Environmental Engineering Reference
In-Depth Information
15.1
Introduction
The 2011 Tohoku Earthquake Tsunami (2011 tsunami) presented its maximum
wave height of 6.7 m on a GPS wave gauge installed off the coast of Iwate Prefecture
(39°15
E) approximately 25 min after the occurrence of the
earthquake (Kawai et al.
2011
), and 40 min afterward, the tsunami reached the
Sendai Plain. In the Sendai Plain, the tsunami runup reached up to 5 km inland from
the coast line (Fig.
15.1
), causing tremendous tsunami damage. In addition, crustal
movement due to the earthquake induced land subsidence by tens of centimeters
along the coast of Sendai Bay (Geospatial Information Authority of Japan
2011
).
In relation to morphology change of the southern Sendai Coast in the past several
decades until the 2011 tsunami, the enhancement of coastal erosion was relatively
being suppressed as a result of erosion prevention measures although the coast had
previously been eroded rapidly due to coastal developments and dam constructions
during the post-war period (Udo et al.
2012
). The 2011 tsunami caused serious
beach erosion, especially at the Yamamoto Coast (see Fig.
15.1c, d
), around the
river mouths, and old river channels. Also, its damage to seawalls was serious espe-
cially at the Yamamoto Coast.
′
31
″
N, 142°05
′
49
″
Fig. 15.1
Topography of study area before the 2011 tsunami with inundation area due to the tsu-
nami; elevation change due to sediment transport before and after the tsunami. “Land
→
Sea”
shows changes from land to sea area and “Sea
→
Land” from sea to land area.
Red arrows
indicate
directions of aerial video camera (see Fig.
15.5
).
Black numerals
in (
a
) to (
d
) in the fi gure show
changes of elevation (amount of deposition);
Navy-blue
numerals show water depth; and
Red
dashed line
shows the location of seawall (Modifi ed from Udo et al.
2013
) (Source: Udo et al.
2013
(modifi ed); Japan Society of Civil Engineering)
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