A Modified Hydrology-Hydraulic Model to Simulate Surface-Subsurface Hydrologic Dynamics of Low Impact Development Practices in Urban Catchments

Abstract

Hydrologic regimes and their interactions with ecosystems have been greatly altered by urbanization and resulting land cover changes. Low impact development (LID) practices are effective in controlling surface runoff, remediating non-point source pollution, mimicking natural hydrologic processes and restoring water – ecosystem interactions. Storm Water Management Model (SWMM) is one hydrology – hydraulic model that has been widely used to evaluate the hydrologic and environmental benefits of LID practices in urban catchments. However, SWMM highly simplifies the simulation of groundwater system, and it even separates LID practices from groundwater system, making it difficult to evaluate the performance of LID practices in shallow groundwater conditions. This study modified the current SWMM by considering the interactions between LID practices and shallow groundwater. The modified model (called SWMM-LID-GW) was tested in an urban catchment with porous pavements and bioretention cells implemented in shallow groundwater. Long-term dynamics of LID underdrain flow, surface runoff and total hydrologic load of the catchment from both the current SWMM and SWMM-LID-GW were compared with field monitoring data. SWMM-LID-GW showed better performance in simulating the hydrologic performance of LID practices (i.e., underdrain flow) and the urban catchment (i.e., total hydrologic load) in shallow groundwater than the current SWMM. SWMM-LID-GW was further tested through a group of hypothetical case studies with various native soil types, rainfall patterns, and groundwater levels. SWMM-LID-GW showed improved performance over current SWMM for a wide range of conditions, proving it to be a versatile modeling tool to evaluate hydrologic performance of LID practices in shallow groundwater.