Island topographies to reduce short-circuiting in stormwater detention ponds and treatment wetlands

Urban stormwater is an increasing environmental problem for cities worldwide. Many cities have turned to green infrastructure solutions, which provide water treatment and retention while also harnessing other ecosystem services. This study considered the design of detention ponds and treatment wetlands with the goal of improving hydraulic performance (specifically reducing short-circuiting) while also increasing habitat diversity. Fifty-four basin topographies, including a variety of islands and berms, were compared to an open and a traditional serpentine basin. Using scaled physical models the hydraulic performance of each design was evaluated using tracer studies to construct the residence time distribution and to visually observe the circulation pattern. In addition, the earthwork construction cost and habitat diversity index (based on the Shannon-Weaver entropy measure) were estimated at field scale. The results reveal multiple design options that improve hydraulic performance, relative to both the open and serpentine basins, and which represent a range of habit diversity and cost. General guidelines for optimal configurations are discussed.