Hemispherical shaped artificial reefs

Breakwaters, typically used as coastal protection structures, are usually built as water surface piercing structures. However, submerged type breakwaters are being considered more frequently as a ‘soft’ solution in solving coastal engineering problems due to their enhanced environmental attributes.; An array of perforated hollow hemispherical shape artificial reefs is proposed as a submerged breakwater. The proposed submerged breakwater provides environmental enhancement, improved aesthetics and provides protection needed in certain coastal areas due to characteristics that are not found in a conventional breakwater, such as the water circulation and fish habitat enhancement capability.; Wave transmission through various reef structures was investigated at Queens University Coastal Engineering Research Laboratory. The study involved two and three dimensional tests using regular and irregular water waves. The influence of wave steepness (H_i/gT2), reef geometry (h/B), relative height (h/d), relative width (B/gT2) and reef configuration on wave transmission was studied.; From the experiments, it is shown that the transmission coefficient (KT = H_t,/H_i which is the ratio of transmitted wave height to incident wave height) decreases as relative height (h/d) increases. Tests at low depths had the lowest values of KT while those at higher depth had the highest average value of KT for the same wave height. It was also found that the transmission coefficient (KT) decreases as the wave steepness (H_i/gT2) increases for both two-dimensional and three-dimensional tests. An increase in the length of the reef array (B) will reduce the transmission coefficient. The transmission coefficient was also found to decrease with increasing crest width for a given water depth and wave period. For the same reef configuration, the difference between wave transmission obtained from regular and irregular tests is not significant in two-dimensional tests. However, the transmission coefficient for three-dimensional tests is higher than two-dimensional tests. This is probably due to the more complex wave characteristics in the three-dimensional tests and as a consequence of propagated diffracted energy from breakwater head in both ends.; Equations to predict wave transmission were developed and can be used as initial estimation of wave transmission, while physical model tests are suggested to confirm the final design parameters for a large project.