DISSIPATION IN RANDOM WAVE GROUPS INCIDENT ON A BEACH

Variations in short-wave properties on the time-scale of wave groups provide important mechanisms in the generation of long waves. An essential component of models that describe the propagation of wave groups is the description of the slowly varying dissipation due to wave breaking. A model is proposed for the time-varying dissipation rate. As the time-varying dissipation rate cannot be obtained from direct measurements, calibration and verification is performed in an indirect way. The formulation is incorporated in several models of the time-averaged dissipation by combining it with a number of theoretical probability distributions for the wave energy. These models predict measurable quantities such as the mean dissipation, the fraction of breaking waves and some statistical wave height parameters. The parameters in the dissipation formulation are calibrated against some available measurements of the mean wave energy. A verification is then performed for some internal parameters in the models and for other datasets. The calibrated models of the mean dissipation rate in random waves show some improvements in the prediction of internal parameters. The usefulness of these models is also enhanced because the calibration coefficients can be kept constant over a wide range of conditions. The calibrated formulation of the time-varying dissipation rate is quite simple and can be readily used in wave propagation models that take into account variations on the time-scale of wave groups.