INFLUENCE OF THE CROSS-SECTION ON THE EROSION CRITERIA FOR PARTLY COHESIVE SEDIMENTS

Erosion of sediment mixtures comprising cohesive as well as non-cohesi ve sediments. has been studied in straight laboratory flumes of circul ar and rectangular cross-sections. Erosion of mixed sediments depended on the mixture composition (cohesive material content), the type of c ohesive sediment. and the shape of the flume cross-section. By increas ing the cohesive material content, the erosion resistance of the sedim ent mixture also increased and the erosion pattern changed from ripple s and dunes (noncohesive) to a groove or wavy surface (cohesive). In c ircular channels, the influence of the ''side'' walls on sediment tran sport is important, but the criteria for incipient motion seem to be t he same as in the rectangular channels. Hence. sediment transport mode ls developed for rectangular channels cannot be readily applied to cir cular channels.