Environmental Engineering Reference
In-Depth Information
Fig. 13.12
Panorama images taken at three specifi ed locations (March 25, 2011). The locations A,
B and C are indicated in Figs.
13.9
and
13.14
observations on the status of pine trees, steel fence and pipeline on the land side
demonstrated the different performance of seawalls: behind the 6 m seawall, most
local properties were conserved; on the contrary, signifi cant damage developed
behind the 4.2 m seawall with pine trees, fence and pipeline being ruined away.
Further north beyond the water gate, many seawall blocks were broken and moved
landward by the tsunami. The panorama photo Fig.
13.12b
taken at location “B” in
Fig.
13.9
presents the destruction of seawalls. Since the highest water level due to
the tsunami at the seawall is more or less 7 m as confi rmed in Fig.
13.8
, it is consid-
ered that the criterion of the seawall collapse is in between 1 and 2.8 m by the over-
fl ow depth. In this area, the relative seawall height was around 2 m with the ground
elevation being around 2 m T.P. At location between 1,100 and 1,600 m (in the
vicinity of point “C” in Fig.
13.9
), all seawall blocks were broken as revealed from
Figs.
13.9
and
13.12c
.
Some seawall blocks were even pushed across the road, and found far away inland
as shown in Fig.
13.13
. During the fi eld survey, the survey team found one broken
seawall block transported 35 m landward from its original location. This concrete
block had a dimension of 0.5 (upper boundary)×1.7 (lower bound-
ary)×2 (height)×10 m (length) with an estimated mass of approximate 53 ton,
which demonstrated the massive power of the tsunami as described by Liu et al.
(
2014
). At location 1,500 m north from the river mouth, it is found the ground eleva-
tion increases to 4 m at the north end as it approaches to the Cape Ryuugu.
Correspondingly, the seawall height increases to 5.6 m T.P. fi nally. Nevertheless, the
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