CONTINUOUS-TIME WATER AND SEDIMENT ROUTING MODEL FOR LARGE BASINS

Simulation models are needed to evaluate the impact of changes in land use and agricultural management on streamflow and sediment yields fro m watersheds and river basins. Current agricultural-management models are limited by spatial scale, and river-basin models do not simulate l and use and management adequately to evaluate management strategies. A model called ROTO (routing outputs to the outlet) was developed to es timate water and sediment yield on large basins (several thousand squa re miles). ROTO is a continuous model operating on a daily time step t hat accepts inputs from continuous-time soil-water balance models. Com ponents 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 s mall watershed, watershed, and river basin. At the small watershed sca le, ARS station G (17.7 kg(2)) at Riesel, Texas, is used for validatio n of water and sediment yields. White Rock Lake watershed (257 km(2)) near Dallas was simulated and model output was compared to USGS stream flow and reservoir sedimentation data. The Lower Colorado River basin was simulated and compared to measured USGS streamflow data to test th e model on a relatively large river basin (9,000 km(2)).