Environmental Engineering Reference
In-Depth Information
Fig. 13.17
Reconstruction Plan of the Iwama District, Iwaki City, as compared with a post-
tsunami aerial photograph
which increased the runup height. The seawall height required for the Level-1
tsunami was computed by a numerical tsunami propagation model, which was
found lower than the runup height of the storm wave. The shore parallel green belt
will be constructed by a landfi ll with the same height of the seawall, with a purpose
of reducing tsunami overfl ow and thus helping secure evacuation for the infrequent
tsunami larger than the design level of the seawall.
Partially damaged seawalls remain capable of reducing tsunami effects for tsuna-
mis exceeding their design level (Level-1) as revealed in many tsunami surveys
including the survey described in this article. Hence the shore protection structures
should remain even effective for an event larger than the design level, unless the
structures were totally destroyed. Therefore, it is important to construct such
structures with the consideration of tsunamis beyond the design level (Level-1).
Seawalls should be designed to maintain partial effectiveness even for
“beyond-the-design-basis” conditions. This design concept is called “Nebari” in
Japanese, which implies tenacity, toughness and resilience or never giving up.
Careful fi eld observations on damaged seawalls as described in this article should
lead to valuable insights for how to design seawalls using the 'Nebari' concept.
References
Iwaki City (2013) Reconstruction plan of the Iwama District,
https://www.city.iwaki.fukushima.
jp/machi/seibi/015625.html
.
Accessed Feb 2014
Liu H, Shimozono T, Takagawa T, Okayasu A, Fritz HM, Sato S, Tajima Y (2013) The 11 March
2011 Tohoku Tsunami survey in Rikuzentakata and comparison with historical events. Pure
Appl Geophys 170(6-8):1033-1046. doi:
10.1007/s00024-012-0496-2
Liu H, Sakashita T, Sato S (2014) An experimental study on the tsunami boulder movement. In:
Proceedings of the 34th international conference on coastal engineering, ASCE, 2014
(accepted)
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