Wave reflections from breakwaters

Abstract

A new method is presented for estimating the reflection of a random, multi-directional 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 for wave incidence angles less than about 30 deg the new technique provides accurate and robust estimates of the gross properties of incident and reflected waves. 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 creasing 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.