Effect of Breakwaters on Reduction of Fatality Ratio during the 2011 Great East Japan Earthquake and Tsunami

抄録

 Based on lesson learned from the 2011 Great East Japan tsunami, tsunami height is the most influential factor on fatality of people living in coastal area. This paper proposes effect of breakwaters on fatality ratio of people and investigate a reduction of fatality ratio due to the existence of breakwaters. For preliminary study, 24 fishery ports equipped with breakwaters were selected to study how breakwaters affect to loss of fatality ratio along Sanriku ria-coast from Taro to Ishinomaki. The port area behind breakwaters was considered to calculate fatality ratio from number of fatality divided by total number of people and then fatality ratio was linearly correlated with observed tsunami height. In order to estimate fatality ratio in case of ports without breakwaters, simulated tsunami height was calculated by TUNAMI modeling with nesting grids of 1350 m, 450 m, 150 m, and 50 m. For the overall image, breakwaters could reduce fatality ratio of people in the port area with a percentage of reduction approximately 30%. Considering the effect of breakwaters at each port, it was found that fatality ratio of ports equipped with breakwaters is less than those in case of ports without breakwaters for most of ports. In addition to these 24 ports, 18 additional ports equipped with breakwaters were conducted to additional study and compared with 24 ports having no breakwaters. For the overall image, the percentage of reduction became 1%, which is much lower than the reduction in the preliminary study. Focusing on each port, two third of them still provided the reduction of fatality ratio.