Soil detachment capacity by rill flow for five typical loess soils on the Loess Plateau of China

Abstract

The loess region of China is one of the most heavily eroded areas in the world. Soil detachment capacity by rill flow (Dc) is a key parameter for quantifying intensity of rill erosion in many process-based erosion models. However, only a limited number of studies have been devoted to soil detachment capacity for the various types of loess soil such as is found on the Loess Plateau, where there is variation from south to north and in terms of soil particle size composition. The objectives of this study were (1) to discriminate differences in soil detachment capacity by rill flow (Dc) among five loess soils, (2) to investigate the relationship between Dc and hydrodynamic parameters, and the relationship between Dc and soil properties, and (3) to establish an equation to model soil detachment capacity by rill flow for the loess region. Soil detachment capacity by rill flow for five typical loess soils found on the Loess Plateau of China was investigated through a flume experiment by varying five flow discharges and five slope gradients. The results show that Dc of SM sandy loess is the largest with a mean of 2.2145 kg m−2 s−1, followed by YL clay loess, DB sandy loess, AS loess, and CW loess. Stream power is the best hydrodynamic parameter to describe the dynamic process of soil detachment capacity by rill flow for these five loess soils. Soil detachment capacity by rill flow was negatively correlated with soil cohesion and effective silt content (P < 0.05), while it was positively correlated with effective median soil particle size (P < 0.01) and effective sand content (P < 0.05). Soil detachment capacity by rill flow for various hydraulic and soil conditions in the loess region could be modeled using a quaternary power function of slope gradient, flow discharge, soil cohesion and effective median particle size (NSE = 0.96), or it could be modeled by a ternary power function which calculates the variation of soil detachment capacity with stream power, soil cohesion and effective median size (NSE = 0.96). The results of this study reveal the mechanism of soil detachment by rill flow and advance development of a physically-based rill erosion model. Future research should focus on the impact of effective particle size on Dc to ensure a full understanding of soil erosion processes.