SIMULATING HYDROLOGY AND WATER QUALITY OF A CLAYPAN SOIL WATERSHED

Authors: Ghidey, Fessehaie; Sadler, Edward; Alberts, Edward; Lerch, Robert; BAFFAUT, CLAIRE - UNIVERSITY OF MISSOURI

Submitted to: ASAE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/16/2005
Publication Date: 7/17/2005
Citation: Ghidey, F., Sadler, E.J., Alberts, E.E., Lerch, R.N., Baffaut, C. 2005. Simulating hydrology and water quality of a claypan soil watershed. American Society of Agricultural Engineers Annual International Meeting. Paper No. 052084.

Interpretive Summary: Federal support of conservation programs aimed at enhancing environmental quality now exceeds $1 billion annually. To help quantify the benefits of these programs, the U.S. Department of Agriculture established the Conservation Effects Assessment Project (CEAP) in 2003. Twelve ARS watershed research locations were selected to assess the impact of conservation programs on water and soil quality. In Missouri, the Salt River basin that drains into Mark Twain Lake was identified for additional research because of known sediment and herbicide contamination problems. One major objective of CEAP is to develop a set of regional watershed assessment models to better understand and quantify the impact of conservation programs and their accompanying practices on water quality. In this study, we tested the ability of the Soil and Water Assessment Tool (SWAT) computer model to predict water quantity and quality from the Goodwater Creek watershed, a small sub-watershed within the Salt River basin where extensive hydrology and water quality research has been conducted since 1992. We found that the default model parameters did not accurately predict streamflow, erosion, or water quality of Goodwater Creek. Once calibrated to soil and hydrologic properties specific to Goodwater Creek watershed, SWAT accurately predicted monthly and annual streamflow from the outlet of the watershed. Future work with SWAT will focus on calibrating the sediment and chemical components of the model to ensure that it can be used to assess the impact of conservation practices on water quality throughout the Salt River basin. Results will be useful to policymakers and program managers to evaluate the impact of existing conservation programs on water quality and to develop new programs, if necessary, to meet water quality and other important environmental goals.

Technical Abstract: The Soil and Water Assessment Tool (SWAT) model was the primary model selected for use in the Conservation Effects Assessment Project-Watershed Assessment Study (CEAP-WAS). In this paper, the performance of SWAT in simulating streamflow, sediment yield, and atrazine loss from Goodwater Creek, a 72 km**2 watershed located in the claypan soil region of north-central Missouri, was evaluated. When the model was run using default parameters, it overestimated average annual streamflow by 32%, underestimated average annual sediment yield by 23%, and overestimated average annual atrazine loss by 8%. The Nash-Sutctliff coefficient (Ens) values were < 0.35 when annual estimated and measured values were compared. The model was calibrated for streamflow using data collected from 1992 through 1996. After calibration, the difference between measured and estimated average annual flow was < 5%, and the Ens values for annual and monthly simulation results were 0.90 and 0.85, respectively. After calibration, the model did not perform well in estimating streamflow on a daily basis (Ens=0.3). The calibrated model was also validated using data collected from 1997 through 2002 from the Goodwater Creek watershed and the performance of the model was good with Ens=0.88 for annual streamflow and Ens=0.68 for monthly streamflow. Overall, the annual and monthly streamflow predictions of the model were good. Future plans include (1) improving streamflow estimation on a daily basis, and (2) calibrating the sediment and pesticide components of the model.