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Spring Hill Realty designed a stormwater
management system for Shelly Square Shopping Center, completed in 2006, using a unique “stacked” approach. To provide enhanced management
for on-site stormwater runoff from the area’s impervious surfaces,
Spring Hill Realty implemented the following three Best Management
Practices: 1) Underground detention basin; 2) Sediment forebay;
and 3) Wetland.
1) Underground
Detention Basin
An underground detention basin catches rainwater from drains in the
parking lot and is located underneath the paved parking area in
front of the retail and office fronts. Rainwater is conveyed into the
detention basin via perforated pipes and stone trenches. Besides
filtering the stormwater, the basin detains stormwater during peak flow
rates. The basin controls the quantities of water released, thus
reducing water velocity and its negative implications. The detention
basin is designed to release the collected stormwater within 24
hours of a storm event.
2) Sediment Forebay
Overflow and un-infiltrated stormwater from the underground holding tank
are deflected through a sediment forebay located on the western side of
the development. Wild grasses grow on the upper
slopes of this forebay, and rocks at the pipes’ outlet allow for the dry
collection of sediment. The sediment forebay protects the adjacent
wetland, and ultimately Perkiomen Creek, from the sediment, oil, and
grease associated with parking lot runoff.
3) Wetland
The constructed wetland not only traps and purifies runoff as the third
step in the stormwater management process, but it also provides
functional wetland habitat for wildlife. The wetland acts as a final
guard to prevent Perkiomen Creek’s exposure to high velocity stormwater
flows and pollutants. The wetland mitigation area is adjacent to Perkiomen
Creek on the south end of the site.
A half foot of natural topsoil was set aside
during the construction of the wetland, and was resituated when native
wildflowers, bulrushes, sedges and
trees were planted. For a plant list click
here.
Water slowly flows through the wetland mitigation area, where the
remaining pollutants are trapped by the plants or are deposited for
future removal. A natural spring provides the wetland with fresh
groundwater, helping to sustain the wetland’s wildlife. Community response to the
project has been very positive, especially towards the landscaping of
the naturalized basin, and wildlife that has made the basin its home.
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