HUDSON VALLEY REGIONAL COUNCIL

Transcription

1 PROJECT AREA: WARWICK/GREENWOOD LAKE HUDSON VALLEY REGIONAL COUNCIL 3 Washington Center, Newburgh NY Google Earth 2011 GREEN INFRASTRUCTURE CONCEPT PLAN FOR PINE ISLAND ELEMENTARY SCHOOL SITE Project type: School campus parking lot retrofit DECEMBER 2011 Proposed practices: 1- Bioretention 2- Tree planting

2 The following report describes a schematic landscape design proposal using green infrastructure practices for stormwater management. This plan is intended to give practical guidance for the owner, design professionals, contractors, and other interested parties to use in developing a final design. It is not intended to be used as a final design or for construction documents. OVERVIEW The Pine Island Elementary School (PIES) site is located in the hamlet of Pine Island in the Town of Warwick, NY, in the heart of the black dirt agricultural region. Much of this area is a low, flat floodplain in the Wallkill River watershed that was once known as the drowned lands, and most of it was drained many years ago for farmland. Pine Island is located in an upland area within this large floodplain and the PIES site is a high point in the hamlet. The Warwick Valley Central School District decided to close this elementary school to address budget challenges and it was closed as a school earlier in As of this writing (Dec. 2011), the future plans for this site are unknown (part of the building is currently leased to a local church.) Working with Ed Sattler, an environmental science teacher at the district s High School who was at the time on special assignment working on an Environment, Conservation and Energy Education Demonstration project for the whole school district, we surveyed the PIES site in 2010 for green infrastructure planning opportunities. The proposed GI plan for this site, as detailed below, includes installation of a bioretention area in an open lawn area at the northern end of the lower parking lot, where an existing catch basin can potentially be utilized as part of designing an overflow system. The proposed plan also includes planting trees on the uphill (east) side of this lower lot. This concept plan shows two practices along the parking lot on the north end of the site near School House Road. Bioretention garden Tree planting Potential benefits from implementing GI practices at this site, based on information provided by Mr. Sattler, include the potential to mitigate flooding of nearby properties downstream, which could be receiving some runoff from the PIES site (we have not evaluated runoff patterns in the area, except for a cursory evaluation of the PIES site itself and the immediately adjacent roadside ditch, and it is unknown whether or how much the site is contributing to runoff that s reaching any other property.) The trees that are proposed near the parking lot would be roughly on the east side of this lot, so they could provide shade for parked cars. There is some minor erosion in the roadside swale downhill of the lower parking lot and the proposed GI practices may help to mitigate this. Implementing GI at this site can also potentially provide a useful education and demonstration site on a public property in an region where flooding is a chronic issue, though it s probably not feasible that this or any other site-scale GI project can mitigate the kind of larger-scale floods that are a major focus of concern in and around the Pine Island community. There are additional opportunities for implementing GI practices at the PIES site that were identified during the site evaluation but which are not discussed in more detail in this report. These practices deserve further consideration for their potential to reduce runoff and erosion on parts of the site and downhill of the site. Specific opportunities include several locations along the north side of the upper parking lot where runoff could be routed out of the lot and onto adjacent lawn areas. At one location near the uphill end of this lot, shown in the photo below, the asphalt curb has been damaged so there is already, in effect, a curb cut. Farther downhill along the same side of the upper parking lot, there s an opportunity to add a curb cut and retrofit an existing catch basin inlet to route water onto the adjacent lawn. Appropriate GI practices for these locations may include rain gardens, bioretention and/or trees. Finally, pervious paving for some parts of the parking lots at the site can be considered. 2

3 LOCATION Street Address: 20 Schoolhouse Road, Pine Island NY Section 14, Block 3, Lot 3 OWNERSHIP Warwick Valley Central School District EXISTING CONDITIONS SURFACE COVER/CONTRIBUTING AREA This plan involves the lower parking lot at the Pine Island Elementary School and the lawn areas adjacent to it. The parking lot is approximately 9,700 square feet. The lawn area to the north where the rain garden is proposed is approximately 3,500 square feet. SOILS AND TOPOGRAPHY To the east a large hillside slopes toward the level of the lower parking lot. To the west of the parking lot the grade drops sharply to the swale and road below. The gentle slope on the east edge and uphill of the lot would be appropriate for tree planting. Approximately 80% of the parking lot drains to the inlet in the northwest corner. There is a gentle slope away from the lot to the north where the bioretention area is proposed and at least a 5 foot drop from that location to the swale below. The Web Soil Survey Report of the area indicates Mardin gravelly silt loam, 3 to 8 percent slopes 1 classified in hydrological soil group C. Actual soil conditions in the areas of the proposed practices would need to be determined through onsite testing. A bioretention garden in a C soil would require an underdrain, which would discharge to the swale. SOLAR EXPOSURE AND VEGETATION The area is fully exposed to the sun. There is low hedge along the west side of the parking lot and lawn the north and east. The shrub planting area to the west of the lot probably provides very little stormwater benefit and it might be appropriate to consider replacing shrubs with trees in this area for better runoff reduction. 1 Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Web Soil Survey. Available online at Accessed [6/22/2011]. 3

4 Figure 1 Parking lot in foreground, with school building in background, looking south at proposed tree planting location Figure 2 Parking lot lower corner looking west at proposed rain garden location with existing catch basin Figure 3 Potential location of another practice uphill Damaged curb near uphill end of upper parking lot, where additional evaluation can be conducted for routing runoff out of the parking lot into a green infrastructure practice. 4

5 Figure 4 Concept Plan (An 11x17 version of the plan is included at the end of the report.) 5

6 1- BIORETENTION GARDEN DESIGN The concept plan shows a 750 square foot bioretention garden on the north end of the parking lot that would receive runoff through a new curb cut by the existing inlet at the northwest corner. An infiltration test should be conducted. Given the C soil indicated on the survey, unless the site evaluation finds betterdrained soils, an underdrain would be installed to discharge to swale below. Water above the ponding limit would exit through an overflow device. Attractive stones would be placed along the inflow path to prevent washing out of the soil and mulch. Figure 5 Regrading to bypass inlet Orange County Community College rain garden installation (Photo courtesy of Kevin Sumner 2010 ) Figure 6 Example of bioretention garden for parking lot Photo: National Resource Conservation Service 6

7 Figure 7 : Bioretention design. Esign Manual, page CONSTRUCTION STEPS MATERIALS Excavate to the depth required by the final design Retrofit inlet and curb to channel runoff to garden (Rose Street) Backfill with layer of clean washed gravel Install underdrain Fill to required depth with soil mix Construct stone diaphragm Install plantings Apply mulch and stone PLANTS Plants with well-established root systems would be required in order to establish the garden quickly and effectively. Plants would be selected that are adaptable to wet and dry conditions, easy to maintain, and make an attractive contribution to the garden area overall. Native trees, shrubs, grasses, and herbaceous plants that grow in wetland and upland areas recommended by the New York State Department of Environmental Conservation can be found in Appendix H of the NYS Stormwater Design Manua 2010 (Design Manual). SOIL AND MULCH Components and proportions would be specified in the final design. Recommendations in the Design Manual (Appendix H, page 6 ) for bioretention area soils and mulch are as follows: 7

8 OTHER MATERIALS Planting Soil Bed Characteristics The characteristics of the soil for the bioretention facility are perhaps as important as the facility location, size, and treatment volume. The soil must be permeable enough to allow runoff to filter through the media, while having characteristics suitable to promote and sustain a robust vegetative cover crop. In addition, much of the nutrient pollutant uptake (nitrogen and phosphorus) is accomplished through adsorption and microbial activity within the soil profile. Therefore, the soils must balance soil chemistry and physical properties to support biotic communities above and below ground. The planting soil should be a sandy loam, loamy sand, loam (USDA), or a loam/sand mix (should contain a minimum 35 to 60% sand, by volume). The clay content for these soils should by less than 25% by volume. Soils should fall within the SM, or ML classifications of the Unified Soil Classification System (USCS). A permeability of at least 1.0 feet per day (0.5"/hr) is required (a conservative value of 0.5 feet per day is used for design). The soil should be free of stones, stumps, roots, or other woody material over 1" in diameter. Brush or seeds from noxious weeds. Placement of the planting soil should be in lifts of 12 to 18", loosely compacted (tamped lightly with a dozer or backhoe bucket). Mulch Layer The mulch layer plays an important role in the performance of the bioretention system. The mulch layer helps maintain soil moisture and avoid surface sealing which reduces permeability. Mulch helps prevent erosion, and provides a micro-environment suitable for soil biota at the mulch/soil interface. It also serves as a pretreatment layer, trapping the finer sediments which remain suspended after the primary pretreatment. The mulch layer should be standard landscape style, single or double, shredded hardwood mulch or chips. The mulch layer should be well aged (stockpiled or stored for at least 12 months), uniform in color, and free of other materials, such as weed seeds, soil, roots, etc. The mulch should be applied to a maximum depth of three inches. Grass clippings should not be used as a mulch material. Concrete for curb and inlet retrofit Stone inflow path as required in final design Perforated pipe and overflow device MAINTENANCE Bioretention areas are intended to be 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. They should be treated as a component of the landscaping, with routine maintenance including the occasional replacement of plants, mulching, weeding and thinning to maintain the desired appearance. The gravel diaphragm requires regular maintenance to clean sediments and debris. COST 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. 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. The information 8

9 was compiled in 2006, so an increase about 10 percent should be factored in to account of cost of living increases. SIZING CALCULATIONS Surface area provided for Bioretention Area 750 ft 2 Total Drainage Area 7700 Ft 2 1: Calculate Water Quality Volume (WQv) WQv = (P) (Rv) (A) / 12 P = 90% rainfall number = 1.3 inches Rv = (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 = 7700 Ft 2 WQv = 792 Ft 3 2 Bioretention Details WQv*df/k(hf+df)(tf) df = depth of soil medium = 3 ft k = Coefficient of permeability of planting soils 0.5 ft/day hf = Average ponding depth (max depth/ ft tf = filter time (days) = 2 days 3. Calculation Af = Required surface area for bioretention 732 Ft 2 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 Warwick 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 = (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. 9

10 2- 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 runoff reduction and stormwater management functions, trees can provide many other benefits including shading and cooling, buffering wind and noise, purifying air and beautification. DESIGN Trees Four large trees are indicated on the plan along the east side of the parking lot within 10 feet from the edge of the pavement and would and eventually cast shade on it. (According to the DEC Manual only the trees within ten feet of the paving would qualify for runoff reduction credit). Three more are shown on the east side of the bioretention garden for added aesthetic appeal and other benefits. The trees would provide shade in the earlier part of the day and longer as they mature and their broad canopies extend out over the parking lot. A variety of tree species should be selected based on a careful analysis of the site. 2 The soil volume is adequate for trees with mature canopies of 50 feet or more. 3 To maximize stormwater management functions, tree species with a large mature canopy size and a high Leaf Area Index (LAI) should be selected. The LAI of a tree represents the relative surface area of leaves and branches. The LAI is important in terms of potential for trapping small rainfall events and thus potential for reduction of storm water runoff. LAI is also an important factor in a tree s ability to yield various benefits of air pollution reduction. Values for LAI for various common tree species are currently under development. 4 Soil and Soil Amendments: Plant selection and site preparation would be based on soil conditions revealed in the site assessment, including drainage, ph range, compaction levels, texture and other factors. Mulch An organic mulch layer would be provided around the trees. The mulch would provide multiple benefits related to the soil, protect against damage from mowers and trimmers, and suppress weeds. CONSTRUCTION STEPS Amend soil as required by final design Plant trees Apply mulch MATERIALS Compost: as required in final design Deciduous Trees various species with mature canopy in the range 50 or more Mulch: Three inch layer in area at least 5 feet in diameter around the base of the tree (below the root flare). 3 See Appendix x for a fuller discussion methods for calculating soil volume. 4 Urban Watershed Forestry Manual,Part 3:.Urban Tree Planting Guide. Cappiella, Schueler, Tomlinson, Wright. Center for Watershed Protection and USDA Forest Service, Sept 2006, page

11 MAINTENANCE CONSIDERATIONS Well-prepared planting areas designed with appropriate plants and soils require routine maintenance. During the establishment period just after planting the 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 would include occasional pruning and replacements, twice yearly clean up and yearly application of mulch. A WORD ON COSTS 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. 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. The information was compiled in 2006, so an increase about 10 percent should be factored in to account of cost of living increases. In the Warwick area, the local engineering and planning firm Lehman & Getz P.C. has experience with designing and implementing bioretention and other GI practices and may be a good source of advice about local costs for this type of project. The Orange County Soil and Water Conservation District, which has designed a number of rain gardens, is another good source, and the Cornell Cooperative Extension of Orange County is actively involved in some related training and demonstration projects and may be a useful contact point as well. COMMUNITY INVOLVEMENT & RESOURCES The Town of Warwick, the Warwick Valley Central School District, and a number of local non-profit organizations have an active focus on environmental goals, sustainability, beautification, agriculture and gardening, making it a promising area for finding the resources and capacity for implementing innovative practices like green infrastructure. Organizations working in the community on related initiatives and that may be instrumental in helping to plan, implement, and maintain green infrastructure practices include the Sustainable Warwick citizens organization; several different organizations that focus on landscaping and beautification including Warwick in Bloom, the Warwick Valley Gardeners, and the Garden Club of Dutchess and Orange Counties; and the locally-based land trust, the Warwick Conservancy. The Pine Island Chamber of Commerce is a local organization that may be interested in helping. The Warwick Valley Central School District has an active agriculture program (perhaps the last of its kind in any school district in Orange County) and with the Town and Sustainable Warwick, the school district is leading a community initiative to implement energy efficiency measures in homes and other buildings. The involvement of some or all of these organizations will be an important asset for implementing and maintaining green infrastructure practices over time. Plan by Simon Gruber and Marcy Denker. Thanks to Michael Sweeton, Supervisor, Town of Warwick; and Ed Sattler, Matthew Ryan, and Peter Lyons Hall for their support and contributions. 11