Comparison of Flow and Sediment Modeling Using SWAT and HSPF for Watersheds in the Illinois River Basin

The Illinois State Water Survey has been developing hydrologic and hydraulic models for watersheds in the Illinois River basin as part of the Illinois Rivers Decision Support System (ELRDSS). The hydrologic model is based on the U.S. Environmental Protection Agency's BASINS 3.1 modeling system. The Soil and Water Assessment Tool (SWAT) and Hydrologic Simulation Program — Fortran (HSPF), which are part of the BASINS system, were used to simulate the hydrology of watersheds in the Illinois River basin. Both SWAT and HSPF are comprehensive watershed models that also have the capability to simulate sediment transport. Based on the topographic, and hydrographic, land use, and soil types data, hydrologic models (SWAT and HSPF) were developed for the Court Creek watershed. The Court Creek watershed was divided into 35 subwatersheds and 346 HRUs. Two outlets specified in the models correspond to the streamflow gaging/sediment monitoring stations in the Court Creek watershed. Both models use the same precipitation and temperature data, and the potential evapotranspiration (PEVT), potential surface evaporation (EVAP), and other climate data. The simulation flow and sediments from the HSPF and SWAT models were compared graphically and statistically. Overall relative errors of simulated flow to the observed flow are –0.2 and 3.8% for HSPF and SWAT, respectively, and the relative errors of sediment load are –15 and –47%, respectively. Based on the correlation and the Nash-Sutcliffe Efficiency coefficients of simulated flows, the HSPF model outperformed the SWAT model for daily and monthly flow. However, the models performed almost equally well on the annual average. As for the suspended sediment load, the HSPF model performed slightly better than the SWAT model.