Narrow Results

Based on a large amount of published laboratory results, reliable models are developed for computing the average rate of energy dissipation in regular and irregular breaking waves. The average energy dissipation rate is assumed to be proportional to the difference between the local mean energy density and stable energy density. Wave height transformation is computed from the energy flux conservation law based on the linear wave theory. The models are examined and verified extensively for a variety of wave and bottom conditions, including small and large scale laboratory and field experiments. Reasonable good agreements are obtained between the measured and computed wave heights and root mean square wave heights.

Waves entering the surf zone initially develop higher harmonics which disappear after two or three wave lengths. The default Lumped Triad Approximation (LTA) in the SWAN wave model generates only (persistent) second harmonics. An alternative approximation (DCTA) is suggested which is based on an analogy with quadruplet wave-wave interactions. It initially generates all (transient) higher harmonics and subsequently a smooth universal spectral tail, in agreement with observations. The DCTA is calibrated with 31 published laboratory cases and then applied to 20 other, one- and two-dimensional cases, including field cases. The conclusion is that using the DCTA instead of the LTA barely affects the significant wave height but improves the mean period and spectral tail of the computed spectra. Further improvements are expected with enhanced high-frequency dissipation.