Evaluation of the applicability of three sediment transport capacity equations on steep colluvial slopes and their modifications

Abstract Accurate estimations of the sediment transport capacity ( T c ) are essential for soil erosion modelling. However, the applicability of existing T c equations to colluvial soils with high steep slopes and high gravel content is limited. In this study, the variation of T c with shear stress ( τ ), unit stream power ( P ) and stream power ( ω ) is investigated for different slopes and flow discharge. We also evaluate the applicability of the Yalin, Govers and GUEST equations (based on τ , P and ω , respectively) for estimating T c on steep–slope colluvial deposits. Experiments were conducted using colluvial soil in a non‐erodible rill flume. The results reveal that T c follows a power function with τ and ω and a linear function with P . The regression results of the three hydrodynamic parameters and T c agree with the T c equation forms of the corresponding equations. The Yalin equation, developed based on gently sloping erodible bed conditions, simulates overall low T c values for steep sloping non‐erodible bed conditions (P.O. 0.5–2 = 42.8%). The accuracy is significantly improved by correcting the sediment transport coefficient K t (P.O. 0.5–2 = 100%). The accuracy of the Govers‐simulated T c values under steep slope conditions, based on gentle slope conditions, decreases with increasing slope gradient (P.O. 0.5–2 = 37.14%), which is attributed to the large amount of coarse‐grained sediment present in this study. Thus, we retained the original form of the equation and further improved its accuracy by adjusting the coefficients (P.O. 0.5–2 = 94.29%). As T c increases, the GUEST equation can accurately simulate T c . The accuracy is improved by calibrating the F ‐value (P.O. 0.5–2 = 100%). Using dimensional analysis, the equations built based on hydraulic conditions (excess current power, shear stress, flow velocity, etc.) and median particle size can accurately simulate T c values (P.O. 0.5–2 = 100%). These findings provide a basis for the development of erosion models for avalanche deposits on steep slopes.