Development of a Grid-Based Erosion Model for Large Catchments and Its Application to the Lushi Basin in China

摘要

Grid-based modeling is an effective approach for handling the spatial heterogeneity of basin characteristics, such as land use, soil, rainfall and topographic information. In this study, the grid-based BTOPMC model (Block-wise use of TOPMODEL together with the Muskingum-Cunge) was improved with an erosion module to estimate soil erosion and sediment outflow during storm events. Instead of assigning the grids with the unique erosion type, the model accounts for interrill erosion, rill erosion and channel erosion in each grid cell. In this study, the lumped interrill and rill erosions were simulated using the Universal Soil Loss Equation (USLE). Generally, USLE fails to predict the soil losses during hydrologic events, especially for arid region. The cause is due to the neglect of runoff in predicting the rainfall erosivity index. In this paper, the erosivity index in USLE is modified by relating the kinetic energy with rainfall and runoff processes. The modified USLE model is verified to reflect the hydrological processes more accurately and to be capable of estimating event soil losses. The sediment transport process is simulated using the river networks assumed by the BTOPMC model, which avoids the problems caused by the difference between the channel widths in the upstream area and the downstream area and enables the model to be applicable in simulating soil erosion and sediment outflow from a large river basin. GIS techniques have been utilized in the model to delineate the river network and extract the basin information from the DEM data. Through a case study in the Lushi basin, China, the proposed rainfall-runoff-erosion model got an overall satisfactory performance in simulating the river discharge and the sediment outflow.