Similarity of Local Scour Profiles Downstream of Stepped Spillways

Abstract

Local scour downstream of hydraulic structures is one of the critical phenomena, which has absorbed a vast amount of interests by researchers. The designers of hydraulic structures, particularly, spillways try to utilize proper means to minimize the consequences of excess energies downstream of such structures which usually tend to erode their immediate downstream reaches. The stepped spillway is designed to create a large amount of energy losses by action of its steps to lessen the amount of scour evolution at its immediate downstream. This article presents the results of 67 experiments conducted at two different scales of stepped spillways, to study the local scour downstream of the structure. The experiments were planned to consider a wide range of geometrical factors, flow characteristics, and sediment properties. The time duration of experiments was ranged from 6 to 24 h which produced more than 80000 data points for analytical considerations. The results were used to render some regression equations to define the similarity among the scour hole profile and its geometrical characteristics. It was observed that a long-term observation would be required to reach the equilibrium state. However, semi-equilibrium conditions will be achieved some times after 24 h. It was also noted that the depth of scour hole adjacent to channel walls was bigger than that of centerline. Finally, it was realized that the stepped spillway causes energy dissipation between 42.06 and 74.82% which results in a shallower scour hole compared to ogee spillways.