Environmental Engineering Reference
In-Depth Information
10.1
Introduction
Because the basic guidelines for reconstruction have stated that 'multiple defense'
should be used to shape a disaster-resilient community (Reconstruction Agency of
Japan 2011 ), a new act in Japan (Act No. 123/2011) that mandates tsunami-safe
cities requires local governments to simulate the impacts of massive tsunamis in the
development of zoning policy (Cyranosky 2012 ). Because of the implementation of
this concept, two levels for potential tsunami-affected areas have been proposed as
follows (e.g., Shibayama et al. 2013 ).
Tsunami area Level 1 (the Tsunami Protection level): These tsunami events
represent events with a return period of several decades to slightly over 100
years. The Japanese expression that has been used in coastal engineering discus-
sions would literally translate as a return period from 50-60 to 150-160 years.
These tsunamis would generate relatively shallow inundation depths, typically
less than 7-10 m.
Tsunami area Level 2 (the Tsunami Evacuation level): These events, in contrast,
would be far rarer events, typically taking place at intervals between every few hun-
dred and a few thousand years. The tsunami inundation depths would be much
larger, typically over 10 m, but would include inundations of up to 20-30 m. Both
the 2004 Indian Ocean tsunami and the 2011 Great Eastern Japan Earthquake and
Tsunami would fall within this category.
In the post-disaster areas, the application of this concept is taking place by sim-
ply relocating people to higher ground if there are natural hills available nearby. In
these locations, lowland areas will be elevated to the same height as the maximum
tsunami fl ow depth generated by earthquakes with a return period less than
150 years. The high ground, where the new settlement will be located, should be
higher than the maximum possible tsunami with a return period longer than centu-
ries (e.g., Bureau of Reconstruction and Minami-Sanriku town 2012 ).
In the plains, however, tsunamis can penetrate farther inland. The determination
of Level 1 and Level 2 areas, therefore, should be conducted in a more careful man-
ner. The absence of natural hills implies the need to construct more artifi cial barriers
along the shore, which attempt to reduce the damage to property and the loss of lives
(e.g., Sendai Reconstruction Bureau 2012). The determination of tsunami Level 1
and Level 2 areas in this context plays a fundamental role as the basis for the land
use planning.
This article proposes a method to determine tsunami Level 1 and Level 2 areas.
In the fi rst part, we demonstrate the use of numerical simulations to provide input
for GIS modeling to classify post-disaster areas. We model tsunamis from historical
and future possible earthquakes that have affected or may affect the Sendai plain.
We will show the different impacts of the tsunamis in the existing and in the future
topographic conditions by following the reconstruction plan of Sendai City. We
developed an improved GIS framework to estimate the affected ratio and the statisti-
cal description of variable tsunami fl ow depths that impact a particular location
inside the tsunami inundation area.
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