Experimental study on sheet erosion process of loess and its suitability of hydraulic parameters on gentle slopes

Abstract

In order to determine erosion-limited conditions and the suitability of hydraulic parameters in sheet erosion of loess gentle slope, simulated rainfall test was used in this study, under condition of 60 mm/h rainfall intensity, 3 slopes (7.5°, 10°, 15°) and 2 slope lengths (5 m and 10 m), to verify the feasibility of sediment concentration as a characterization parameter to determine the erosion-limited conditions in the process of sheet erosion, and to propose an evaluation method to test the suitability of the relationship between hydraulic parameters and sediment yield. The test results showed that sheet erosion process could be divided into three erosion stages:transport-limited stage, detachment-limited stage Ⅰ and detachment-limited stage Ⅱ according to the change of sediment concentration with runoff, and the amount of erosion in detachment-limited stage Ⅰ was dominant absolutely. For the suitability of hydraulic parameters, both stream power and Reynolds number could well characterize the relationship with sediment yield, while flow shear stress and Froude number could not effectively reflect the relationship with sediment yield. In different erosion-limited stages, steam power and Reynolds number have different relationship with sediment yield. In the transport-limited stage and detachment-limited stage Ⅱ, steam power and Reynolds number showed exponential and linear positive correlation with sediment yield, respectively. In the detachment-limited stage Ⅰ, stream power and Reynolds number had a linear negative correlation with sediment yield, but the interaction was not unique, with different slope length and Reynolds number critical value. That is, in the transport-limited stage and detachment-limited stage Ⅱ, the relationship between stream power, the Reynolds number and the sediment yield was not affected by the effect of slope length; in the detachment-limited stage Ⅰ, the joint influence of slope length and the critical value of Reynolds number should be considered simultaneously. The results of this study can provide valuable information for a better understand of the complexity of sheet erosion process.