APRU-IRIDES MULTI-HAZARDS VIRTUAL
SUMMER SCHOOLJULY 22Mikio Ishiwatari, PhD
Visiting Professor
The University of Tokyo

KEY MESSAGE
Japan is fighting against floodingand use such experience to support other countries.

1. TORRENTIAL RAINFALL IN JULY 2020
ON-GOING 梅雨

RAINFALL FROM JULY 3 - 17

Record high July 1-10
 Total rainfall throughout the country : 216.1 mm/ station
 The number of monitoring stations recorded over 50mm/hr: 82

KUMAGAWA RIVER, KUMAMOTO PREFECTURE
Inundated area: 2060Ha

Flooded houses: 6,100

TORRENTIAL RAINFALL IN JULY 2020
ON-GOING
As of July 18
 Death 77
 Missing 7
 Damaged houses over 15,000 2,277 people at evacuation centers

2. TYPHOON HAGIBIS2019

1. TYPHOON HAGIBIS 2019
TAMAGAWA RIVER, BETWEEN TOKYO AND KAWASAKI, OCT 12 SATFROM TOKYO SOUTHERN BOARDEREVACUATION CENTER

FLOODING FORM
TAMAGAWA RIVERINLAND URBAN FLOODING IN DENENCHOFU

2. RECORD-BREAKING RAINFALL

EFFECT OF
CLIMATE CHANGE?
10 years ago

EFFECT OF
CLIMATE CHANGE?
YESSea temperature

DAMAGE THROUGHOUT THE
CENTRAL AND EAST JAPAN140 areas in 71 rivers12 areas in 7 rivers (National)
128 areas in 67 rivers (Pref.)DAMAGE
104 died, 3 missing
70-80% are the elderly
30% in vehicle
Inundated houses: > 100,000
Dyke broken
12 sites in 7 rivers managed by national gov.
127 sites managed by pref. gov.

3. HOW COULD BE TOKYO PROTECTED?

A. WHAT ARE RISKS IN TOKYO?
TYPHOON KATHLEEN (1947)
KILLED >1,100, FLOODED > 300,000 HOUSESFLOODING RISKFROM TONEGAWA RIVER
Death toll: 2,600
Isolated: 1.1 million

Inundated: 530㎞2
Flooded houses：680,000

日本の災害対策 [2019/3/5閲覧]
http://www.bousai.go.jp/1info/pdf/saigaipamphlet_je.pdf

FLOODING RISKFROM ARAKAWA RIVER

Dike break point

Flooding hight
5.0m< H
2.0m< H <5.0m
1.0m< H <2.0m
0.5m< H <1.0m
H <0.5m

Flooding area (km2)
Population in flooding area

110
1,200,000

Akihabara
Tokyo station
Ginza

24

Tonegawa
21.0 20.7

Water levels were at critical level

Record high 2019

ARAKAWA
11.3 12.8

Record high 2019

RISK IN TOKYO METROPOLITANTYPHOON KATHLEEN (1947)
KILLED >1,100, FLOODED >300,000 HOUSESB. DAMS STORED FLOODS IN UPSTREAMDams store
145milliom m3
Tonegawa RiverNew Yanba Damstore 75milliom m3

Dam store
45milliom m3
Arakawa RiverYANBA DAM TRIAL OPERATIONSTORE 75 MILLION M3

YANBA DAM TRIAL OPERATIONSTORE 75 MILLION M3

C. RESERVOIRS STORED IN MIDDLE STREAM
Watarase Reservoir
stored 160milliom m3
reservoirs stored
90 million m3

Arakawa Reservoir
stored 35milliom m3

WATARASEWATARASERESERVOIRRESEIVOIR 160 MILL M3

WATARASE RESERVOIR 160 MILL M3

D. CHANNELS DIVERTED FLOODS IN LOW STREAMDiversion Channel

UNDERGROUND TUNNEL312MILLION M

ARAKAWA CHANNELEFFORTS FOR THE PAST CENTURY
7 Dams TONEGAWA
1957-1990
New Yanba Damtrial operationWataraseReservoir
1989
Tonegawa Reservoir
1960

3 Dams ARAKAWA
1999, 2011, 2004
Arakawa Reservoir
2003

Diversion Channel
1930 Arakawa
2006 Tunnel

3. JICA PROJECTSUSING JAPANESE EXPERIENCE

A. VIETNAM

MAKING RESILIENT SOCIETY IN CENTRAL REGION
Purpose： to establish disaster management system focusing
on community-based activities
1. Strengthening capacities of local governments
2. Formulating manuals of community-based DM

3. Developing measures to protect river banks from erosion
4. Strengthening capacities of central government

RIVERBANK EROSION

1 COMMUNITY BASED ACTIVATES
Participants
 local gov.

 Women, Youth,Fishermen, Farmers
Hazardmapping

EVACUATIONDRILLEVACUATIONDM EDUCATION

2 COUNTERMEASURES AGAINST BANKEROSIONPRACTICESa) Technical capabilityb) Material availabilityb) Financial reasonability

3 CAPACITY BUILDING
Hazard mapping
CBDRM
Bank erosion

B. Metro Manila

KEY MESSAGE
Japan is fighting against flooding
and use such experience to support othercountries.

THANK YOU

ISHIWATARI.MIKIO@JICA.GO.JP