Measurements of Near-Bottom Velocities in Random Waves on a Constant Slope

This paper describes near-bottom velocity variations measured under both monochromatic and random waves on a 1/20 slope. Characteristics of velocity field under random waves, such as distributions of orbital velocity amplitude, the asymmetry in velocity variations and undertow velocity, were discussed in comparison with those under monochromatic waves. The applicability of the linear and nonlinear wave theories to the evaluation of orbital velocity amplitudes was examined. A model was proposed for evaluating the undertow velocity in random waves as a function of the root-mean-square of wave height and the ratio of the number of breaking waves to the total number of waves.