The United States will spend billions of dollars over the next couple of decades to upgrade its water infrastructure. Municipalities rely heavily on software such as the USEPA’s storm water management model (SWMM) to simulate stormwater and wastewater infrastructure performance as an enhanced decision-making tool. As such, the accuracy of SWMM should be rigorously analyzed to ensure adequate model performance.
The main objective of this study was to quantify how accurately SWMM v5.1.10 simulates the hydraulic activity of previously monitored low impact development storm control measures. Model performance was evaluated by mathematically comparing empirical data to model results using a multi-event, multi-objective calibration method. The calibration methodology utilized PEST software, a parameter estimation tool, to determine unmeasured hydraulic parameters for SWMM’s low impact development modules. The calibrated LID modules had a range 0.65-0.94 Nash-Sutcliffe efficiencies and 0.67-0.97 correlation ratios. While this study led to several model improvement recommendations, SWMM’s most severe limitation is that it does not model lateral exfiltration of water out of the storage layer of an infiltration trench. Nevertheless, SWMM can often successfully simulate eight of the nine LIDs’ performance that were considered, given accurate model configuration, parameter measurement and model calibration to site-specific hydraulic data.
Michelle Simon is the associate director of science for the Water Systems Division of the Office of Research and Development for the U.S. Environmental Protection Agency. She is the primary technical point of contact for the storm water management model (SWMM) and also works with other watershed models, such as the Stormwater Calculator, HSPF, KINEROS2, HEC and SWAT. She worked with HYDRUS and MODFLOW while working on EPA’s Superfund Sites. She holds a Ph.D. in evironmental science from The University of Arizona, an M.S. in chemical engineering from the Colorado School of Mines and a B.S. in chemical engineering from the University of Notre Dame.