1988 年 41 巻 3 号 p. 343-350
The height of a sea wall is usually designed based on water levels of large tsunamis experienced in the past. Behaviors of tsunamis exceeding the design height are examined by means of numerical experiments taking the sea walls at Matsuzaki, Shizuoka prefecture and at Taro, Iwate prefecture. In the case of Matsuzaki, the inundated area reduces to 70 percents of the original one by the presence of the wall although the invasion of tsunami through the river mouth, where no water gate is constructed, is noticeable. In the case of Taro, the sea wall height is designed at 10 meters that equals the height of the 1933 Sanriku tsunami. According to our experiment, however, if a tsunami has the same height as that of the 1933 tsunami, the water level close to the wall front becomes higher than the height of the sea wall. In this case, the water level at some places in the town becomes so high as to give rise to human and material damage in spite of the construction of the sea wall. It is recommended, therefore, that local inhabitants take refuge onto hilltop, unless a small height is predicted by the tsunami warning.