Calibrating SWMM on a Large Scale: Can the LID Control Editor in SWMM 5 accurately represent Low Impact Development in a Sewershed?

The Storm Water Management Model (SWMM) software is used to design and analyze runoff quantity and quality response to precipitation events, primarily in the urban or suburban landscape. Eight low impact development (LID) features were included in a recent update to SWMM, allowing users to evaluate the performance of proposed or built stormwater control measures (SCMs). Few studies have attempted to calibrate SWMM 5’s LID tools to actual hydrologic data. This is particularly the case when multiple LID features exist within the modeled watershed. Most previous SWMM LID studies have focused on a single bioretention system using short-term data sets to calibrate the model. In this study, over six years of hyetographs and resultant hydrographs were used to calibrate SWMM models for three sewersheds in Columbus, Ohio, USA. In each sewershed, data were collected before, during, and after the SCMs were installed as a part of Blueprint Columbus. Construction details were used to properly recreate bioretention cells in PC-SWMM, and simulated hydrographs were plotted alongside observed. The Sensitivity-based Radio Tuning Calibration tool (SRTC) in PC-SWMM was used to modify the models to statistically improve goodness-of-fit relative to observed data. Statistical analysis shows SWMM 5 LID controls provide improved correlation to observed data compared to LID modeling methods pre-update. The discussion will elaborate on the usefulness of the results to future SWMM users. Results from this study may add validity to SWMM 5 LID controls and may provide guidance for calibration of large SWMM modeling efforts at sewershed scales.