Effects of Rock Fragment Cover on the Sediment Transport Capacity of Overland Flow

The reliable prediction of sediment transport capacity (Tc) is essential for soil erosion models. Although rock fragments are a common surface cover type, quantitative studies on their relationship with Tc are limited. Tc typically follows a power function with slope gradient (S) and flow discharge (q) under bare flumes, but varying exponents complicate practical application. This study aims to investigate the effect of rock fragment cover on Tc, explore the interactive effects of S, q, and cover on Tc, and ultimately develop a universal Tc prediction equation and assess its feasibility for different scenarios. Flume experiments on Tc with rock fragment cover have been conducted, and many existing Tc prediction equations have been reviewed. The results revealed that the effects of S and q on the relationship between rock fragment cover and Tc were minor and that the impact of rock fragment cover on the relationships of S and q with Tc was also not significant. Consequently, a new universal equation for Tc incorporating cover was developed. This equation featured fixed exponents of 1.66 for S and 1.22 for q and was applicable across various slope gradient, flow discharge, coverage and cover type conditions. Moreover, the impact of rock fragment cover on Tc reduction was significantly less than those of litter cover and stem basal cover (P < 0.05). Therefore, the role of rock fragments should be considered separately in soil erosion models. These findings could significantly advance the practical application of the Tc prediction equation.