Identifying sediment transport capacity of raindrop-impacted overland flow within transport-limited system of interrill erosion processes on steep loess hillslopes of China

Interrill erosion processes typically involve such scientific issues as detachment-limited and transport-limited erosion behaviour. An accurate estimation of the sediment transport capacity (Tc) by raindrop-impacted overland flow is critical for interrill erosion modelling and for evaluating sediment budgets under erosion-limiting conditions. Simulated rainfall experiments with rainfall intensities from 0.8 to 2.5 mm min−1 over a three-area soil pan with slope gradients from 12.7% to 46.6% were conducted to identify the transport-limited cases and determine Tc by raindrop-impacted overland flow within the transport-limited systems of interrill erosion processes. Results indicated that Tc increased as a power function of rainfall intensity and slope gradient (R2 = 0.84, NSE = 0.75), and Tc was more sensitive to rainfall intensity than to slope gradient. In terms of R2 and NSE, stream power was the key hydraulic parameter that influenced Tc among flow velocity (R2 = 0.64, NSE = 0.39), shear stress (R2 = 0.53, NSE = 0.23), stream power (R2 = 0.76, NSE = 0.52) and unit stream power (R2 = 0.49, NSE = 0.16). The addition of rainfall physical parameters in response equations of Tc in addition to hydraulic parameter, could improve an accuracy of Tc modelling. Stream power combined with rainfall kinetic energy can best describe the Tc of raindrop-impacted overland flow within the transport-limited system of interrill erosion processes by a power-exponent function (R2 = 0.90, NSE = 0.72). Rainfall kinetic energy can reduce the Darcy-Weisbach resistance coefficient of raindrop-impacted overland flow and thus benefit sediment transporting. This study provides another method for directly identifying the Tc of raindrop-impacted overland flow in interrill erosion processes on steep loess slopes, and points out that rainfall impacts should be particularly considered when studying Tc by raindrop-impacted overland flow.