GIS-based upland erosion modeling, geovisualization and grid size effects on erosion simulations with CASC2D-SED

The recent development of two-dimensional models for the simulation of upland erosion and sediment yield from watersheds facilitates the analysis of washload in rivers and assists in the planning of soil conservation systems. Process-based upland erosion models are affected by both the change in landscape representation and the change in the hydrological model.; The objectives of this research are to: (1) extend the development of the CASC2D-SED upland erosion; (2) couple the model time-series output grids with a GIS that will allow the geovisualization of sediment transport dynamics by size fraction and the spatial erosion and deposition patterns; and (3) investigate the effects of grid resolution on the simulated erosion rates.; The calibration and validation runs of CASC2D-SED show that the model appropriately predicts hydrographs and sediment graphs at the basin outlet and other internal locations. Washload is simulated to be transported through the system by streamflow with very little deposition, carried primarily in suspension while coarser fractions move as bed-material with local deposition. Sediment yields are predicted within ±50% of the observed data. Spatially, CASC2D-SED predicts areas of net erosion on steep slopes, depending on the land use and soil type. Zones of deposition were simulated in valley bottoms or forested areas. Geovisualization and time-series animation of the erosion dynamics and distribution of net erosion represents a form of model validation and facilitates model testing at internal locations.; The input grid cell size affected the CASC2D-SED erosion predictions. Equilibrium discharge, sediment yield and gross erosion decreased and at increasingly larger grid cell sizes. From the results of the calibration and validation runs of CASC2D-SED on Goodwin Creek, MS, it is concluded that a grid cell size smaller that 150-m should be used to identify regions vulnerable to erosion on a watershed for the implementation of a suitable erosion control measure. For the prediction of sediment delivery ratios closer to field observations, a grid size smaller than 90-m is preferable.