Hydrologic Modeling of the Fox River Watershed Using SWAT2000: Model Development, Calibration, and Validation

Regional water-supply planning efforts in Illinois are attempting to better understand potential impacts of climate change on low flow hydrology and surface water availability for meeting increasing water use. For this purpose, models are being developed for selected priority watersheds to analyze hydrologic sensitivity to a range of climate scenarios. One of these watersheds is the Fox River watershed, which is located in southeastern Wisconsin and northeastern Illinois with a total watershed area of 2658 square miles. A suite of hydrologic models was developed for streamflow simulations in the Fox River watershed. The FORTRAN version of the USDA’s Soil and Water Assessment Tool (SWAT) and its ArcView interface (AVSWAT2000) were used in developing the hydrologic simulation models.The AVSWAT2000 was mainly used in preparing input data for watershed simulation. Hydrologic models were developed for three subwatersheds, designated as Subwatershed I, Subwatershed II, and Subwatershed III; a single model was also designed for the entire Fox River watershed. The development of subwatershed models serves two important purposes: (1) it ensures distributed parameter calibration, and (2) more observed data can be used during model parameter estimation. The hydrologic models developed in this study will be used to analyze potential impacts of various climate change scenarios on flows and surface water availability. In order to ensure the model’s ability in simulating the response in streamflow to various climate conditions, the hydrologic model was calibrated under two calibration scenarios representing drought and average conditions. This report presents the hydrologic model development for the Fox River watershed and calibration and validation of the model for streamflows. The report is divided into five sections. The first section is the introduction and the second section presents a brief description of the hydrologic model (SWAT) and the major hydrologic processes that the model is capable of simulating. The third section describes hydrologic modeling of the Fox River watershed, which includes the types of input data used and data processing involved. The fourth section describes calibration and validation of the hydrologic models developed, the automatic calibration method used, and the calibration procedure employed. This section also presents results of the model calibration and long-term model evaluations. Finally, the fifth section summarizes the hydrologic model development, calibration, and validation results.