Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)
Online ISSN : 2185-4688
ISSN-L : 2185-4688
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Paper (In Japanese)
  • Shota HIRAI, Tomohiro YASUDA
    2020 Volume 76 Issue 1 Pages 1-11
    Published: 2020
    Released: February 20, 2020
    JOURNALS RESTRICTED ACCESS

     Companies damaged by natural disasters can receive the insurance payout if they have contract in advance. Then, they can start recovery work in the early stage with budget and can minimize the losses due to interruption of business activities. On the other hand, number of examples in coastal disasters especially storm surge disaster is limited, and a few studies on probabilistic risk assessment have been done. Therefore, it is currently difficult for property and casualty insurance companies to estimate the amount of insurance payout to contracted companies. Settlement of accounts in the business year and insurance contracts are basically every year, it is also important to estimate annual expected damage. This study assesses annual aggregate risk of storm surge by typhoons which attack Japanese major bays by employing synthetic typhoon datasets made by the stochastic typhoon model. Storm surges are calculated by an empirical formula and a nonlinear shallow water equation model. This study estimates loss function by using the results of inundation simulation, and calculates damage using asset map. Risk curves from 1 area to 5 areas are estimated by the relationship of annual exceedance probability and annual aggregate loss. Annual expected loss are calculated by risk curves. It was shown that proposed risk curves enable us to perform more appropriate assessment close to the actual situation by conducting an annual aggregate risk assessment in an arbitrary region.

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Technical Report (In Japanese)
  • Hiroshi TAKAGI, Md Rezuanul ISLAM, Le Tuan ANH, Atsuhei TAKAHASHI, Tak ...
    2020 Volume 76 Issue 1 Pages 12-21
    Published: 2020
    Released: February 20, 2020
    JOURNALS RESTRICTED ACCESS

     This report summarizes our reconnaissance survey after Typhoon No. 15 (Faxai), which struck Tokyo Bay on September 9, 2019. In Kanagawa, there was no major damage on the Sagami Bay side, but on the Tokyo Bay side, overtopping over an upright revetment with a height of 3.3 m above the sea occurred. In Chiba, there was no conspicuous high wave damage, except a building in Kujukurihama Beach that was obviously struck by wave run-up and splash. On the other hand, wind disasters were severe, and damage occurred in various places, such as the scattering of building roofs and the collapse of power poles. Wave-damage in Ibaraki was also minor. In Ibaraki, the breakwaters should have been constructed against severe winter storms, and the embankments have been substantially upgraded after the 2011 Earthquake and Tsunami. These structural resilience may have contributed to limiting typhoon impacts. Based on our wave model verified by the observations at three stations inside/outside the bay, the peak wave height during the typhoon was estimated to be 3.4 m off the coast of Yokohama. Compared with other 16 major typhoons that landed in the Kanto region, this typhoon was characterized as a strong small typhoon that slowly moved through Tokyo Bay. The result of the wave hindcast suggests that wind waves were rapidly intensified within the bay, resulting in significant damage in particular coasts, exacerbated by a storm surge of up to 1 m.

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