Transport/Detachment Regimes of Different Size Class Sediment Particles and Enlightenments for Transport Capacity Prediction for Rain-Induced Overland Flow Erosion

Abstract

The transport/detachment regimes of each particle size vary with size. Moreover, the changing transport/detachment regimes of sediments with size and their related mechanisms considerably affect sediment transport capacity (Tc). To investigate the transport/detachment regimes of each particle size and their explanation for Tc prediction, 27 simulated rainfall experiments were conducted under slope gradients of 8.7%, 17.6%, and 26.7% and rainfall intensities of 60, 90, and 120 mm h−1. The experimental soil was Cumulic Anthrosols, and the duration of each rainfall was 1 h. Results showed that for rain-induced overland flow erosion, the average transport ratios (Trs) of clay, fine silt, and coarse sand (<0.002, 0.002–0.02, and >0.25 mm, respectively) for rainfall, were greater than 1.0, and their erosion regimes were detachment-limited. The Trs of coarse silt and fine sand (0.02–0.05 mm and 0.05–0.25 mm, respectively) were less than 1.0, and their erosion regimes were transport-limited. The transport-/detachment-limited degree of each size class of particles, except for coarse sand, increased with the slope gradient, but slightly and complexly changed with rainfall intensity. The Trs of each size class of particles on the gentle slope (8.7%, 17.6%) increased with the Trs of total sediments. In the case of the steep slope (27.6%), however, the Trs of fine silt and clay increased with a decrease in the Trs of the total sediment particles. Different prediction equations were established to simulate the Tcs of sediments with different sizes in the two slope ranges (R2 > 0.823, p < 0.01). The findings will help to elucidate the selective transport mechanisms of all sizes of sediment particles and improve the prediction of Tc in the future.