WAVE KINEMATICS AND SURFACE PARAMETERS OF STEEP WAVES TRAVELING ON SHEARED CURRENTS

Measurements have been made of the velocity field and wave parameters for large waves on a moderately sheared current in a wave flume. Compa risons are made between the velocity fields measured with particle ima ge velocimetry (PIV), the predictions due to irrotational wave theory combined with current stretching, and a fully nonlinear constant vorti city model. The stretching theory is found to be in good agreement wit h the constant vorticity model. The experimentally measured velocity p rofiles are well predicted by the models, except in the steepest cases (above 60% steepness), where the crest velocities are overpredicted a nd the trough velocities are underpredicted. Values of the equivalent current derived for the surface parameters are compared with near surf ace current weighting methods. It is found that the surface current va lue is closer to the equivalent current than any of the weighting meth ods.