A sediment transport equation for interrill overland flow on rough surfaces

A model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3.4 to 43.4 mm, flow velocities from 0.09 to 0.65 m s(-1), Reynolds numbers from 5000 to 26949, Froude numbers from 0.23 to 2.93, bed slopes from 2.7 degrees to 10 degrees, sediment diameters from 0.098 to 1.16 mm. volumetric sediment concentrations from 0.002 to 0.304, roughness concentrations from 0 to 0.57, roughness diameters from 1.0 to 91.3 mm, rainfall intensities from 0 to 159 mm h(-1), flow densities from 1002 to 1501 kg m(-3), and flow kinematic viscosities from 0.913 to 2.556 x 10(-6) m(2) s(-1). Stones, cylinders and miniature ornamental trees are used as roughness elements. Given the diverse shapes, sizes and concentrations of these elements, the transport model is likely to apply to a wide range of ground surface morphologies. Using dimensional analysis, a total-load transport equation is developed for open-channel flows, and this equation is shown to apply to interrill flows both with and without rainfall. The equation indicates that the dimensionless sediment transport rate phi is a function of, and therefore can be predicted by, the dimensionless shear stress theta, its critical value theta (c), the resistance coefficient u/u*, the inertial settling velocity of the sediment w(i) the roughness concentration C-r, and the roughness diameter D-r. The model has the form phi = a theta (1.5) (1 - theta (c)/theta)(3.4) (u/u*)(c) (W-i/u*)(-0.5) where log a = -0.42 C-r/D-r(0.20) = and c = 1 + 0.42 C-r/D-r(0.2). Testing reveals that the model gives good unbiased predictions of phi in flows with sediment concentrations less than 0.20. Flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model. Copyright (C) 2001 John Wiley & Sons, Ltd.