Small- to Mid-Size River Development Projects【Contents】¾Small- to Mid-Size
River Development
Projects¾Recent issues
Kanda River1

1.1 The rivers of Tokyo■Four river systems run through the Tokyo Metropolitan Area (the Tone, Ara, Tama, and Tsurumi Rivers)■Class A Rivers (Minister-administrated): 92 rivers; Class B Rivers (Governor-administrated): 15 rivers

3. Sediment disasterprevention

1. Flood measures for smalland medium-size rivers

2. Storm surge andearthquake measuresfor lowland rivers

4. Preservation and maintenance of river environment2

1.2 Prior damage: Large-scale flood damage caused by Kanogawa Typhoon (starting point of TMG flood-control measures)■Sept. 1958 Typhoon No. 22 (Kanogawa Typhoon)
Conditions Min. pressure: 878hPa (post-WWII low), storm radius 400-500km,
max wind speed 70m/s
Evening of the 26th: 76mm/hr recorded (total rainfall 444.1㎜)

Damage Small- and medium-size rivers in the Santama region and 23 Special Wards overflowed, causing
great damage, and heavy rainfall caused additional damage in lowland areas, leaving 203
dead, 480,000 houses flooded, and a flood area of 211km2.

Kamata, Ota City: State of flooding near Nomi River’s Taishido, City of Setagaya: Condition of collapsed
revetments near Karasuyama River’s Taishi Bridge
Shobu Bridge

Rainfall condition of 9:00, 26, Sept.- 0:00, 27, Sept. 1958

90

State of flooding at Shakujii River

Total rainfall 444.1mm(22-27)80

State of flooding at Naka River

Map of inundation conditions and extent

76mm/hr rainfall caused worst damage since WWII

76

降雨量 （mm/h)

706050403020
1006Disaster災害 名810 12 14 16 18
9月26日

年 Date月 日

Kanogawa
狩野川
昭和33年9月27日
1958.9.27
Typhoon
台風

20 220 227日

Houses
浸水 flooded
棟 数
total
above
floor below
床 下床 floor
上計(ha)(棟)(棟)(棟)
21,103 337,731 142,802 480,533
Area
flooded

浸水面積

LegendInundation extent

31.3 The progress of urbanization
Progress of urban area
Late 1940s
Rate of urbanization 56%

Late 1950s-early 1960s
Rate of urbanization 75%

2002
Rateof urbanization 96%
平成13年

Rate of urbanization・Population trends
2,500

100

2,00090

1,500

80
70,

1
1,000
00
0 500

Population
人口Rateof urbanization
市街化率ppl)0Ｓ２０ Ｓ３０ Ｓ４０ Ｓ５０ Ｓ６０

Ｈ７Ｈ１１60450

Rate of urbanization (%)

Basin pop. (Late 1960s-early1970s
Rate of urbanization 94%

Late 1980s
Rate of urbanization
94%

1.4 An urban runoff model(Ex.) Evolution of the Kanda River basin’surbanization rate
100

Rate of urbanization（ ） (%)○ Tokyo has experienced drasticurbanization○ Increase in runoff accompanyingurbanization

90

市街化
率

80％

4096％

70
60
50

36% increase in60 years!

60％

Kanda
River

神田川

30
201001920

Increased runoff due to urbanization○Rainwater permeates ground○Surface water stopped from running into river1940

1960

1980

2000

○Development has spurred increase in impermeable regions○A high volume of surface water runs into river during short
5time

5

1.5 Major incidents of flood damage in recent years

HandrailRiverKitahara
BridgeRoadby Nakano Ward

Aug. 1989 Wada, Suginami City

Aug. 1993 Yayoi, Nakano City

Sept. 2005 Kamitakada, Nakano City

(Kanda River)(Kanda River)(Myoshoji River)

Torrential rainfall
Total rainfall

276mm (Nakano)

Max hourly rainfall
Flood area

70mm (Nakano)

52ha

Number of flooded homes

Typhoon No. 11
Total rainfall

Max hourly rainfall
Flood area

2,669(Kanda River)

Torrential rainfall

288mm (Yayoi)
47mm (Yayoi)

85ha

Number of flooded homes

Total rainfall

Flood area
3,117

(in the most severe area)

263mm (Shimoigusa)

Max hourly rainfall

112mm（Shimoigusa)

Approx. 70ha

Number of flooded homes

3,103(Shinjuku Ciyu, Nakano City, Suginami City)

6(Figures based on flash report)

1.6 Flood control measures of small- and medium-size rivers～Development standard and overall plan～(1) Development standard: Handle 50mm/hr rainfall(2) Overall plan: Develop 324km of revetments along 46 rivers①② (As of April, 2011)
Length of post-maintenance revetments
204.2km
Revetment development rate
63%
Development rate including effects of detention basins, etc. 75%

Hyetograph for use in planning (50mm/h)
50mm

100
90
80
70
ｒ
60(mm/ｈｒ）
50
40
30
20
10
0
1

3

5

7

9

1113

15

17

1921

23

1
2
345
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Total

1.87
1.99
2.14
2.31
2.53
2.81
3.17
3.68
4.44
5.75
14.62
50.40
20.96
6.86
4.99
4.01
3.40
2.98
2.66
2.422.22
2.06
1.93
1.81
152.0ｔ(hr)LegendPost-maintenancePre-maintenance7

Storm Surge Project Zone

1.7 Small- to Mid-Size River Development Projects○ Fundamental plan to conduct river
improvements (revetment development) in orderfrom lower reaches
・Purchase land along river and widen river width・Lower riverbed○ In areas where land acquisition requires
extended time or revetment development provesdifficult・Develop detention basins and diversion channels andincrease safety level81.8 River repairs (revetment development)

LegendPre-maintenance rivers

9

1.9 State of repairs on the Kanda RiverBefore

After10

1.10 Diversion channel

Diversion11

1.11 State of diversion channel development

Shinmejiro-DoriKanda River

Outlet of the Takadanobaba
diversion channel

121.12 Regulating Reservoir (Sunken type)
Regulating Reservoir (Sunken type)

Overflow weirRiver channel

Regulating Reservoir

13

1.13 Regulating Reservoir (Underground type)
Regulating Reservoir (Underground type)

Overflow weirRiver channel

Regulating Reservoir(Underground type)14

1.14 Kanda River/ Loop Road No.7 Underground Regulating Reservoir
環七地下調節池 平面・断面図

Stage 1 Project (2,000 m- long)(started water intake from April, 1997)

Kanda River

SubwayStage 2 Project (2,500 m- long)(started water intake from, Sep. 2005)

Zenpukuji River

Oume Street

Waseda Street

SubwayMyosyoji River

JR Cyuo Line15

1.15 Effects of the Kanda River/ Loop Road No.7 Underground
Regulating Reservoir
Kanda River

7

Storage facility

KannanaRoad

Kanda River/ Loop Road
No. Underground
Regulating Reservoir (StageI project)

Intake facility

Flood area caused by 1993 Typhoon No. 11

Shinjuku city

Suginamia city

Nakano city
中野通り

Zenpukuji River
Kanda River intake facility

Shibuya city

Kanda River

Comparison of 1993 Typhoon No. 11 and 2004 Typhoon No. 22
Inflow conditions at the Kanda
River intake facility

Typhoon No.11(27, August, 1993)
Storage water level

Inflow reached 90% of storage capacity(240,000m3)

Typhoon No.22(October 9, 2004)

Total Rainfall(per hour)

288mm(47mm)

284mm(57mm)

Area Flooded

85 haunder 3 ha

Housesflooded(above andbelow floor)

3,117 houses

46houses

The number of flooded homes
浸水家屋数の比較
戸

3500

2500
2000
1500
1000

※Rainfall record is of the Yayoicho Observation Station

3,117 houses

3000

The number offlooded homes
decreaseddrastically500

46 houses

0

Typhoon No.11,
1993

Typhoon No.22,
16
2004

1.16 Flood control measures of small- and medium-size
rivers ～Practical examples～

Tama River development（Karabori River: Higashimurayamacity)
River widening throughrevetment development(Kanda River: Nakano city)

Securing crosscross-sectionalriver area via diversion
channels(Kanda River: Bunkyo city)

Kanda River/ Loop Road No.7 Underground
Regulating Reservoir:
17(Kanda river: Suginami city)

1.16 River basin measures
Establish storage and infiltration facilities in limited urban areas
A storage facility used as a tennis court

Storagefacility

Rain runoff
controlfacilities

Infiltration facility located below street and house

Infiltration
facility

Permeablepavement
Leaching pipe

18
Leaching well

浸透ます18Recent issues• The state of future riverdevelopment• Emergency measures for
torrential rains (concerningriver development)

19

2.1 Recent trends in intense rainfalls in Tokyo
Downpours showing an increase

Downpours concentrated in one region

Regarding the frequency of rainfall exceeding 50mm/hr from1989 to late September 2008, the latter half of this period(1999-2008) has shown definite signs of an increase over theformer half (1989-1998).

Rains exceeding 50mm/hr have a tendency to concentrate in the region
from Kanroku-Dori to Kanpachi-Dori, or the western section of the 23
Special Wards and the Tama region.
Viewed by region, there are areas along the Shakujii, Kanda, Shibuya, andNo Rivers with high downpour frequencies
Areas frequently receiving over 75mm/hr downpours are concentrated in
the upper reaches of the Kanda River and Shakujii River, or the northwest
area of the 23 Special Wards, including Nakano City and Nerima City

Number of rainfalls with over 50mm/hr from 1989 to late September 2008
1989-1998
41 times

Rainfall over 50mm

1999-2008
60 times（回）151413■■■

1212Over 50mm
3-4 times
5-6 times
over 7 times

50ミリ以上降雨回数1110(past 15 years)

988
7776

6

655

74555

Rainfall over 75mm

54443

3

3

3
2

2
100
平成12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

1920 （年）■Over 75mm
over 2 times(past 15 years)

Source: “Record of flood damage” Bureau of Constructions, TMG

Occurrence distribution of rainfall over 50mm, 75mm per hour (1991- 2005)20

2.2 The state of future river development
Speed up the “50mm-countermeasure”

Consideration of river development

Maintenance of the Furukawa Underground Detention Basin （H20～27）
EarthcoverAbout
30m-Consider the state of river improvements based upon
the Basic Policy for Intense Rainfalls and withconsideration given to handling 75mm rainfalls, suchas during the Kanogawa Typhoon

土 被り 約 30m～
内径
φ7.5m

Inner diameter7.5 m
古川地下調節池Tunnel length: about 3.3km
Storage volume: about 135,000m3

Surrounded by the Metropolitan
Expressway Company and buildings

Resume development of the Shirako River Underground Detention Basin （H21～29）
Work done on starting
shaft from 1991-1998, but
discontinued
白子川地下調節池

The current condition of the starting shaft
At the Kan-Etsu Expressway D Ramp

Image of UndergroundReservoir

Development of the Irumagawa diversion channel （H21～24）
民有地

車道

歩道

歩道

民有地

Handle a rain of 75mm
Kanogawa Typhoon
brought unprecedented
damage to Tokyo
Sep, 1958
Area flooded: 211km２
House flooded: over 460,000
Dead and injured: 203 people
Total rainfall: 444 mmMax. per hour: 76 mm

Raise the flood-safety level frombeing able to handle a 50mm
rainfall (1 in 3 years)↓to a rainfall of 75mm (1 in 15years)○ Commission investigation (FY2009-2010)
For example, analysis of previous rainfall data, assessmentof existing river facilities, general consideration of newriver facilities, the effects of development

入間川分水路○ Predicated on the investigation results and advice of
those with experience, formulate early on an outline of thenature of river development

2～5m程度

2.8m程度Cross section of upstream
Houses stand alongside theriver (downstream of theShinmei Bridge)

21

Diversion channel length: 約１．２ｋｍ
Water flow: １０㎥/s: inundation Area of Sep.4, 2005

3.1 Formulate new emergency measures for torrential rains ～Protect Tokyo fromlocal downpours～

Fundamental approach
Previous initiatives
River ・Expand rivers and develop revetments

・Develop diversion channels and detention basins

key facilities, including sewage trunk
Sewage ・Develop
lines and pump sites
・Implement the Rainwater Maintenance Quick Plan
・Promote rainwater infiltration facilities for plots ofover 500m2
・Aid in the construction of infiltration facilities forprivate housing (ward and city)

Local
development○ Heavy rains exceeding 100mm/hr also occur
Half1.5倍に増加
time

50ミリ以上降雨回数128

1989-1998
平成元～１０年
Ave
平均4.1/Year
4.1 回

7611109545

1999-2008
平成１１～２０年
Ave
平均 6/Year
６ 回

12

Promote temporary storage facilities utilizing public facilities

8777・Consider effective storage use of public facilities (schools, parks, municipal housing), andpromote establishment of temporary storage facilities

6655

Intake water into underground detention basin from other watersheds・Consider water intake into the Shirako River Underground Detention Basin from the Shakujii River・Shorten the schedule for the Shirako River Underground Detention Basin currently under constructionby 1 year

・Include five additional districts, including Ginza, in underground city measures and accelerate
development of sewage facilities (storage pipes)
・Accelerated development of the sewage facilities (storage pipes, etc.) for the Kanda, Shakujii, andShirako River basins
・Assist the formulation of an evacuation plan in 9 areas, including Kabuki-cho’s underground city（回）1513

Emergency measuresExpand measures for large-scale underground cities, etc.

Current issues○ Local heavy rains exceeding 50mm/hr appear frequently incertain areas

14○ Give concentrated treatment to areas highest threatened by flood damage○ Flood damage can be promptly mitigated through emergency measures○ Close cooperation between prefecture, ward and city, and citizens

55
44
3

4

3

3
2

32

Provide disaster information to protect lives and lifeways

010
平成12345678910111213

14151617181920（年）平成元年から平成20年までに発生した１時間50ミリ以上の降雨が発生した回数

Frequency of heavy rains exceeding 50mm/hr (within Tokyo)○ Flooding risk increases with intensive use of subway andunderground cities○ While river- and sewage-development are showing progress,
time still remains until completion

・In addition to an information system, establish surveillance system (cameras, etc.) and implement
advance provisioning of new emergency information for Shakujii River sent immediately to citizens,with the basin area’s cooperation

22
Formulate new intense rainfall emergency measures
Implement viable measures from FY2011

3.2 Policy for intense rainfall emergency measures
Water intake into underground basin from other watersheds

Shirako River

Shakujii River

Promote temporary storage facilities utilizing public facilities

Intake facility

Shirako river underground regulating
reservoir(Shortened work period)

Water intake visualization
Schoolyard storage example (underground type)
Expand measures for large-scale underground cities, etc.

Provide disaster information to protect lives and lifeways

Sewage facility example (storage pipe)

23
Response situation of the flood prevention headquarters