Erosion of sediment mixtures, comprising cohesive as well as non-cohesive sediments, has been studied in straight laboratory flumes of circular and rectangular cross-sections. Erosion of mixed sediments depended on the mixture composition (cohesive material content), the type of cohesive sediment, and the shape of the flume cross-section. By increasing the cohesive material content, the erosion resistance of the sediment mixture also increased and the erosion pattern changed from ripples and dunes (noncohesive) to a groove or wavy surface (cohesive). In circular channels, the influence of the “side” walls on sediment transport is important, but the criteria for incipient motion seem to be the same as in the rectangular channels. Hence, sediment transport models developed for rectangular channels cannot be readily applied to circular channels.

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