ARS | Publication request: Hydrologic calibration and validation of the Soil and Water Assessment Tool for the Leon River watershed

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2008
Publication Date: November 1, 2008
Citation: Rossi, C.G., Dybala, T.J., Moriasi, D.N., Arnold, J.G., Amonett, C., Marek, T. 2008. Hydrologic calibration and validation of the Soil and Water Assessment Tool for the Leon River watershed. Journal of Soil and Water Conservation. 63(6):533-541.

Interpretive Summary: In 2003, the Leon River watershed was selected as a Conservation Effects Assessment Project watershed due to its proximity to the Bosque watershed which has major water quality concerns. The Leon River watershed drains directly into Lake Belton, which is a main drinking waters supply for Central Texas residents. The Leon River watershed is an area with a high amount of dairy production and a need for proper waste disposal. By using the Soil and Water Assessment Tool (SWAT) model, different management scenarios can be conducted to identify possible solutions to manure management. This study identified that the SWAT model was able to predict the hydrology of the basin including the inputs from reservoirs, ponds and treatment facilities. Understanding and correctly simulating the water balance of the watershed allows for future studies on pollutants to be carried out as well as other environmental management scenarios.

Technical Abstract: The Leon River watershed (LRW), in central Texas, is a Conservation Effects Assessment Project (CEAP) designated benchmark and special emphasis watershed. The Soil and Water Assessment Tool (SWAT) water quality model is being used to assess point and non-point source pollution within this watershed. The model’s simulation accuracy is evaluated with hydrologic data collected from the Leon River watershed, which drains into Lake Belton, a main drinking water supply for Central Texas residents. This watershed represents an area impacted by a high density of dairy production and manure management. The objectives of this study are to calibrate and validate the SWAT version 2005 (SWAT2005) model in the LRW for flow and to estimate model uncertainties in model input and output using statistical criteria including the Nash-Sutcliffe efficiency (ENS) value, percent bias (PBIAS) and the root mean square error (RMSE)-standard deviation ratio (RSR). The SWAT version 2005 simulated runoff well (ENS between 0.65 and 0.75 - good) to very well (ENS greater than 0.75 - very good) as evidenced by statistical measures during both the calibration and validation simulations. The average magnitude of the simulated streamflow was much closer to the observed streamflow during the calibration period (PBIAS within 10 – very good) than during the validation period (PBIAS greater or equal to 25 – unsatisfactory), however this one stream gauge is not present in a dairy impacted area.