TSUNAMI DAMAGES OF NAKOSO COAST DUE TO THE 2011 TOHOKU TSUNAMI

Shinji Sato, Haijiang Liu, Satoshi Takewaka, Hisamichi Nobuoka, Shin-ichi Aoki

Abstract


A post-2011 Tohoku earthquake tsunami survey was conducted at the Nakoso Coast, Fukushima Prefecture, Japan, on Mar 24-25 and Apr 1-2, 2011. Spatial distribution of the tsunami inundation height, together with the seawall height and damages, was investigated. We found a sharp contrast of tsunami damages within the target area; tsunami damage is the most serious in the north region (north of the Samegawa River) where seawalls with different heights played diverse roles for protection of local community. A relatively high seawall in this region kept intact after tsunami attack, and protected the lee side human properties; whereas, 71% of the low seawalls were broken during the tsunami and the disaster developed in the corresponding sheltered area. A sharp contrast at the boundary of these two types of seawalls was observed. Behind the high seawall, the tsunami intensity and velocity were significantly reduced and the inundation depth is only 0.6 m. Nevertheless, tsunami intensity was enhanced in the seawall-broken area with an inland inundation depth being 4.7 m, which ruins away the local houses. In the middle region between the Samegawa River and the Bindagawa River, the high seawall survived from the tsunami attack. We confirmed that the coastal pine tree forest, serving as a buffer zone, played a significant role in reducing the tsunami height approximately by 4 m within a cross-shore distance of 230 m. To the south of the Bindagawa River, the tsunami damage is the mildest due to the protection by the robust high seawall as well as high elevation of land topography.

Keywords


coastal disaster; tsunami; seawall; flooding

References


Sato, S., T. Kajimura, M. Abe, M. Isobe. 2004. Sand movement and long-term beach evolution in a fluvial system composed of the Samegawa River and the Nakoso Coast, Coastal Engineering Journal, 46(2), 219-241.http://dx.doi.org/10.1142/S057856340400104X

Tohoku Earthquake Tsunami Information. 2011. http://www.coastal.jp/tsunami2011/


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