Existing detention basins can be modified to provide greater hydrologic and water quality benefits. In designing a stormwater wetland, the goal is to modify the water flow to create a two-stage release during low flow periods, while not compromising the original design to control large storm outflow. To obtain maximum length of stay for low and medium flow storms, a series of meanders and gravel berms should be implemented, along with forebays at either inlet or outlet areas to capture sediment. Other goals include developing the site to be low maintenance and aesthetically pleasing.

An existing stormwater detention basin on Villanova University property has been converted into an extended detention wetland BMP (Center for Watershed Protection 1996) using the design concepts presented in the Pennsylvania Handbook of Best Management Practices for Developing Areas (PACD 1998). The stormwater wetland treats runoff from a 41 acre site that includes approximately 16 acres of impervious surface, that forms the headwaters of a watershed listed as medium priority on the degraded watershed list, and treats flows that impact a high priority stream segment on the 303(d) list.

In the design and construction of the extended detention wetland, multiple meanders and gravel berms were placed to maximize water storage. A sediment forebay was installed off-center to allow for sedimentation of small to medium size storms, but to be bypassed by larger storms, so that resedimentation does not occur. Multiple wetlands plants were planted throughout the site to allow for competitive selection and maximum nutrient uptake.

The site has been instrumented to collect flow and level data, as well as conductivity, dissolved oxygen, pH, and temperature measurements. Numerous presentations and tours have been conducted at the sight. An educational sign has been installed to enhance the learning experience. In November 2001, a statewide symposium was held at Villanova University, further showcasing the project. Research focusing on the pollutant removal and hydraulic performance of the stormwater wetlands is currently underway.