Comparison of AnnAGNPS and SWAT model simulation results in USDA-CEAP agricultural watersheds in south-central Kansas

This study was conducted under the USDA-Conservation Effects Assessment Project (CEAP) in the Cheney Lake watershed in south-central Kansas. The Cheney Lake watershed has been identified as ‘impaired waters’ under Section 303(d) of the Federal Clean Water Act for sediments and total phosphorus. The USDA-CEAP seeks to quantify environmental benefits of conservation programmes on water quality by monitoring and modelling. Two of the most widely used USDA watershed-scale models are Annualized AGricultural Non-Point Source (AnnAGNPS) and Soil and Water Assessment Tool (SWAT). The objectives of this study were to compare hydrology, sediment, and total phosphorus simulation results from AnnAGNPS and SWAT in separate calibration and validation watersheds. Models were calibrated in Red Rock Creek watershed and validated in Goose Creek watershed, both sub-watersheds of the Cheney Lake watershed. Forty-five months (January 1997 to September 2000) of monthly measured flow and water quality data were used to evaluate the two models. Both models generally provided from fair to very good correlation and model efficiency for simulating surface runoff and sediment yield during calibration and validation (correlation coefficient; R2, from 0Ð50 to 0Ð89, Nash Sutcliffe efficiency index, E, from 0Ð47 to 0Ð73, root mean square error, RMSE, from 0Ð25 to 0Ð45 m3 s 1 for flow, from 158 to 312 Mg for sediment yield). Total phosphorus predictions from calibration and validation of SWAT indicated good correlation and model efficiency (R2 from 0Ð60 to 0Ð70, E from 0Ð63 to 0Ð68) while total phosphorus predictions from validation of AnnAGNPS were from unsatisfactory to very good (R2 from 0Ð60 to 0Ð77, E from 2Ð38 to 0Ð32). The root mean square error–observations standard deviation ratio (RSR) was estimated as excellent (from 0Ð08 to 0Ð25) for the all model simulated parameters during the calibration and validation study. The percentage bias (PBIAS) of the model simulated parameters varied from unsatisfactory to excellent (from 128 to 3). This study determined SWAT to be the most appropriate model for this watershed based on calibration and validation results. Copyright  2008 John Wiley & Sons, Ltd.