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PROJECT AREA: YONKERS

HUDSON VALLEY REGIONAL COUNCIL

3 Washington Center, Newburgh, NY 12550 http://www.hudsonvalleyregionalcouncil.com/

GREEN INFRASTRUCTURE CONCEPT PLAN FOR LINCOLN HIGH SCHOOL

Project type: High School Campus Retrofits December 2011 Concept Plans: 1- Street Tree Planting 2- Rain barrels 3- Stormwater Planter

4-Green roof 5- Permeable Paving

Google 2011

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The following draft report describes a schematic landscape design proposal using green infrastructure practices for stormwater management. The illustrated plan and report are intended to give practical guidance for the owner, design professionals, contractors, and other interested parties to use in developing a final design. They are not intended to be used as final design and construction documents.

OVERVIEW: THE SITE AND THE CONCEPT PLANS

The Lincoln High School campus occupies approximately 15 acres on a steeply sloped hillside to the east of Tibbett’s Brook Park .Approximately half of the site covered with impervious surfaces—roof and paving.

School Principal Edwin Quezada supports developing plans on the site that would have an educational component and involve students in the implementation. He recommended working with two educators at the school, Jim McManus and Peter Hatem, to develop plans for green infrastructure, since they have created an outdoor learning center called the Eco Park on an interior rooftop courtyard. , In addition, John Carr, the Executive Director of Facilities for Yonkers Public Schools, and members of the City’s planning and engineering departments recommended developing a plan for green infrastructure on the site to help mitigate flooding problems. Impervious building and groundcover surfaces on the property contribute to flooding in the residential neighborhood and the park to the west. To reduce flooding in a steep hillside setting like this one a variety of stormwater management practices, including green infrastructure and conventional storage and detention systems could be used. By multiplying green infrastructure practices across the site and the neighborhood green infrastructure could make a significant contribution. The effectiveness for stormwater management of the practices in the following plans is described in terms of what is known as the Water Quality Volume (WQv), which is designed to improve water quality sizing to capture and treat 90% of the average annual stormwater runoff volume for that area. For Yonkers this is the 1.3 inches of rain. GI practices target the sediments and the pollutants that wash off of impervious area in these smaller rain events or the first part of a larger storm, and they aim to reduce the volume of runoff entering the storm drains, especially in areas with combined sewers. This report includes concept plans for four locations on the site:

1. Kneeland Avenue streetscape -- Tree planting 2. Roof garden retrofits, large and small

a. Rain barrels b. Stormwater planter c. Green roof

3. Driveway/maintenance area at the north end of the building -- Permeable Paving 4. Rear parking lot -- Permeable Paving

The tree planting and rooftop rainwater harvesting are discussed with student and teacher participation in mind. The concept plans for permeable paving present two alternative approaches proposed for permeable paving are initiatives that could have an educational component, but would require professional expertise.

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LOCATION

Street Address: 375 Kneeland Avenue, Yonkers, NY 10705 Parcel Number 6038001

OWNERSHIP

Yonkers Board of Education

FOUR PROJECT AREAS FOR CONCEPTUALGREEN INFRASTRUCTURE PLANS

1 - Street Tree Planting 2 – Rooftop Strategies— A. Rain barrels B. Stormwater planter C. Green roof 3 – Permeable paving by maintenance garage 4 – Permeable Paving in rear parking lot

Four locations for gi plans (NYSGIS2009 aerial)

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THE CONCEPT PLANS IN BRIEF

Following is a brief discussion of the concept plan for each of the individual practices. The detailed discussion of design issues, materials, maintenance and costs is provided in the last section.

1 TREE PLANTING

Tree plantings intercept rainfall in the canopy and release it through evapotranspiration. Street tree pits with good quality, uncompacted soil will infiltrate runoff, and tree roots and leaf litter enhance the soil conditions for infiltration. In addition to these stormwater management functions, trees can provide many other benefits including shading and cooling, buffering wind and noise, purifying air and beautification.

Tree plantings along the sidewalk and upper parking lot on Kneeland Avenue area proposed. The site assessment and plant selection could be carried out as a student project using guidance from Cornell University‘s Urban Horticulture Institute. The planting bed preparation and tree planting could also be carried about by students with neighborhood involvement.

2 ROOFTOP STRATEGIES

Rain Barrels

A set of rain barrels would be installed to be used for watering the ornamental plants in the EcoPark and to serve as a demonstration of the benefits of rain barrels on the broad scale for stormwater management.

Rain Barrels provide many stormwater management benefits, including:

• Reduced stormwater runoff entering the drainage system,

not only reduced volumes, but also delayed and/or reduced peak runoff flow rates during the water quality storm event.

• Reduced transport of pollutants associated with atmospheric deposition on rooftops into

receiving waters, especially heavy metals and other airborne pollutants (USEPA, 2005).

• Reduced water consumption for nonpotable uses, which ultimately reduces the demand on

municipal water systems. Water from rain barrels and cisterns, if managed correctly, may be used to water lawns and landscaping , wash automobiles, and top off pools (MEDP, 2009)

• Reduced runoff volumes in areas where there is a high percentage of impervious cover, soils

are compacted, groundwater levels are high, and/ or hot-spot conditions exist that preclude infiltration of runoff.

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Stormwater planter The New York State Stormwater Management Design Manual 2010 (Design Manual) describes stormwater planters as “small landscaped stormwater treatment devices that can be placed above or

1 Design Manual, pages 5-106-107.

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below ground …They use soil infiltration and biogeochemical processes to decrease stormwater quantity and improve water quality, similar to rain gardens and green roofs”

(page 5-97).

A stormwater planter is a good option for residential properties and streetscapes with limited green space. In the students’ EcoPark, the planter could be a small demonstration project designed and built by students. Downspouts would be attached to a small shed and a flow through planter would be designed and constructed to capture the runoff from the little roof. The filtered water would flow through the planter and out though a weephole, and then drain to the existing tree pit.

Green roof Green roofs reduce stormwater runoff volumes and attenuate peak flows by capturing rainwater and allowing evaporation and evapotranspiration. In addition the extra insulation that the green roof system provides reduces energy costs, absorbs noise and protects the rooftop materials, and extends the life of the roof. Additional benefits include reducing urban heat island effect, improving air quality, and providing habitat for birds and butterflies

(5-87 and 5-88).

A green roof is proposed for a portion of the interior courtyard roof at the time when the roofing membrane needs replacement. The system would be the low profile, type known as an “extensive” green roof system. One of the prefabricated systems available from various companies in the region could be used. These are preplanted modules or rolls that include a light weight soil medium and short, hardy plants like sedums.

3 PERMEABLE PAVING

Permeable paving allows rain water to pass through the material or through the spaces between units into a stone base, and then infiltrate into the underlying soils or, if necessary, exit through an underdrain. Its benefits include augmenting groundwater recharge, runoff reduction, some pollutant treatment and aesthetic improvement. Lighter colored pavers result in lower temperatures at the paving surface than asphalt.

Permeable pavers are proposed for two areas on the site — on the north side of the building, at the maintenance garage, and on the rear parking lot. This report focuses on the using open concrete cells filled with gravel or a new system called PaveDrain®.

Typical permeable paving section. NTS Unilock® Directions in Sustainable Design

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A WORD ON COSTS

Green infrastructure costs for retrofits are hard to state accurately. In new construction there is often considerably lower cost up front using and green infrastructure practices and planning versus conventional, big pipe systems. But where that “gray infrastructure” is already in place, assessing the value of adding a gi practice requires a fuller accounting. A recent report by the Center for Clean Air Policy states:

The value of green infrastructure actions is calculated by comparison to the cost of “hard” infrastructure alternatives, the value of avoided damages, or market preferences that enhance value (e.g. property value). Green infrastructure benefits generally can be divided into five categories of environmental protection:

(1) Land-value, (2) Quality of life, (3) Public health, (4) Hazard mitigation, and (5) Regulatory compliance.

The report sites, for example, New York City’s 2010 Green Infrastructure Plan, “which aims to reduce the city’s sewer management costs by $2.4 billion over 20 years. The plan estimates that every fully vegetated acre of green infrastructure would provide total annual benefits of $8,522 in reduced energy demand, $166 in reduced CO2 emissions, $1,044 in improved air quality, and $4,725 in increased property value. It estimates that the city can reduce CSO volumes by 2 billion gallons by 2030, using green practices at a total cost of $1.5 billion less than traditional methods.

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Two Sources of Cost Data

For installation, maintenance costs and lifespan data for the practices discussed here, the Cost Sheet developed by the Center for Neighborhood Technology (CNT) in collaboration with the US EPA Office of Wetlands, Oceans, and Watersheds (OWOW), Assessment and Watershed Protection Division, Non-Point Source Branch, provides useful information based on examples from various locations. It may be found at their website. http://greenvalues.cnt.org/national/cost_detail.php

Another useful source of cost data can be found in the Center of Watershed Protection's Urban Subwatershed Restoration Manual Series. Manual 3: Urban Stormwater Retrofit Practices, pages E-1 though 14, includes a discussion of costs in terms of the amount of stormwater treated. http://www.cwp.org/categoryblog/92-urban-subwatershed-restoration-manual-series.html

2 The Value of Green Infrastructure for Urban Climate Adaptation. Center for Clean Air Policy. Josh Foster, Ashley Lowe, Steve

Winkelman. February 2011.

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Green Infrastructure Sizing and Design

The green infrastructure practices included in these plans are among those considered acceptable for runoff reduction in the New York State Department of Environmental Conservation Stormwater Management Design Manual 2010 (DEC Manual). The green infrastructure techniques that are included in the DEC Manual include practices that:

reduce calculated runoff from contributing areas

capture the required water quality volume. The Water Quality Volume (denoted as the WQv) is designed to improve water quality sizing to capture and treat 90% of the average annual stormwater runoff volume. For Yonkers this 90% rainfall number is 1.3 inches. The WQv is directly related to the amount of impervious cover created at a site. The following equation can be used to determine the water quality storage volume WQv (in acre-feet of storage):

WQv = (P) (Rv)(A) 12 where: WQv = water quality volume (in acre-feet) P = 90% Rainfall Event Number Rv = 0.05 + 0.009(I), where I is percent impervious cover A = site area in acres (Contributing area) A minimum Rv of 0.2 will be applied to regulated sites.

For the most part, the plans included here focus on limiting the practices to a size that would capture the WQv in order to demonstrate clearly how the practices might fit within the particular settings and may be achieved within restricted budgets. However, in settings with sewer overflows and flooding problems, expanding the practices to capture greater volumes would be recommended.

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CONCEPT PLAN ONE: STREET TREE PLANTINGS

A linear planting of street trees is proposed for the northeast boundary of the site along Kneeland Avenue, along the upper parking lot. Appropriate species selection, good quality soils, adequate space for the roots, and protection from compaction are the key features of the plan. In addition to stormwater quality benefits and runoff reduction, the trees would provide shade on the adjacent impervious surfaces and beautify the street. With detailed guidance and assistance from landscape nurseries and contractors, students could plant the trees and provide the important initial maintenance.

EXISTING CONDITIONS

As shown in the photos below, the planting strip between the sidewalk and parking lot is wider than the strip along the street, and it is set back from the overhead wires. A chainlink fence runs along the length of the lot, but there is no gate. The space between the sidewalk and the ball courts is narrower and a portion of it has been paved with asphalt. Areas at the parking lot entrance show evidence of compaction due to foot traffic.

SURFACE COVER/CONTRIBUTING AREA

The area for the proposed plantings is the wider grassy strip between the parking and the sidewalk. The area is approximately 10 feet wide.

SOILS AND TOPOGRAPHY

The area under consideration slopes gently to the south. The USDA Soil Survey of shows two soil types: UpB—Urban land-Paxton complex, 2 to 8 percent slopes or Uf—Urban land. Paxton complex is classified as a Hydrologic Soil Group C.

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SOLAR AND WIND EXPOSURE

The Kneeland Avenue planting strip is exposed to the sun fully on all sides. According to Peter Hatem, it is very windy.

VEGETATION

There is one tree along the planting strip. It has been severely pruned around the power line.

SITE CONSTRAINTS

There are overhead wires which will limit the size and location of the trees.

3 Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil

Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. (Accessed [6/7/2011].

Kneeland Avenue View South Kneeland Avenue, View North

Asphalt along tennis court

Existing tree

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Concept Plan for Tree planting along north parking lot and Kneeland Avenue

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Eighteen small canopy trees are shown spaced 25 feet apart in the wide strip along the parking lot. The small tree spacing is based on a calculation of the soil volume for small street trees with a mature canopy diameter of approximately 20’.

Soil volume calculations should take into account a variety of specific factors including the soil type, whether the tree is growing in an open space or surrounded by paving, local climate conditions such as reflected heat and from cars, and other factors revealed in the complete site assessment. The chart shown below, developed by James Urban, shows that assuming a depth of3 feet, the soil volume available in a tree pit 25’ x 10’ would be adequate for a tree with a mature canopy in the range of 400 square feet (about 22’ feet in diameter).

The concept plan calls for removing the asphalt along the tennis court to allow for planting in this location. A small tree or a group of shrubs could be planted there. The chain link fence would be removed to make soil preparation easier, avoid conflict with the trees in the long term as the trunks grow wider, and improve the appearance of the streetscape. A wide mulched area would be provided around the base of each tree and the remainder of the planting strip would remain as turf. Shrub plantings on each side of the parking lot entrance would provide a barrier to foot traffic Trees: Trees would be selected according to aesthetic and functional criteria, and to maximize their benefits for stormwater management through evapotranspiration and infiltration. If the soil analysis indicates a heavy soil with a high bulk density and poor drainage, tree species should be selected that can tolerate these conditions. Planting a selection of visually compatible trees of several species rather than one species is recommended where there is a desire to avoid planting a monoculture. In this case, the planting is small enough that this concern may not be warranted. All selections should be species that can withstand urban stress. See the Cornell University Urban Horticulture Institute;’s website http://www.hort.cornell.edu/uhi/ for excellent resources on tree selection. Soil and Soil Amendments: Plant selection and planting specifications also would be based on an analysis of the soils to determine pH, wet and dry conditions, and compaction. The soil survey indicates that the soil may be heavy and slow to drain. If this is the case, tilling in compost to a depth of at least 18” over the entire planting bed to reduce bulk density should be considered. Even if this were done, trees that tolerate wet soils should still be chosen.

The soil volume required for various size trees assumes a soil depth

of 3 feet. (Source: James Urban) in Urban Watershed Forestry Manual - Part 3 page 26.)

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CONSTRUCTION STEPS

Amend soil as required by final design

Plant trees

Apply mulch

MATERIALS

Compost: as required in final design

Deciduous Trees: 18 small trees (mature canopy in the 20’ range)

Shrubs: Evergreen shrubs

Mulch: Three inch layer in area at least 5 feet in diameter around the base of the tree (below the root flare).

MAINTENANCE CONSIDERATIONS

Well-prepared planting areas designed with appropriate plants and soils require routine maintenance. During the establishment period new tree plantings would be watered using water bags and spot watering with a clear understanding of the requirements of the trees to avoid over- or under-watering. Ongoing maintenance for the trees would include occasional pruning and replacements, twice yearly clean up and yearly application of mulch and inspections and treatment for damage and disease.

COST

Costs will depend mostly on the size of the nursery stock. The project could involve donated funds or materials as well as volunteer labor.

RESOURCES

The following resources on site assessment and tree selection are recommended: From Urban Horticulture Institute of Cornell University at http://www.hort.cornell.edu/uhi/:

Recommended Urban Trees: Site Assessment and Tree Selection for Urban Tolerance. Urban

Horticulture Institute, Department of Horticulture, Cornell University, Ithaca, NY. Visual Similarity and Biological Diversity: Street Tree Selection and Design. Bassuk, Nina,.

Trowbridge, Peter. Grohs, Carol. From the Center for Watershed Protection http://www.cwp.org/documents/cat_view/69-urban-watershed-forestry-manual-series.html

Urban Watershed Forestry Manual,Part 3:.Urban Tree Planting Guide. Cappiella, Schueler, Tomlinson, Wright. Center for Watershed Protection and USDA Forest Service, Sept 2006.

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CONCEPT PLAN 2: ROOFTOP STORMWATER STATEGIES—RAIN BARRELS. STORMWATER PLANTER AND GREEN ROOF

The school building is designed with a central courtyard space in which two roofs are separated by a narrow tree pit planted with large shade trees. One roof is slightly higher than the other. The lower roof was built to have the load bearing capacity for student gatherings and has recently been converted to an outdoor learning center. The higher level roof is a conventional flat roof, and while it is not meant to be used for congregating it is a good candidate for conversion to a green roof system.

Instructors Peter Hatem and Jim McManus initiated the rooftop garden learning center called the “Eco Park”. They have organized students to help create planters, water features and small structures with a variety of materials—mostly recycled-- and have planted a variety of shrubs, perennials, and trees. They would like to capture rainwater to use in the garden.

This concept plan shows the following green infrastructure practices:

A. Rain barrels located next to the downspouts from the upper roof that currently drain onto a roof

adjacent to the garden

B. Flow through planter to capture rainwater from a small shed known as the “doll house.”

C. Green roof

Concept plan for interior roofscape

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EXISTING CONDITIONS

SURFACE COVER/CONTRIBUTING AREA

The rooftop courtyard is approximately 19,850 sf of which approximately 90 percent is impervious surface. The remainder comprises the tree pit,planters and small planting areas on the Eco Roof portion.

SOLAR AND WIND

The roof has good sun exposure. The area in the center shaded by the trees and the building walls cast shed on portions depending on the time of day and year.

The wind can be very strong within the courtyard due to the building configuration. According to Peter Hatem “The wind seems to enter at one end of the park and travels around the walls and picks up speed. There is evidence of "mini-twisters," in the bark mulch and large heavier cold frame boxes moving around. We are always "moving things back into place" following storms. Occasionally, ground debris is found hung in the tree branches following storms with high winds.”

VEGETATION

There are large deciduous trees in the central tree pit and various small trees, shrubs and perennial plants.

Upper roof, downspout and roof drain

Eco Park

Classroom windows and upper roof

Doll House shed

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2- A RAIN BARRELS

Two downspouts on the west side of the roof area would be outfitted with diverters to direct runoff first to a small chamber to capture the first few gallons of water that contain the first flush of sediments. Once this fills up, runoff would flow into connected series of rain barrels and the overflow would drain out onto the roof, as it does now. The barrels could be constructed and embellished as a special project or purchased prefabricated. They would be equipped with a hose or pipe to the Eco Park so that the water could be used to water ornamental plants as needed. The rain barrels for stormwater management need to be emptied between rain events.

The diagram below shows how the water can be diverted to drop out the initial flush of water, which could be drained into a small pilot green roof section after a rain.

Instead of a rain garden, a small area of

green roof modules could be used

Instead of one storage tank, a set of

connected rain barrels could be used

Rainwater harvesting diagram Rainwater Harvesting 101, page 2. Council on the Environment NYC http://www.grownyc.org/files/osg/RWH.how.to.pdf. Accessed 7/18/2011.

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CONSTRUCTION STEPS

The following excerpt from the City of Portland Environmental Services fact sheet on Rain Barrels gives the basic steps for rain barrel construction. For more information on this and other resources see Appendix x. Inlet: Create an opening with fine screening through which the rain barrel will collect water from the downspout elbow. This can be a single screened opening large enough to accommodate the downspout elbow (as shown in the photo), or a series of smaller screened openings directly in the top of the barrel. Overflow: Drill a hole near the top of the barrel to accommodate an overflow pipe that is at least 2 inches in diameter. If the overflow pipe elbow seals and seats securely, it can be threaded directly into the barrel opening. If not, it should be secured with washers on both sides of the barrel and a nut on the inside. Use Teflon tape around the threads and a bead of silicon caulking around the opening to ensure a tight seal. Foundation: Create a raised, stable, level base (like concrete blocks) for the rain barrel to sit on. You might want to test stability by filling the rain barrel with water before attaching to your structure. A full rain barrel is very heavy and tipping is a risk if it’s unsecured or on an uneven surface. Downspout: Cut the downspout with a hacksaw so that the elbow will sit just above the rain barrel inlet. Attach the elbow over the downspout with a screw and secure the downspout to the house with the strap. Attach Barrel: Set up the barrel beneath the elbow and secure the barrel to the house with a strap. Cut and attach the overflow pipe to the overflow elbow and direct to the existing discharge location. Outlet: Drill a hole near the bottom of the empty barrel to attach the drain spigot. If the spigot seals and seats securely, it can be threaded directly into the barrel opening. If not, it should be secured with washers on both sides of the barrel and a nut on the inside. Use Teflon tape around the threads and a bead of silicon caulking around the opening to ensure a tight seal.

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MATERIALS

Two good sources of information on construction with materials lists:

Rainwater Harvesting 101 Council on the Environment of NYC http://www.grownyc.org/files/osg/RWH.how.to.pdf How to Manage Stormwater: Rain Barrels Environmental Services City of Portland http://www.portlandonline.com/shared/cfm/image.cfm?id=182095

MAINTENANCE

Rain barrels should be drained routinely between rainfall events during the wet season (usually spring) and other periods of frequent rain events in order to maximize stormwater runoff reduction benefits. Drain and disconnect rain barrels in fall to prevent freezing, and reconnect in spring. Inspect periodically for leaks, especially spigots and other connection points. Make sure debris does not clog the system. Screen all vents to prevent mosquito breeding. Clean the interior of the barrels by brushing or disinfecting with vinegar or other non-toxic cleaner annually and dispose of well-diluted washout in planting areas.

COST

Do-it yourself rain barrels can be constructed for under $30. Readymade 55 gallon to 90 gallon rain barrels generally cost from $100 to $300 installed. A rain barrel and its system components have a life-span of about 20 years.*

SIZING COMPUTATIONS FOR RAIN BARRELS

4How to Build A Rain Barrel, page 5. http://www.portlandonline.com/bes/index.cfm?c=50367&a=182095

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Typical rain barrels hold 55 gallons of water, or approximately 330 gallons total, which would be a small percentage of the WQv of the part of the large upper roof that drains to these downspouts.

2 B - STORMWATER PLANTER

DESIGN

The NYS DEC describes stormwater planters as “small landscaped stormwater treatment devices that can be placed above or below ground …They use soil infiltration and biogeochemical processes to decrease stormwater quantity and improve water quality, similar to rain gardens and green roofs” (page 5-7).For this location, a type known as a flow through planter would be used, which would allow the runoff to flow through the planter and out though a weep hole onto the roof, where it would drain to the existing tree pit. The roof of the shed would be equipped with gutters on each side that would capture the runoff and send it to the planter below. Rain chains can be used to direct the flow, and they could be constructed by the students so that they capture and release the water in artful ways. Rocks would be installed at the two outfalls to prevent splashing.

The conceptual design is for an planter of concrete, wood or other materials to contain a well drained soil mix over a gravel drainage layer. During a rain event, once these layers become saturated, water will pond in the upper six inches of the planter. If the ponding limit is exceeded, water will flow through a weephole near the bottom of the face or one side of the planter. The planter as shown on the plan would be 3 feet high with a surface area of about 7 square feet. The overflow from this section would exit the planter through a small pipe set just above the ponding limit, which would be connected to the perforated pipe below. .

Flow through planter diagram

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MATERIALS

The container Materials for construction of the planter would vary according to the final design. Materials suitable for planter wall construction include stone, concrete, brick, clay, plastic, wood,or other durable material. Treated wood may leach toxic chemicals and contaminate stormwater, and should not be used.

Plants Vegetation selected for stormwater planters should be relatively self-sustaining and adaptable. Native plant species are recommended, and fertilizer and pesticide use should be avoided whenever possible. A list of recommended native plants can be found in Design Manual, Appendix H. Soil The growing medium in stormwater planters consists of organic soil medium. According to the Design Manual soils in the planter would meet the following specifications:

Growing media --a uniform mixture of 70% sand (100% passing the 1-inch sieve and 5% passing the No. 200 sieve) and 30% topsoil with an average of 5% organic material, such as compost or peat, free of stones, roots and woody debris and animal waste. Drainage layer-- clean sand with 100% passing the 1-inch sieve and 5% passing the No. 200 sieve. Growing medium should allow an infiltration rate of 2 inches per hour Other Materials Washed gravel for the drainage layer should allow an infiltration rate of 5 inches per hour. Filter fabric Overflow pipe

CONSTRUCTION STEPS

Planter: The construction steps would vary according to the final design.

Plan view of doll house roof and stormwater planter

Gutter sends water to rain chain

Rocks at outfall

Plants

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MAINTENANCE

Planters should be treated as a component of the landscaping, with routine attention including the occasional replacement of plants, mulching, weeding and thinning to maintain the desired appearance. The planter would be small and the plantings would require relatively low maintenance. Weeding and watering are essential in the first year and can be minimized with the use of a weed free mulch layer.

A regular and thorough inspection regime should be established so that the planter functions well. planters. Following construction, planters should be inspected after each storm event greater than 0.5 inches, and at least twice in the first six months. Subsequently, inspections should be conducted seasonally and after storm events equal to or greater than the 1-year storm event.

Since stormwater planters are not typically preceded by pre-treatment practices, the soil surface should be inspected for evidence of sediment build-up from the connected impervious surface and for surface ponding. Attention should be paid to additional seasonal maintenance needs as well as the first growing season. (Design Manual, page 5-105)

COST

The cost will depend on the types of materials used.

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SIZING COMPUTATIONS

The drainage area is the shed roof, is approximately 40 square feet. The surface area of the proposed planter is 7 square feet, which is in excess of the 6 square feet of surface area required to treat the WQv of 4 cubic feet.

Total Drainage Area 40 Ft2

Step 1: Calculate Water Quality Volume (WQv)

WQv = (P) (Rv) (A) / 12 P = 90% rainfall number = 1.3 inches

Rv = 0.05+0.009 (I), if Rv < 20%, use Rv = 20% 95% I = percent impervious of area draining to planter = 100% % of Total area that drains to planter 100% A = Area draining to practice = 40 Ft2

WQv = 4 Ft3

Step 2: Calculate required surface area:

Af = required surface area in sq ft = WQv*(df) / [k*(hf +df) (tf)] where: WQv = 4 ft3

df = depth of soil medium = 2.5 ft

k = hydraulic conductivity = 4 ft/day

hf = Average height of water above planter bed = 0.25 ft

tf = filter time (days) = 0.17 day

Af = Required surface area for planter 6 Ft2

2- ROOFTOP GARDEN RETROFITS: GREEN ROOF

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2-C GREEN ROOF

DESIGN

At the time that the waterproof roofing membrane needs to be replaced a green roof should be considered. It could be installed using one of the prefabricated systems available from various companies in the region. It would be visible from the building windows that face the courtyard and would be easily accessible for demonstration purposes and for maintenance. The simplest, least expensive system would be the low profile type known as an “extensive” green roof. It could be installed using prefabricated modules or rolls that include a light weight soil medium and short, hardy plants like sedums.

The first step for greening an existing roof is an assessment of the structure to determine the load bearing capacity. “Generally, green roofs weighing more than 17 pounds per square foot (saturated) require consultation with a structural engineer.”

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Stormwater treatment in green roofs occurs via evaporation, transpiration, and filtration, so the deeper the storage media and denser the plant the material the greater the benefits, and the heavier the load. Extensive green roofs systems, such as XeroFlor range from 8 to 24 pounds saturated weight per square foot. Other companies, such as Barrett have systems with minimum weights above 20 pounds per square foot. The prefabricated systems come in mats, rolls or trays.

Besides the load bearing capacity of the roof, other factors to consider in developing a final design in include stormwater management function, local wind and solar exposure, and aesthetic goals. As mentioned previously winds on the roof courtyard at Lincoln High School can be very strong and could result in uplift and depositing debris. To protect the new planting from wind erosion, erosion control matting can be used or densely vegetated mats embedded in a fibrous base can be placed on the soil, like sod.

Since the roof captures runoff from the roof above and not just the rain that falls directly on it, an outfall area and flowpath to the roof drains would need to be incorporated in the design. While drought tolerant plants would be used on the roof, irrigation would be necessary during establishment and periods of prolonged drought. A rain tank or additional rain barrels could be used to store water from the downspouts as described in the previous section.

5 Barr Engineering, 2003 in the Design Manual, p.5-93.

2- ROOFTOP GARDEN RETROFITS: GREEN ROOF

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MATERIALS

The general components of any green roof system include:

• a roof structure capable of supporting the weight of a green roof system

• a waterproofing barrier layer designed to protect the building and roof structure

• a drainage layer consisting of a porous media capable of water storage for plant uptake and storm

buffering

• a geosynthetic layer to prevent fine soil media from clogging the porous media soil with

appropriate characteristics to support selected green roof plants Soil medium

• plants with appropriate tolerance for regional climate variation, harsh rooftop conditions and

shallow rooting depths (NYS DEC SWMDM 5-86).

CONSTRUCTION STEPS

For any system, the first steps would be to inspect the underlying roof components and install edging as required. The specific construction steps would be determined by the final design. The steps shown below are for a roll type system. The basic installation steps for a mat or roll type green roof system would be as follows Install:

Root barrier

Drain Mat

Retention Fleece

Growing Medium

Vegetation Mat

http://www.glwi.uwm.edu/

Example profiles Roll out system (left); modular tray system (right).

2- ROOFTOP GARDEN RETROFITS: GREEN ROOF

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Fill in or redistribute displaced growing medium

Water thoroughly

MAINTENANCE CONSIDERATIONS

Green roof maintenance may include watering, fertilizing and weeding and is typically greatest in the first two years as plants become established. Roof drains should be cleared when soil substrate, vegetation or debris clog the drain inlet. Maintenance largely depends on the type of green roof system installed and the type of vegetation planted. Maintenance requirements in intensive systems are generally more costly and continuous, compared to extensive systems. The use of native vegetation is recommended to reduce plant maintenance in both extensive and intensive systems (Design Manual, page 5-94).

SIZING COMPUTATIONS FOR GREEN ROOF

The sizing computations for an extensive green roof with a 3 inch soil layer and 2” drainage layer are given below. The storage volume would exceed the water quality volume. The final design would determine the actual runoff reduction.

Roof area 8,200 ft2

WQv = (P)(Rv)(A)/12 where:

P = 90% rainfall number = 1.3 in Rv = 0.05+0.009 (I) = 0.05+0.009(100) = 0.95 0.95 I = the percentage of impervious area draining to site = 100% 100% A = area draining to practice = 8200 ft2 WQv = 843.9167 ft3

Step 2: Calculate the drainage layer and soil media storage volume:

where:

AGR = green roof surface area = 8,200 ft2 DSM = depth soil media = 0.25 ft DDL = depth drainage layer = 0.17 ft PSM = porosity of soil media = 0.2 PDL = porosity of drainage layer = 0.25 VSM = AGR x DSM x PSM 410 VDL = AGR x DDL x PDL 348.5 DP = ponding depth = 0.5 inches = 0.04 ft 0.04 ft Storage Volume =VSM+VDL+(DP x AGR) = 1086.5 ft3

3- PERMEABLE PAVING

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3 CONCEPT PLAN THREE: PERMEABLE PAVING IN TWO LOCATIONS

The permeable paving plans presented here would call for concrete pavers. While pervious asphalt and poured concrete are also available this plan considers two types of unit pavers. The water storage capacity of the reservoir for any of the materials could be sized the same for any of the surface materials. The two types of pavers discussed could be considered for either of the two locations.

Permeable Concrete Interlocking Pavers These pavers are for low speed traffic roads and parking lanes and large lots, sidewalks and plazas.

. 6500 sf parking lot was completed by North Carolina State University: Four different types of permeable pavement including: one pervious concrete section, one concrete grid paver with gaps filled with sand, and two sections of Permeable Interlocking Concrete Pavers (PICP) filled with pea gravel. The two types of PICP varied in gap size.

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PaveDrain®

The PaveDrain® permeable paver system is a recent introduction. Like the typical permeable concrete unit paver system, it allows runoff to flow through cracks between the units into the gravel base course, but the arched design allows for the elimination of the finer setting bed aggregrate,which may reduce the likelihood of clogging. The units are assembled into mats for easy installation, and the size of the mat can be customized. This would allow for a design where the mat is intended to be lifted periodically for cleaning a filter zone below.

6 http://greene.ces.ncsu.edu/content/Permeable+Pavement+Project-Kinston Accessed 10/4/2011.

PaveDrain® arched design (left) and installation of wired mats.

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EXISTING CONDITONS

SURFACE COVER/CONTRIBUTING AREA

North side -- maintenance area The proposed practice would be located at the low end of the by the athletic field gate, in front of the maintenance garage. As shown in the photos, the paving in this area is deteriorated near the catch basin inlets due to spills from trucks. West side –parking lot The existing parking area in the rear of the building includes an unpaved section with a gravel surface and a section for district vehicles that is paved with asphalt as are the driveway and delivery area. While all of these areas are potential candidates for conversion to permeable paving, the concept plan shows new paving on just the gravel area on the southwest corner. This parking area is flat, but abuts a steep slope that is eroding and needs to be retained.

Location for proposed paving. View east Location for proposed paving. View west.

Inlet Inlet

Figure Gravel parking lot in rear of building, view north. Figure Steep slope at west edge of lot

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SOILS AND TOPOGRAPHY

The Web Soil Survey Report of the areas where paving is proposed includes two soil types: Urban Land and Udorthents smoothed.

7 The Urban soil is mapped in directly north of the building in the paved area.

Areas north and to the west, including the parking area of interest, are mapped Udorthents smoothed, which is classified as Hydrological Soil Group A, a well drained soil suitable for infiltration practices. Soil tests would need to be performed to determine whether the infiltration rate is adequate for an installation without an underdrain. The soils on the steep slope adjacent to the parking area consist of UlD, Urban Land-Charlton-Chatfield Complex, hilly, very rocky. Charlton and Chatfiled are classified as B soils.

.

DESIGN –NORTH SIDE MAINTENANCE AREA

This location appears to be suitable for a paving plan that factors in the potential for occasional vehicle spills and dripping. The plan proposes permeable paving to replace approximately 4,000 SF of asphalt. The paving would not be installed directly next to the building foundation.

7 7 Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web

Soil Survey. Available online at http://websoilsurvey.nrcs.usda.gov/. Accessed [6/7/2011].

Concept Plan for Permeable paving on north side

Permeable paving

Drainage area (blue)

Locations of existing inlets to be capped

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A gravel base would be installed to depth required to accommodate the vehicle loading and to achieve the desired storage volume. This reservoir would hold the rain that falls directly onto the paving as well as runoff from the adjacent surfaces that flows to it. Soil infiltration tests would be required in order to develop a final design. The gravel reservoir can be sized larger for larger storm events to increase the benefits in reducing flooding. The example described in the discussion of sizing calculations, in the last section of the report, would have an 18” base. The option of installing a storage chamber below the surface could also be considered.

DESIGN – REAR PARKING

Approximately 20,000 of compacted gravel in the rear of the building would be replaced with permeable pavers. A retaining wall on the west side would be required. The option of installing storage chambers or a cistern for gray water use could also be considered.

Concept plan for permeable paving on rear parking lot

Permeable paving

Drainage area

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TYPICAL CONSTRUCTION STEPS

The constructions steps would follow specifications developed by a qualified professional and would vary with according to the type of permeable paver used. Typical construction steps are as follows:

Excavate to proposed depth and level the bottom of infiltration bed.

Place geotextile if required

Place sub base as required by final designInstall edge restraint

Place permeable interlocking pavers or paving mats

Place joint aggregate if required

MATERIALS

Typical manufacture’s specifications for permeable interlocking concrete pavers require the following materials, and as previously mentioned, the PaveDrain system would not require the granular base (setting bed).

Concrete pavers

Granular subbase

Granular base

Bedding and void opening aggregates

Edge restraints

Underdrain if required

Geotextile fabric (optional)

MAINTENANCE CONSIDERATIONS

Two excellent fact sheets on permeable and porous paving are available from the NC State University Stormwater Engineering Group at http://www.bae.ncsu.edu/stormwater/pubs.htm:

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Research Update and Design Implications

Maintaining Permeable Pavements

The paving should be kept clean of debris. Vacuum sweep as needed. Upland and adjacent areas should be kept mowed and bare areas should be seeded.

COST INFORMATION

According to the PaveDrain® website: Depending on location and project size a conservative installed cost of the PaveDrain System is $10-11 per SF. This typically includes an installed 6 - 12" layer of clear stone (#3, #57 (TBD) and 1-inch of #8). The installation of the PaveDrain blocks or mats will be around $2.00- $2.50 per SF. The materials cost will be $5.00-$6.00/Sft. Delivery will add $0.50-$1.00 per SF depending on the distance to the jobsite. Color blocks adds ± $1 per SF.

9

8 Urban Waterways, NC State University and A&T State University Cooperative Extension.2011.

9 http://www.pavedrain.com/faqs.php (accessed 11/9/2011).

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SIZING COMPUTATIONS FOR PERMEABLE PAVING ON NORTH SIDE

The drainage area includes lawn and the asphalt. The calculations below address the runoff from the impervious surfaces, or about half of the total drainage area. For the proposed 4,000 ft2

of paving with a

reservoir (trench depth) of 18”, the surface area required for the permeable paving would be 1,490 Ft2. If

the goal is simply to capture and treat the WQv, the amount of permeable paving could be reduced, but given the goal to reduce flooding; converting this whole area to permeable paving would be recommended. The storage volume of 894 Ft3

could be increased by creating a deeper trench, and the

option of installing storage chambers below of the paving could be considered.

Total Drainage Area 33000 Ft2

Available Surface Area 4000 Ft2

Step 1: Calculate Water Quality Volume (WQv)

WQv = (P) (Rv) (A) / 12

P = 90% rainfall number = 1.3 inches Rv = 0.05+0.009 (I), if Rv < 20%, use Rv = 20% 50% I = percent impervious of area draining to practice = 50% % of Total area that drains to practice 100%

A = Area draining to practice = 16500 Ft2

WQv = 893.8 Ft3

Step 2: Calculate required surface area for pavement:

Ap = WQv / n x dt

where n = assumed porosity 0.4 dt =trench depth 1.5 ft

AP= 1490 Ft2

OR

Step 2: Calculate the available storage volume in the storage reservoir:

Storage Volume = Ap*n*dt

where:

n = assumed porosity = 0.4 dt = gravel bed/reservoir depth = 1.5 Ft Reservoir Storage Volume = 893.75 Ft3

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SIZING COMPUTATIONS FOR PERMEABLE PAVING ON REAR PARKING

For the proposed 20,000 ft2 of paving with a reservoir (trench depth) of 18”, the surface area required for

the permeable paving would be 8,233Ft2. If the goal is simply to capture and treat the WQv, the amount of

permeable paving could be reduced, but given the goal to reduce flooding; converting this whole area to permeable paving would be recommended. The storage volume of 4.940 Ft

3 could be increased by

creating a deeper trench, and the option of installing storage chambers or a below of the paving could be considered.

Total Drainage Area 48000 Ft2

Available Surface Area 20000 Ft2

Step 1: Calculate Water Quality Volume (WQv)

WQv = (P) (Rv) (A) / 12

P = 90% rainfall number = 1.3 inches

Rv = 0.05+0.009 (I), if Rv < 20%, use Rv = 20% 95%

I = percent impervious of area draining to practice = 100%

% of Total area that drains to practice 100%

A = Area draining to practice = 48000 Ft2

WQv = 4940.0 Ft3

Step 2: Calculate required surface area for pavement:

Ap = WQv / n x dt

where n = assumed porosity 0.4

dt =trench depth 1.5 ft

AP= 8233 Ft2

OR

Step 2: Calculate the available storage volume in the storage reservoir:

Storage Volume = Ap*n*dt

where:

n = assumed porosity = 0.4

dt = gravel bed/reservoir depth = 1.5 Ft

Reservoir Storage Volume = 4940 cf Concept Plan by Marcy Denker Mention of trade names and commercial enterprises is for information only and does not imply endorsement.