Shelly Square Shopping Center Stormwater Management Techniques


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: an Underground Detention Basin, a Sediment Forebay, and a Wetland.

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Shelly Square

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.

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.

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.


County: Montgomery
Watershed: Perkiomen Creek

Shelly Square Shopping Center is a 80,000 square foot retail development and office park located in Harleysville at 2700 Shelly Road at the intersection of Rt. 63.


Montgomery County Conservation District
Spring Hill Realty
Reading Site Contractors (engineering and construction)




Bryan Hunsberger 
Spring Hill Realty, Inc.

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