Estimating hydrologic budgets for three Illinois watersheds

It is important to simulate the major components of the hydrologic budget to determine the impacts of proposed land management, vegetative changes, groundwater withdrawals, and reservoir management on water supply and water quality. As acquisition of field data is costly and time consuming, models have been created to test various land use practices and their concomitant effects on the hydrologic budget of watersheds. To simulate such management scenarios realistically, a model should be able to simulate the individual components of the hydrologic budget. However, most field studies at the watershed scale attempt to measure only one component (e.g. total streamflow, evapotranspiration (ET), etc.) and are not suitable for validating individual components of a comprehensive model. A field study was completed in the 1950s to estimate several major hydrologic components including surface runoff, groundwater flow, groundwater ET, ET in the soil profile, groundwater recharge, and groundwater heights from measured data from three watersheds in Illinois. These data were used to validate a multicomponent water budget model called SWAT. Comparison of measured and predicted values demonstrated that each component of the model gave reasonable output and that the interaction among components was realistic. This fact should allow more realistic appraisal of various land use management practices on a basin-wide scale.