●Research Trends and Results

Technical study of the creation of communities
resistant to tsunami disasters
SUWA Yoshio, Head
KATO Fuminori, Senior Researcher
River Department, Coast Division(Key Words) tsunami, swell head, tsunami inundation assumption, tsunami protection facility
1. Outline
Past tsunami countermeasures have been focused
primarily on structures such as coastal dikes
hypothesizing a tsunami level of constant frequency,
but in reaction to the tsunami produced by the Great
East Japan Earthquake, the Ministry of Land,
Infrastructure, Transport and Tourism has studied andlegally prescribed the creation of communities
resistant to tsunami disasters. The creation ofcommunities resistant to tsunami disasters isestablished to protect human lives even when thelargest class of tsunami strikes by, based on theinundation assumption and under the concept of“multifaceted protective mechanisms” which, combine
structural and non-structural countermeasures,comprehensively promoting the provision of tsunami
protection facilities, the restriction of development
activities, and the construction of warning andevacuation systems. Among these, methods ofevaluating the swell head of tsunami on the front
surface of a building etc. serving an as evacuation site,
technical standards for filling and cutting of theground during development activities in districts
which might be inundated, and technical standards fortsunami protection facilities were studied.
2. Methods of evaluating the swell head of tsunami
When a prefectural governor designates a tsunami
disaster caution district or a tsunami disaster special
caution district, the government publicly announces astandard water level (inundation depth consideringswell head). The mayors of cities, towns, or villages
can apply this standard water level to designatedobjects complying with a fixed standard within thetsunami disaster caution district as designatedevacuation facilities. And one essential condition forauthorization of a social welfare facility, school, or
medical treatment facility etc. (below called a,“designated development activity”) in a tsunami
disaster special caution district is that the heights ofthe floors of habitable rooms be equal to or higher
than the standard water level.
The standard water level adopted is the maximum
value of the specific energy of each calculation meshobtained by a tsunami inundation simulation
performed to hypothesize a tsunami inundation. Its

suitability has been confirmed by a tsunami inundation
simulation including a hypothetical arrangement ofbuildings and by a verification using the trace heightof past tsunamis.
3. Technical standards for filling and cutting
A study is done of a technical standard which
ensures that a precipice formed by filling and cutting
executed as part of a designated development activity
is safe against a tsunami which has run up.
・A precipice which is not covered with a retaining
wall shall be protected by sodding instead of sprayedmortar based on the result of using a tsunami
inundation simulation to calculate the depth of erosionof the cliff surface based on the flow regime of thetsunami.
・Stability against scouring of the toe of the slope of
the precipice shall be analyzed based on circular slip
while considering the maximum scouring depth
hypothesized, and based on the results, protective
work shall be installed or a fill and cut setback shall beformed premised on scouring.
・It is presumed that the overflow of the tsunami will
erode the top edge of the precipice, so
countermeasures are taken using regulations for thecrest work of the low water revetment of the river.
4. Technical standards for tsunami protection
facilities
Tsunami protection facilities, which are intended tosave the lives of people from the largest class oftsunami, include embanked structures, revetments,
levee walls, or lock gate, which have functions toprevent inundation by tsunami of the backgroundurban district on dry land. Under the technicalstandards, after the target achievement performanceand safety performance of a tsunami protection facility
have been decided, the conditions and the methods
which should be considered to verify these shall beorganized.
[Reference]
Materials of the technical committee for creation ofcommunities resistant to tsunami disasters.
http://www.mlit.go.jp/river/shinngikai_blog/tsunamibousaitiiki/index.html