Hydrologic calibration and validation of the Soil and Water Assessment Tool for the Leon River watershed

The Leon River watershed which drains into Lake Belton, a primary drinking water supply for central Texas residents, is being affected by high-density daily production and manure management. Our objective was to apply the Soil and Water Assessment Tool (SWAT) model to evaluate its ability to simulate the hydrology of the Leon River watershed including water discharge from treatment facilities, reservoirs, and point sources. The 2005 version of SWAT (SWAT2005) was calibrated and verified using hydrologic data from the watershed. Runoff was simulated well (0.65 E(NS) <= 0.75 vertical bar good vertical bar) to very well (E(NS) > 0.75 vertical bar very good vertical bar) based on the Nash-Sutcliffe efficiency (E(NS)) value. Average streamflow simulations agreed well with observed values during the calibration phase (PBIAS < +/- 10 vertical bar very good vertical bar). but the validation period agreement (PBIAS >= +/-25 vertical bar unsatisfactory vertical bar) was less than desired because one of the five validates stream gauges fell into the unsatisfactory range. These results demonstrate the rigor needed to calibrate and validate simulation models for the Conservation Effects Assessment Project, and although additional studies are needed, they also confirm that SWAT2005 can be an effective tool for evaluating the hydrology within the Leon River watershed.