Development and validation of the Texas Best Management Practice Evaluation Tool (TBET)

Abstract

Conservation planners need simple yet accurate tools to predict sediment and nutrient losses from agricultural fields to guide conservation practice implementation and increase cost-effectiveness. The Texas Best Management Practice Evaluation Tool (TBET), which serves as an input/output interpreter and vastly simplified interface for the Soil and Water Assessment Tool (SWAT), was developed to predict mean annual runoff, sediment, nitrogen (N), and phosphorus (P) losses from agricultural fields in Texas under a variety of management scenarios and conservation practices. The Texas Best Management Practice Evaluation Tool was developed to provide a scientific basis for decision making, evaluation, and reporting in state and federal conservation programs. A rigorous, data-intensive calibration and validation process was employed in TBET development. First, hydrology outputs were calibrated with basin scale streamflow data from 20 US Geological Survey sites. Then, runoff, sediment, total N, and total P outputs were calibrated and validated with measured field scale data (260+ site years). Even without calibration, TBET was able to make “good” to “very good” predictions of mean annual runoff and total P losses according to commonly applied model evaluation methods. Calibrated TBET predictions of sediment and total N losses were not as accurate but were still “satisfactory.” These much-improved results relative to those of often applied tools such as P Indices are very encouraging since the design goals of simple operation and accurate predictions for diverse Texas conditions with only readily available inputs were certainly met. Thus, TBET meets an important need by providing accurate, science-based estimates of conservation practice benefits at the field scale.