Submitted to: Journal Hydrologic Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/1/2006
Publication Date: 3/1/2007
Citation: Van Liew, M.W., Veith, T.L., Bosch, D.D., Arnold, J.G. 2007. Suitability of SWAT for the Conservation Effects Assessment Project: Comparison on USDA Agricultural Research Service Watersheds. Journal Hydrologic Engineering. 12:(2)173-189. Interpretive Summary: It is widely assumed that conservation programs developed and implemented by the U.S. Department of Agricultural have improved the water quality in many agricultural watersheds across the U.S. However, the degree to which these watersheds have been improved is largely unknown. The US Department of Agriculture’s (USDA) Conservation Effects Assessment Project (CEAP) was designed to better quantify this impact and to provide guidance for future programs. As part of this effort, a rigorous examination of the suitability of the Soil and Water Assessment Tool (SWAT) watershed scale hydrologic simulation model was conducted using data from five Agricultural Research Service Watersheds covering a diverse range of geographic and hydrologic conditions. Based upon this examination, the model provided accurate simulations of hydrologic responses across a wide range in topographic, soils, and land use conditions. Results further indicated that SWAT may be better suited for CEAP investigations in wetter regions of the Eastern part of the United States that are predominantly cultivated than the dryer regions of the West that are more characteristically rangeland. These results will provide key guidance for future model applications within CEAP.
Technical Abstract: Recent interest in tracking environmental benefits of conservation practices on agricultural watersheds throughout the United States has led to the development of the US Department of Agriculture’s (USDA) Conservation Effects Assessment Project (CEAP). The purpose of CEAP is to assess environmental benefits derived from implementing various USDA conservation programs for cultivated, range, and irrigated lands. Watershed scale, hydrologic simulation models such as the Soil and Water Assessment Tool (SWAT) will be used to relate principal source areas of contaminants to transport paths and processes under a range in climatic, soils, topographic and land use conditions on agricultural watersheds. To better understand SWAT’s strengths and weaknesses, the model’s performance under a range of climatic, topographic, soils, and land use conditions was evaluated. Hydrologic responses were simulated on five USDA Agricultural Research Service watersheds that included Mahantango Creek Experimental Watershed in Pennsylvania and Reynolds Creek Experimental Watershed in Idaho in the northern part of the US, and Little River Experimental Watershed in Georgia, Little Washita River Experimental Watershed in Oklahoma, and Walnut Gulch Experimental Watershed in Arizona in the south. A newly developed autocalibration tool for the SWAT model was employed to calibrate eleven parameters that govern surface and subsurface response for the three southern watersheds, and an additional five parameters that govern the accumulation of snow and snowmelt runoff processes for the two northern watersheds. Based on a comparison of measured versus simulated average annual streamflow, SWAT exhibits an element of robustness in estimating hydrologic responses across a range in topographic, soils, and land use conditions. However, SWAT generally performed better on watersheds in more humid climates than in desert or semi-desert climates. The model may therefore be better suited for CEAP investigations in wetter regions of the Eastern part of the United States that are predominantly cultivated than the dryer regions of the West that are more characteristically rangeland.