Critical Bed-Shear Stress for Cohesive Sediment Deposition under Steady Flows

Results of two laboratory experiments on the cohesive sediment deposition behavior are presented. Data indicate that an annular flume, either with or without the channel bed and the top ring rotating in opposite directions to minimize the secondary circulation, can be used to study the deposition behavior of cohesive sediments. Direct observations on when and where the bed is formed suggest that deposition only occurs when the local bed-shear stress ( τb ) is less than a critical value. Secondary circulation in the flume, which produced upward current near the inner corner and downward current near the outer corner, did not prevent deposition near the inner corner (because of the small τb ) nor promote deposition near the outer corner (because of the relatively large τb ).