Washington Street West watershed - City of Champaign

Draft ReportWest Washington Street Watershed Master Plan5.6 MODEL CALIBRATIONFigure 5-4Problem Area Map – West Washington Street Drainage AreaModel calibration was performed to test a physically-based model (i.e. XP-SWMM) againstobserved flooding conditions. The calibration exercise is used to adjust the model in order toprovide a model approximation to observations at the West Washington Street and North RussellStreet intersection. In a hydrologic and hydraulic model, the adjustments typically made are to:1) percent impervious; 2) sub-catchment slope (time to peak flow); 3) sub-catchment width, and4) infiltration parameters (soil infiltration rate). In the case of West Washington Street modelcalibration, the only adjustments made were to the percent impervious variable.The flow rate and tailwater elevation from the Copper Slough XP-SWMM model and the knownflooding along the West Washington Street corridor were the only variables that were availablefor the calibration process. The calibrated XP-SWMM model approximated the observedflooding depth near the West Washington Street and North Russell Street intersection (based onCity staff observations).The Copper Slough XP-SWMM model uses five subbasins to represent the drainage area of theWest Washington Street watershed and was developed for floodplain and primary drainageanalysis. It is therefore more applicable to larger wet weather events. The Copper Slough modeluses the SCS method as the infiltration calculation method and employs other parameters thatrepresent medium density residential land usage to develop a drainage model that estimatesobserved flows in the Copper Slough.September 20095-10Clark Dietz, Inc.