Conceptual Bed‐Load Transport Model and Verification for Sediment Mixtures

Because of hydraulic sorting (selective transport of grains by the flow), bed‐load transport of mixtures of sand and gravel in streams is difficult to predict. The transported gradation is generally different from the gradation of bed‐surface material or the upstream imposed load, and should be treated as a new unknown variable. A conceptual transport model for bed‐load mixtures is proposed, in which the transported gradation is predicted using the concept of joint probability. In this approach, instead of using a hiding factor or exposure correction, the relative mobility of each particle size and the availability of each size class on the bed surface are considered. The total transport rate is then determined by mean hydraulic conditions of the flow and properties of the transported material. This approach allows easier calibration procedures for transport of mixtures. The method is verified through comparison with an irreversible overloading and underloading flume experiment.