GLIMPSES OF A WAVE BOUNDARY-LAYER

Measurements obtained with a profiling laser-Doppler velocimeter revea l the vertical structure of velocity in a wave boundary layer over a s and beach during two periods of approximately stationary forcing, each with a duration of several hours. The measurements indicate clearly t he reduction in variance and the increase in phase, relative to the ov erlying flow, that are expected in an oscillatory boundary layer. The measurements also indicate a distortion of the mean alongshore velocit y within the wave boundary layer, which has previously been predicted theoretically and observed in laboratory experiments. The thickness an d structure of the boundary layer are approximately consistent with co mputations based on an existing eddy viscosity model, and model-based best fit estimates of bottom roughness are approximately consistent wi th existing semiempirical descriptions of wave-formed sand ripples.