Quantitative Assessment of Environmental Site Design Versus Traditional Storage-Based Stormwater Management: Impacts on Catchment Hydrology of Minebank Run, Baltimore, MD.

Environmental Site Design (ESD) is a stormwater management approach that prioritizes use of infiltration-based non-structural techniques to mimic the natural hydrologic cycle by reducing impervious surfaces, slowing runoff, and increasing infiltration. Traditional storage-based stormwater management is designed for flood control by quickly diverting runoff from developed areas. This study compared the effect of ESD and only storage-based stormwater management practices on the hydrology of an urban watershed in Baltimore County, Maryland, USA. Minebank Run is a 8.47 km 2 flashy urban stream with a catchment largely developed without stormwater management. A calibrated SWMM model was used to simulate changes in catchment hydrology resulting from ESD and detention basins over a 54-year period, from the onset of urbanization in 1948 to urbanization in 2001. The model results were analyzed by quantifying and comparing different hydrologic metrics to evaluate runoff quantity and flow variability. Results indicated that although storage ponds performed similarly to ESD in reducing annual maximum peak flows (43% versus 45% reduction, respectively), ESD reduced mean annual runoff coefficients significantly more than ponds (28% versus 2.7%, p < 0.0001). The Richards-Baker Index was reduced from 0.46 to 0.32 with the implementation of ESD, as compared to 0.36 with detention ponds. This study also tested the hypothesis that the impact of urbanization on the hydrology of the Minebank Run watershed would have been reduced if it had been developed with ESD. The results indicated that implementation of ESD would have reduced annual maximum peak flows by an average of 46%, annual mean runoff coefficients by 51%, and Richard Baker Index by 37%. The study provides quantitative insights into the performance of traditional and innovative stormwater management techniques at the catchment scale, illustrating the benefits of a combination of both infiltration practices and detention storage in reducing the hydrologic impacts of urbanization.