Temporal and spatial flow variations over a movable scour hole downstream of a grade-control structure with a PIV system

Weirs or grade-control structures (GCSs) are frequently adopted to protect bridges or control riverbed degradation. Scour holes may develop downstream of these hydraulic structures. Laboratory experiments have been performed in this study, using sophisticated equipment and newly developed procedures. The purpose was to investigate important characteristics of the turbulent flow in the movable scour hole. The results of these experiments demonstrated the significance of instantaneous shear stress in the scouring process. The measured Reynolds stress can be fitted with the theoretical equation reasonably well. Furthermore, the results revealed that the normalized mean vertical velocity profiles in the diffusion region of the scour hole can be fitted with a Gaussian curve. An analysis of the turbulence intensity measurements showed that the turbulent flow is anisotropic in the scour hole. The turbulence intensities also decreased with time as the scour hole gradually approached equilibrium.