The Coupling of WEPP and 3ST1D Numerical Models for Improved Estimation of Runoff and Sediment Yield at Watershed Scales

Abstract

One of the major problems in watershed hydrology and sedimentology is to accurately simulate the transport of water and sediment from their sources to the watershed outlet. Current numerical models have been extensively used to determine upland erosion, but their application is primarily limited to the field/hillslope scale without providing an estimation for the sediment delivery to the main channels. Along the same lines, hydrodynamic and sediment transport models of the in-stream channel processes have been developed assuming that the channel system is isolated from its surrounding hills. This lack of connectivity between the upland erosion and the in-stream channel processes introduces significant error in the water and sediment yield estimates along the channel network. The main objective of our study is to provide a modeling framework to evaluate transport of water and sediment from the fields to the main channels. To meet this objective, two numerical models will be coupled; the well established WEPP model, which is a continuous process-based upland erosion simulation model capable of accounting for the effects of crop rotation, and the one-dimensional 3ST1D model which is used to calculate flow and sediment transport within the channels. The main advantage of 3ST1D is that it can handle transcritical flows without violating the flow continuity equation, it is applicable for both cohesive and non-cohesive sediments and includes various formulas for determining the sediment transport capacity as well as incipient motion criteria. It is envisaged that the coupled model will improve water and sediment yield estimates at the watershed scale, thus making it possible to evaluate the efficiency of various erosion prevention Best Management Practices, currently being evaluated primarily at the hillslope scale.