Stormwater quality calibration by SWMM : a case study in Northern Spain

This article presents an application of the Storm Water Management Model (SWMM) in order to predict the pollution in rainy weather in a combined sewer system catchment in Santander, Spain. Suspended solids (SS), chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) were measured at the exit of the catchment and these parameters were used for the calibration and validation of the model. The process of hydraulic and quality calibration is described and the values of the adjusted parameters are presented, comparing them with those obtained from other studies. The calibrated model simulated accurately the hydrograph's shape and the time of presentation of the peak flows. The accuracy of adjustment of the volume was 96%. As for the quality validation, the accuracy of adjustment among the total simulated loads of SS, COD and TKN, and those measured at the end of the rainfall events were 93, 95 and 78% respectively, confirming the accurate confirming the relative accuracy of the model in the prediction mode. The phenomenon of the first flush was analysed, and it was determined that 65, 57 and 54% of the polluting loads of COD, SS and TKN respectively, were swept along by the first 30% of the volume in the rainfall events used for the calibration of the model.