Effects of unsteady characteristics of sediment-laden overland flow on soil detachment rate

Abstract

Currently, experimental research is lacking on unsteady flow in the study of factors affecting the detachment capacity (Dr) of overland flow, which is critical for understanding soil erosion. This study analysed the response mechanism of Dr to the hydrodynamic characteristics of roll waves relative to a non-unstable sediment-laden overland flow (according to a gradually varied flow) using an indoor fixed bed test under five slope gradients, five flow rates and five sediment concentrations. Owing to the instability of the roll wave and its effect on the soil detachment-transport process, the Dr of the roll wave flow was larger than that of the gradually varied flow as a whole. Dr decreases with an increase in sediment content, but the downward trend is different with or without a roll wave; the Dr is more sensitive to changes in the slope when a roll wave exists. When no roll wave exists, the flow has a greater influence on the Dr. Sediment load improves the influence of flow on Dr under different flow conditions; under different experimental conditions, the flow velocity and water depth are positively correlated with the Dr. The specific energy can better fit Dr with roll waves, and the stream power can better predict the Dr under the two water flow conditions; by introducing the relative parameters, it was found that the detachment effect of the roll wave will decrease with the increase of the influence of the wave-current; the soil detachment prediction model of stream power and sediment concentration was constructed by introducing fluctuation influence parameters δ (represented by relative wave height), which has high reliability (R² > 0.8, N_SE > 0.7). The results showed that the effects of the altered flow state and sediment load significantly affected the hydrodynamic characteristics of the overland flow and the soil detachment rate.