ABSTRACT
Hydraulic structures cause disturbances in uniform flow and sediment transport. Downstream of these structures, flow velocities increase due to constriction by the structure. The bed is often protected in order to decrease the maximum dimensions of the scour hole and to shift the scour holes that involve a potential risk to structural stability to a greater distance from the hydraulic structure. Flow characteristics and turbulence intensities determined by the geometry of the hydraulic structure and bed roughness characterise the flow pattern in the vicinity of the hydraulic structure and thus provide a measure of the erosion in the scour hole just downstream of the hydraulic structure. The shape of grains, the surface packing of grains and multiple layers of different bed materials are additional factors for the scour process. The aim of risk assessment is to establish the risks that need to be managed and to identify means to control them to acceptable levels.
