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Hydraulic Analysis of Submergence Damage by Typhoon 9918

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Hydraulic Analysis of Submergence Damage by Typhoon 9918
Bull., Geo-Environmental Science, Rissho Univ., Vol.5(2003)
Hydraulic Analysis of Submergence Damage by Typhoon 9918
Keisuke SAITO* and Susumu OGAWA**
1. INTRODUCTION
The study of natural disaster is one of the most important ones in order to protect the lives and properties of victims. Various studies about disaster by a
high tide and high waves with an attack of typhoon
have been done till now. These were inspected from a
viewpoint of meteorology and coastal engineering.
However, without the estimate for rainfall, inflow
from the back hill, and chronological order of submergence to be distributed widely, the satisfactory
accuracy is not guaranteed. Therefore, these estimates are big factors of submergence damage. An
Figure 1 Courses of Typhoons 9918 and 9119
amount of breakwater wave overtopping was required in this study. Furthermore, the rainfall and
(Hashimoto et al., 2000; Sato et al., 2000).
rainwater inflow and submergence states were estimated using GIS with actual field survey, and hydro-
2. 2. Study area
logical and remote sensing data.
South New Moji area (about 180.6 ha), Moji district,
Kita-kyushu city, Fukuoka prefecture, was the target
in this study (Figure 2). This district was reclaimed
2. STUDY TARGETS
land with two constructed banks. A bank of the north
2. 1. Typhoon 9918
Typhoon
and
south side (No. 2) has 1,171-m extension (Total ex-
Yamaguchi areas in the early morning of September
tension becomes 1,985m). However, these banks were
24, 1999. This typhoon resembled Typhoon 9119 in
destroyed at 10 points by the wave force of the ty-
power and course in 1991 (Figure 1). However, such
phoon invasion (Takahashi et al., 2000). A large
damage magnitude as Typhoon 5915 in 1959 was
amount of seawater invaded by wave overtopping and
brought by Typhoon 9918. Because this typhoon hit
influence of bank collapse. Therefore, this area suf-
there at the same time of a flood tide and a high tide.
fered the serious inundation damage. The bank No. 2
Fortunately, Typhoon 9119 hit there at an ebb tide.
was divided into two (A and B) for convenience in
In addition, it was one of causes that an east wind was
this study (Figure 2). Especially, the bank No. 2A
blowing a gale from the west Suo Nada Sea. A signifi-
that received terrible damage was inspected. All the
cant wave height and a significant wave period of the
heights were described with a value of the chart
past maximum were observed off Kanda, Kita-
datum level (C. D. L) in the following sections and
kyushu, where the center of the typhoon passed
figures.
*
**
9918
side (No. 1) has 814-m extension, while a bank of the
attacked
north
Kyusyu
Graduate Student of Geo-Environmental Science, Rissho University
Faculty of Geo-Environmental Science, Rissho University
37
Hydraulic Analysis of Submergence Damage by Typhoon 9918 (SAITO・OGAWA)
deep water waves in the offing were referred to data
by Kita-Kyushu-City Harbor Office (Table 1). The
target time was 5:00 to 10:00 a.m., September 24.
Most of collapse parts were at jointed concrete parts.
The collapse time was not clear precisely. It was supposed to be before 7:00 a.m. because the surge was the
most prominent at that time. Those conditions were
classed in standing straight banks without vanishingwave-tetrapod concrete block mounds.
Figure 2 New Moji Port, south area
Data at Kanda, Simonoseki, and Kagumeyoshi meteorological observatory stations were used for rainfall
in the study area (Table 2). The serial rainfall during
3. METHODS
Typhoon 9918 passage was added up every meteoro-
The inundation of the coastal area by the typhoon in-
logical observatory. The rainfall of the study area
vasion was formed by inflow from seawater, rainfall,
was calculated with the isohyetal method. The pene-
and the back hill. The causes of inundation in the
tration or the losses were not considered in this study
study area were analyzed by the following methodol-
by the following reasons. It was shown that study
ogy. In addition, estimate of a storage amount in a
area was paved more than 60% from a result of super-
submergence area was carried out.
vised land cover classification with NVIR bands of
Terra/Aster (Bands 1, 2, and 3N in Figure 7). Analy-
3. 1. Estimate of inflow from deep water waves
sis for chronological order of water levels in the whole
The existing design standards for banks and dikes are
reclaimed land was not enough at this step, too.
derived from the instructions by Goda ( JSCE, 2001).
Next, rainwater inflow from the back hill was esti-
Generally, an amount of wave overtopping is esti-
mated as follows. Area of the basin where rainwater
mated with the diagrams of wave overtopping de-
flowed into the target area was obtained by 50-m-
signed by Goda (1990) in Figure 3. An amount of
mesh DEM. The runoff coefficient was estimated to
wave overtopping was calculated under the following
be 0.8 because the back hill was a steep incline (JSCE,
conditions in this study.
1985).
The target was bank No. 2A (Its extension is 526.5m).
One point of representative equivalent deep water
3. 2. Storage discharge
waves in the offing wave height H0 ' in front of the
A storage amount is a volume of between the ground
bank was used. The representative equivalent deep
and submergence surfaces. The ground level data
water waves and the representative-period equivalent
were made from a result of ground elevation survey-
Figure 3 Goda diagrams for wave overtopping
38
Bull., Geo-Environmental Science, Rissho Univ., Vol.5(2003)
Table 1 Parameters for estimate of wave overtopping
Time
Tide
(m)
Frequency
T (sec)
Wave length
L0 (m)
Depth Equivalent deep water wave
H0'/L0
h (m)
H0' (m)
h/H0'
hC
(m)
hC/H0'
5:00
3.18
6.2
59.97
6.68
1.94
0.032
3.44
2.32
1.20
6:00
4.08
6.9
74.27
7.58
7:00
5.18
8.1
102.35
8.68
2.37
0.032
3.20
1.42
0.60
2.73
0.027
3.18
0.32
0.12
8:00
5.31
8.1
102.35
9:00
4.62
6.3
61.92
8.81
2.31
0.023
3.81
0.19
0.08
8.12
1.64
0.026
4.95
0.88
0.54
10:00
3.88
4.2
27.52
7.38
0.80
0.029
9.23
1.62
2.03
Table 2 Rainfall each meteorological observatory on September 24, 1999
Time
(unit : mm)
9:00
Total
0:00
1:00
2:00
3:00
4:00
5:00
6:00
7:00
8:00
Shimonoseki
5
7
2
1
0
2
4
8
21
0
50
Yahata
10
3
2
2
0
3
9
19
16
1
65
Kagumeyoshi
3
1
1
1
0
4
9
29
12
1
61
ing in the target area. The submergence data were ob-
(Figure 4). This area exceeded the back area of bank
tained from the flood damage reports by Kita-
No. 2A. The estimated amount of water that flowed
Kyushu City. Finally, ground elevation profiles of the
into the back area of bank No. 2A was about 6,000m3.
target area were made from these data.
The rainfall storage amount at the disaster increased
by 30 % considering the inflow from the back hill.
4. RESULTS
4. 2. Storage amount
4. 1. Inflow of deep water waves
An average submergence surface was obtained from
Wave overflow was calculated from the values esti-
the heights of the ground and submergence (Figures
mated by the Goda diagrams. The result was shown
5 and 6). However, it did not form a smooth surface
in Table 3. Inflow of seawater became about 2 times
by influence of surge fluctuations and a spatial distri-
by bank collapse. The total estimated amount of rain-
bution of the measurement points. The average sub-
fall in the submergence damage was 55 mm in depth,
mergence surface was estimated as +6.7 m. The result
3
and it was about 27,000m in the whole target area. A
was shown in Table 4. It was found out that most of
2
the areas were flooded. In particular, the damage
basin area of the reclaimed land was about 554,000m
through East and West roads were huge. The result
of ground elevation surveying showed the tendency
that roads sank lower than the circumstance. In the
Figure 4 Basin area
Figure 5 Flooded water and ground elevations
39
Hydraulic Analysis of Submergence Damage by Typhoon 9918 (SAITO・OGAWA)
Table 3 Inflow from the sea
Time
5:00
No collapse section
0
(unit : m3)
Collapse section
Total
0
Table 4 Estimated storage volume
Ground height (m) Depth (m) Area (m2) Quantity (m3)
0
4.9 - 5.1
1.6
3,096
4,954
6:00
9,444
1,272
10,716
5.1 - 5.3
1.4
17,763
24,868
7:00
90,065
67,398
157,463
5.3 - 5.5
1.2
56,594
67,913
8:00
62,313
62,951
125,264
5.5 - 5.7
1
114,701
114,701
9:00
1,553
4,603
6,156
5.7 - 5.9
0.8
85,216
68,173
10:00
0
0
0
5.9 - 6.1
0.6
100,341
60,205
Total
163,375
136,223
299,598
6.1 - 6.3
0.4
29,214
11,685
6.3 - 6.5
0.2
11,724
2,345
6.5 - 6.7
0
3,174
0
Total
354,843
Figure 6 Ground elevation map
Figure 7 Land-cover classification of the study area
reclaimed land, seaward is lower than land side for
amount of water was considerably large by results of
drainage. However, some points became the topogra-
this study.
phy like a hollow by local settlement. Drainages for
rainwater existed in the target area. However, there
were no water gate or no countercurrent prevention
5. DISCUSSION
functions. Accordingly the rainwater drainage in the
The submergence damage by Typhoon 9918 was
target area was in bad condition. Most rainwater con-
evaluated in the south part of New Moji area. The
centrated into the target area. It was shown that the
main cause of inundation was wave overflow and
40
Bull., Geo-Environmental Science, Rissho Univ., Vol.5(2003)
Aerial photograph
VNIR of Terra/Aster (Bands 1, 2, and 3N)
SWIR of Terra/Aster (Bands 4, 5, and 9)
TIR of Terra/Aster (Band 13)
Figure 8 Various images of the study area
bank collapse, but the topography of the reclaimed
order to investigate the submergence damage more
land and the back hill became causes of damage ex-
precisely. Construction of non-routine water budget
pansion, too. Improvement of estimate accuracy for
simulation in a target area at typhoon invasion will
submergence damage was proposed as a future theme.
be executed. Finally, detailed reproduction at the dis-
It is necessary to investigate elevation of the ground,
aster should be carried out, and it will be contributed
land covers of the target area, and rainwater drain-
to inundation damage reduction in a coastal area.
age function more in detail in order to analyze surge
of water in the inundation area particularly. NVIR
References
bands of Terra/Aster were used for land cover classi-
Goda, Y., 1990. Design of wave hindcasting for harbor struc-
fication in this study (Figure 8b). These bands detect
presence of vegetation very well, but classification of
roadsides and bare land was not so well. Besides,
Terra/Aster data have six SWIR bands (bands 4 to 9
in Figure 8c) and five TIR bands (bands 10 to 14 in
tures, Kajima Institute Publishing Co., 118-131.
Hashimoto, N., Maki, T., and Yoshimatsu, M. (2000). Investigation of storm waves caused by Typhoon 9918 with
wave hindcasting methods, WAM and MRI, Technical note
of the Port and Harbor Research Institute, Ministry of
Transport, Japan, Dec., No.970.
Figure 8d). White pixels in Figure 8 were identified as
Japan Society of Civil Engineers (2001). New wave
bare land by actual ground truth. However, the re-
hindcasting method and design for coastal structures, 190-
flections were obviously different in accordance with
200.
bands in other bare lands. Using those bands, a
method to estimate indispensable information such as
permeability of soils, the roughness, a ground eleva-
Japan Society of Civil Engineers (1985). Hydraulic formula
series, 30, 31, 529-534.
Sato, T., Yamamoto, S., Hashimoto, N., Hiraishi, T.,
Kitazawa, S., Matsushima, K., and Ohkawa, I. (2000),
tion, or soil moisture will be developed in future in
41
Hydraulic Analysis of Submergence Damage by Typhoon 9918 (SAITO・OGAWA)
High tide damage by Typhoon 9918 in Suo Nada Sea area
Ishinuki, K. (2000). Seawall failures by Typhoon 9918 and
and its degree of dangerness estimate, Proceedings of
their reproduction in wave flume experiments, Technical
Coastal Engineering, JSCE, 47 (1), 316-320.
note of the Port and Harbor Research Institute, Ministry of
Takahashi, S., Ohki, Y., Shimosako, K., Isayama, S., and
Transport, Japan, Dec., No.973.
台風9918号による浸水被害の水理解析
斎藤
*
恵介*・小川
立正大学大学院生
進**
**
立正大学地球環境科学部
本研究では9918号台風襲来による浸水災害について、 護岸越波量と冠水状態の推定に加え、 GIS を
用いて降雨量と雨水流入量の推定を行った。 対象地は福岡県北九州市新門司埋立地区である。 護岸越波
量の推定は合田による直立護岸の越波流量推定図を用いて行った。 平均降雨量は近隣3箇所の気象庁測
候所における記録を用いて算定した。 背後地からの雨水流入量は50m メッシュ DEM より流域界を切
り、 平均降雨量に流出係数を乗じて求めた。 冠水位の分布は地盤高測量結果と湛水深より推定した。 こ
れらの結果より、 被害原因および埋立地構造上の問題点についても考察した。
42
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