Evaluating the role of low impact development recharge for sustainable groundwater resources

Abstract

Low impact development (LID) is an innovative ecological and landscaped based design framework that is used in urban planning to imitate pre-development hydrologic systems. LID is a new concept in stormwater management that is replacing conventional stormwater systems in urban environments due to its effectiveness in retaining large volume of stormwater runoff and treatment of water quality. Cities around the world are actively installing hundreds of LID Best Managed Practices (BMPs) without underdrains, which can enhance groundwater recharge to underlying aquifers. Previous research on LID recharge has focused on local and neighborhood scales and only a few studies have quantified LID recharge beneath individual BMPs. Given the widespread installation of LID, I hypothesized that the cumulative LID recharge at the watershed scale could have a significant effect on the groundwater budget, potentially increasing groundwater storage in urban aquifers. To test this hypothesis, I analyzed the discharge and LID recharge in the Lake Merced watershed. For this study, I used PCSWMM, a GIS based hydraulic model created by Computational Hydraulics International (CHI) that integrates the U.S EPA Storm Water Management Model (SWMM). Using PCSWMM, four models of the study area with different area coverage of LID (0%, 0.5%, 1% & 2% LID coverage) were created, compared and analyzed. Model outputs of discharge, stormwater inflow into LID, infiltration beneath LID (recharge), and recharge efficiency were created and analyzed. Results showed that despite 0.5% LID coverage model having the largest infiltration beneath the LID, it had the lowest recharge efficiency of all models and had the largest stormwater inflow and discharge. These results show that by increasing the %LID coverage, there is lower volume of stormwater flowing into LID, which ultimately increases the recharge efficiency.