Assessing an overland flow resistance approach under equilibrium sediment transport conditions

In this study, for the first time, a theoretically deduced flow resistance equation was tested for an overland flow under equilibrium sediment transport conditions using available experimental data by Liu et al. for five Chinese soils. Initially the relationship among the velocity profile parameter Γ, the channel slope, the flow Reynolds number, the Froude number and the sediment concentration was calibrated using 90 measurements of the available database (Loessial, Cinnamon and Black soil) and tested by other 60 measurements (Red and Purple soil). The results proved that the Darcy–Weisbach friction factor can be accurately estimated by the proposed theoretical approach, with errors that are always less than or equal to ± 5%. Then, using mean values of the exponents of Froude number, slope, sediment concentration and Reynolds number (Eq. 7), the calibration was carried out for each soil type to attribute the soil effect on the velocity profile parameter and flow resistance to the scale factor a. This analysis demonstrated that the a coefficient increases with the transportability of soil particles, which is associated to a decrease of both the flow energy required for sediment transport and the Darcy–Weisbach friction factor.