The change in a transmission coefficient of a submerged breakwater under large deformation is investigated. The transmission coefficient and deformed profile of the submerged breakwater are measured in a three-dimensional experiment. The change in the transmission coefficient is explained on the basis of the changes in the depth above the crest of the submerged breakwater. At first, the depth above the crest decreases due to the accretion of rubble stones on the crest and then increases because the rubble stones accreted on the crest rolled down in the onshore direction. However, the authors show that the value of the transmission coefficient did not increase in many cases.
In designs of coastal structures, stability and hydraulic performances of the structures are usually investigated under the conditions of design wave. However, larger waves than the design waves can attack coastal structures. Therefore, deformation and change in hydraulic performances of coastal structures should be investigated under the conditions of the incidence of larger waves in order to understand behavior of the coastal structures at an ultimate state. This kind of investigation is also important in a new design method, such as performance based design. Hydraulic performances of rubble mound structures gradually change according to the progress of its deformation. Therefore, the authors investigated characteristics of deformations and hydraulic performances of submerged breakwaters which have several environmental advantages by carrying out hydraulic experiments.
The index of the main hydraulic performance of submerged breakwater is transmission coefficients. The transmission coefficient of submerged breakwater was measured under regular wave by Tanaka (1976) and was measured under irregular wave by Takayama et al. (1985). Sawaragi and Deguchi (1992) analytically investigated the reduction of wave height on a permeable layer.
