flood control works in japan · 2017-06-29 · flood control projects have long reduced the area of...
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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
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平元 平2
平3
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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
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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