Local scour downstream of grade control structures

Grade control structures are used to prevent from excessive channel-bed degradation, but the erosive action of the flowing water causes downstream local scour. This scour can endanger the stability of the structure and cause the risk of a failure, if the foundations are not designed taking into account the maximum scour depth. This study investigates experimentally the scour downstream of a grade control structure, followed by a rigid apron, in clear water scour conditions. Eight experiments are run, changing the discharge and the tailwater depth of the flow, in order to investigate the influence of these parameters on the development of the scour hole. The temporal evolution of the scour, its maximum depth and length are recorded by a video camera and measured using image analysis techniques. The velocity field, measured by an ultrasonic velocity profiler, both on the rigid apron and in the scour hole is shown.3