Application of SWAT to model the water balance of the Woady Yaloak River catchment, Australia

The widespread land use changes that are expected to occur across the Corangamite region in southwest Victoria, Australia, have the potential to significantly alter the water balance of catchments. Adoption of the Soil and Water Assessment Tool (SWAT), which is a long-term water balance model, as a tool for predicting land use change impacts on catchment water balance for the Corangamite region is currently being considered. This paper describes the initial application of SWAT to the Woady Yaloak River catchment, located within the Corangamite region, to carry out an evaluation of its abilities for simulating the long-term water balance dynamics of the catchment. The performance of the model for predicting runoff at annual and monthly time scales was found to be very good. The excessive recharge of the shallow aquifer that occurred during winter, despite the subsoil being relatively impermeable, ultimately contributed to overestimation of baseflow and underestimation of interflow. The actual evapotranspiration from hydrologic response units (HRU s) containing eucalyptus trees was significantly less than that from HRUs containing pasture, a problem attributed to the incorrect simulation of Leaf Area Index (LAI) and biomass by the model for mature stands of eucalyptus trees and also to assigning inadequate values for two parameters that directly influence evapotranspiration. SWAT has very good potential for being used as tool to study land use change impacts across the Corangamite region provided that several modifications are made to the model to overcome some of the shortcomings and deficiencies that were identified in this initial application.