Environmental Engineering Reference
In-Depth Information
Based on the exercises in the post-disaster area, we apply a similar technique in
a pre-disaster area. Because the act mandating simulation-based zoning will be
applied in all coastal cities in Japan, the determination of the tsunami Level 1 and
Level 2 areas is also crucial in pre-disaster areas. The future improvement of struc-
tural and non-structural countermeasures should rely on such information because
relocating the existing residents of coastal areas might be diffi cult. The results pre-
sented in this paper are expected to be applied not only in Japan but also in the other
tsunami-prone areas worldwide.
10.2
Data and Modeling Framework
10.2.1
Input Data for Numerical Model
We conducted numerical simulations in two locations to represent post- and pre-
disaster areas. Sendai City was chosen as an example of a post-disaster area. The
city is now applying the concept explained in the previous section to the reconstruc-
tion process following the 2011 tsunami event. The numerical simulation on the
Sendai plain was performed using a set of nested grid systems (Fig. 10.1 ). The data
we used in regions 1-4 were obtained from the Disaster Management Council
(Cabinet Offi ce of Japan) and have accuracies of 1,350 m, 450 m, 150 m and 50 m.
We resampled these data into 1,215 m, 405 m, 135 m and 45 m cell sizes for use in
regions 1, 2, 3 and 4, respectively. In the smallest region, we used the surveyed
ground elevation data of the Geospatial Information Authority in Japan prior to the
2011 Japan tsunami. These digital elevation data have an original accuracy of 5 m,
but they were gridded into 15 m cells to ensure the stability of the numerical model.
For the pre-disaster situation, Owase City in Mie Prefecture, Japan, located in the
south of Honshu Island, was selected as a case study. Presently, this city and all
areas in the south of Japan in general are facing the potential of a large earthquake
that could generate a huge tsunami from the Tokai, Nankai and Tonankai troughs
(Earthquake Research Committee 2005 ). The selection of this area as a case study
is therefore highly relevant. To construct the numerical domain, we used the topo-
graphic data obtained from the local government of Owase City. A high-resolution
Digital Terrain Model (DTM) and a Digital Surface Model (DSM) are available,
with 10 m grid accuracy. In addition, the other input data used to establish a nested
grid system with fi ve sub-domains are also available with grid sizes of 810 m,
270 m, 90 m and 30 m (Fig. 10.2 ).
The numerical simulation utilized the linear and nonlinear shallow water equa-
tions, which were discretized in the leapfrog scheme (Imamura 1996 ). For both
areas, the tsunami was modeled for 3 hours of simulation time. The effect of the
bottom roughness of the Sendai plain was considered by assigning a homogeneous
value of 0.025 for the bottom friction coeffi cient. This value represents the condi-
tion of smooth sand or natural channels in good condition (Linsley and Franzini
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