Storm Event and Continuous Modeling of an Illinois Watershed to Evaluate Surface Water Supplies

Based on recent reviews of leading watershed-scale hydrologic and nonpoint-source pollution models, the long-term continuous model SWAT was selected to enhance with storm event simulation algorithms from a storm event model to be used as a source-water protection and assessment tool for small public water supply systems. This enhanced SWAT will simulate hydrology, soil erosion, and transport of sediment and agrochemicals during storm events with short time intervals (minutes or hours) to capture rapid changes, especially during severe events causing most of the environmental damages, in addition to long-term simulations with longer time intervals (days, months, and years) while studying long-term impacts. The 8,400 km2 Little Wabash River watershed in Illinois was selected for this study because of its favorable small drinking water supply and watershed attributes. Using multi-year period (1995-2002) of observed precipitation, stream flow, and concentrations of sediment and water quality data, the continuous model is being calibrated and validated. Established statistical indicators (coefficient of determination and Nash-Sutcliffe coefficient) are used to measure and improve model predictions. Using storm event rainfall and flow data at smaller (15 minute) time intervals, the storm event hydrology model is also being calibrated and validated. The calibrated and validated model will be used for both long-term and storm event water quantity and quality evaluations throughout the watershed, including at intakes of small public water supply systems under existing and alternative land use and management practices. Flow calibration results at an upstream station reveal that the storm event hydrology model with less parameter predicts more accurate flows, especially peak flows, than the continuous daily model.