Abstract
In the East Japan Great disaster, a large number of people were dead and some number of persons were still missing, especially by giant tsunami attacks. One of the causes of the disaster was a significant amplification of tsunami height in a ria bay, typically Sanriku District, Tohoku area. In the last fifty years, in order to prevent and minimize the tsunami disaster in Sanriku Dsitrict, tsunami breakwaters have been constructed or under construction at the mouse of ria bays. However, in the last great disaster, almost all tsunami breakwaters were collapsed or partly destroyed. Consequently the disaster level was significantly expanded. In this study, effective layout of tsunami breakwaters at he mouth of ria bay has been exten-sively studied. The concept of a water wave resonator for reducing incoming tsunami waves is introduced. The new type of wave resonator developed in the authors' previous study has been adopted to reduce tsunami heights in the most shore side of a ria bay. The more practical layout of the breakwater deduced from the previous study is also examined.
