Optimizing urban stormwater control strategies and assessing aquifer recharge through drywells in an urban watershed

A coupled simulation-optimization model (SOM) is developed in this work that links the US Environmental Protection Agency’s Storm Water Management Model (SWMM) with a genetic algorithm. The SOM simulates rainfall-runoff processes in urban watersheds and optimizes the implementation of drywells (DWs), bio-retention cells (BCs), and permeable pavement (PP) for stormwater control and aquifer recharge in District 6 of Tehran Municipality, Iran. Feasible DWs are selected through site inspection and considering stormwater quality criteria to prevent aquifer contamination. This study compares the current rates of urban runoff and groundwater recharge (baseline scenario) with new stormwater management strategies, which were designed based on several levels of funding. Results show the highest rate of runoff reduction and infiltration, as well as the most cost-effective options, would be achieved when DWs are added to the combination of BCs and PP for stormwater management. The runoff reduction rate in the presence of DWs would rise by 11.7, 7.0, and 6.1% in comparison to their absence for 12-, 17-, and 22-million-dollar budget levels, respectively. Implementation of BCs and PP would cause infiltration of about 235, 274, and 279 thousand m³ for the three cited budget levels, while combining DWs with BCs and PP would increase infiltration by 19, 15.6, and 14% for the three levels of investment, respectively. These results demonstrate the benefits of using local nonfunctional wells and qanats to reduce peak flows, replenish urban aquifers, and improve the economic efficiency of urban stormwater management projects.