85 - Long-term and Design Rainfall-Runoff Simulations of Infiltration Swales along Alabama Roads

With the rapid development of urbanization, the expansion and renovation of urban roads face the challenges of stormwater management. Traditional road design and construction methods substantially alter the hydrological response of urban areas to rainfall events, leading to increased runoff and/or flooding. Therefore, low-impact development (LID) emerged as a design strategy to improve urban road systems and reduce adverse impacts by promoting sustainable stormwater management. This study uses the EPA Stormwater Management Model (SWMM) to simulate and analyze the impact of infiltration swales along roads for the reduction of surface runoff under design rainfall and long-term rainfall events. SWMM and CivilStorm were used to model the hydrologic performance of a possible infiltration swale configuration that may be designed for an Alabama highway. These infiltration swales were designed using 95th percentile daily rainfall and the Alabama Department of Transportation (ALDOT) small storm hydrology method. The four-layer infiltration swales were approximated and simulated using SWMM’s three-layer bio-retention cell LID control module. This study focused on simulating and analyzing the impact of changing the conductivity of the soil layer to evaluate the efficiency of infiltration swales in reducing surface runoff by modifying the combinations of two types of top soils in the soil layer. The National Stormwater Calculator was used to obtain land use characteristics, soil type, and long-term rainfall data in the study area for SWMM and CivilStorm model development. The results show that infiltration swales can effectively reduce the runoff volume. This research helps practitioners better understand the performance and benefits of infiltration swales over a period of 15-year historical rainfall events. Long-term performance simulations provide better guidance for urban planners and engineers so that infiltration swales along roads can provide maximum efficiency and will continue to play a key role in urban development planning and provide new possibilities for sustainable urban development.