An evaluation of the performance of the new breakwater at Ofunato Bay, with an equal emphasis on disaster prevention and environmental protection

As the environmental value of waterfront areas has gained recognition, it has become evident that breakwaters are required which function not only to keep the water surface within harbors calm but also to maintain water quality. In this situation, we investigated the effectiveness of the new Ofunato breakwater design. We carried out experimental and numerical analysis with/without breakwater. In both analyses, we made a comparison of the situation with and without a breakwater. From experiments it was found that the breakwater causes a delay of a few seconds (a real scale delay of about 10 minutes) in the time it takes for waves to reach the continental areas. From our calculation results, we found that the existence of a breakwater decreases seawater exchange. Comparing the two types of breakwater, it was seen that the new plan, with the feed-water pipes, is the better one from the perspective of seawater exchange enhancement. It is considered that the new breakwater design is superior in terms of having an equal emphasis on disaster prevention and environmental protection.