An experimental and numerical study on the spatial and temporal evolution of a scour hole downstream of a rigid bed

The present study consists of a new mathematical-experimental investigation on local scour downstream of a rigid bed. New scouring experiments, under both steady and unsteady flow conditions, were carried out and the scour patterns were measured with a 3D Laser Scanner. The initial bed shear stress induced by the turbulent flow over the sand bed was estimated by analysing velocity profiles. A mathematical model simulating the local scour downstream of a rigid bed and using both information relating to the turbulent flow and the physical and mechanical properties of the sand was developed. The mathematical structure of the model includes a second order partial differential parabolic equation with the shape of the mobile bed as unknown parameter. The sediment transport was computed by the Einstein approach. The space-time evolution of the simulated scour holes are in good agreement with the measured ones for both steady and unsteady flow tests.