Entrainment of bed sediment into suspension

The literature abounds with apparently conflicting relations for predicting the reference near-bed concentration of suspended sediment or the entrainment rate of noncohesive bed sediment into suspension. Most of these relations have been developed for uniform material. In this paper, seven such relations are compared against a common set of experimental data for which direct measurements of near-bed concentration are available. The relations put forward by Van Rijn and by Smith and McLean are found to perform best. A new relation for uniform material, having similar predictive capabilities, is developed using the same experimental data. The new relation is generalized to handle sediment mixtures with the aid of field data. The generalization accounts for the hiding effect due to the presence of grains of different sizes. A test against an independent field data set indicates that the empirical fit can provide reasonable estimates of the sediment entrainment coefficient for beds covered with nonuniform material.