chapter 5 national case studies - rfcd |...

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EXHIBIT 5.1AUSTIN WATERSHED MASTER PLANSTORMWATER QUALITY PLANNING

Chapter 5NATIONAL CASE STUDIES

As part of Denver s commitment to not reinvent the wheel with regard to stormwater qualitymanagement, five communities with reputations for advanced stormwater management programswere selected for review. These communities and the aspect of their program of primary focusfor purposes of this Plan include:

4 City of Austin, Texas: Watershed Protection Master Plan4 City of Portland, Oregon: Clean Rivers Plan4 Snohomish County, Washington: Drainage Needs Report4 City of San Diego, California: Think Blue San Diego!4 Prince George s County, Maryland: Low Impact Development

Although the climates in most of these communities differ from Denver, the planning processthat each has undertaken is relevant nonetheless. The level of detail and topics addressed in thecase studies vary depending on the specific reason that the community was selected. Forexample, fairly detailed discussions of the planning processes implemented in Austin, Portlandand Snohomish County are provided, while more topic-specific information is provided for SanDiego with regard to public education and for Prince George s County with regard to LowImpact Development. Interviews with key managers, literature reviews and website reviewswere completed to obtain information on each of the communities programs. The highlights ofeach are provided in the remainder of this chapter, along with a summary of key themes relevantto Denver s stormwater planning process.

CITY OF AUSTIN, TEXAS: WATERSHED PROTECTION MASTERPLAN

In 2001, the City of Austin, Texas completed a multi-year,$2.1 million watershed protection report titled the WatershedProtection Master Plan Phase I Watersheds Report (Exhibit5.1). This plan is cutting-edge in many ways, two of whichinclude: 1) its integrated approach to flooding, erosion andwater quality issues; and 2) its extensive use of GeographicInformation Systems (GIS) as a tool for watershed planning.Some of the highlights of this plan follow.

As background, Austin formed its Watershed ProtectionDepartment in 1996 from several existing departments toreduce the impact of flooding, erosion and water pollutionon the community in order to protect lives, property and theenvironment. To accomplish this mission, the WatershedProtection Department completed Phase I of a WatershedProtection Master Plan to better prioritize service needs andrefine program direction.

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The master plan included an extensive public input process that resulted in multiple goals andobjectives. The first part of the plan details the development of a system to identify and assessthe severity of problem areas, including methods to assign numeric scores to the problem areas,which could in turn be used in GIS mapping. Once this system was developed, each streamsegment was assessed regarding creek and local flooding, erosion, and water quality degradation.The water quality assessment, referred to as the environmental integrity index, included not onlychemical constituents, but also sediment quality, physical integrity, recreation/aesthetics, aquaticlife support, and channel stability. Following the assessments, the stream segments were scoredand mapped with GIS. Integrated problem area watershed maps were developed by overlayingthe results of individual assessments to identify areas of concurrent flooding, erosion, and waterquality problems.

The next step in the process was to inventory potential solutions to the identified problems.From this inventory, a set of preferred solutions was developed for various situations. Exhibit5.2 summarizes the preferred solutions by watershed type developed as a result of the MasterPlan.

EXHIBIT 5.2CITY OF AUSTIN PREFERRED ALTERNATIVES BY WATERSHED TYPE

Reinforced Earth [erosion side slopeprojects]Gabions/Concrete Riprap [erosionside slope proj.]Geomorphically-Referenced RiverEngineering (GRRE)Erosion Detention [Little Wal. &Shoal headwaters]Wet Ponds/WetlandsWet Ponds + Baseflow ExtendedDetention

Reinforced Earth [erosion side slopeprojects]Gabions/Concrete Riprap [erosionside slope proj.]Geomorphically-Referenced RiverEngineering (GRRE)Erosion DetentionErosion Detention + Wet PondsErosion Detention + Wet Ponds +Baseflow Extended DetentionRetention-Irrigation Ponds

Geomorphically-Referenced RiverEngineering (GRRE)Wet Pond/WetlandsRetention-Irrigation Ponds

Solution Options for Erosion andWater Quality



Property Acquisition (Buyouts) forFlood ControlFlood DetentionChannelizationFlow Diversion: Channels andTunnelsReplacement of StructuralConstrictionsLevees and Floodwalls


No flooding problems in Barton Creek

Solution Options for Flood ControlSolution Options for Flood ControlSolution Options for Flood Control

Existing ImperviousCover >50%Net Future ImperviousCover Increase <5%

Existing ImperviousCover >15%Net Future ImperviousCover Increase >5%

Future ImperviousCover <15%

Urbanized Watershed CharacteristicsDeveloping Watershed CharacteristicsRural Watershed Characteristics

URBANIZEDWATERSHEDS

DEVELOPINGWATERSHEDS

RURALWATERSHEDS

Reinforced Earth [erosion side slopeprojects]Gabions/Concrete Riprap [erosionside slope proj.]Geomorphically-Referenced RiverEngineering (GRRE)Erosion Detention [Little Wal. &Shoal headwaters]Wet Ponds/WetlandsWet Ponds + Baseflow ExtendedDetention

Reinforced Earth [erosion side slopeprojects]Gabions/Concrete Riprap [erosionside slope proj.]Geomorphically-Referenced RiverEngineering (GRRE)Erosion DetentionErosion Detention + Wet PondsErosion Detention + Wet Ponds +Baseflow Extended DetentionRetention-Irrigation Ponds

Geomorphically-Referenced RiverEngineering (GRRE)Wet Pond/WetlandsRetention-Irrigation Ponds






No flooding problems in Barton Creek

Solution Options for Flood ControlSolution Options for Flood ControlSolution Options for Flood Control

Existing ImperviousCover >50%Net Future ImperviousCover Increase <5%

Existing ImperviousCover >15%Net Future ImperviousCover Increase >5%

Future ImperviousCover <15%

Urbanized Watershed CharacteristicsDeveloping Watershed CharacteristicsRural Watershed Characteristics

URBANIZEDWATERSHEDS

DEVELOPINGWATERSHEDS

RURALWATERSHEDS

Denver Water Quality Management Plan

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To address the problems characterized by the watershed studies, the Master Plan identified theneed to implement a combination of watershed solutions including:

4 Capital Infrastructure Projects: Over $800 million in capital funds to construct integratedwatershed protection facilities including detention ponds, channel stabilization projects,and other flood, erosion, and water quality controls.

4 Operating Program Enhancements: Additional funding of $2 to 5 million per year forinfrastructure maintenance, development review and inspection, public education, anddesign support.

4 Regulatory Modifications: Changes to various codes and criteria to improve customerservice, provide developer incentives, reduce long-term maintenance needs, and preventthe creation of new watershed problems in the future.

If the additional resources and funding are made available, the city anticipates that it can meet itserosion and flood goals; however, the city does not expect to be able to attain all of its waterquality goals based on its Phase I Master Plan solutions. Some of the reasons identified in thereport and in a follow-up interview with Jean Drew, the city s Watershed Master PlanCoordinator, include:

4 Limited regional retrofit opportunities in urban watersheds and inadequate regulatorycontrols in areas outside the city's jurisdiction.

4 Setting potentially unrealistically high water quality goals. (For example, restoration ofbase flows is a significant problem that is not easily addressed.)

4 Inability of the Master Plan scoring system to credit non-structural BMP methods inreducing pollution. (For example, improved lawn care practices were not considered as aquantifiable factor in nutrient reductions in streams.)

Follow-up interviews with Jean Drew, City of Austin, and Michael Barrett, University of Texas,identified some of the challenges encountered during the Austin Watershed Master Plan processthat have applicability to Denver s on-going and future work, including:

4 Striking a balance between extensive public involvement and keeping the project movingforward in a timely manner.

4 Striking a balance between multiple priorities within city departments.

4 Agreeing on level of detail/refinement in assessing the problem (e.g., assigning numericscores to problems has its benefits and limitations).

4 Agreeing on appropriate level of refinement/precision for modeling results.

4 Providing an adequate level of cost projections for future work, while still working withinthe framework of a planning-level document.


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EXHIBIT 5.3ATTRACTIVE WETLAND/POND IN AUSTIN

4 Securing future funding to implement the projects identified in the plan.

Several specific aspects of the City of Austin s watershed program that are relevant to Denver sefforts include:

4 Capital projects are financed by bond monies, transfers from the Watershed ProtectionDepartment s normal operating funds, Urban Water Quality Ordinance fees and RegionalStormwater Management Participation Fees.

4 All water quality controls within the City of Austin s jurisdiction must achieve aminimum runoff capture volume of at least the first one-half inch of runoff from thecontributing area once a site reaches 20 percent impervious cover, and the volumeincreases based on percent impervious cover. Under the Save Our Spring (SOS)regulations in the Barton Springs Zone, higher capture volumes are required for meetingthe pollution reduction standard of no increase in the average annual pollutant load, andthere is no minimum impervious cover trigger. It is possible that capture volumes couldbe increased as a potential modification of the requirements under the Phase I Report.

4 Runoff treatment standards are based on providing treatment equivalent to asedimentation/filtration system designed in accordance with the City of Austin sEnvironmental Criteria Manual.

4 Austin encourages redevelopment as a means of promoting infill development. TheMaster Plan notes that waiving existing development standards is one mechanism topromote redevelopment; however, a consequence of waiving development standards isworsening of inner city flooding, erosion and water quality problems.

4 In the urbanized/developedwatersheds in Austin, imperviouscover is already high and streamchannel enlargement processesare already advanced. SinceAustin s preferred solutions forrunoff treatment aredetention/retention pond solutionsor wetlands that require landavailability (Exhibit 5.3), Austinworked to inventory as manypotential pond locations aspractical.

4 Austin has pursued projects underits Regional StormwaterManagement Program forpotential retrofits to provide water quality functions. These projects have also taken intoconsideration Low Impact Development techniques. As part of the Watershed Protection


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EXHIBIT 5.4PORTLAND S CLEAN RIVER PLAN

Department s analysis, Austin determined that runoff from at least 25 percent of existingdevelopment needs to be treated to have a significant impact on water quality. For high-priority receiving waters, runoff from preferably up to 50 percent of existingdevelopment should be treated. More detailed site-specific investigations were identifiedas necessary to determine the best combinations of large-scale regional water qualityponds and existing pond retrofits.

CITY OF PORTLAND, OREGON:CLEAN RIVER PLANThe Bureau of Environmental Services inPortland, Oregon, is responsible for treatingwastewater, providing stormwater drainageservices, reducing stormwater pollution,restoring native vegetation and improving waterquality in rivers and streams. The Bureau servesover 500,000 people in an 85,000-acre areacomprised of four major watersheds. There aretwo key components of their program: theStormwater Management Manual, updated in2002, and Portland s Clean River Plan, whichwas released in 2000 and revolves around tenactions for success and which identified $877million worth of needed projects. The CleanRiver Plan is the primary focus of thisdiscussion.

Because much of Portland s effort was driven by significant problems relating to combinedsewer overflows (CSOs), Portland s Clean River Plan provides a cutting-edge perspective onreducing storm flow volumes in concert with improving water quality through a variety ofinnovative approaches. The plan, itself, provides a concise big-picture vision, along withspecific goals, in the form of a relatively brief, full-color document that can be widely distributedand understood by citizens and officials with widely varying backgrounds. Some of thehighlights of Portland s Clean River Plan follow.

One of the main thrusts of Portland s Clean River Plan is to address the city s water qualityproblems using solutions that address more than one problem at a time in order to minimizecostly single-purpose infrastructure such as large pipes, expanded treatment plants and pumpstations. The planning strategy involved reviewing each of the four watersheds using consistentassessment strategies and solution option evaluations. As was the case for the City of Austin,numeric scoring criteria were developed and assigned as part of the process.

As a result of this process, Ten Actions to improve the rivers, along with cost estimates for theprogram over a 20-year planning horizon, were developed. A brief overview of these actionsfollows. Actions that are particularly innovative and/or potentially applicable to Denver arediscussed in more detail.


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4 Plant trees, native vegetation and create buffers and shade along streams (Cost: $54million). Tree planting is particularly important to Portland due to stream temperaturestandard violations and threatened and endangered fish species issues. The presence ofwoody debris in streams is also important for fish habitat. The city has a program forpartnerships with streamside landowners to preserve natural riparian vegetation, planttrees and native vegetation, and remove invasive, non-native plants. There is also a goalto increase urban canopy. The adoption and enforcement of existing and newdevelopment standards to protect existing stream buffers and create new stream buffers isalso high priority.

4 Reduce stormwater flow and pollutants reaching streams (Cost: $53 million). Theprimary focus is Low Impact Development techniques including disconnectingdownspouts, expanding the roof garden program, and a series of pilot projects to reducestormwater flows. Examples of pilot projects include stream diversions, downspoutdisconnection, parking lot detention, eco-roof and landscape infiltration projects.Another priority is to enforce the requirements of the city s Stormwater ManagementManual, which strongly encourages Low Impact Development techniques as the firstpriority, followed by swales, ponds, constructed wetlands, vaults, and other stormwatertreatment systems. They also are developing incentive programs for existingdevelopments to provide treatment.

4 Enhance Erosion Control from Construction and Development (Cost: $7 million).Key actions include providing inspection personnel and equipment, an Erosion ControlCertification Program and a Citizen Reporting System for erosion problems.

4 Increase pollution prevention and source control efforts (Cost: $7 million). Thisprogram focuses on removing illicit discharges, increasing outreach to businesses,developing a comprehensive recognition program modeled on the Eco-Logical BusinessProgram, expanding outreach to medium and small businesses that have non-permittedindustries to assist them with techniques to prevent pollution, and enhancing andmaintaining the Soil-Trader website. Some specific examples of these efforts includepartnering with specific industry groups each year to develop a set of BMPs for thatindustry and developing a technical assistance guide. The Soil Trader website is a way toexchange information to recycle clean excavated soil, rather than dispose of it. Anotherexample includes a five-year pilot project working with dentists to recycle X-ray fixerdue to its silver content and lead foil and amalgam from pump traps due to mercurycontent.

4 Education and Stewardship (Cost: $9 million). This includes K-12 and adultinformation programs, stewardship grants to local groups that organize and carry outenvironmental enhancement work, and development of other educational information.Public education is a key component of the city s overall strategy. Free educationprograms are offered to schools and communities, in addition to providing communityservice projects, stewardship grants and curriculum resources for check out. A websitehas Clean River Games and kid s pages.


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EXHIBIT 5.5PORTLAND S BUREAU COORDINATION NEEDS

4 Floodplain Restoration (Cost: $4.5 million). This involves acquiring flood-proneproperties through willing-seller programs and restoring floodplain functions in specificwatersheds.

4 Monitoring and Watershed Assessments (Cost: $7.5 million). The key purpose ofthese assessments is to provide information to evaluate how the watersheds change overtime. Monitoring is the foundation of the adaptive management approach. Themonitoring program includes establishing baseline conditions, monitoring water qualityfor a consistent set of constituents, assessing flooding, fish habitat, riparian vegetation,flow/geomorphology,and stewardship.Additional tracking ofprogram effectiveness isalso included.

4 Coordination andPartnership. (Cost:included in baseline citybudgets). The matrix inExhibit 5.5 helps toconsolidate which citydepartments are involved ineach of the Clean River Plangoals. Additionalcoordination with state andfederal agencies is alsoimportant, particularly withregard to the Threatened andEndangered Species issues.

With regard to Portland sStormwater Management Manual,which is the foundation of stormwater management strategy described above, the key strategybeing emphasized is on-site stormwater management practices. The city now requires all newdevelopment and redevelopment projects to include onsite stormwater facilities. The manualemphasizes the simplified approach to stormwater management, which focuses on rooftopsystems, porous pavement, planter boxes, vegetated swales, filter strips and basins, sand filtersand soakage trenches, and trees. Alternative methods include the more traditional stormwaterpractices of grassy swales, ponds, constructed wetlands, detention facilities, drywells,manufactured systems, oil/water separators, and stormwater reuse. The manual also providesspecific guidance for activity-based pollution controls for fuel-dispensing facilities, above-ground storage of liquid materials, solid waste storage areas, exterior storage of bulk materials,material transfer areas/loading docks, equipment/vehicle washing areas, stormwater disposal fordevelopment on recycled land, covered vehicle parking areas, and other requirements. Themanual specifically outlines facility landscaping requirements for all BMPs involving vegetation.


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EXHIBIT 5.6PORTLAND S BMP MAINTENANCE GUIDANCE

This includes recommended plant lists, mulch, irrigation, facility screening, and other measures.Specific operations and maintenance requirements are provided for each BMP.

Property owners are legally responsible for inspecting and maintaining the facilities, and the cityhas developed illustrated handbooks (Exhibit 5.6) for homeowners and property owners thatclearly describe stormwater facility operation and maintenance guidelines, including inspectionrecord forms.

Other highlights of the Portland program withregard to financing and stormwater treatment criteriainclude:

4 Financing is through sewer fees. Sewer ratesare expected to increase from $33/month to$97/month by 2020.

4 All new development and redevelopmentwith over 500 sq. ft. of imperviousdevelopment footprint area is required tocomply with Portland s stormwater manualrequirements. The requirement is removal of70 percent of total suspended solids (TSS)from runoff generated by a design storm upto and including 0.83 inches of rainfall over a24-hour period. In addition to this standard,projects discharging to waterbodies withestablished TMDLs also have to comply withpollutant removal requirements for thatwaterbody. On-site infiltration is required to the maximum extent possible due to theCSO problem.

4 A new department called the Sustainable Stormwater Management Group has beenformed to focus solely on stormwater management opportunities in new development andredevelopment and other acute problem areas (Liptan 2003).


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EXHIBIT 5.7SNOHOMISH COUNTY DRAINAGE NEEDS REPORT

SNOHOMISH COUNTY, WASHINGTON

Snohomish County, WA, recently completed a two-year, $12 million study called the DrainageNeeds Report (Exhibit 5.7). The goals of this report were to develop a better understanding ofdrainage systems, streams and wetlands and to plan for existing and future infrastructure needs ina way that:

4 Reduces road and property flooding4 Protects and enhances aquatic habitat4 Reduces stormwater pollution and erosion from stormwater runoff

Snohomish County s Surface Water Management Division selected this integrated approachbecause they have found that flooding problems (and their solutions) are usually intertwined withother surface water issues, such as aquatic habitat, water quality and erosion. This is alsoparticularly true in their area due to threatened and endangered species issues. The plan reliedheavily on Global Positioning System (GPS) and GIS mapping of drainage systems that covered73 square miles. As part of the study, 11 individual drainage systems were evaluated in detailregarding the following issues:

4 Drainage problem area4 Water quality4 Aquatic habitat4 Size and location of culverts/pipes for drainage and fish passage4 Other drainage-specific information

Studies in the larger basins included significant hydrologic and hydraulic computer modeling.Recommendations for improvements to all of the basins were provided. The study resulted in378 recommended projects totalingapproximately $123 million. Themajority ($84 million) of theprojects involved flooding issuestypically combined with other issues,while $4.1 million addressed waterquality only, $6.9 million addressederosion only and $27 millionaddressed habitat only.

Specific components of the DrainageNeeds Report include: a drainageinventory, information on how to usethe report, project implementationstrategies, guiding principles andmethodology for evaluating thedrainage basins, overall programrecommendations, and study resultsfor each of the 11 basins. The


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EXHIBIT 5.8SNOHOMISH ANNUAL ACHIEVEMENT REPORT HIGHIGHTS DETENTION FACILITY RETROFITS

individual basin reports, which formed the basis for the overall report, addressed these topics:

4 Basin characteristics4 Hydrologic and hydraulic modeling to address flooding4 Habitat assessment4 Water quality analysis4 Channel erosion assessment4 Capital Improvement Project (CIP) guidelines4 Existing and future problems4 CIP development, alternatives analysis, and recommend solutions4 Recommended plan

GIS and scoring-type approaches were used to prioritize project recommendations.Implementation considerations such as land acquisition, public or private ownership, andwhether the project required early action were also noted. Project sequencing, funding,permitting, maintenance, and additional study requirements were also identified.

Several general recommendations of the report included retrofitting detention ponds (Exhibit 5.8)and open ditches to provide water quality benefits and working with landowners to implementBMPs such as preserving streamside vegetation, properly managing livestock, maintaining septicsystems, etc.


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In addition to the Drainage Needs Report, there are other key components to the Surface WaterManagement Division s program. Extensive information is available on their website, includinga detailed description and photograph catalogue of water quality problems and a reportinghotline number. Key programs covered by their department include community partnerships,water quality, aquatic habitat, urban drainage, and river flooding. The community partnershipprogram is well developed with specific programs to address native plants, salmon, watershededucation, watershed stewardship, and volunteer opportunities. Some of the activity areashighlighted in a recent annual achievement report (2001) include:

4 Stormwater detention facility retrofits to incorporate stormwater quality benefits andsmaller storm detention into older facilities.

4 Detention facility maintenance program. This program has a database inventory of over800 residential and Public Works drainage facilities, owned and maintained by either theCounty or homeowners. Over 200 facilities are inspected yearly and County crewsmaintained approximately 60 facilities in 2001, including some large rehabilitationprojects to improve facility performance. The program has a strong public educationprogram, making hundreds of citizen contacts annually. The cost of this program wasabout $440,000 for the year.

4 Large woody debris program. The program involved providing large woody debris tostreams for aquatic habitat and streambank stabilization. The cost of the program was$154,000 for the year.

Other aspects of Snohomish County s program, including stormwater treatment criteria, include:

4 Annual service charges are billed in conjunction with property taxes based on land useclassification and/or amount of impervious surface coverage as identified in their Indexof Land Use Classifications and Rate Categories. In areas designated as Clean WaterDistricts, representative annual service charges are $33.01/single family parcel up to$99.02/quarter acre of very heavy development.

4 Snohomish County s stormwater criteria are based on the Washington Department ofEcology s criteria. On-site stormwater management is required for new development if2,000 square feet or more of impervious area is added or replaced and land-disturbingactivity includes 7,000 square feet or greater. Additional measures including runofftreatment, flow control and other measures are required if the new development createsor adds 5,000 square feet of impervious surface, converts ¾ or more acres of nativevegetation to lawn or landscaped areas or converts 2.5 or more acres to pasture. Therequirements for redevelopment are similar but provide some flexibility to not discourageredevelopment.

4 On-site stormwater management (referenced above) requires BMPs that infiltrate,disperse and retain stormwater runoff onsite to the maximum extent feasible withoutcausing flooding or erosion impacts. Roof downspout control BMPs and dispersion andsoil quality BMPs (or their functional equivalents) are required to reduce the hydrologic


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EXHIBIT 5.9THINK BLUE SAN DIEGO!

disruption of developed sites. The intent is to use inexpensive practices on individualproperties to reduce the amount of disruption to the natural hydrologic characteristics ofthe site.

4 Runoff treatment (referenced above) requires construction of stormwater treatmentfacilities based on pollution generating impervious surfaces (PGIS) and pollutiongenerating pervious surfaces (PGPS).

4 Snohomish County has a well organized website with detailed information available atwww.surfacewater.info.

4 The Surface Water Management Division has about 75 people, who Director Joan Lee,P.E., credits for a high level of competence and cooperation, enabling the success of theprogram (Lee 2003).

SAN DIEGO, CALIFORNIA

The goals of San Diego s Stormwater PollutionDivision and their stormwater program include:

4 Investigation: This includes testing forpollutants at over 300 locations andrecognizing that everyday activities are a keypollutant source.

4 Pollution abatement: Key successes haveincluded adjusting sprinklers/wateringschedules and working to reduce pollutionfrom construction sites and restaurants.

4 Education: Think Blue San Diego (www.thinkbluesd.org) (Exhibit 5.9).

4 Enforcement: This includes a Stormwater Code Enforcement Team ( stormwater cops ),citations and fines of $100-10,000/day, and a pollution reporting hotline.

4 Additional Funding: The city recognizes its need for more funding for cleaning andmaintenance of the storm drain system and has identified obtaining additional funding asa priority.

The City of San Diego has won multiple national awards over the last several years for theirpublic education work related to stormwater. Award-winning aspects include the Think Bluecampaign and the Stormwater and You employee education video. The Think Blueeducation and outreach campaign was chosen as part of EPA s urban city model program in itsnon-point source pollution toolbox for municipal agencies. With its strong emphasis on publiceducation, Karen Henry, Deputy Director of Public Works, notes that the greatest benefits willbe seen in long-term behavioral changes. A user-friendly website is part of their on-going public


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EXHIBIT 5.10SAN DIEGO S USER-FRIENDLY WEBSITE

education program (Exhibit 5.10). The city is conducting annual surveys to try to measure howbehavior is changing with regard towater protection practices (Henry2003).

In addition to the education campaigns,the city also has a formal Urban RunoffManagement Plan that has identifiedabout $30 million in needed projects.The city recently updated itsStormwater Standards (City of SanDiego 2003), which identifyrequirements for stormwater qualitytreatment. One innovative aspect ofthis document is that it provides a GISmap of water-quality sensitive areas sothat developers and planners are awareof areas requiring special protection.The plan also includes a BMP selectionmatrix that recommends selection ofdifferent BMP types based on theexpected pollutants of concern. Thedocument also provides a standard development project and priority project stormwaterBMP requirements matrix.

PRINCE GEORGE S COUNTY, MARYLAND AND LOW IMPACTDEVELOPMENT

Prince George s County, Maryland, and Associate Director of the Department of EnvironmentalResources, Larry Coffman, are nationally known for their leadership in implementation of LowImpact Development (LID) strategies beginning in the early 1980s. LID techniques are the focusof this discussion. When discussing LID, it is important to note that many LID techniques havethe effect of minimizing directly connected impervious area, which is a foundational conceptof stormwater management in Denver (UDFCD 1999).

LID practices help to control pollutants, reduce runoff volume, manage runoff timing, andaddress other ecological concerns. The goal of LID is to mimic a site's predevelopmenthydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoffclose to its source. Instead of conveying and treating stormwater in facilities located at thebottom of drainage areas, LID addresses stormwater through small, landscape features at the lotlevel (Exhibits 5.11-5.13). These landscape features, or Integrated Management Practices(IMPs), are the building blocks of LID (Coffman 2001). Examples of LID techniques includebioretention, permeable pavers, tree box planters, rain gardens, and disconnected downspouts.


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EXHIBITS 5.11-5.13LOW IMPACT DEVELOPMENT FEATURES

Source: lowimpactdevelopment.org. From top to bottom:landscaped parking lot infiltration, residential landscapedinfiltration and porous pavement. .

Larry Coffman (2001) provides thefollowing statement regarding thefoundations of LID:

The LID principles and practices arebased on what we have learned overthe years about stormwatermanagement and the transfer oftechnology from other fields ofengineering and science, such assanitary engineering, agriculture,forestry, soil science,phytoremediation, bioremediationand ecology. As an example, take alook at the data on the 50-yearhistory of successful landapplication and treatment ofwastewater effluent (slow rateirrigation, overland flow, and highrate infiltration). Add to this theexisting and growing body of dataon the performance of bioswales,bioretention, filter strips and turffrom universities (Maryland,Virginia, and Washington State),Federal Highway Administration,USEPA, and others. When you lookat the entire body of relatedscientific andengineering/environmentaltechnologies, you begin to see theadvantages and benefits of LID smultiple systems (treatment train)approach.

An advantage of LID is that it is acomprehensive multi-systemsapproach that has built-inredundancy, which greatly reducesthe possibility of failure. Basicsubdivision and infrastructure designfeatures include: reducing the use ofpipes, ponds, curbs and gutters;maintaining recharge areas, bufferzones, and drainage courses; using


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infiltration swales, grading strategies, and open drainage systems; reducing impervious surfacesand disconnecting those that must be used; and conserving open space. The key factor in thesuccess of LID is to ensure that the landscape practices (such as rain gardens) are attractive andperceived by the property owner as adding value to the property. If these LID practices areviewed as assets, the primary motivation for their long-term maintenance is that of propertyowners protecting their vested economic interests (Coffman 2001; http://www.lid-stormwater.net/).

Another advantage of the LID approach is with regard to preserving stream integrity. Aspreviously discussed, it is important that a stormwater system specifically addresses the frequentstorms that occur on a regular basis (weekly or monthly). By using decentralized site-basedsource controls, LID uses the stormwater from these more frequent events as a resource and is aneffective ecosystem approach. LID techniques can also be combined into hybrid programs thataddress major flood control events, if needed (Coffman 2001; http://www.lid-stormwater.net/).

The Department of Environmental Resources in Prince George s County, Maryland recentlypresented results of side-by-side monitoring of two small residential watersheds in the SomersetHeights subdivision (Cheng, et al. 2003). One watershed was developed using conventionalcurb-and-gutter systems, whereas the other was developed using preliminary LID practices,including only grassed swales, bioretention areas, and disconnected impervious areas. It isimportant to note that the subdivision was designed and constructed prior to development ofdesign criteria for LID practices. Regardless, over a two-year period, statistically significantdifferences were measured between the two watersheds in the number of runoff events, the totalrunoff volumes, and in peak event flow rates. Monitoring revealed that the LID watershed had20 percent fewer runoff events, and the average peak flow rate was only 56 percent ofconventional watersheds. Including groundwater/interflow, the total flow volume at the LID sitewas approximately 80 percent of the conventional site surface runoff. In the LID watershed,peak flow rates were reduced by approximately 44 percent per acre. Since monitoring occurredprior to site stabilization and without full-scale implementation of LID approaches, water qualitycomparisons between the sites were not considered to be representative of long-termperformance according to current LID design practices.

Not all developments in Prince George s County have been planned using LID techniques.Older developments are usually based on more traditional drainage practices and some areas areconducive to hybrid approaches that combine traditional drainage practices with LID(Coffman 2003). With regard to long-term maintenance concerns, Coffman notes that severalfactors can help promote more effective long-term maintenance, including:

4 Comprehensive site planning, including conserving natural soils, amending soils withorganic materials, providing gentle slopes, and conserving drainage patterns.

4 Providing site grading and design that are aesthetically-pleasing amenities and thatcomplement rather than interfere with desirable site uses.

4 Providing a fudge factor in site designs that allows a certain degree of failure in thesystem.


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4 Establishing covenants and outreach programs to train people on how to maintain raingardens and other features to preserve their function and aesthetics.

SUMMARY

Several big-picture, planning-level lessons from innovative communities relevant to Denver scurrent stormwater quality planning process include:

4 Comprehensive approaches are being used to address drainage, flooding, erosion, aquaticlife, habitat, and water quality in an integrated manner.

4 Stormwater management approaches that are multi-layered, combining a variety ofstructural and non-structural practices, are advocated and implemented.

4 Watershed-based approaches are being used for planning and problem solving.

4 GIS tools are being used effectively to prioritize stormwater improvements and to moreeffectively communicate to citizens, staff and developers.

4 Storm runoff volume reduction practices are being used in the majority of thesecommunities. These practices included a variety of LID techniques such as eco-roofs andrain gardens, tree planting, and irrigation controls.

4 Long-term maintenance of BMPs is recognized as being critical to the success of BMPs.

4 Strong public education campaigns in combination with extensive web sites aresubstantive components of these programs with significant budget allocations. Educationis not an afterthought it is being aggressively used in several of these communities asa key strategy to improve runoff quality.

4 Significant financial investments, spanning from several hundred thousand to severalmillion dollars, have been required for these communities to complete their planningprocesses. Most of the communities also recognize that significant future expendituresfrom tens to hundreds of million dollars will be required to meet their future goals and areplanning accordingly.

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