Transport Capacity of Overland Flow with High Sediment Concentration

The concept and estimation of sediment transport capacity of overland flows are pivotal to soil erosion, sediment transport, and deposition modeling. There is a limited understanding of the effect of high sediment concentration on the transport capacity of overland flow, although sediments in suspension are known to affect turbulent mixing and settling velocity in rivers. A new functional relationship between a dimensionless parameter involving stream power and settling velocity and the volumetric concentration at the transport limit was developed using a set of flume experiments with slope up to 46.6%, unit discharge up to 50 cm2·s−1, median particle size of 0.326 mm, and sediment concentration up to 1,140 kg·m−3. The new relationship has two theoretical limits on sediment concentration at the transport limit. Under low flow conditions, the sediment concentration is limited by the available stream power. At high stream power, the sediment concentration is limited by the space available in flow to accommodate sediments in motion. As a predictor of the sediment concentration at the transport limit, the new relationship worked very well with the Nash-Sutcliffe coefficient of efficiency of 0.95 and was shown to be superior to empirical relationships based on stream power and other commonly used predictors of the transport capacity for rivers. The paper also shows that formulas for the transport capacity which have been validated and widely used for rivers with high sediment concentrations are inaccurate and should not be used to predict the transport capacity of overland flow.