Effect of open-area ratios on wave attenuation over a submerged reef breakwater: An experimental study

The reef-type submerged breakwater (RSB) has been implemented around the world to provide coastal protection and natural shelter and habitat for marine species at the same time. A series of laboratory experiments are conducted in a wave flume to study wave propagation and transmission over RSBs with the four open-area ratios of 0.047, 0.131, 0.257, and 0.560. The experimental results demonstrate that the RSB significantly alters the wave propagation characteristics. The RSBs with the open-area ratio of 0.047 and 0.131 reduce the wave height to ∼70%. The RSBs with the open-area ratio of 0.047 and 0.131 perform better in attenuating than those with the open-area ratio of 0.257, and 0.560. As the open-area ratio decreases, the transmission coefficient decreases, while the dissipation coefficient increases. An empirical formula is proposed to calculate the wave transmission coefficient as a function of the RSB open-area ratio and wave steepness under regular waves. A cubic empirical formula with one unknown is also proposed to relate the distance from RSB stoss face to wave breaking point and the open-area ratio. The present study is expected to optimize RSB design for coastal protection.