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Method of setting design tsunami water level andguidelines on tsunami inundation simulations

SUWA Yoshio, Head
KATO Fuminori, Senior Researcher
WATANABE Kunihiro (Ph.D), Researcher
River Department, Coast Division(Key Words) Design tsunami, coastal dike, tsunami inundation simulation
1. Outline
Under the interim report of the Committee forTechnical Investigation of Countermeasures for
Earthquakes and Tsunamis Based on lessons
learned from the 2011 off the Pacific Coast ofTohoku Earthquake of the Central DisasterManagement Council (June 26, 2011), the provisionof coastal protection facilities to deal with aconstant tsunami height which occurs relatively
frequently will continue, and, by hypothesizing thetop class tsunami, comprehensive countermeasures
including all feasible methods, both structural andnon-structural, will be taken. Regarding the former,
ministries related to coastal protection has enacted amethod of setting the water level for the design
tsunami of coastal dikes. Regarding the latter, theCoast Division has, cooperatively with the Sea
Coast Office of the Water and Disaster
Management Bureau,
MinistryofLand,Infrastructure, Transport and Tourism, prepared theguidelines on tsunami inundation simulations fortsunami countermeasures based on the 2011 off thePacific Coast of Tohoku Earthquake. Prefectures
were informed of both on July 8, 2011.
2. Method of setting design tsunami water level
The design tsunami, which is needed to provide
coastal conservation facilities such as coastal dikes,
is basically set for each region’s coastline (dividing
a coastal region into coherent coastlines considering
natural conditions such as the shapes of bays, thedistribution of coastal cliffs, etc.).
The water level of the design tsunami is set by
the following procedure.
・The actual heights of past tsunami are organized.
・When it is not possible to obtain adequate data
concerning actual tsunami heights, the tsunami
height is calculated by a simulation.
・A graph is prepared plotting the year of thetsunami on the axis of abscissas and the tsunami
height along the coastline on the axis of ordinates.
The aggregation of tsunami hypothesized to arrive
at a frequency of once in a few decades up to
between 100 and 200 years is selected as the object
tsunami group for the design tsunami water levelsetting.
・By performing a simulation of tsunami in theobject tsunami group on the condition that tsunami
intrusion is prevented at the locations of dikes on
the region’s coastline, the tsunami water level
distribution along the region’s coastline iscalculated to set the water level of the design
tsunami.
3. Guidelines on tsunami inundation simulations
The guidelines present a standard method ofperforming fast and suitable tsunami inundation
simulations in order to support the enactment ofreconstruction and recovery plans for disasterregions.
The following are the major items in theguidelines.
・The object earthquake fault model is basically set
by revising the optimum fault model from theperspective of tsunami (model verified as suitable
over a wide area) so that it complies with the tracevalues along each region’s coast.
・ Topographical data are basically prepared basedon high precision data obtained by a laser profiler
after the Great East Japan Earthquake.
・ A prediction simulation basically considers
damage to structures caused by the earthquake
motion and tsunami.
・In order to understand the run up of tsunami on theland, the plane distribution of maximum inundation
depth etc. and the cross-shore distribution of themaximum water level on a typical section are output
as the results of the simulation.
[Reference]
Guidelines on tsunami inundation simulations fortsunami countermeasures based on the 2011 off thePacific Coast of Tohoku Earthquake.
http://www.nilim.go.jp/lab/bcg/
kisya/journal/kisya110711.pdf