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Simulation models are needed to evaluate the impact of changes in land use and agricultural management on streamflow and sediment yields from watersheds and river basins. Current agricultural-management models are limited by spatial scale, and river-basin models do not simulate land use and management adequately to evaluate management strategies. A model called ROTO (routing outputs to the outlet) was developed to estimate water and sediment yield on large basins (several thousand square miles). ROTO is a continuous model operating on a daily time step that accepts inputs from continuous-time soil-water balance models. Components for water and sediment movement in channels and reservoirs are developed within a comprehensive basin-scale agricultural management model. The model is validated on three different spatial scales: the small watershed, watershed, and river basin. At the small watershed scale, ARS station G (17.7 kg 2 ) at Riesel, Texas, is used for validation of water and sediment yields. White Rock Lake watershed (257 km 2 ) near Dallas was simulated and model output was compared to USGS streamflow and reservoir sedimentation data. The Lower Colorado River basin was simulated and compared to measured USGS streamflow data to test the model on a relatively large river basin (9,000 km 2 ).
Arnold et al. (Wed,) studied this question.