garden with a surface area of 200 x 0.34= 68 m2. To keep the water in the rain garden a berm is used. To prevent erosion, the berm should be covered with mulch or grass or dry-tolerant species. The plant selection should be based on native plants, considering the height, bloom time, colour and its overall texture. Heights, shapes, and textures should be mixed to give the garden depth and dimension. Randomly clump individual species in groups of 3-7 plants. Only plants with well-established root system should be



used. Local stones, ornamental fences, trails, and benches can be used to enhance the appearance of the garden. For more information see: www.raingardens.org



17. Monitoring

Watershed and subwatershed studies normally provide recommendations on setting up monitoring plans for the watershed/subwatershed in question. Where no such studies are available a monitoring program should be prepared as part of a new development proposal. The individual monitoring tasks applicable for individual BMPs and for the proposed development area should be selected from the following list.

Monitoring Group Components Details

Stream flows Flow hydrographs • For different storm events, comparison of before and after development

Physical parameters • TSS, DO, pH in streams upstream and downstream of project, or at the mouth

Water quality

Chemical parameters • Metals, nutrients, hydrocarbons in streams upstream and downstream of project, or at the mouth

Pollutant loadings Runoff quality • Before, during and after project completion

In-stream habitat • Fish habitat, algae in streams upstream and downstream of project, or at the mouth

Productivity • Periphyton, plankton, macrophytes

Fish community • Species, populations, migration

Aquatic habitat

Invertebrates • Species, numbers, diversity, biomass

Upland vegetation • Vegetative cover during all seasons

Vegetation

Riparian vegetation • Structure, composition, condition, function, change in seasons

Soil erosion Land erosion • Estimate annual or seasonal erosion rates

Plan view • Sinuosity, width, riffles, pools,

Stream morphology and changes over time

Cross-sections • Bankfull depth, width, width/depth ratio



Monitoring Group Components Details

Profile • Bed particle distribution, water surface slope, bed slope

canada; stormwater management guidelines - halifax

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