The objective of the retrofit project was to incorporate stormwater Best Management Practices (BMPs) into the recreational improvements being planned by the Township with an overall goal of improving water quality and water resource conditions in the Darby-Cobbs Creek watershed as well as controlling local flooding. The improvements planned included replacing a baseball field with three basketball courts and expanding the parking lot. Stormwater management practices were planned to coincide with site improvements and include a porous parking lot and subsurface infiltration bed, a stormwater tree trench and a rain garden/bioinfiltraton area which total together more than 11,000 cubic feet of stormwater storage.
To provide enhanced stormwater management for on site stormwater and runoff from an adjacent street, the Township implemented the following BMPs: Porous Pavement Basketball Courts, a Tree Trench, and a Shallow Grassy Basin (originally conceived as a rain garden/bioinfiltration area).
Porous Pavement Basketball Courts
The three new basketball courts are made of porous material, and lie above 9,000 cubic feet of storage volume within an infiltration bed. This system provides temporary storage for runoff generated by the courts and the adjacent alley north of the site. The infiltration system consists of a shallow stone-filled infiltration-storage bed (average depth of 18 inches) wrapped with geotextile fabric. Stormwater accumulating in the subsurface infiltration bed readily soaks into the surrounding earth, recharging local groundwater. The infiltration bed is designed with a positive overflow that ensures the bed fills to capacity before overflowing into the Township’s storm system. This positive overflow feature prevents stormwater from backing up or collecting in the porous asphalt. For a porous pavement diagram drawn by Cahill Associates, Inc. click here. For an infiltration bed diagram, also drawn by Cahill Associates, Inc. click here.
An existing macadam swale on the south edge of the site was removed and replaced with a tree trench to provide stormwater management to capture runoff from the adjacent parking area. This tree trench feature is composed of an elongated subsurface stone-filled infiltration bed lined with geotextile topped off with planting soil in order to support tree growth. This system also includes an 8” perforated pipe that allows for additional stormwater storage. Honey Locust trees were selected for this tree trench due to their tolerance for the site conditions. This system reduces runoff volumes entering the Township’s storm system by providing stormwater percolation. The trees and soil in the tree trench provide the important function of filtering out common stormwater runoff pollutants and absorbing stormwater runoff that subsequently evaporates. For a tree trench diagram, click here.
This BMP was designed as a rain garden but was constructed as a shallow grassy basin. The rain garden was designed as a shallow landscaped depression that would manage stormwater runoff by filling up to a maximum depth of 6 to 10 inches. The rain garden was designed to be planted with native species tolerant of both wet and dry conditions. The plants and soil in a rain garden have important functions filtering common stormwater runoff pollutants (sediment, nutrients, oil grease from passenger vehicles) and absorbing stormwater runoff, which subsequently evapotranspirates. The bioinfiltration area was designed to receive any overflow from the tree trench, which is conveyed to the area through a subsurface conveyance pipe. In the event stormwater accumulation exceeds 10 inches in depth, any excess is drained through a dome riser outlet and conveyed into the Township’s storm sewer system. This BMP was designed to reduce the volume of stormwater runoff by providing for infiltration, evaporation and evapotranspiration. Due to Township concerns about using plantings, the basin was planted with turf grass, rather than native plants. As such, it will be maintained as a conventional basin until an updated planting plan is developed and the basin is modified. For a bioretention diagram click here.
Watershed: Darby-Cobbs Creek
Second Ward Park & Playground is located at the intersection of Church Lane and Emerson Avenue in Upper Darby Township. The Park is approximately 2.8 acres, surrounded by high-density urban residential housing.
Darby-Cobbs Watershed Partnership
Delaware County Planning Department
Delaware County Conservation District
Darby Creek Valley Association
Philadelphia Water Department Office of Watersheds
Pennsylvania Environmental Council
Porous pavement’s construction and materials: approx. $31,000.
Subsurface storage/infiltration system under the three basketball courts: approx. $102,000.
Shallow infiltration basin construction: approx. $27,000. Tree trench construction and ten 2-2.5 inch caliper Honey Locust trees: approx. $44,000.
This project’s concept design, prepared by Cahill Associates, Inc., was provided through the Pennsylvania Environmental Council’s (PEC’s)Stormwater Retrofit Technical Assistance Program, which is funded through a Pennsylvania DEP Coastal Zone Management Program Grant and through the William Penn Foundation. Final Design & Implementation was funded by Upper Darby Township and construction was completed by a local firm. The Environmental Fund for Pennsylvania was also a co-sponsor.
Allison A. Lee
L. Fernando Baldivieso, P.E.
Township Engineer & Director of Public Works
Upper Darby Township
Department of Public Works
100 Garrett Road, Rm 301
Upper Darby, PA 19082