Experimental studies on energy dissipation in breaking waves

A plunging wave breaking in a transient wave train was generated in a two-dimensional wave flume using a wave energy focussing techniqne. Surface elevation measurements of the transient wave train were made at several locations before and after the isolated plunging breaker. Applying a nonlinear decomposition approach to the measured elevation (Zhang et al. 1996), the free-wave components comprising the transient wave train were derived. By excluding the contribution from bound waves, a comparison of the spectra of free-wave components before and after wave breaking will accurately reveal the energy loss due to the breaking as a function of frequency. It was found that the energy loss is exclusively from wave components at frequencies higher than the spectral peak, especially from those wave components whose energy levels exceed the corresponding saturated level in a fully developed wave spectrum.