Integrated Flood Management for Urbanized River Basins in ... · Heights and Hilly Zones of the Suburban Areas in the Three Major Metropolitan Regions. Extensive Housing Land Development

Acting Director of ICHARM　　　　

Public Works Research Institute (PWRI)

Tsukuba, Japan

Akira TERAKAWA

Integrated Flood Management for Urbanized River Basins

in Japan

I am going to talk about

� Scheme for River Management in Japan

� Integrated Flood Risk Management Measures in Urbanized River Basins

Geographic Conditions of Japan

� 70% of land is covered with forests and mostly mountaneous

� 50% of popuration and 75% of assets are concentrated in flood plains (10% of land)

� Heavy rainfall occur during rainy season in June-July and in the typhoon season in August-October

� Rivers are short and steep, causing sharp hydrograph

� The ratio of maximum/minimum discharge is extremely high (about 100 for Tone River)

Inhabitable area / National land area

87 8771 69 67

37

0

20

40

60

80

100

Engla

nd

Neth

erla

nd

U SA

Fran

ce

Ger

man

y

Japa

n

（％

）

(Prepared by MLIT)

Population in flood plain / Total population

7 7 9

17

51

64

0

10

20

30

40

50

60

70

England France USA G erm any Japan Netherland

（％

）

(Prepared by MLIT)

Amendment of the River Law

○○○○Introduction of integrated river system management

○○○○Enhancement of water-useregulations

○○○○Improvement and conservation of river environment

○○○○Introduction of plans reflecting public opinions

(River Bureau, MLIT)

Tasks of River Administrator

Flood managementRiver water use managementRiver environment management

Activities of River Administration Offices

・Observe rainfall, river water level, river water quality・Research the environment of river and river basin・Study river improvement and environment・Plan, design and construct river structures・Patrol to observe problems of structures, illegal acts・Administrate use of river area

　　　　　　　　Contents⇒ Goal of River Development　　　　 Contents of River Works and River Maintenance

Original plan

Academic expert

Reflection of opinions of local people (Hearing)

Governor of a local authority

opinion

River W

orks

　Old S

ystem

　　　　Contents ⇒Basic Policy, Design Flood, Design Flood Discharge etc.　　　　Main contents of river works

Basic P

lan of Work O

peration

Draw up the basic plan draftof works operation

Determination of the basic plan of works operation

River Council（Class A river system）Reflection

River Im

provem

ent Works and M

aintenance

　Ne

w S

ystem

　　　　　　　　Contents ⇒ Basic Policy　　　　 Design Flood, Design Flood Discharge etc.

Draw up the draft plan

Determination and publication of the plan

Social capital improvement

Council（Class A river system）Prefectures’ River Council（Class B river system）

opinion

The case that the prefecture has its River Council

River Im

provem

ent Plan

Basic R

iver M

anagem

ent Policy

Draw up the draft plan

opinion

Determination and publication of the plan

opinion

New scheme for river management

(River Bureau, MLIT)

Scheme for River PlanningBasic River Management Policy

　　　Social Infrastructure Council

・Basic policy on flood control measures, water use and environment conservation

・Unregulated peak discharge on target level

・Design flood discharge

River Basin Implementation Plan ( for 20 ～～～～ 30 years )

Persons experiences or academic standing

Reflection of local opinions through public hearing

Governor of local government

・Flood control facilities (Dam, Retarding Basin)

・Embankment, bank heightening, river widening, dredging, bank protection, pumping station, etc.

Tama River Implementation Plan

(1) River improvement for disaster prevention or mitigation for flood and high tide, including measures to cope with excessive event

(2) Appropriate usage of river water including maintaining the basic function of rivers

(3) Preservation and restoration of river environment and enhancement of education for citizens for historical, cultural and ecological value of Tama river

Seminars (8 times) and river basin commission meetings (5 times) for 2 years

with the participation of citizens, local governments, literates and river managers

for consensus building among various stakeholders

before establishing the plan in 2002

The Tsurumi River basin in Kanagawa Prefecture has seen a much higher population growth rate than the national average

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

S30 S 35 S 40 S 45 S 50 S55 S 60 H 2 H7 H 12

人口

の伸

び

鶴見川

日本全国鶴見川

日本全国Location of Tsurumi River

Pop

ulat

ion

grow

th

Tsurumi River

Whole Japan

Tsurumi River

Whole Japan

Tokyo Central

Railway Station

Tsurumi River

１９５５

１９６０

１９６５

１９７０

１９７５

１９８０

１９８５

１９９０

１９９５

２０００

Urbanization rate

of 10% I n 1958

Urbanization rate

of 60% in 1975

Urbanization rate of 84.3% in 1997

Flooding of September 1976

Developments of Heights and Hilly Zones: Tsurumi River (through Tokyo metropolis and Kanagawa Prefecture)

Flooded areas

Extensive Housing Land Development has been in Progress in the Heights and Hilly Zones of the Suburban Areas in the Three Major Metropolitan Regions.

Extensive Housing Land Development has been in Progress iExtensive Housing Land Development has been in Progress in the n the Heights and Hilly Zones of the Suburban Areas in the Three MajoHeights and Hilly Zones of the Suburban Areas in the Three Major r Metropolitan Regions.Metropolitan Regions.

Non-urbanized area

Urbanized area

Before

Before

After

After

Effect of urbanization on flood runoff

Tsurumi River

（By simulation）

1975現況

1958当時

　　　　Reduction of Water Retention and Retarding Functions of River 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Basin Results in Increase in Peak Discharge.

　　　　　　　　Reduction of Water Retention and Retarding Functions of River Reduction of Water Retention and Retarding Functions of River 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　Basin Results in Increase in Peak Discharge.Basin Results in Increase in Peak Discharge.

Source: Interim Report (June 1977) of Tsurumi River Basin Flood Disaster Prevention Planning Committee

Flo

od d

isch

arge

at

Och

iaiB

ridge

Rainfall depth considered

After 80% development in future

Actual conditions as of 1975

As of 1958

Undeveloped river basin

Time

Hou

rly r

ainf

all d

epth

Tsurumi River Naka River and Ayase River

出典：『鶴見川とその流域の再生鶴見川流域水マスタープラン策定に向けた提言』

出典：パンフレット『水害から私たちのまちを守るためには…』

Widening of river channel is difficult in the highly urbanized areaWidening of river channel is difficult in Widening of river channel is difficult in the highly urbanized areathe highly urbanized area

Source: “Tsurumi River and Renewal of Its Basin –Suggestions toward Formulation of Master Plan for Development of Tsurumi River Basin Water Resources”

Source: Brochure “For Prptecing Our Town from Flood Disasters”

Comprehensive Flood Disaster Prevention Measures

Basin Councilconsisted of the representatives of the regional development bureau of MLIT, river related departments and the urban, housing and land department of the prefectural and municipal governments concerned, to discuss the implementation scenario of the comprehensive measures for the river basin.

Basin improvement planThe Council studies and selects concrete measures appropriate to the characteristics of the particular basin and make up a basin improvement plan.

Retention areas・Maintenance of controlled urbanization districts・Conservation of nature・Construction of reservoirs and regulating basins・Installation of permeable pavements and seepage sumps

Detention areas・Preservation of urbanization control zones・Control of landfill・Promotion of conditions favorable to agricultural activities

Low-lying areas・Development of drainage facilities・Construction of storage facilities・Encouragement of use of flood-proof buildings

Basin Improvement Plan

River Improvement - 1

Tsurumi River

River Channel Improvement (Embankment , dredging etc.)

Before improvement

After improvement

　 How the neighborhood of Shiotsuru Bridge has changed after river dredging.

River Improvement - 2

Multipurpose Retarding Basin for Tsurumi River

Construction of Retarding Basin and Diversion Tunnel

Retarding basin Tsurumi River

Yokohama International General Athletic Stadium

Dike Overflow type dike Dike

Ove

rflo

w ty

pe d

ike

Tsu

rum

i Riv

er

Basin Measures - 1With the basin divided into three zones, namely, Water Retention Zone, Retarding Zone and Low-lying Zone, basin improvement measures appropriate to the characteristics of the respective zones have been implemented.

Naka River and Ayase River

Division into three zonesN

on-flooded zone

Floode

d zone

Water retention zone

Retarding

zone

Low-lying

zone

Planned development zone

Urbanization controlled

zone

Urbanizedzone

Example of general storm water detention pond

Aerial view of a group of stormwater detention ponds

Storm water detention ponds covered with bluish green screens

Basin Measures - 2

Construction of Storm Water Detention Pond

In normal times

Kirigaoka Regulating Pond (Tsurumi River)

In flood times

Example of Use as Multipurpose Facilities

Basin Measures - 3

School ground storage

Shinkashi River

Construction of Rainwater Storage Facilities

Basin Measures - 4

Permeable pavement Permeable tile pavement

Tokyo Metropolis

Construction of Permeable Pavements and Infiltration Inlets

Basin Measures - 5

Storm water infiltration facilities

Construction of Permeable Pavement and Infiltration Inlet

Infiltration inlet Infiltration trench

Storm water infiltration trench Storm water infiltration inlet

Damage Reduction Measures - 1

▲Located near the Tsurumi River, the building, learning from past experience, adopts a piloti type structure to protect it from flood damage.

Tsurumi River

Encouraging Construction of Waterproof Buildings

▲Constructed in a multipurpose retarding basin for the Tsurumi River, this building has adopted a piloti type structure to permit the use of the retarding basin during floods.

Damage Reduction Measures - 2Official Announcement of Flooded Areas or Flood Hazard Areas

Flood Hazard Areas of Shinkashi River Basin

高規格堤防高規格堤防と一体となって地域づくりを進める区域

堤防の高さの３０倍程度

河川区域

堤防の高さ(h)

通常堤防の幅

High-standard levees

A high-standard levee is an embankment designed as part of a community to prevent destructive damage resulting from a levee break caused by a flood greater than the design flood.

Ara River (Komatsukawaarea)

High-standard levee projects are integrated with urban redevelopment projects to make efficient use of limited space in built-up areas.

Construction of high-standard levees ("super levees")

Area to be integrated with a high-standard levee as part of a community

Levee height

Width of conventional levee

About 30 t imes as high as a conventional levee

River area

High-standard levee

Flood Hazard MapExample of Fujimi City, Saitama Prefecture

Evacuation direction

Evacuation area

Lessons learned

• Preventive measures are often more efficient than proactive measures

• Involvement of various stakeholders in the planning process, consequently saves time and cost

• Excessive event should be taken into account for minimizing losses

• Hydrological impact assessment due to basin development should be assessed and appropriate measures be taken for preventing or mitigating the negative impacts

ENDENDThank you for your attention

http://www.icharm.pwri.go.jp

Emergency ResponseFlood fightingInformation sharingEvacuation orderRescue operationEvacuation camp

PreventionRiver improvementStrengthening of leveeStorage facilityLand use regulationembankment

MitigationFlood hazard mapFlood forecasting/warningFlood insuranceDisaster prevention drillWater proofing of buildings

RecoveryRecovery operationPrevention of epidemicsReconstruction of buildingsInvestigation of causeDrawing lessons

Proactive Reactive

Integrated risk management considering the total balance of proactive and reactive measures is important

Comprehensive Flood Disaster Prevention Measures

総

合

治

水

対

策

③被害軽減対策

Water retention area

Retarding area

Low-lying area

•Improvement of river channel (construction of dikes, dredging, etc.) •Construction of retarding basin, diversion tunnel, etc.

•Preservation of urbanization controlled area •Conservation of non-urbanized areas•Construction of storm water detention pond, etc.•Construction of storm water storage facilities•Provision of permeable pavements, infiltration inlets, etc.

•Preservation of urbanization controlled areas•Restrictions on banking•Improvement of farming environment

•Construction/improvement of inner basin drainage facilities•Construction of storm water storage facilit ies•Encouraging construction of waterproof buildings•Establishment of flood warning and evacuation system•Enhancement of flood defense system•Offi cial announcement of flooded areas and flood hazard areas•Encouraging construction of waterproof buildings•Publicity activities directed toward community residents

Local Governments in River Basins (Prefecturaland municipal governments)

RiverAdministratorsand Local Governments in River Basins

Com

preh

ensi

ve F

lood

Dis

aste

r P

reve

ntio

n M

easu

res

② Basin Improvement Measures

③ Flood Damage Reduction Measures

①River Improvement

River Administrators (Central, prefectural and municipal governments)

DesignatedDesignated　　　　　　　　Urban River Urban River InundationInundation　　　　　　　　Prevention Prevention （２００３）（２００３）（２００３）（２００３）（２００３）（２００３）（２００３）（２００３）

The purpose of the Act is to prevent inundation damage in a designated urban river basin (where severe inundation disaster has occurred or is likely to occur and also where conventional measures such as channel improvement is difficult due to urbanization

Drawing a comprehensive river basin inundation mitigation planConstructing storm water retention and infiltration as river management activitiesand other necessary measures

Storm water does not infiltrate into underground by housing land development, etc., and flows into rivers at the same time, causing flood damage

Permission of Actions hampering storm water retention and infiltration function of the basin (Article 9-22)

Change of land shape for Change of land shape for Change of land shape for Change of land shape for housing area developmenthousing area developmenthousing area developmenthousing area development

Land pavement due to Land pavement due to Land pavement due to Land pavement due to change of agricultural change of agricultural change of agricultural change of agricultural land to parking arealand to parking arealand to parking arealand to parking area

Construction of golf Construction of golf Construction of golf Construction of golf coursecoursecoursecourse

etc.etc.etc.etc.

needs a permission from needs a permission from needs a permission from needs a permission from prefecturalprefecturalprefecturalprefectural GovernorGovernorGovernorGovernor