WAVE REFLECTION FROM BREAKWATER

A new method is presented for estimating the reflection of a random, multidirectional sea from a coastal structure. The technique is applicable to an array of wave gauges of arbitrary geometry deployed seaward of the reflector. An expansion for small oblique wave-incidence angles is used to derive an approximate relationship between measured array cross-spectra and a small number of parameters that describe the incident-wave properties and the reflectivity of the structure. Model tests with simulated array data demonstrate that the gross properties of incident and reflected waves can be accurately estimated for wave-incidence angles less than about 30 degrees C. The new method is applied to array data acquired offshore of a permeable, rubble-mound breakwater in Monterey Bay, California. The estimated reflection coefficients decrease approximately linearly with increasing frequency. Whereas the observed reflections depend only weakly on the incident-wave energy, the fraction of the incident-wave energy flux transmitted through the breakwater decreases with increasing wave energy, suggesting that dissipation is enhanced with large-amplitude waves.