Two-dimensional rainfall-runoff and soil erosion model on an irregularly rilled hillslope

Abstract

The spatial characteristics of rills and non-planar hillslope could dramatically alter the mechanisms of the hydrologic and geomorphic processes, which were usually neglected in previous studies. Based on a two-layer soil infiltration model, a two-dimensional (2D) diffusion wave model, and modified WEPP erosion modeling approaches, a 2D distributed hillslope runoff and soil erosion model was developed to account for these effects. The interrill and rill areas are distinguished based on the high resolution topographic data. The model is tested against experimental erosion data from a hillslope subjected to three successive rainfall events, resulting in irregular rill networks. Good agreements between the modeled and observed results are found in runoff depth, erosion and its spatial distribution. A sensitivity analysis was also performed for the related parameters and found that the sensitive parameters for interrill erosion are rainfall intensity and interrill erodibility factor, while the sensitive parameters for rill erosion are the rainfall intensity, Manning’s friction coefficient, rill erodibility factor and soil critical shear stress. Moreover, the role of the dendritic rill network and concave hillslope have been examined and both of them can greatly affect the overland flow routing and increase the rill erosion, which is not accounted for in previous models such as WEPP. These results are valuable for rainfall-runoff and soil erosion prediction on irregularly rilled hillslopes.