Characterizing the Instantaneous Dissipation in Breaking Waves

The characterization of breaking waves in models has seen much advance in recent years. This characterization, in turn, can be applied to data in order to obtain information on instantaneous breaking characteristics. Using several high-resolution laboratory data sets of wave breaking in shallow water, the threshold parameter of Zelt (1991 Coastal Eng.) breaking formulation is parameterized at each gage location using the corresponding bulk dissipation calculated from each dataset. Although this parameter is defined as a constant value for solitary waves over the constant depth in the original formulation, adjustment of this value allows its application to a wider range of wave conditions. The calibrated parameter then is used to calculate the instantaneous dissipation from time series of free surface elevation. We show that the relationship between this parameter and normalized water depth is best expressed as a hyperbolic tangent curve. A similar trend between third moments of the free surface and the calibrated parameter exists. These parameters are also applied to find a relationship between the slope of the free surface elevation spectra and the slope of the associated dissipation coefficient. We determine that previous work on the trends of the frequency dependence of dissipation, while changed with this calibrated parameter, is not invalidated.

Keywords: Surf zone, Wave breaking, Bulk dissipation, Instantaneous dissipation