Bedload transport resistance in rough open‐channel flows

During bedload movement by saltation, streamwise momentum is transferred from the flow to the saltating grains. When the grains collide with other grains on the bed or in the flow, streamwise momentum is reduced, and there is a decrease in streamwise flow velocity and an increase in flow resistance, herein termed bedload transport resistance fbt. Based on experiments in two flumes with fixed and mobile plane beds and previously published data, an equation is developed that may be used to predict fbt for both capacity and non‐capacity flows. The variables in this equation are identified by dimensional analysis and the coefficients are determined by non‐linear regression. This equation applies to rough turbulent open‐channel flows, where the relative submergence is between 1 and 20 and the entire sediment load moves by saltation. An investigation of the relative magnitudes of fbt and grain resistance fc suggests that where dimensionless shear stress θ is less than 1 and saltation is the dominant mode of bedload transport, fbt/fc increases with θ but never exceeds 1.