Bed Shear Stress and Scour over Bed‐Type River Intake

Laboratory experiments are carried out to determine the increase in bed shear stress and local scour over the zone of suction associated with a bed‐type river intake in a channel with a mobile bed. Bed shear stress is estimated first by observing the movement of indicator grains whose threshold shear stress in uniform flow was already known, and second by observing the rate at which local scour takes place. Evaluation of the two sets of results indicates that, at the onset of scour when particles are lifted from the bed by increased bed shear stress, they do not strike the bed again until they are clear of the scour zone. The final scour depth is found to be directly proportional to the difference between the initial bed shear stress because of suction and the threshold bed shear stress for the bed grains in the presence of suction.