In order to mitigate secondary effects caused by high reflection waves from a conventional curtainwalled breakwater, a new type of breakwater consisting of two different walls was proposed. One wall is an impermeable curtain wall and located on the shore side of the breakwater. The other is consisted of an array of inclined plates with the same gap and located on the offshore side. For the practicalapplication of the new breakwater, the influence of a super structure on the performance was examined extensively. Furthermore, presuming the sea area with significant tidal difference such as the Seto Inland Sea, effect of water levels on the performance of the breakwater was also clarified. The dissipation mechanism used here is to enhance the generation of vortex flows from the plate-array front wall. By using the Helmholtz mode wave resonance between the two walls, enhancement of the vortex flow is realized.
