HUDSON VALLEY REGIONAL COUNCIL 3 Washington Center, Newburgh NY

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1 PROJECT AREA: HYDE PARK HUDSON VALLEY REGIONAL COUNCIL 3 Washington Center, Newburgh NY Insert aerial site photo with streets labeled GREEN INFRASTRUCTURE CONCEPT PLAN FOR NORTH PARK ELEMENTARY SCHOOL-PARKING Project type: Parking Lot Drainage Retrofit October 2011 Proposed practices: Sheet Flow to Grass Filter Strip, Possible Tree Planting

2 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. LOCATION Street Address: 1593 Route 9G, Hyde Park Grid# OWNERSHIP The parcel is owned by the Hyde Park Central School District. 2

3 OVERVIEW This plan outlines a proposed retrofit to the southern parking area at North Park Elementary School. Currently the edge of the parking lot is eroding because of two factors: (1) drivers parallel parking partially on the grass and (2) concentrated flow from the northern half of the parking lot which has damaged a section of grass. The grassed area between the parking lot and the Crum Elbow Creek (approximately 200 feet away) could provide a grassed filter area, but the runoff should be converted to sheet flow for proper treatment. Creating a vegetated level spreader would capture runoff and allow it to sheet flow to the grass, which could be maintained as a filter strip that would provide primary treatment to capture sediment and automotive pollutants. A row of trees could also be included along the edge of the parking lot to provide shade for the parking area, as well as capturing some of the precipitation that would otherwise fall on the pavement. Background: North Park Elementary is part of the Hyde Park Central School District, which encompasses seven school campuses. In 2010 and 2011, students from North Park s first and second grades teamed up with students from the neighboring FDR High School to plant stream buffers along 700 feet of the Crum Elbow Creek, a class A stream that runs through the two campuses. Teachers and administrators alike have been extremely supportive of this effort to enhance students environmental education while involving them in a service project. The proposed improvements near the parking lot would work together with the newly enhanced stream buffer to provide complete filtration of runoff, protecting the Crum Elbow Creek. This plan has been discussed with the school district s Project Team led by Assistant Superintendent Wayne Kurlander. Several variations were proposed, including addition of a row of parking spaces made with permeable pavers. The school opted for the simplest solution of treating the existing runoff without major structural changes to the parking lot. North Park students have planted stream buffers along the Crum Elbow Creek. 2

4 SITE ASSESSMENT SURFACE COVER/CONTRIBUTING AREA The parking area is approximately 12,200 square feet. The southern half sheet flows to the grass, while the northern half (approximately 6,000 SF) concentrates at the central curb and flows in a stream toward the grass, causing an eroded area. Surface view of erosion 3

5 SOILS AND TOPOGRAPHY The topography of the site is fairly flat around the school and parking area, sloping down to the Crum Elbow creek and adjacent wetlands to the east and south. Soils are classified as Udorthents, meaning that the area has been filled in the past. Udorthents are considered hydrologic group A, meaning that they typically are highly permeable. HP-2 SOLAR AND WIND EXPOSURE The site has full exposure to sun and wind. VEGETATION Vegetation is mainly grass. SITE CONSTRAINTS The land is owned by the Hyde Park Central School District, and the site is easily accessible. Utilities would need to be investigated. During a recent construction project, underground utilities were marked out, and it appeared that a power cable runs under the western side of the parking lot. SHEET FLOW TO GRASS FILTER AREA The grassed lawn area can provide filtration of parking lot runoff if properly managed. The NYS Stormwater Management Design Manual 2010 (Design Manual), section 5.3.2, provides the guidelines for sheetflow to riparian buffers and filter strips. In this case, the parking area would drain to a grassed filter strip of approximately 150 foot width, and subsequently to a forested buffer of approximately 50 feet. SIZING CALCULATIONS The Design Manual specifies that the first ten feet of the filter should be no more than 2% slope, which this site meets. The maximum overall slope should be no more than 8%, and this site has a total drop of about 5-7%, based on examination of topographic maps. There is a specification that no more than 75 feet of impervious surface should contribute to the filter strip. In this case the parking lot is about 80 feet wide. However, in a retrofit scenario, this seems close enough. CONSTRUCTION STEPS & MATERIALS The filter strip will work best if an engineered level spreader is designed to even out the flow to the filter to prevent erosion as is currently occurring. The spreader should be designed to capture the concentrated flow from the north side of the parking lot, as well as the direct flow from the southern portion. The level spreader would convert these flows to an even sheet flow. The level spreader is an earthen structure constructed by shaping the soil. The NYS Standards and Specifications for Erosion Control should be consulted for design of a level spreader. The final design may include adding geotextile and/or gravel to stabilize the inlet. The area could be planted with native grasses or other vegetation. 4

6 MAINTENANCE CONSIDERATIONS HP-2 The level spreader and grass filter strip should be very low maintenance. The inlet to the spreader should be cleaned periodically. The grassed filter area may be converted to naturalized meadow, which would require less frequent maintenance than the current lawn. If it is maintained as lawn, compost amendments and aeration should be considered to maintain permeability of the soil. COST This practice would have a minimal cost. An engineered design would be needed for the level spreader, and fabric or gravel might be needed, as well as plant materials. The remaining cost would simply be labor, which might be provided by school employees. OPTIONAL ADD-ON: TREE PLANTING Addition of a row of trees or other plantings along the southern edge of the parking area would provide multiple benefits: By discouraging drivers from parking partially off the pavement, a major source of erosion would be eliminated. The trees could also provide shade for the parking area and intercept rainfall before it hits the pavement. They would also provide an aesthetic benefit. 5

7 SCHEMATIC PLAN Locate entry to level spreader at point of concentrated runoff. Additional runoff enters along south edge of parking lot. The diagram shows two optional additional features: (1) Tree planting along the edge of the parking lot, and (2) conversion of the grass lawn to a naturalized meadow for greater infiltration and ecosystem value. Plan created by: Peter Karis, RLA, Taconic Site Design & Landscape Architecture Emily Svenson, Mid-Hudson Ecological Services, LLC, on behalf of Hudson River Sloop Clearwater through the 604B Green Infrastructure Planning Project 6