Existing stormwater management facilities at Wild Goose Farm, a residential development, include three dry detention basins, a conveyance system comprised of a series of concrete swales, and a storm sewer system. The current system was designed to manage the stormwater rate control, but not to reduce water levels or improve on-site conditions. In fact, poor design and maintenance of current control structures has rendered these devices ineffective. All stormwater runoff is diverted directly into Goose Creek, and therefore water velocity and pollutants negatively impact the health of the creek.
If the following retrofit recommendations were carried out, stream bed and base-flow deterioration would be reversed, downstream flooding and overall pollution would be reduced, and the beauty of Wild Goose Farm would be enhanced.
Stormwater Best Management Practices (BMPs) include: Naturalization of the Three Basins with Outlet and Channel Replacement, Addition of Level Spreaders and Sediment Forebays, Cooperation of Homeowners Through a Front Yard/Backyard Rain Barrel or Rain Garden Program.
The success of these recommended stormwater management facilities depend on regular inspection and maintenance.
Naturalization of the Three Basins with Outlet and Channel Replacement
It is recommended that the Homeowner’s Association and proposed project partners retrofit the three detention basins. The first step in this process is the modification of outlet control structures. If the lowest orifice is removed and a higher drain is put in place, stormwater could be regularly detained. The advantages of detaining stormwater run-off include improved conditions for fauna and flora, evapotranspiration by vegetation, settlement and elimination of sediment and contaminants, and improved water recharge to natural underground aquifers.
Planting native plants that are tolerant of varying moisture conditions will morph the presently bare sod basins into beautiful meadow-like wetlands. The roots of planted grasses, shrubs and trees will cleanse water before it filters into Goose Creek or into underground aquifers. Concrete low-flow channels (like the one pictured) should be removed and re-vegetated with moisture-tolerant plants similar to the basin plantings. Because naturalized basins need only be mowed annually or bi-annually, the maintenance practice of weekly mowing would be no longer necessary. Inlets, outlets, and all structural components should be cleared of vegetation on a regular basis though, to avoid improper functioning.
Two of Wild Goose Farm’s three current basins could also benefit from the addition of meandering vegetated channels with check dams where the flow path within the basin would be extended. With such an improvement, better control rates would be obtained during heavy rainfall, plants would have more moisture in dry periods, and the overall vitality of the system would be improved. For a diagram of a typical bioretention basin, created by Cahill Associates, Inc. click here.
Addition of Level Spreaders and Sediment Forebays
Installing a level spreader would calm and diffuse water entering the basin through the in-flow point. This would leave plants undisturbed by water velocity, but would also be beneficial by equally distributing moisture to vegetation. Adding a sediment forebay, where sediment and debris are centralized within a “berm” is recommended so that they can be readily removed from the basins, which will reduce time for clean-up and maintenance. This forebay would capture and pre-treat stormwater run-off before its entry into the basin’s wetland area. A low-rise “berm” can be constructed out of rock, concrete, or excavated earth.
Cooperation of Homeowners through a Front yard/ Backyard Rain Barrel or Rain Garden Program
The site offers many opportunities for individual residents to install rain barrels or rain gardens on their properties to manage their own stormwater from roofs or driveways. The active participation of homeowners will reduce some of the pressure on community facilities to effectively manage all aggregate stormwater. The storage and reuse of stormwater is a management tool that can be very effective with the public’s participation.
Watershed: Chester Creek
Wild Goose Farm is a single family residential development composed of 50 single family homes on approximately 1/8-acre lots.
Concept Design was prepared by Borton-Lawson Engineering, as part of 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.
Pennsylvania Environmental Council SE Office
123 Chestnut Street, Suite 401
Philadelphia PA 19106