Evaluation of runoff, erosion, and phosphorus modeling system - SIMPLE

The purpose of this study was to evaluate the performance of Spatially Inte grated Models for Phosphorus Loading and Erosion (SIMPLE) in predicting run off volume, sediment loss, and phosphorus loading from two watersheds. The modeling system was applied to the 334 ha QOD subwatershed, part of the Owl Run watershed, located in Fauquier County, Virginia, and to the 2240 ha wa tershed, Battle Branch, located in Delaware County, Oklahoma. Simulation ru ns were conducted at cell and field scales, and simulation results were com pared with observed data. Runoff volume and dissolved phosphorus loading we re measured at the Battle Branch watershed. Runoff volume, sediment yield, and total phosphorus loading were measured at the QOD site. SIMPLE tended t o underestimate runoff volumes during the dormant period, from November to March. The comparison between observed and predicted dissolved phosphorus s howed better correlation than for observed and predicted total phosphorus l oading. Cell level simulations provided similar estimates of runoff volume and phosphorus loading when compared to field level simulations for both wa tersheds. However, observed sediment yields better compared with the values predicted from the cell level simulation when compared to field level simu lation. Finally, results of model evaluation indicated that SIMPLE's predic tive ability is acceptable for screening applications but not for site-spec ific quantitative predictions.