SWAT Literature Database for Peer-Reviewed Journal Articles

Title:Evaluation of the TBET Model for potential improvement of Southern P Indices 
Authors:Forsberg, A., D.E. Radcliffe, C.H. Bolster, A. Mittelstet, D.E. Storm and D. Osmond 
Journal:Journal of Environmental Quality 
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URL (non-DOI journals): 
Broad Application Category:pollutant only 
Primary Application Category:GIS interface, GIS utility, or other type of interface/utility 
Secondary Application Category:phosphorus cycling/loss and transport 
Watershed Description:18 total field sites located in Washington County, Arkansas, Putnam county, Georgia, or Henderson County, North Carolina, U.S. 
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Abstract:Due to a shortage of available phosphorus (P)-loss datasets, simulated data from an accurate quantitative P transport model could be used to evaluate a P Index. The objective of this study was to compare predictions from the Texas Best Management Practice Evaluation Tool (TBET) against measured P-loss data to determine whether the model could be used to improve P Indices in the southern region. Measured P-loss data from field-scale study sites in Arkansas, Georgia, and North Carolina were used to assess the accuracy of TBET for predicting fieldscale loss of P. We found that event-based predictions using an uncalibrated model were generally poor. Calibration improved runoff predictions and produced scatterplot regression lines that had slopes near one and intercepts near zero. However, TBET predictions of runoff met the performance criteria (Nash–Sutcliffe efficiency ³ 0.3, percent bias £ 35%, and mean absolute error £ 10 mm) in only one out of six comparisons: North Carolina during calibration. Sediment predictions were imprecise, and dissolved P predictions underestimated measured losses. In North Carolina, total P-loss predictions were reasonably accurate because TBET did a slightly better job of predicting sediment losses from cultivated land. In Arkansas and Georgia, where the experimental sites were in forage production, the underprediction of dissolved P led directly to the underpredictions of total P. We conclude that TBET cannot be used to improve southern P Indices, but a curve number approach could be incorporated into P Indices to improve runoff predictions.