Effectiveness and Downstream Impacts of Stormwater Detention Ponds Required for Land Development

Abstract

It is widely recognized that land development, especially in urban areas, is responsible for significant changes in hydrological runoff characteristics. Stormwater detention is one of the most popular methods that are used in stormwater management and required for urban land development by many local management authorities. The stormwater detention aims to detain the extra runoff increased by land development and reduce the peak flows to pre-development or existing conditions. Many detention ponds are typically designed on site-by-site basis, but their watershed-wide performance and effectiveness cannot be assured. Some design policies not only require local reduction on peak discharge but also require approving no negative impacts on downstream locations at a watershed scale. Can we design detention ponds to achieve this goal? What are challenges and dilemma between the design policy and effectiveness of stormwater detention ponds? This study presents several case studies of detention pond design and evaluates effectiveness of the ponds on reducing peak discharges at various downstream locations. We investigated performances of the detention ponds located at upstream or downstream portion of the watershed and how watershed characteristics such as shape influence on the performance of the ponds. Stormwater detention ponds implemented at upstream portion of a watershed were found typically more effective in reducing negative impacts on downstream locations than at other locations.