Scour Downstream of a Rough Rigid Apron

A series of experiments was conducted to investigate the erosion behaviors of the noncohesive sediments downstream of smooth and rough aprons. A total of 33 tests were carried out with five different roughness conditions (k =0, 1, 1.85, 3.35 and 5mm) in a flume 0.5m wide, 0.6m deep and 9m long. For each run, s measurements were taken of the scour-hole profiles at the asymptotic or equilibrium state of scour. The results showed that the main characteristics of the scour holes, such as the maximum scour depth and its distance from the end of the apron, the maximum extension of the hole, the dune height and its distance from the end of the apron, were much smaller for rough than smooth aprons. A minimum reduction of 60% was obtained for the maximum scour depth with respect to the smooth beds. Also, the effect of submergence on the maximum scour depth was investigated. It was found that as the submergence factor increased, the maximum scour depth decreased. Finally, it was observed that the shape of the scoured beds was different in rough and smooth beds and that the mound region was more flat for rough aprons.