Evaluating Optimal Detention Pond Locations at a Watershed Scale

Structural BMPs like stormwater basins (detention and retention basins), wetlands, filter strips and grassland swales are extensively used as stormwater runoff controls. BMPs are often designed for peak flow reduction or pollution control or can be considered for dual purpose in that they provide both water quality and quantity benefits by relying upon storage allocation and key mechanisms of setting filtration, sorption, biodegradation and evapotranspiration. In spite of previous studies, there exists neither a methodology nor a generalized model for selecting, placing, and sizing BMP combinations that cost-effectively promotes achievement of treatment goals at larger spatial scales. This paper presents part of an ongoing research effort to develop a new, comprehensive decision support tool for watershed-scale BMP design. The current model is designed to identify detention pond sizes that best achieve target peak flow reduction criteria. It is developed by coupling the U.S. Department of Agriculture's (USDA) Soil and Water Assessment Tool (SWAT) and a genetic algorithm. The model is applied to Silver Creek watershed, a subbasin of the larger Lower Kaskaskia watershed in Illinois. The results show that detention ponds can be designed at a holistic, watershed scale to more effectively achieve peak flow reduction goals. Future work will focus on expansion of the model, which will also be disseminated through outreach workshops in portions of Illinois and surrounding states.