THE BEHAVIOR OF TSUNAMI-INDUCED DRIFTAGEAND IT’S PROBLEM IN THE FISHING AREAS
Koji OTSUKA*, Hiroyuki KATOH**, Ken-ichi SATOH***, Koji FUJIMA***** Senior Consultant, The Japanese Institute of Technology on Fishing Ports, Grounds and Communities** Chief Researcher, The Japanese Institute of Technology on Fishing Ports, Grounds and Communities*** Manager, Emergency Management Division, General Affairs Department, Kesennuma-City**** Prof. Department of Civil and Environmental Engineering, National Defense Academy
Japan has received the damage of a lot of Earthquakes and Tsunamis in the past. The fishingcommunities are especially susceptible to damage from Earthquakes and Tsunami in the coastal regions.
They set aquaculture cages, fishing gears, mooring fishing vessels, work vehicles, etc. close to the edgeof the water. When the Tsunami attacks a fishing community, some of these items are set adrift by huge
waves of Tsunami, which may further expand the damage. The Tsunami-induced driftage blockades theroute to the port and may hinder or prevent closing of the sea route at the time of disaster and marinetransport for immediate rescue and restoration. Some fishing communities may even be completely
isolated due to the paralyzed sea route. We carried out simulation studies to understand how the driftage
behaves in Tsunami through simulation studies, and specifies problems..
Key Words : Tsunami, aquaculture rafts, driftage, disaster mitigation

1．Purpose of the Study
There are aquaculture rafts, fishing gears, fishing vessels,
work vehicles, etc. close to the edge of the coast. When theTsunami attacks a fishing village, these objects are set adrift
by Tsunami, which may further expand the damage. The
Tsunami-induced driftage blockades the sea route at the timeof disaster and marine transport for immediate rescue andrestoration. Some fishing villages may even be completely
isolated due to the blocked sea route. Our study aims tounderstand how the driftage behaves by Tsunami, andspecifies problems.

basin are blockaded, and the danger of the village isolation
holds the problem of height etc. by cutting the road inpieces.
As a result, the obstacle is caused to the emergency rescue
and the remediation activity, a weak characteristic is
possessed for the Earthquake and the Tsunami hazard, and it
has experienced having repeated a lot of painful damage upto now1).
⑩Hokkaido-nansei-oki Earthqake（Ｍ７ .８ ）【１９９３/７/１２】○The dead and missing person ２３０○Height of the maximum run-up ３０ｍ①Meiji Sanrik u Earthquak e Tsunami（Ｍ８.５ ）【 １８９６/ ６/ １５】○T h e dead an d m issin g pe r so n ２２， ０００○He igh t o f t h e m axim u m r u n - up ３８． ２ｍ⑨Nihonkai-chubu Earthqake（Ｍ７ .７ ）【１９８３/５/２６】○The dead and missing person １０４○Height of the maximum tsunami １４ｍ⑩③Kita-Tango Earthqake（Ｍ７ .３ ）④Syowa Sanrik u Earthqak e Tsunami（Ｍ８.1）⑨【１９２７/３/７】○The dead and missing person ２，９２５①④⑪Great Hanshin-Awaji Earthqake（７.３ ）⑥Mikawa Earthqake（Ｍ６ .８ ）⑫Fukuoka Seiho-oki Earthqake（ Ｍ７. ０）【２００５/３/２０】○The dead and missing person １○負傷者数 １，０８７人

③⑫⑪②
⑪⑦

In our country, about 3,000 fishing ports are locatedthroughout the country, and there are about 6,000 fishingvillages behind the fishing ports. Up to now, our country has
been overcome by a lot of Earthquakes and Tsunamis. The
fishery villages are formed in the coast area, there arelocated in the littoral region in the isolated islands, peninsula,and remote rural area, etc., and a lot of that the dense
villages are formed in narrow-minded geographical features
where the mountain approaches behind.
Therefore, the open space that can be used when thedisaster occurs cannot be secured, the fishing boats and theaquaculture rafts become wreckages, the sea route and the127②G reat Kanto Earthqake（Ｍ７ .９）【１９２３/９/１】○The dead and missing person１４２，８０７【１９９５/１/１７】○The dead and missing person ６，４３６

2 ． Probability of Earthquakes Occurrence
Next 30 Years【 １９３３/ ３/ ３】○T h e dead an d m issin g pe r so n ３， ０５４○He igh t o f t h e m axim u m r u n - up ２９ｍ⑥⑤⑤⑦【１９４５/１/１３】○The dead and missing person １，９６１⑥Chile Earthqake Tsunami（Ｍ９.５ ）【１９６０/５/２３】○The dead and missing person １４２○Height of the maximum tsunami ６ｍ⑦Nankai Earthqake（Ｍ８ .０ ）⑤Tonankai Earthqake（Ｍ７ .９ ）【１９４６/１２/２１】○The dead and missing person １，４４３○Height of the maximum tsunami ６ｍ【１９４４/１２/７】○The dead and missing person ９９８

Fig. 1 Occurrence Past Earthquake and Tsunami inJapan
The probability that the Earthquake will occur within 30
years in the future especially has the drawing near level ofeach earthquake of Miyagi-ken-oki Earthquake (99%) andTokai Earthquake (87%), Tonankai Earthquake (60-70%),
and Nankai Earthquake (60%) in an extremely high situationhigh in the whole area of the Pacific Ocean and Tohoku andthe Hokkaido region as show as Fig. 22).

Ho kkaido No r t h - We st（ ≒Ｍ7 . 8 ） ０．１％

Nemu ro（ ≒Ｍ7 . 9 ） ４０％

Akita

Tokachi（ ≒Ｍ7 . 5 ） ３％

（ ≒Ｍ8 . 1 ） 0 . 2 ～2 ％Sado Island

Sanriku North（ ≒Ｍ7 . 8 ） ６％

（ ≒Ｍ8 . 0 ） ７％

Aki～Bun go

Miyagi（≒Ｍ7.5）
９９％（ Ｍ6 . 7 ～7 . 4 ） ４０％

Kesen-numa

Sanriku～Bo soHyu ga（ ≒Ｍ7 . 6 ） １０％（ ≒Ｍ7 . 1 ） 7 0 ～8 0 ％・ 津波型≒M8 . 2 ２０％・ 正断層型 ≒M8 . 2 ７％

Genroku Kan to（ ≒Ｍ8 . 1 ） ０％

So uth Kan to（ ≒Ｍ6 . 7 ～7 . 2 ） ７０％

Nankai（ ≒Ｍ8 . 4 ） ６０％

To n an kai（ ≒Ｍ8 . 1 ）６０～７０％Tokai（ ≒Ｍ8 . 0 ） ８7 ％Taisho Kan to（ ≒Ｍ7 . 9 ） ０． ９％

Fig. 4 General Situation of Fishery Region

Fig. 2 Probability of Earthquakes Occurrence andScale within Next 30 Years

Rescue BaseFig. 3 shows probability of Miyagi Offshore Earthquakes
occurrence at offshore of Kesen-numa Bay. Miyagi Offshore
Earthquake, single type, is presumed the occurrence ofprobability of 99% and 80 ～90%.

RARD
RARD
ROAD
(for Car)（forCar)（forCar)Possibility
Possibility
Closing
Closing 46％
46％

Possibility
Possibility
Closing
Closing 81％
81％

Therefore,
Therefore, when
when thethedisasterdisaster occurs,
occurs, sea
sea
route
route has
has key
key role.
role.

AIRAIRRoute
AIR Route
Route(for（forHeliport)（forHelicopter)
Heliport)
SEA
Route
SEA Route(forShip)(for Ship)

Miyagi（Single）

Fig. 5 Vulnerability in Fishery Region
to Disaster (1)（≒Ｍ７.５）９９％

Kesen-numa
Miyagi（Single）（≒Ｍ７.７）８０～９０％

The
The Headquarters
Headquarters
forfor Earthquake
Earthquake
ResearchResearch Promotion,Promotion,Government
Government ofof Japan
Japan

According to the data 2005 by Fishery Agency, as a resultof surveying the fishing village in the whole country, all of
the three routes closed caused by the Earthquake and theTsunami, there are about 38％ of 4,696 fishing villages. In
addition, 87％ fishing village that can be secured only by
one route is included (Fig. 6) 1) .

Miyagi（Synchronized）（≒Ｍ８）

Fig. 3 Probability of Miyagi Offshore Earthquakes
Occurrence Next 30 Years

2 Rotes
(584)
12.4%

3．Vulnerability in Fishery Region to Disaster3 Routes(13)
0.3%

No Route(1,761)
37.5%

1 Rout(2,338)
49.8%

The fishing villages are especially susceptible to damage
from Earthquakes and Tsunami in the coastal regions. In thefishing village, there are three routes of the road, the airroute, and the sea route. It should secure the fishing village
and these routes be secured according to the Earthquake andthe Tsunami for the rescue and restoration. The possibility
closing the road it due to the disaster is 81%. The possibility
closing the air route as heliport is 46%. Therefore, when thedisaster occurs, the sea route has the key role as show as Fig
4, 5．

2005, by Fishery Agency

AllAll ofof thethe three
three routes
routesclosedclosed caused
caused byby thetheEEarthquake
arthquake andand thetheTTsunami,sunami,
sunami there
there areareabout％ of38
about 38％
38％
of 4,696
4,696
fishingfishing villages.
villages.
In％87In addition,addition, 87％
87％
fishingfishing village
village thatthat
cancan be
be secured
secured only
onlybyby one
one route
route isisincluded.
included.

Fig. 6 Vulnerability in Fishery Region
to Disaster (2)A large-scale Kesen-numa fishing port is located in theKesen-numa bay. A lot of small fishing ports and villages
are located in the surrounding area. The Kesen-numa fishingport has the role as the rescue base in the fishing village inthe surrounding area. On the other hand, the aquaculture
rafts are arranged in the Kesen-numa Bay. When these128aquaculture rafts will drift by the tsunami, the sea route isclosed. As a result, a lot of fishing villages are isolated (Fig.
7)3).

Fig. 9 shows the drift simulation of the aquaculture rafts
by Miyagi Synchronized Type Earthquake.
Based on the drift simulation of the aquaculture rafts, thesea route is blockaded by the raft's drifting, and dispersing
them in the bay. Therefore, It becomes impossible for thevessels to sail. A disaster reduction measures necessary tosecure the function of the fishing port when the Tsunami
raids are mainly the driftage measures4).

KesenKesen-numa Fishing Port（Rescue Base）
Base）
City Area

Small Fishing
Ports & Villages

Aquaculture

5．Damage of Tsunami by Chilean Earthquake2010
End of this February, Chilean Tsunami attacked
Kesen-numa City. A lot of aquaculture rafts were greatdamaged as drift by the Chilean Tsunami 2010 as show as
Fig. 10.

Oshima Island

Fig. 7 Vulnerability in Fishery Region to Disasterin Kesen-numa Bay

Max.
Max. Velocity<3m/s
Velocity<3m/s(calculated(calculated byby Dr.
Dr. Fijima)
Fijima)4．Situation of Kesen-numa Bay
Kesen-numa fishing port is located at bottom ofKesen-numa Bay. There are a lot of objects in the market as
fish selecting machines, fish boxes, many kind of vehicles
and workers. On the other hand, there are a lot of objects
also in the bay as fishing vessels, vehicles, aquaculture rafts
as show as Fig. 8.
Vehicles
VehiclesBigBig Fishing
Fishing
Vessels
Vessels

Raft Type
Type(Oyster)(Oyster)

Trawl line Type(Seaweed
Seaweed)Fig. 10 Damage of Aquaculture Rafts

SmallSmall Fishing
Fishing
Vessels
VesselsFig. 11 shows the result of Tsunami Current Simulation
by Dr. Fujima. According to the calculation by Dr. Fujima,
maximum current velocity was over 3m/s. When current
velocity 1m/s is exceeded, it is reported that the aquaculture
rafts damage begins to appear by Dr. Shyuto and Dr.
Imamura5).

Aquaculture
Aquaculture
Rafts
Rafts (Seaweed)(Seaweed)

Aquaculture
Aquaculture
Rafts
Rafts (Oyster)(Oyster)Max.
Max. Velocity
Velocity >> 3m/s3m/s(calculated(calculated byby Dr.
Dr. Fijima)
Fijima)Fig. 8 Objects in Kesen-numa Bay
Miyagi （（SynchronizedSynchronized Type）ype）
Type）

Distributed
Distributed Aquaculture
Aquaculture Rafts
Rafts

Raft’
Raft’ Drifting,Drifting, Dispersing
Dispersing

When
When Current
Current Velocity
Velocity 1m/sec
1m/sec isis exceeded,exceeded,it
it isis reported
reported thatthat thethe aquaculture
aquaculture rafts
rafts damage
damagebegin
begin toto appear
appear at
at Chile
Chile Tsunami
Tsunami 1960
1960 bybyDr.
Dr. Shyuto
Shyuto andand Dr.
Dr. Imamura.
Imamura.

Fig. 11 Result of Tsunami Current Simulation

6．Influence and Problem by Driftage

Sea Rout Is
Blockaded

The sea route is blockaded caused by driftage. As a result,the following two problems will occur6).
① Big Scale Fishing Port：
It becomes impossible for sailing and mooring the fishing

Fig. 9 Result of Drift Simulation of
the Aquaculture Rafts

129

boat, and also unloading the marine products caused bydriftage. Consequently, an extensive loss is given to theregional economy.

8．Conclusion
Most of the aquaculture rafts are moored within bays inJapan. When Tsunami raids, it was found that the mooringropes sever and the rafts are turned into driftage. Suchdriftage scatters throughout the area and block the route.
Many of fishing areas are located on islands or peninsulas.
The results of the present study made clear the necessity
to make efforts to secure sea routes in the aftermath ofEarthquake and Tsunami for rescue and restoration. It issuggested to strengthen the mooring devices and to preventthe driftage from diffusing a measure against occurrence ofdriftage.

② Small Scale Fishing Villages：
The small-scale fishing village located in the isolatedisland and the remote rural area depends on the rescue andsave operation from the outside. It becomes impossible notto enter port about the rescue ship from the outside causedby driftage and the rescue and rescue operation stagnate. As
a result, the fishing village might be isolated.
KesenKesen-numa Fishing Port（Rescue Base）
Base）

City Area

参考文献
1) 災害に強い漁業地域づくりガイドライン，(社)全国漁港漁Small Fishing Ports &Villages

場協会，2006
2) 海溝型地震の長期評価の概要：文部科学省地震調査研究推進本部，2010

Aquaculture3) 大塚浩二・伊藤敏朗・中村隆・風間隆宏：地震・津波災

Oshima Island

害時における漁村の孤立危険性について，日本沿岸域学会研究討論会講演概要集 No.19，pp250～253，2006

Fig. 12 Influence and problem by Driftage4) 水谷将・大塚浩二・中村隆・伊藤敏朗：津波シミュレー
ションを用いた災害に強い漁業地域づくり，第 5 回全国
漁港漁場整備技術研究発表会講演集，pp134～143，2006

7．Countermeasures for Minimization ofDamage5) 藤間功司・鴫原良典・加藤広之・丹治雄一：2010 年チリ
津波による養殖施設の被害調査，地域安全学会梗概集

7.1 Necessity of Countermeasures

No.26，2010

It is assumed to cause the immediate damage but also themassive damage for the rescue, restoration, and the fisheryactivities. Therefore, it is an important problem for thefishery region to prevent the aquaculture facilities fromdrifting, and is necessary to execute it immediately.

7.2 Countermeasures against Driftage
There are two kinds of countermeasures against driftage.
- To strengthen the reservation so as not to drift in theaquaculture rafts by private sector.
- To prevent the driftage from diffusing by public sector.
Advance measures are necessary by party concernedcombine.

1306) Koji OTSUKA・Hiroyuki KATO・Ken-ichi SATOH・Koji F
UJIMA ： THE BEHAVIOR OF TSUNAMI-INDUCEDDRIFTAGE AND IT’S PROBLEM IN THE FISHING
AREAS, PACON 2010, pp83