|
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: 1) Porous pavement
basketball courts; 2) Tree trench; and 3) Shallow grassy
basin, originally conceived as a rain garden/bioinfiltration area.
1)
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.
2)
Tree Trench
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.
3) Bioinfiltration Area
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.
|
|
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.
|
|
Allison A. Lee
Project
Engineer
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
610-734-7635
www.upperdarby.org |
