Sediment transport capacity must be considered when developing physical models of soil erosion. The effects of related hydraulic parameters (e.g., flow discharge, slope gradient, and flow velocity), and of force predictors (e.g., shear stress, stream power, and unit stream power) on sediment transport capacity in rill erosion are still poorly known on the farmland of the Loess Plateau in China where rill erosion is common. We conducted a series of experiments to simulate and evaluate the sediment transport capacity of rill flow in a nonerodible rill flume. The test sediment was the loessial soil of the farmland of the Loess Plateau. Five flow discharges ranging from 0.22 to 0.67 × 10−3 m2 s−1 (0.00237 to 0.00721 ft2 sec−1) and five slope gradients ranging from 15.8% to 38.4% were tested. Sediment transport capacity increased with both flow discharge and slope gradient, as expected, but was more sensitive to flow discharge than to slope gradient, unlike other similar studies. Mean flow velocity, related to the flow discharge, was strongly correlated with sediment transport capacity (r2 = 0.93). Stream power was the best predictor of sediment transport capacity; shear stress and unit stream power, with critical values of 0.55 W m−2 and 0.02 m s−1 (0.04 mi hr−1) respectively, were poor predictors. An empirical equation of sediment transport capacity of the loessial soil for rill flow was developed. Our results present a different view, compared to previous studies, of the relationship of sediment transport capacity with discharge and slopes, especially with lower discharges, steep slopes, and loessial soil. Further study should be conducted to evaluate the performance of farmland soil at various slopes and discharges.
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