Laboratory experiments were performed to investigate characteristics of boundary layer flows under different types of bores. Temporal variations of nearbed velocity profile were measured by a PIV technique and compared with solutions of the boundary layer equation under upper boundary conditions given by the measured free-stream velocities. The results suggested that the boundary layer remained laminar at the bore front even for the case of a fully-developed turbulent bore. The bore-induced turbulence affected the boundary layer after a certain period of time and resulted in a significant rise in bed shear stress. It was also found that the bed-generated turbulence tends to be dominant during the late stage of bore propagation.
