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 ahigh tide and high waves with an attack of typhoon
have been done till now. These were inspected from aviewpoint 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
Typhoonandsouth 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 were24, 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, suchphoon invasion (Takahashi et al., 2000). A large

damage magnitude as Typhoon 5915 in 1959 wasamount of seawater invaded by wave overtopping andbrought 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 inIn addition, it was one of causes that an east wind wasthis 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 thecant wave height and a significant wave period of theheights were described with a value of the chart

past maximum were observed off Kanda, Kita-

datum level (C. D. L) in the following sections andkyushu, where the center of the typhoon passedfigures.

＊＊＊9918

side (No. 1) has 814-m extension, while a bank of theattacked

north

KyusyuGraduate Student of Geo-Environmental Science, Rissho University
Faculty of Geo-Environmental Science, Rissho University37

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). Thetarget 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 themost prominent at that time. Those conditions wereclassed 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 areavasion was formed by inflow from seawater, rainfall,

was calculated with the isohyetal method. The pene-

and the back hill. The causes of inundation in thetration 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 studyogy. In addition, estimate of a storage amount in aarea was paved more than 60% from a result of super-submergence area was carried out.

vised land cover classification with NVIR bands ofTerra/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 arereclaimed 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 ofmesh DEM. The runoff coefficient was estimated towave 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 theA storage amount is a volume of between the groundbank was used. The representative equivalent deepand submergence surfaces. The ground level datawater waves and the representative-period equivalent

were made from a result of ground elevation survey-Figure 3 Goda diagrams for wave overtopping

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Bull., Geo-Environmental Science, Rissho Univ., Vol.5(2003)

Table 1 Parameters for estimate of wave overtopping
TimeTide(m)Frequency
T (sec)Wave length
L0 (m)

Depth Equivalent deep water wave
H0'/L0h (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

7:00

5.18

6.9

74.27

7.58

2.37

0.032

3.20

1.42

0.60

8.1

102.35

8.68

2.73

0.027

3.18

0.32

0.12

8:00
9:00

5.31

8.1

102.35

8.81

2.31

0.023

3.81

0.19

0.08

4.62

6.3

61.92

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

(unit : mm)
9:00
Total

Time

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

Shimonoseki

572

1024

8

21050

Yahata

1032

203

919

16

165

Kagumeyoshi

311

104

929

12161

ing in the target area. The submergence data were ob-(Figure 4). This area exceeded the back area of banktained from the flood damage reports by Kita-No. 2A. The estimated amount of water that flowed

Kyushu City. Finally, ground elevation profiles of theinto 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 increasedby 30 % considering the inflow from the back hill.

4. RESULTS

4. 2. Storage amount4. 1. Inflow of deep water waves

An average submergence surface was obtained fromWave 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 surfacein 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

3and it was about 27,000m in the whole target area. Awas shown in Table 4. It was found out that most of2

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 resultof ground elevation surveying showed the tendency
that roads sank lower than the circumstance. In theFigure 4 Basin area

Figure 5 Flooded water and ground elevations

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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
Total0

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

17,76324,868

7:00

90,06567,398

157,463

5.3 - 5.5

1.2

56,594

67,913

8:00

62,31362,951

125,264

5.5 - 5.7

1114,701

114,701

9:00

1,553

4,603

6,156

5.7 - 5.9

0.8

85,216

68,173

10:00

000

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

11,7242,345

6.5 - 6.7

03,1740

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 foramount of water was considerably large by results ofdrainage. However, some points became the topogra-

this study.

phy like a hollow by local settlement. Drainages forrainwater existed in the target area. However, there
were no water gate or no countercurrent prevention

5. DISCUSSIONfunctions. Accordingly the rainwater drainage in theThe submergence damage by Typhoon 9918 wastarget area was in bad condition. Most rainwater con-evaluated in the south part of New Moji area. Thecentrated into the target area. It was shown that themain cause of inundation was wave overflow and40

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 moreland 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 surgeof 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 detectpresence of vegetation very well, but classification ofroadsides and bare land was not so well. Besides,Terra/Aster data have six SWIR bands (bands 4 to 9in Figure 8c) and five TIR bands (bands 10 to 14 intures, Kajima Institute Publishing Co., 118-131.
Hashimoto, N., Maki, T., and Yoshimatsu, M. (2000). Investigation of storm waves caused by Typhoon 9918 withwave hindcasting methods, WAM and MRI, Technical noteof the Port and Harbor Research Institute, Ministry ofTransport, 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 with200.

bands in other bare lands. Using those bands, amethod to estimate indispensable information such aspermeability 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 in41

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 andand its degree of dangerness estimate, Proceedings oftheir reproduction in wave flume experiments, Technical

Coastal Engineering, JSCE, 47 (1), 316-320.

note of the Port and Harbor Research Institute, Ministry ofTakahashi, S., Ohki, Y., Shimosako, K., Isayama, S., andTransport, 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｡

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