Cohesion influences on erosion and bed load transport

Studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge. Results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open-channel flow are presented. The sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10% to 50% and fine gravel, fine sand in equal proportion (by weight) mixed with clay proportions again varying from 10% to 50% by weight. Experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments. Also, it is different from the detachment process of cohesive sediment mixtures not containing coarser-size material. Experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented. On the basis of dimensional considerations, a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures. Clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments. In the absence of cohesion, the proposed method reduces to the Patel and Ranga Raju (1996) method for bed load transport rate computation of nonuniform cohesionless sediments.