Figure. 3 Characteristics of flood runoff in Japan

FLOOD CONTROL WORKS IN JAPAN

~ ACHIEVEMENTS TO DATE AND FUTURE OUTLOOK

Tsuneyoshi MOCHIZUKI1, Takeshi UEDA

2

1 History of flood control projects

1.1 Natural and social conditions in Japan

(1) Natural conditions

The islands of Japan are located between 20°25' and

45°30' north latitudes, or in temperate Monsoon Asia.

Seventy percent of the land is covered with steep

mountains, many of which are volcanic. The geology

consists of weak soils.

Temperature is affected by the southeastern wind

from the Pacific in the summer and by the northwestern

wind from the Eurasian continent in the winter owing to the

location of the islands. Areas along the Sea of Japan are

covered with world-class heavy snow in the winter. Both

seasonal rain and typhoons hit the nation in the summer, often inducing downpours. In areas along the

Pacific coast in particular, 50 to 60% of annual precipitation is concentrated during the summer.

Rivers that catch water in their basin while flowing are greatly affected by the topography

and climate described above, and exhibit the following characteristics as compared with large rivers on

the European continent and in other places.

(a) Japanese rivers

are steep-sloped

Many of the Japanese

rivers are steep-sloped

and flow down

mountains quickly to

the sea from their

headwaters over short

distances.

(b) Water level rises

quickly in Japanese

rivers

Japanese rivers have much smaller catchment areas than

major European rivers. Even Japan's largest catchment

area of 16,840 km2 of the Tone River is only one-fifth of

that of the Seine. Heavy rains frequently fall locally in

Japan. Water level rises in rivers with a small catchment

area as soon as the entire catchment area receives heavy

rains. Actually, once rain falls, the water level rises at a rate of

dozens of centimeters per hour.

1 Director, River Improvement and Management Division, River Bureau, Ministry of Land, Infrastructure and

Transport(MLIT),2-1-3Kasumigaseki, Chiyoda-ku, Tokyo, 100-8918, Japan 2 Vice-Director, Water Resources Division, Japan Institute of Construction Engineering (JICE)

3-12-1, Toranomon, Minato-ku, Tokyo, 105-0001 Japan

Figure. 1 Monthly precipitation in Tokyo,

Paris and New York

Notes: Source:Rivers in Japan(MLIT)

Notes: Source:Rivers in Japan(MLIT)

Figure. 2 Longitudinal slopes of rivers in Japan and other countries

Joganji River

Loire River

Rhine River

Abe RiverTone River

Chikugo RiverYoshino River

Shinano River

Kitakami River

Senine River

Mekong River

Colorado River

River Elevation (meters) Distance from river

mouth(kilometers)

Notes: Source:Rivers in Japan(MLIT)

(c) Great variation in volume of river water throughout the year

Japan's steep-sloped rivers with a small catchment area experience quick rise in water level during

heavy rains and soon go dry during lasting droughts.

(d) Great effect of sediment transport

Japanese rivers flow swiftly and soils are loose, so more sediment is transported into rivers than in

Europe. Alluvial plains where many people have settled were originally formed by the sediment

transported by rivers. Containing rivers with embankments soon caused sediment to be deposited and

thus made rivers even shallower, which in turn created flood-prone conditions.

(2) Social conditions

Owing to the natural conditions described above, 50% of nation's population and 75% of national

assets are concentrated on alluvial plains that account for only 10% of land. Flooding therefore could

cause devastating damage.

Damage has actually been caused every year by rainfalls during the rainy season and

typhoon-induced downpours. Last year in particular, serious damage was sustained in the Tokai district,

the central part of Japan, centering around Nagoya. The high percentage of general damage to homes

and offices was noticeable. Flood control projects have long reduced the area of inundation.

Concentration of assets in floodplains, however, has increased their value per unit area. Thus the

amount of damage has hardly decreased.

Figure. 4 Changes in density of flood damage to ordinary assets, etc. (average in the past five years)

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

昭3

6

昭3

7

昭3

8

昭3

9

昭4

0

昭41

昭4

2

昭4

3

昭4

4

昭4

5

昭4

6

昭4

7

昭4

8

昭4

9

昭5

0

昭51

昭5

2

昭5

3

昭5

4

昭5

5

昭5

6

昭5

7

昭5

8

昭5

9

昭6

0

昭61

昭6

2

昭6

3

平元 平2

平3

平4

平5

平6

平7

平8

平9

平10

平11

平12

公益事業等

公共土木施設

一般資産等

単位 億円

注1 成 確定値 成 速報値 あ 各 水害被害額 成 価格 実質化したも あ注2 昭和36 公益事業等被害 い 調査さ い い注3 グラ 中 各 カッコ書 数値 水害被害総額 大 い順 位 位 付与した数値 あ

た 丸 数値 一般資産等被害額 大 い順 位 位 付与した数値 あ注4 昭和36 ～ 成11 均値 7,143億円 うち 一般資産等 2,310億円 公共土木施設 4,720億円 公益事業等 113億円

9,938

2,027

85

12計 12,050

(4) (2) (1) (5)(5)(5)(5)

第二室戸台風

主水害原因

豪雨長崎水害

東東東東豪雨豪雨豪雨豪雨

七月豪雨

台風17号 長良川堤防決壊

(3)

In hundreds of millions of yen

2000 total:

12,050

20

00

19

99

19

98

19

97

19

96

19

95

19

94

19

93

19

92

19

91

19

90

19

89

19

87

19

86

19

85

19

84

19

83

19

82

19

81

19

80

19

79

19

78

19

77

19

76

19

75

19

74

19

73

19

72

19

71

19

70

19

69

19

68

19

67

19

66

19

65

19

64

19

63

19

62

19

61

Major

cause of

flood damage

Typhoon

Daini-muroto July downpour Downpour

(flood damage in

Nagasaki)

Tokai

downpour

Note 1: Final data are shown up to 1999. Data for 2000 are preliminary. Amounts of flood damage have actually been presented in 2000 price.

Note 2: No investigations were made of the damage to public utilities services in 1961.

Note 3: Figures in the parentheses indicate the ranks in total flood damage amount (top five in the descending order). Encircled figuresindicate the ranks in the amount of flood damage to ordinary assets (top five in the descending order).

Note 4: Average in the period between 1961 and 1999: 714.3 billion yen (ordinary assets: 23.1 billion yen, pubic works facilities: 47.2

billion yen, public utilities services: 11.3 billion yen)

Public utilities services

Public works facilities

Ordinary assets

Typhoon No.17

(collapse of embankments in

the Nagara River

1.2 History of flood control projects

Recent flood damage has been described above. Japan's flood control projects have been carried out

assiduously to tame natural conditions.

(a) Flood control by local protection (before the Meiji Era (1868-1912))

Japan's oldest recorded flood control project is said to date back almost to the third century when the

Manda Embankment was built in the Yodo River.

In those days, flood control mainly aimed at protecting local areas from disasters. In order

to protect local agricultural fields and communities from flood damage, measures were taken

according to the importance of the locality or topographic and other natural condition. Embankments

were designed to have varying heights on both banks of rivers or in upper and lower reaches.

Embankments were installed near the community not along the river to prevent the inflow of flood

waters. And forests for controlling flood disasters were created in the places where flood waters were

to be let overflow to mitigate the energy of flood waters. In areas constantly hit by floods, land was

elevated and shelters were installed on highland, and boats were prepared for evacuation. Thus local

residents took anti-flood measures by themselves.

With the concentration of authority, flood control gradually became one of the key national

projects for political leaders not only to stabilize people's life but also to develop new agricultural

fields in flood-prone lowland for the growth of national strength. It was widely believed that "Those

who rule rivers rule the nation." In the age of civil wars, large flood control projects were implemented

in some areas.

(b) Navigation on rivers and low-flow channel improvement

(in early days through middle of the Meiji Era)

Following the Meiji Restoration (1868), the development of new industries was encourage to establish

a modern state. Inland transport of large volumes of goods at the time depended mainly on navigation,

so rivers served as the main economic artery. River improvement was the nucleus of the national

economic policy. Low-flow channel improvement work was carried out by the national government in

the Yodo River in 1880. Flood protection work, on the other hand, was performed mainly by local

administrative agencies focusing on local benefits.

Flood damage was sustained frequently in late 1870s through early 1890s in large rivers

such as the Yodo, Tone and Kiso Rivers. Thus the need for drastic flood control measures was realized.

In the meantime, the development of railway networks reduced the role of navigation, and rapidly

made low-flow channel improvement works to facilitate navigation less important.

(c) Approach to flood control led by the national government

(late in the Meiji Era through mid 1940s)

The River Law was established in 1896 and the Sediment Control Law and the Forest Law were

enacted in 1897, laying the foundations for modern flood control. The River Law provided basic

principles for river administration in Japan until its revision in 1964.

The River Law defined rivers as facilities built by the national government and stipulated

that they should be managed by local administrative agencies as national organizations. Private rights

were eliminated to the use of rivers, river terraces and flowing water as long as they have an important

bearing on public interest. The Law held local administrative agencies primarily responsible for river

works and maintenance of rivers as in the past. However, for the works that were expected to affect

other prefectures, require high-level techniques because of difficult nature, cost more than a local

government can bear or be important improvement projects based on a total plan, the national

government was made to assume the responsibility for implementation.

Nationwide great flood damage in 1910 triggered a study of the first-phase flood control

program. The rivers requiring national projects for improvement were selected, and construction

priorities, periods and costs were discussed. Accordingly, the government appropriated necessary fund

and started flood control works.

(d) Development of infrastructure for economic growth

(in mid 1940s through mid 1960s)

Flood control projects made only a limited progress during World War II. Typhoon Catherine and a

succession of other large typhoons frequently hit the land devastated by the war in mid 1950s through

late 1950s causing great damage. In the wake of Typhoon Ise Bay of 1959, the Erosion and Flood

Control Emergency Measures Law and the Flood Control Special Account Law were instituted in

1960, and Japan's first long-term (ten-year or five-year) flood control programs were developed based

on the laws.

In the meantime, in order to meet the rapidly growing demand for industrial and municipal

water owing to economic development, water resources were developed by building multi-purpose

dams for flood control and water use, and the construction and management of dams were centrally

controlled by river administrators.

As a result of economic and social development and the modification of administrative

systems since mid 1950s, the River Law was completely revised in 1964. This is because needs arose

to review distributed river management by prefectural governors by administrative district as a result

of a considerable reform of nation's administrative system with the establishment of the existing

constitution, because the needs increased to revise the conventional section-based river management

system and to introduce integrated management of entire river systems in order to respond to the

development of riparian zones and the increase in demand for various types of water use with the

social and economic development, because the needs increased to improve water use related

regulations for coordinating new water use with existing water use with the progress of water use

projects, and because the needs arose to enact regulations for controlling damage caused by dam

operation with the building of numerous large dams using advanced construction techniques.

Then, establishing "basic plans for implementing construction works" was made mandatory

in river administration. Thus a great shift was made from management of river sections to integrated

management of river systems covering lower through upper reaches.

(e) River improvement corresponding to rapid urbanization

(in mid 1960s to present)

With the advent of the high economic growth period around the time when the new River Law was

instituted, cities and industries grew rapidly. At the same time, accelerated urbanization induced

various problems in relation to rivers such as water pollution in rivers and lakes, frequent urban flood

damage due to delays in flood control measures, serious water shortages including the drought in 1964

when the Olympic Games were held in Japan and rapid increases of sediment disasters.

Measures have been taken sequentially to control the pollution of river water, to

comprehensively control floods by establishing warning and evacuation systems as well as detaining

rainwater, and controlling infiltration and sediment disasters while improving rivers, and to control

droughts by building dams. In order to avoid catastrophic damage in urban areas where assets are

concentrated and critical jobs are performed, by the failure of embankments due to floods that exceed

the design level, the idea of high-standard embankment has been introduced.

At present, various projects including the development of flow conservation channels and

nature-oriented river works are being implemented for better river environments not only to control

and use water but also to improve water quality, preserve resting and breeding areas for wildlife

species and offer people easier access to waterfront.

In 1997, the River Law was revised to incorporate the conservation and improvement of

river environments as one of the objectives of the law.

The next chapter describes the role that flood control projects have played using typical

examples in the metropolitan area.

2 Flood control projects in metropolitan area

2.1 Eastward relocation of Tone River

(metropolitan flood control project started at the end of the 16th century)

2.1.1 Outline of eastward relocation project

The Tone River in the pre-modern days belonged to a river system different from the one that

incorporated the Kinu and Kokai Rivers, and flew over the Saitama Plains in several threads toward

Tokyo Bay. After Tokugawa Ieyasu, a warlord, moved to Edo (ancient name of Tokyo) in 1590, Ina,

the local governor, led rerouting of the Tone River in several phases during the first 60 years in the

Edo Era (1603-1867). As a result, the present alignment of the Tone River was formed that flows into

the Pacific.

The project to move the Tone River eastward took place during the 60-year improvement

works between the coffering of the Kaino River in 1594 and the discharge of water in the Akahori

River in 1654.

Conceivable goals of the eastward relocation of the Tone River include "protection of Edo

from floods", "development of new agricultural fields", "securing of navigable channels", "military

defense against the Date clan" and "improvement of roads". Without the river improvement project,

Edo would not have existed. The eastward move of the Tone River that was started 400 years ago laid

the foundations for later large-scale urban development leading to a flourishing Tokyo.

Coffering of theKaino River in 1594

Coffering of the Moto-araRiver in 1629

Open cut of Shinkawadori in

Open cut of the Akahori River since 1621 (water discharge in 1654)

Open cut of the Sakase River in 1641

Open cut of the Edo River in 1635-1641 period

Open cut of Ohki hills along the Kinu River in 1629

Relocation of the Kokai River in 1630

Open cut of the Shin-tone

River in 1666-1672 period

Coffering the Shin-tone River in 1669

Open cut of the Shogen River in 1676

Coffering of the Tone River in 1666,

Removal of cofferdam in 1669

Legend Present alignment Alignment in the Edo Era

Figure. 5 Eastward relocation of Tone River

Tone River

Ara River

Kokai River

Kinu River

Notes: Source :MLIT

2.1.2 Effects of eastward relocation on the development of new agricultural fields

Moving the Tone River to the east integrated the Tone and Ara and other rivers that use to be turbulent

channels on lowland in the east of Saitama prefecture, and enhanced drainage in the swamp, creating a

great farm belt in the basin of the Tone River.

The development of new fields increased not only the yields but also the population and

villages. The yields from paddies in the Musashi province consisting of Katsushika, Saitama and

Adachi gun (counties) that were affected most by the relocation of the Tone River grew about 200% in

the 100-year period since 1550. The number of villages increased accordingly.

2.2 Construction of the floodway of the Ara River

(modern flood control project started at the end of the 19th century)

2.2.1 Outline of the floodway construction project

Flood damage that had been sustained

approximately once in three years since the Meiji

Restoration became more serious with the

urbanization of Tokyo. The national government in

the Meiji Era built groups of cement, shipbuilding

and fertilizer plants near the mouth of the Sumida

River as national priorities. After the Sino- and

Russo-Japanese wars, the industrial area in the

east of Tokyo endowed with navigation channels

expanded. In early 1900s, plants were also

constructed in the middle reaches that were in use

for a water retarding area, owing to the construction

of the Nihon and Sumida embankments.

As a result of the great flood in 1910 and

in view of the need to build the port of Tokyo,

construction of a floodway of the Ara River

was started as a critical measure to protect

the downtown area of Tokyo from flood damage.

The large scale project to excavate the floodway

22 km long and 500 m wide was completed in

1930, 20 years after the commencement of work. At the completion of the project, Tokyo's economic

strength exceeded that of Osaka, then the center of the Japanese economy, which has led to the present

growth.

2.2.2 Effects of flood control project in urban areas (lower Ara River and Tokyo metropolitan area)

(1) Changes in land use

Changes in land use for the past 100 years along the floodway in the Tokyo metropolitan area are

discussed below. Urbanization along the floodway progressed in two major districts that were formed

before and after the completion of the floodway.

(a) Area urbanized before the completion of the floodway

(on the right bank of the floodway)

Urbanization progressed centering around the old city center of the Edo Era and along the railways

laid in the Meiji Era. As a result, urbanization was completed on the right bank of the floodway before

the completion of the floodway except some parts along the floodway.

(b) Area where urbanization progressed after the completion of the floodway

(Adachi, Katsushika and Edogawa wards on the left bank of the floodway)

Floodway

Figure .6 Construction of floodway of the Ara River

Notes: Source: MLIT

Urbanization progressed to the left bank of the floodway after the completion of the floodway in 1930

centering on railway stations and in districts subjected to land rearrangement. Urbanization started at

bridges and trunk roads over the floodway or around railway stations, progressed to surrounding areas

and was nearly completed in the 1980s.

In 1910, the development of the urban area in the east of Tokyo was at a standstill, restrained

by flood-prone swamps. The lowland that used to be vulnerable to flooding of the Ara and Edo Rivers

turned to the present condition with more than 1.6 million population and concentrated assets, owing

to the completion of the floodway in 1930, after experiencing the damage by World War II and

post-war economic growth.

(2) Effects of flood control project

(a)

The flood control project by constructing the floodway of the Ara River not only mitigated flood

damage to the riparian zones but also satisfied the key requirements for regional development by

increasing the safety of land from floods. Thus, the project created ripple effects on the development

of building land, and improvement of transportation and other urban infrastructure systems, resulting

in the revitalization of economic activities in the city. In Japan, the effects of flood control projects are

now evaluated not solely in terms of disaster control but the need to evaluate projects as the

"infrastructure of infrastructures" based on long-term judgement of overall regional social and

economic performance is being realized again.

The project for constructing the floodway of the Ara River produced the following ripple

effects on various socioeconomic activities in the following steps over the past 90 years.

Figure. 7 Phases of urbanization

Notes: Source :MLIT

Legend

Up to 1881

From 1882

From1910

1933-1954

From1955

1920-1932

From 1971

From 1988Urbanized

before completionAra River

Urbanized after

completion of floodway

1) The flood control project increased the effectiveness of disaster averting measures, and regional

safety.

2) Increased regional (land) safety promoted the development of building land.

3) Increased regional (land) safety accelerated the improvement of other (transportation, living and

industrial) infrastructure systems.

4) Land development and improvement of infrastructure encouraged the concentration of population

and the starting of business.

5) Economic activities expanded.

(b) Investment in infrastructure and economic activities

1) Effects of concentration of population

In Edogawa, Katsushika and Adachi wards, residential space has been provided to 1.63 million people,

about five times larger than 310,000 90 years ago, during the 90-year period since the commencement

of construction of the floodway.

2) Effects of encouragement of investment in infrastructure

Housing investment increased right after the completion of the floodway in 1930. Cost of urban

development rapidly increased in the 1955-1970 period. Flood control project cost also increased five

years later mainly for areas behind the embankments. The flood control projects mainly consisted of

control of high tides due to settlement and construction of drainage facilities.

3) Effects on economic activities

Manufacture's shipment value started increasing in the three wards around 1950. Then, commercial

sales value also increased from around 1960. This means that the area initially developed as an

－－－－ 治水事業効果 波及プロセス治水事業効果 波及プロセス治水事業効果 波及プロセス治水事業効果 波及プロセス

Phase 1: The area was constantly hit by floods

Phase2:

Creation of usable land

Phase3:

Development of infrastructure

Phase4: Urbanization

Phase5: Expansion of economic activities

Expansion of economic activities

Concentration of population (creation of residential area)

Start of business (development of commercial and industrial areas)

Increase of safety of land Creation of usable land

Flood control project

Paddies existed in floodplains

Railroading Road improvement

Land rearrangement and other two-dimensional improvement

Construction of sewerage system

Construction of waterworks

Increase in manufacturers' shipment value

Increase in income

Increase in tax revenue

Rise in land price

Increase in commercial sales value

Figure. 8 How the effects of flood control project spread

industrial area and then turned into a residential area incorporating a commercial district. Economic

zones have been created in the three wards that now yield a combined total of commercial sales and

industrial shipment at 5 trillion 400 billion yen per year.

3 Jobs to be done on flood control projects

Flood control projects, while supporting the social and economic development of Japan, induced the

concentration of large population and assets on floodplains. The population and assets in potential

flood areas increased about fourfold and 140-fold, respectively in 100 years since 1875.

Failure of embankments in the metropolitan area is therefore expected to have an extremely

serious impact not only in the damaged area but also on Japan's social and economic activities.

In recent years in particular, urban flood damage has been caused in which big cities such

as Tokyo, Nagoya and Fukuoka were hit by heavy rains and urban functions were paralyzed. Urban

flood damage includes not only general damage to homes and offices but also the paralysis of

transport and information exchange systems. Inundation of underground shopping centers even

claimed some lives.

Under the circumstances, emphasis has been placed on the following major jobs.

3.1 Total flood control measures throughout the basin

Flood control measures have been focusing on

river improvement. Today, in addition to proceeding

with river improvement, total flood control

measures are being applied by increasing the water

detention and retardation capacity of basins,

installing facilities to control storm runoff, and

using land and building houses so as to minimize

inundation damage.

Figure. 9 Multi-purpose water

retarding area for the Tsurumi River

Figure.10 System for total flood control

河道改修

分水路放水路[河川 水道]

治水施設 整備 調節地整備事業旧 治水緑地防災調節地流域調節地

河川域貯留 雨水貯留施設 設置[河川]

総 計画調節地 設置[河川 水道]

合

的 市街化調整区域 保持

暫定調節地 設置恒久化

治 保水遊水機能 保全対策 開発者 実施す も

水 流域貯留 透事業雨水貯留施設 透 す等各戸貯留

対 盛土 抑制

策 流域対策

土地利用規制盛土規制開発規制

水害 強い ち く 水実績予想区域 公表等住民意識 向

予警報 ステム避難対策 充実

耐水化 ロティ式建築等 促進

Channel modification

Construction of diversion channels and floodways (in rivers and sewerage works)

Construction of floodcontrol facilities

Water detention

in river basin

Measures taken in the basin

Maintenance of waterdetention and retardation

Flood-resistant

community planning

Installation of detention area (former flood control green area, disaster control detention area and detention area in the basin)

Installation of rainwater detention facilities (in rivers)

Installation of planned detention area (in rivers and

sewerage works)

Maintenance of urbanization control areas

Installation and permanent use of temporary detention

area by developers

Rainwater detention and infiltration projects in the basin (rainwater detention facilities, infiltration pits or other

facilities for household-based rainwater storage)

Restriction on filling works

Restriction on land use (restriction on filling and development)

Public awareness programs by publicizing areas actually inundatedor expected to be inundated

Promotion of flood-resistant structures (e.g. buildings on pilotis)

Enhancement of forecasting and warning systems andevacuation practice

Total flood control

3.2 Preparedness for floods exceeding design level and restoration of urban riparian zones

Many of Japan's cities are located on alluvial plains. Some are at sea level and protected by

embankments as high as 10 m. In these areas, especially in the Tokyo metropolitan area or Kinki

(western Japan) area, failure of embankments could cause devastating damage. Super (high standard)

embankments therefore have been constructed to prevent the failure of embankments by overflowing

floods exceeding the design level from causing catastrophic damage. Construction of such

embankments requires coordination with community planning. Comfortable communities equipped

with building land and parks are planned with the construction of super embankments with moderate

slopes. At present, eliminating districts where wooden houses are densely located is essential not only

to fire fighting but also for restoring and revitalizing urban areas. Creating safe and comfortable

riparian zones in cities by constructing super embankments would greatly help achieve the objective.

3.3 Promotion of development of flood control software

The Tokai disaster in 2000 made the threat

clearly understood that people became less

aware of the danger of flood disaster as a result

of developments in river improvement and

sewerage system development, and

urbanization.Hardware solutions have been

applied. In view of recent flood damage due to

heavy rains, risk management for mitigating

disasters is also being demanded.

For the rivers for which flood

forecasts were made mandatory, dissemination

of information by flood forecasts or other

means has been promoted. At the same time,

flood hazard maps have been prepared to

encourage residents to take shelter by

themselves in emergencies. In the wake of last

year's Tokai heavy rain, the Flood Fighting Law

was revised to enhance flood fighting efforts.

Hazard maps should be prepared in

coordination with municipalities so as to

encourage residents to take appropriate action

in emergencies.

＜ Before construction of super

b k t＞＜After construction of super embankment

＞

Figure. 11 Construction of super embankment

Slope behind the embankment

River area

Height of embankment

Effective use of slope behind the embankment

Special area behind high standard (super) embankment (30 h)

Super embankment

Figure. 12 A hazard map

洪水ハ ドマップ洪水ハ ドマップ洪水ハ ドマップ洪水ハ ドマップ

避難方向避難方向避難方向避難方向

水想定区域

水想定区域

水想定区域

水想定区域

避難対象施設避難対象施設避難対象施設避難対象施設

洪水ハ ドマップ洪水ハ ドマップ洪水ハ ドマップ洪水ハ ドマップ

避難方向避難方向避難方向避難方向

水想定区域

水想定区域

水想定区域

水想定区域

避難対象施設避難対象施設避難対象施設避難対象施設

Flood hazard map

Shelter

Potential inundation

area

Potential

inundation area