A Consideration Aimed at Improving the Resiliency of Protective Structures Against Tsunami - Post-Tsunami Hazard: Reconstruction and Restoration - page 203

Chapter 14
A Consideration Aimed at Improving
the Resiliency of Protective Structures
Against Tsunami

Taro Arikawa and Takayuki Oie

Abstract In this paper the effectiveness of breakwaters to provide protection
against huge tsunami was considered using numerical simulations. Kamaishi Bay,
where large breakwaters had been installed, was selected as the target area, because
about half the breakwaters were washed away by the tsunami produced by the
Tohoku Earthquake in 2011. Therefore, the effect of breakwater protection against
the 2011 tsunami is verified by comparing the different states of damage to break-
waters with numerical simulations. The results show that the protective effect pro-
vided by breakwaters against tsunami depends on the rate of opening gap, and
suggest that this is an efficient way to improve the resiliency of deeper-region
breakwater structures.

Keywords Resiliency • Breakwaters • Tsunami • Overflow • Numerical
simulations

14.1 Introduction

Coastal areas around Japan historically have been protected against storm surge and
tsunami by seawalls and breakwaters. Kamaishi was one such area. Huge breakwa-
ters with caissons more than 30 m high were installed at the mouth of Kamaishi
Bay. While these caissons ranked among the largest in the world, roughly half of the
breakwaters were washed away by the tsunamis subsequent to the 2011 Tohoku
Earthquake, causing severe damage to the hinterland.
The Committee for Technical Investigation on Countermeasures for Earthquakes
and Tsunami, in response to Lessons Learned from the “Great East Japan
Earthquake” (2011) produced by the Central Disaster Management Council pro-
posed that basically two levels of tsunami must be hypothesized to build future