عنوان مقاله [English]
Water passage from steep slopes in river engineering issues and the design of water transfer structures is inevitable. Because of the steep slope of the surface, the surface velocity and surface erosion rates are high. Energy control in high-speed flows is one of the challenges of designing hydraulic structures. These flows, for example, occur in places such as dam overhead structures, drainage systems of urban areas and Mountain Rivers with a steep slope. One of the ways to reduce dimensions or eliminate energy depreciating structures is to use methods to reduce the kinetic energy of flow over the weir, including using of stairs or blocks on the overflow. The use of large-sized stairs or blocks will cause the passing jets of flow to be separated and as a result turbulent, which can effectively deplete the kinetic energy of the current. The problem with using a staircase or block is a huge cost of built and a high risk of cavitation. Another method of energy depreciation is to apply roughness at the overflow bed, which may be an efficient way to reduce energy. Roughness can dramatically reduce the flow turbulence, and thus reduces the risk of cavitation. Also, roughness can reduce the flow power over the overflow and reduce the depth of the lower erosion pit by removing or reducing the dimensions of the relaxation basin. Most studies in this field have investigated the effect of these roughs on the amount of energy depletion, which in addition to energy depletion is also important for lowering the erosion of the structure. However, for the economic design of hydraulic structures, designers need to have full knowledge of the particle mechanics and the dimensions of the scour hole, so that they can consider the requirements for the stability of the structure, which has so far been investigated insufficiently. Therefore, the present study aimed to investigate the effect of roughness density on sloped bed surface on its downstream scour depth.