Coupling community preferences with hydrologic evaluation of low impact development implementation in an urban watershed

Abstract

Stormwater runoff, and its associated pollutants, is a major problem in urban watersheds where the runoff is either channeled into surface water bodies or wastewater treatment plants. One emerging Best Management Practice (BMP) to control stormwater runoff is low impact development (LID). The EPA Stormwater Management Model (SWMM) was used to evaluate the hydrologic effectiveness at a watershed scale of five LID technologies (vegetated swales, bioretention cells, porous pavement, rain barrels and tree boxes) in an existing, typical urban watershed. As implementation focused on public transportation areas, hydrologic effectiveness of runoff reduction was assessed as a function of roadway length: and the impacts of LID implementation on traffic flow were modeled using VISSIM and TransCAD. Vegetated swales, the most cost effective option, captured 32% of the runoff with 100% roadway implementation. However, socio-economic factors limit potential mitigation implementation. Transportation modeling demonstrated negative impacts above 4 km of road length (16%), limiting runoff reduction to 2.5%, and non-roadway options such as rain barrels have limited hydrologic effectiveness. While porous pavement can be implemented without impacting transportation, cost is more prohibitive. Combinations of LID features, especially those that do not impact transportation, increase the amount of runoff mitigated. However, socio-economic considerations still limit runoff reduction at the watershed scale to ~15%, less than prior watershed-level evaluations. Our results demonstrate the need to implement LID approaches that account and plan for socio-economic considerations in addition to environmental factors.