Breaking in a Spectral Wave Model

Spectral wave breaking parameterizations are evaluated using 15 days of field measurements from the Duck94 study at the FRF. Measurements include 14 pressure gauges from 8-m depth to the shoreline and 120 wave events (wave heights of 0.5 to 4 m and periods of 4 to 16 s). The Battjes and Janssen model applied with a full Rayleigh distribution to calculate the percentage of wave breaking gave the smallest errors. Bore-type models like Battjes and Janssen degrade significantly as grid spacing increases (resolution greater than 15 m for the FRF comparisons). For applications with coarser resolution, a limit must be placed on dissipation or a simpler breaker model should be applied. Use of spectral transformation models in the surf zone can reduce RMS error by more than a factor of three compared to a monochromatic model defining breaker height as 0.78 times depth. Including the Battjes and Janssen breaking relationship in a monochromatic model reduces error by a factor of two. Spectral breaking models accurately represent wave height in the surf zone, but do not reproduce changes in spectral shape for multi-peaked incident spectra.