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

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 ( T c ). To investigate the transport/detachment regimes of each particle size and their explanation for T c 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 ( T r s ) 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 T r s 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 T r s of each size class of particles on the gentle slope (8.7%, 17.6%) increased with the T r s of total sediments. In the case of the steep slope (27.6%), however, the T r s of fine silt and clay increased with a decrease in the T r s of the total sediment particles. Different prediction equations were established to simulate the T c s of sediments with different sizes in the two slope ranges ( R 2 > 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 T c in the future.