Boundary Layer Developed Near Surging Front

Wave velocity profiles near the surging front on a dry bed are investigated both theoretically and experimentally. The Rayleigh problem on flows due to the sudden movement of a wall is extended to include the arbitrary wall movement and the convective term, and then is solved numerically. Measurements are performed by the flow visualization technique using the time lines of hydrogen bubbles and a high speed camera. The theoretical solutions are compared to the actual measurements and found to be in close agreement. The original Rayleigh problem proves to be an accurate model for flow fields in the immediate vicinity of the front. It also proved that the velocity profiles are affected by both the convection and deceleration of the upper flow. Singular bottom shear stress is dominant near the surging front, and this is related to the singularity at the wave front, an obstacle to wave runup analyses.