LABORATORY MEASUREMENTS OF BREAKING INCEPTION AND POST- BREAKING DYNAMICS OF STEEP SHORT CRESTED WAVES

Monochromatic short crested waves have been produced in a laboratory flume using a shaped wavemaker. Breaking has been observed to occur near the peak in the amplitude modulation of these waves, over a range of local wave steepness. The conditions for inception and the post-breaking morphology (breaker area, height, length) and dynamics were observed photographically, and are quantified. Breaking inception was observed over a wide range of wave steepness (Hi/gT2) from 0.011 to 0.0335. The latter is in excess of the Stokes limiting steepness for planar waves, and an explanation is suggested based on calculated reductions in crest orbital velocity due to short crestedness. Variations in breaker severity from one wave cycle to the next are observed and are believed to be due to the disturbances left in the water by preceding breakers. A small jet was observed at the initiation of the breaking wave, and a simple estimate of jet dimension is given, based on observed breaker growth rates.