Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2008
Publication Date: 12/15/2008
Citation: Heathman, G.C., Flanagan, D.C., Larose, M., Zuercher, B.W. 2008. Application of the Soil and Water Assessment Tool and Annualized Agricultural Non-Point Source Models in the St. Joseph River Watershed. Journal of Soil and Water Conservation. 63(6):552-568.
Interpretive Summary: In an effort to accomplish specific tasks required in the CEAP objectives, we evaluated the application of the SWAT and the AnnAGNPS models to estimate streamflow, sediment transport and atrazine losses in the 70,820 ha Cedar Creek Watershed (CCW). The CCW encompasses 25 percent of the St. Joseph River Watershed and is one of 14 CEAP benchmark watersheds. The SWAT and AnnAGNPS models were used to estimate streamflow and sediment losses from 1989-2005 and atrazine losses from 1996-2004 in the CCW. Both models were utilized in an uncalibrated mode to eliminate any bias due to parameter optimization. It was also critical that the datasets for both models be as consistent and as similar as possible for model comparisons. Results of this study indicate that uncalibrated, the performance of the SWAT model was numerically superior to that of AnnAGNPS in estimating streamflow with Ens efficiency values for SWAT ranging from 0.77 to 0.25, and values for AnnAGNPS ranging from 0.13 to –2.06, for monthly and annual streamflow, respectively. In terms of estimating sediment losses, AnnAGNPS predicted approximately 3.4 times greater sediment loss from the watershed than SWAT. Neither the uncalibrated SWAT nor AnnAGNPS models adequately simulated monthly atrazine concentrations. SWAT overpredicted concentrations by about 2.8 times, while the AnnAGNPS model greatly underpredicted monthly atrazine concentrations (simulated values were about 1/100th of measured). When considering the usability of each model, in terms of adequate technical and user documentation, model interfaces, input and output file descriptions, model technical support, etc., the SWAT model is currently much more advanced. Overall, results suggest that for model applications in CEAP at the watershed scale for this study, the use of the SWAT model would be preferable to AnnAGNPS in terms of overall model performance and usability of modeling technology.
Technical Abstract: This study evaluated the performance of two water quality models in accordance to specific tasks designated in the USDA Agricultural Research Service Conservation Effects Assessment Project. The Soil and Water Assessment Tool (SWAT) and the Annualized Agricultural Non-Point Source (AnnAGNPS) models were applied uncalibrated to the Cedar Creek watershed within the St. Joseph River watershed in northeastern Indiana to predict streamflow and atrazine losses. In order to ultimately assess the benefits of conservation practices in agricultural watersheds (which is one of the major goals of the Conservation Effects Assessment Project), proper application of the SWAT and AnnAGNPS models is essential including baseline comparisons made in an uncalibrated mode aimed at eliminating bias due to parameter optimization. Streamflow prediction results show that SWAT model performance was superior to AnnAGNPS, with SWAT model efficiency values ranging from 0.66 to 0.25 and AnnAGNPS model efficiency values ranging from 0.13 to -2.06 for monthly and annual streamflow, respectively. For uncalibrated conditions, neither model was able to adequately simulate atrazine loss concentrations. Overall results suggest that for Conservation Effects Assessment Project modeling applications at the Cedar Creek watershed scale in this study, the use of the SWAT model would be preferable to AnnAGNPS in terms of overall model performance and model support technology (e.g., model interface and documentation).