WAVE REFLECTION FROM BREAKWATER

A new method is presented for estimating the reflection of a random, m ultidirectional sea from a coastal structure. The technique is applica ble 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 incid ent-wave properties and the reflectivity of the structure. Model tests with simulated array data demonstrate that the gross properties of in cident and reflected waves can be accurately estimated for wave-incide nce angles less than about 30 degrees C. The new method is applied to array data acquired offshore of a permeable, rubble-mound breakwater i n Monterey Bay, California. The estimated reflection coefficients decr ease approximately linearly with increasing frequency. Whereas the obs erved reflections depend only weakly on the incident-wave energy, the fraction of the incident-wave energy flux transmitted through the brea kwater decreases with increasing wave energy, suggesting that dissipat ion is enhanced with large-amplitude waves.