LAUSR

PurposeThis study aims to evaluate the relationship between loess soil-based sediment transport capacity and the most well-known and extensively used shear stress and unit stream power for different steep slopes. This study also determined the suitability of shear stress- and unit stream power-based transport capacity functions for rill flow on non-erodible bed.Materials and methodsLoess soil was collected from Ansai County, which is located in a typical loessial region in China’s Loess Plateau. The median diameter of the loess soil was 0.04 mm. The experiment was conducted in a rill flume with a soil-feeding hopper. The slope gradients in this study ranged from 10.51 to 38.39%, and the flow discharges per unit width varied from 1.11 × 10−3 to 3.78 × 10−3 m2 s−1. The sediment transport capacity was measured for each combination.Results and discussionResults showed that Tc can be effectively described by the power function shear stress-based equations for various slope gradients with R2 > 0.94 and P < 0.01. Shear stress was a good predictor of Tc for different slope gradients with the Nash–Sutcliffe model efficiency (NSE) from 0.94 to 0.99. Moreover, shear stress was better in predicting Tc when the slope gradient was above 21.26%. Tc can be efficiently described by the power function unit stream power-based equations for various slope gradients with R2 > 0.95 and P < 0.01. Unit stream power was a good predictor of Tc for different slope gradients with NSE that ranged from 0.95 to 0.99. The unit stream power predicted Tc better when the slope gradient was above 26.79%. Unit stream power was more satisfied than shear stress for predicting Tc under different slope gradients. The unit stream power-based LISEM, which was multiplied by 0.62 (i.e., the correction coefficient), predicted well the sediment transport capacity of the rill flow in our experiment, where NSE = 0.93. The shear stress-based Zhang model, which was multiplied by the correction coefficient of 0.77, adequately predicted the sediment transport capacity of rill flow in our experiment, where NSE = 0.81.ConclusionsBy performing the controlled rill flume experiments, this study showed that shear stress and unit stream power strongly influenced Tc for certain slope gradients under non-erodible conditions.