February 8, 2011

New Contingency Plan

Takeo Office of River, Kyushu Regional Bureau, MLIT

JICA Training

Copyright (C) 2011 Takeo Office of River, MLIT. All Rights Reserved. This article was translated by JICA

Altitude1,800 m (T.P)1,000 m

150 m

14 m8-14 m5-8 m3-5 m1-3 m0 (to −1 m)Sea

•• Area at sea levelArea at sea level

(1) Saga Plain is an extensive area of low flatland

(1) Saga Plain is an extensive area of low flatland

(1) Saga Plain is an extensive area of low flatland

Coastline at the beginning of the alluvial period

Coastline about 2,000 years ago

Coastline around 800 AD

Coastline around 1600 AD

Present coastline

Around the 6th century

Rec

lam

atio

n w

orks

Ariake Sea

Rokkaku River

Ushizu RiverSaga City

Figure 1-2(3): Changes in the coastline of the Saga Plain (Shiroishi District)

About 60% of the basin is an inland water area.

(2) The mountain area is smaller than the plain area

Rokkaku River

Ushizu River

Takeo River

Ariake Sea

Haruke River

Rokkaku River

Imade River

Ishihara River

Ushizu River

Myokenbashi

Suminoebashi

Shiomibashi

(3) The rivers meander due to the low flatland (Meandering river)

The tidal range of the Ariake Sea reaches is up to about 6 m. Seawater therefore flows to the upstream section of the rivers at high tide. The hinterland is a low flatland that is 0-3 m above sea level since the tidal mudflats have been converted to land or reclaimed by people. As a result, it is difficult to use the river water.

(4) Ariake Sea has the greatest tidal range in Japan

High tide

Ariake Sea

Saga Plain

Tidal mud flatsLow tide

At low tideAt high tide

(4) Ariake Sea has the greatest tidal range in Japan

Leading the slow and meandering rivers whose the tidal range is up to about 29 km in Japan

Basin area: 341 km2

Main course length: 47 kmPopulation in the basin: About 120,000 peopleExpected flood area: About 201 km2

Population in the expected flood area: About 110,000 people

(4) Ariake Sea has the greatest tidal range in Japan

Legend Basin boundary

Railroad

Highway

Route 34Section under direct control

Expected flood area

Municipal boundaryExisting retarding pond

JR Karatsu Line Sefuri-Ten

Mountain System

Nagasaki Expressway

Mt. Ten (1,046 m high)

Mt. Hachiman (764 m high) Taku City

Mutabe Retarding Pond

Ogi City

Route 34

JR Nagasaki Line

Rokkaku Estuary

Weir

Takeo City

Omachi Town

JR Sasebo Line

Mt. Jinroku (447 m high)

Nishikyushu Expressway

Dainichi Weir

Shiroishi Town

Kohoku Town

Ariake Sea

When a flood has occurred, . . .

August 1980(Takeo City)

Flooding in July 1990

Rokkaku River

Takeo River

Taka

hash

i Riv

er

Route 498

Route 34

Takeo-Taku Line (main local road)

Submerged road

Flooding in July 1990

Submerged Route 34 (Asahi Town, Takeo City)

Flooded Asahi Town, Takeo City

Flood on July 26, 2009

Present Flood Control

(1) Letting floodwater flow safelyConstruction of embankments

(2) Controlling floodwaterDams and retarding ponds

(3) Discharging inland waterDrainage pumps

Bank

Ariake clay layer

Gravel layer

Since the start of the modification of rivers under direct control in 1958, embankments and river channels have been constructed and modified weirs installed to improve the flow-down capability. When constructing embankments, the ultra-soft ground was improved by means of slow banking work.

Improving structure

Improving structure

Image of soft ground improvement

Ultra-soft ground improvement[DJM method]

Kyuragi DamLocation of the Matsuura River System

Matsuura River System

Fukuoka

Saga

Oita

Nagasaki Kumamoto

Miyazaki

Kagoshima

下筌ダム（小国町、中津江村） 松原ダム（大山町、天瀬町）

Flood on July 26, 2009 Flood on July 26, 2009

Right bank of the midstream section of the Ushizu River (15 k100 to 16 k400)[Facility scale] Design scale: 1/100 (Target: Myoken Bridge) Flood control rate: 100 m3/s

Pond area: 53.4 ha Storage: 900,000 m3

Mutabe Retarding Pond

Imade River

Ushizu River

Mutabe Retarding Pond

Overflow levee Drainage

pump station

Arrangement of the Drainage Pump StationsDrainage pump station (MLIT)Drainage pump station (MAFF)Drainage pump station (local government)

Legend

About 350 m3/sAbout 130 m3/s

About 220 m3/s

Total

Ushizu River

Rokkaku River

Takeo City

Taku City

Kohoku Town

Mutabe Retarding

Pond

Myoken Bridge

JR Karatsu Line

Ogi City

Route 203

Ushizu River

Omachi Town

Takahashi DPS

JR Sasebo LineTakeo River

Shiroishi Town

Shiomi Bridge

Ureshino City

Rokkaku

River

Rokkaku Estuary

Weir

Suminoe Bridge

JR N

agas

aki L

ine

Rout

e 20

7

Route 444

Takahashi Drainage Pump Station

Takahashi DPS

Takeo River

Takahashi River

Location: Left side of the Rokkaku River (0/800), Takahashi, Asahi-cho, Takeo-shi, Saga

Completion: March 1997

Design discharge: 50 m3/s (3 pumps, each rated at 16.7 m3/s)

Limits of Disaster Prevention that Relies on Facilities

0

100

200

300

500

400

10

5

(times/ year)

(times/ year)

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

1. Frequency of rains whose hourly precipitation is 50 mm or more

2. Frequency of rains whose hourly precipitation is 100 mm or more

Annual number of hourly rainfall (at about 1,300 AMeDAS points throughout the

country)

2.52.5 times in avg.times in avg.

1988-19971.91.9 times in avgtimes in avg

1978-1987

206206 times in avg.times in avg.

1978-1987

4.84.8 times in avg.times in avg.

1998-2007

318318 times in avg.times in avg.

1998-2007

233233 times in avg.times in avg.

1988-1997

Source: Japan Meteorological Agency

Recent Rise in the Frequency of Torrential Rain

0 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

• It is difficult to completely prevent disasters• Avoiding devastating damage• Minimizing damage to the greatest possible

extentDisaster prevention reliance is based on

physical aspects (hard)

Disaster reduction is based on non-physical resources (soft)

Change in Approach from Disaster Prevention to Disaster Reduction

Plan 1:Plan 1:Making towns in consideration of risk managementPlan 2:Plan 2:

Using new information about disaster prevention

New Contingency PlanNew Contingency PlanNew Contingency Plan

Resident’s sheltering

action

Local flood prevention activities

Government’s information

service

SelfSelf--helphelp

Mutual aidMutual aid Public Public supportsupport

Improving the disaster prevention capabilities of local areas should start

with a review of the relationship between the government and residents.

Thank you for your attention.

Copyright (C) 2011 Takeo Office of River, MLIT. All Rights Reserved. This article was translated by JICA