Bed shear stress in an evolving local scour due to a submerged turbulent jet flow

A scouring experiment was performed and both the temporal evolution of the scour hole and the mean velocity field were measured. A mathematical model simulating the space-time evolution of bed shear stress inside a local scour, due to a submerged turbulent jet is developed. This model, using the scour hole’s temporal evolution as an input, is based on a modified Exner equation accounting for the scour hole’s steepness and then the critical bed shear stress, the bed load formulation and the structure of Exner equation are modified. The measured velocity field shows that the observed submerged jet flow, due to the interaction with the erodible bed changes into an asymmetric free jet flow. The spatial distribution of the hydrodynamic bed shear stress at different scouring stages was calculated for the performed laboratory experiment, and compared with the difference between the critical bed shear stress, accounting for the sloping bed, and the stress due to gravity, showing a gap decreasing as time increases.