EFFICACY OF SWMM APPLICATION

The storm-water management model (SWMM) is applied to a 10-sq-mi urbanized residential area. The application is intentionally constrained to a rather gross spatial scale (no modeling of storm sewer transport) in order to mimic anticipated regional modeling efforts. Three different levels of watershed spatial abstraction are investigated in concert with the impact of using two different parameters for model calibration (pervious depression storage and percent imperviousness) along with three separate calibration events. The calibrated SWMM model performed quite well at predicting both total runoff volume and peak flow rate. Successful application was most sensitive to calibration event selection, with the smallest event resulting in the worst overall performance. The importance of watershed conceptualization level was less significant, with no noticeable difference between the two highest abstraction levels. Use of percent imperviousness, as the single model calibration parameter, was generally more successful than adjustment of pervious depression storage. SWMM water-quality simulation was also quite acceptable, but with a consistent underestimation of in-stream total suspended solids concentrations.