A Comparison of SWAT and HSPF Models for Simulating Hydrologic and Water Quality Responses from an Urbanizing Watershed

A watershed model can be used to better understand the relationship between land use activities and hydrologic and water quality processes occurring within a watershed. Two different models, SWAT (Soil and Water Assessment Tool) and HSPF (Hydrologic Simulation ProgramFortran), were selected in this study to simulate stream flow, sediment, and nutrients loading from the Polecat Creek watershed in Virginia, which is a 12,048 ha in size. Stream flow and water quality data for the period of September 1996 to June 2000 were used for the calibrations of SWAT and HSPF. Data collected from October 1994 to December 1995 were used to validate the models. The outputs from the models were compared against monitored data at the watershed outlet and at several locations within the watershed. The results indicated that both models were generally able to simulate stream flow, sediment, and nutrients loading well during the simulation period on the Polecat Creek watershed. Considering differences in annual loads and the trend of monthly loads, HSPF simulated hydrology and water quality components more accurately than SWAT at all monitoring sites within the watershed. However, HSPF is less user-friendly than SWAT, due to numerous parameters to control and represent hydrologic cycle, sediment and nutrients transport.