Overview of Tokyo Area
RiversAsian Network of Major Cities 21 Flood and Storm Surge Control
Training Program

Jａｎｕａｒｙ 25th, 2011
Tokyo Metropolitan
Government

Presentation Flow
１. Overview of Tokyo
２. River Improvements in Tokyo
３. Urban-designed Comprehensive Flood Control

４. Evacuation System and Information Dissemination
５. Future Challenges & Coping Strategies
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z Tokyo’s annual rainfall is 1,621mm, about twice the world average.

(mm)

40030 (℃)

Average rainfall
Average temperature

300

20200

101000Tokyo
 Area: 2,187 km2
 Population: 13,009,759 persons (Jan. 2010)
 Rainfall: 1,621mm/year (2000~2009)0-10
1 2 3 4 5 6 7 8 9 10 11 12 (month)
Average rain and temperature in Tokyo (2000～2009) 【Tokyo District Meteorological Observatory】

3

1. Overview of Tokyo - Flood Disasters z Many flood disasters have occurred due to typhoons, heavy rains and storm surges.
z River improvements are being steadily progressing. However, heavy rains exceeding thecurrent protection level have been increasing in the recent years and Tokyo still experiences
flood disasters every year.

Flood Damage

Storm surge

By Nakano wordTyphoon Kathleen (1947) Local Heavy Rain (2005)
Hourly rainfall
35mm
Total rainfall
127mm
Houses Flooded
above floor
below floor

80,04145,167

Hourly rainfall
112mm
Total rainfall
263mm
Houses Flooded
above floor
below floor

3,374
2,453

Typhoon Kitty (1949)
Tide level
Inundation area
Houses Flooded
above floor
below floor

A.P +3.15
92km2
73,75164,1274

2. River Improvements in Tokyo - Issues & Measures z River improvement measures are being implemented according to the local
geographical and rainfall characteristics.

WestCentral

East

Tokyo Metropolitan
Saitama Government Officeiverjii RShakuNoSakai Riverr
veRi

AsiveraR

Su Aramida RiverRiver
RiverEdoRiver

Rivers in theKoto Word

Tama RiverMeguroRivero
EdAra Kyu iver
RRiverim
NoiR
Tsurum iver

Chiba
NRi akaver

Yamanashi

er
RivorinbZa

Aki Riverer
RivKarabori

Kanda

Tama River

Kanagawa

River

Tokyo Bay

Sediment Disaster Control
Flood Control in Small & Medium Rivers

Storm Surge/Earthquake
Measures in Lowland Rivers

Conservation and Improvement of River Environment

5

2. River Improvements in Tokyo- Small & Medium River Measures z Small and medium rivers are improved to accommodate once in 3 year rain (50mm/hr)z Principal projects are river channel improvements and development of underground regulatingreservoirs and diversion channels.
River improvement in urban area

Kanda River62. River Improvements in Tokyo- Construction of Diversion channel-

Diversion channel utilizing the space beneath roads along a riverKanda river : Edo river bridge diversion channel

Kanda
River

DiversionChannel

Kanda
River

DiversionChannel

7

2. River Improvements in Tokyo- Kanda River/Loop 7 Underground Regulating Reservoir Tunnel-type regulating reservoir utilizing the space under a roadz 12.5m inner diameter tunnel beneath a mainhighway.
z Take in the flood water from Kanda River,
Zenpukuji River and Myoshoji River.
z Stores about 540,000m3 of flood water.
z Maintenance expense : About 100,000,000,000
yen
Shirako R.

Loop No.7 Road

Shakujii R.

Myoshoji R.

Kanda River/Loop 7 Underground
Regulating Reservoir

Zenpukuji R.
Kanda R.

Meguro R.

Inner Diameter
12.5m

Length
4.5km 98

2. River Improvements in Tokyo- Storm Surge, Koto Inner Rivers & Earthquake Measures Tokyo’s Storm Surge Measures

Gates and tidal defenses
are designed to withstand1m above the historicallyrecorded level!

Ara Naka
Ｒｉｖｅｒ Ｒｉｖｅｒ

Storm surge
measures

Design high tide level(AP+5.1)
Historical record level in Tokyo（AP+4.2）
High tide level （AP+2.1）
Naka river’s surrounding area
has extremely low elevation

Almost completed

Koto Inner Rivers（water level lowered）

Currently most projects
implemented are:Naka river tidal defense

Kamihirai sluice gate

Super Levees
Earthquake
Reinforcement
92. River Improvements in Tokyo- Sumida River Super Levees-

Super levees in harmony with urban community developmentz Thick embankment built together with the urban development.
z Concrete tidal defense walls are being replaced by super levees.

Conventional
Conventional tidal
tidaldefense
defensewallswalls

SuperSuperlevee
levee

Embanked withurban development
Designheight
High tidelevel
River area

River protection area

Tidal defense wall

 Safe against flood but cannot view the river

River area

River protection area (max 50m)

Super Levee Urban river is improved together with theurban development
102. River Improvements in Tokyo- Sumida River Super Levees-

Ohkawabata Area: Before & after development(Before)(After)11

３. Urban-designed Comprehensive Flood Control- Urbanization -(Ex.) Urbanization in Kanda River Basin90

urbanized area（％）

z Urbanization in Tokyo has progressed
dramatically.
z Stormwater runoff into rivers has
increased due to urbanization.

100

80

96％

70
60

36 ％ increase in60 years！

50
4060％

Kanda River

30
20
10

Image of runoff increase

0
1920

1940

1960

1980

2000

(Before development)(After development)
zRainwater infiltrates into the groundzImpermeable area increases due to development
zSurface water running into river is reduced
zLarge amount of runoff flows into rivers in short time12

３. Urban-designed Comprehensive Flood Control- Basin Measures -Installation of storage/infiltration facilities
utilizing the limited spaces available in the city
Storage facility normally used as tennis courts

Storage

Runoffcontrol
facilities

Infiltration facilities in roads and houses

Permeable
pavement
Infiltration
trenchInfiltration

Infiltration
inlet

Infiltration
inlet

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4. Evacuation System and Information Dissemination- Outline of the actions z Provide real-time information on rainfall and river water levels
z Provide flood evacuation information such as inundation maps and hazard maps

Notification of Flood Risks
 Publishing hazard maps

Provision of Disaster Information
 Provision of rainfall information by TokyoAmesh Provision of river information
 Flood warning based on water level
forecasting Sediment disaster warning indicating basedon critical line indicating sediment disasteroccurrence

Drill for flood fighting

Support flood fightingand evacuation

Minimizing Damage
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4. Evacuation System and Information Dissemination- Notification of Flood Risks Flood hazard maps indicating evacuation routes
Publishing flood hazard maps
enlarged picture

flood depth

Legendinundation depth< 0.5m
< 1.0m
< 2.0m
< 5.0m15

4. Evacuation System and Information Dissemination- Provision of Disaster Information Disaster prevention information on internet(Integrated Information System for Flood Damage Prevention)
Integrated Information System for
Flood Damage Prevention

Click on the data you want to see

Click on thelocation you
want toknow about

You can get real-time water level
data for wherever you want!
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4. Evacuation System and Information Dissemination- Provision of Disaster Information Disaster prevention information on internet （Tokyo Amesh）

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4. Evacuation System and Information Dissemination- Operation of Forecasting SystemsForecasting systems for floods(Kanda River flood projection information)● Kanda River flood projection information
zFlood warning is announced once it has determined that
there is an increased risk of the Kanda River overflowing
using predicted river water level for 1 hour later.

Monitoring ofriver water levelchanges
Flood Danger Level

NormalLevel

If there is a risk offlooding⇒Flood warning isannounced!
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4. Evacuation System and Information Dissemination- Operation of Forecasting SystemsForecasting systems for sediment disasters（Sediment disaster warning ）How SEDIMENT DISASTER WARNINGS are announced

5km squareCity A

Critical Line（CL)Divide entire metropolitan
area up into 5km square
blocks (total of 128 blocks)
Forecast risk of sedimentdisaster occurring in eachblock（mm）

Forecast 2 hours
ahead
Trajectory ofrainfall since it
started to fall

Announce sedimentdisaster warning
data for City A!

Soil water index (mm)Check any blocks that are
forecast to exceed CL

Announce sedimentdisaster warning data19

5. Future Challenges & Coping Strategies
climate change impacts

Increase in rainfall
Sea level rise

Intensification oftropical cyclones■ Accelerate flood control measures, and examine futurestate of rivers in light of climate change■ Promote comprehensive flood control measures
including infiltration facilities, etc.
■ Promoting software measures including notification offlood risks and provide real-time information, etc.
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Thank you very muchfor your attention!