Experimental and numerical investigations on degradation of channel bed of cohesive sediment mixtures

Experimental observations on a degradation profile of channel beds consisting of cohesive sediment mixtures are presented. The sediment used for the experimentation consisted of fine gravel mixed with clay in varying proportions (10%–50% by weight) and fine gravel and fine sand in equal proportions mixed with varying proportions of clay (10%–50% by weight). The clay percentage in bed material and unconfined compressive strength of channel bed were found to be the main factors controlling the depth of degradation of channel bed of cohesive sediment mixtures, as degradation depth reduces considerably with an increase in clay percentage and unconfined compressive strength of sediment bed. An algorithm is also proposed to compute transient bed and water surface profiles in a channel bed made up of such cohesive sediment mixtures. For this purpose the predictor‐corrector‐based, essentially nonoscillatory finite difference numerical scheme is utilized for the solution of governing equations through the use of appropriate initial and boundary conditions. The recently proposed relationships by the authors for bed and suspended load transport of cohesive sediment mixtures were used as the auxiliary equations in the proposed algorithm. The observations on degradation of channel beds consisting of such cohesive sediment mixtures have not been reported so far in the literature to the best of our knowledge.