FLOOD CONTROL WORKS IN ~ ACHIEVEMENTS TO DATE AND FUTURE OUTLOOK

Tsuneyoshi MOCHIZUKI1, Takeshi UEDA2

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 Notes: Source:Rivers in Japan(MLIT) Figure. 1 Monthly precipitation in , location of the islands. Areas along the are Paris and New York 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.

Rhine River (a) Japanese rivers are steep-sloped Loire River

Many of the Japanese Joganji River rivers are steep-sloped Colorado River and flow down Senine River mountains quickly to the sea from their Mekong River headwaters over short Elevation distances. (meters) River Distance from river mouth(kilometers) (b) Water level rises Notes: Source:Rivers in Japan(MLIT) quickly in Japanese Figure. 2 Longitudinal slopes of rivers in Japan and other countries 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. Notes: Source:Rivers in Japan(MLIT) Figure. 3 Characteristics of flood runoff in Japan 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 (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.

In hundreds of millions of yen

単位億円 1 8,000 Public utilities services Public公益事業等 works facilities 16,000 公共土木施設 Ordinary assets 2000 1 total:2計 一般資産等 1212,050,050 1 4,000 85 1 2,000 2,027 1 0,000

8,000

6,000 9,938

4,000

2,000

0 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 1 1 0 2 1 2 3 4 5 6 7 8 9 36 37 38 39 40 4 42 43 44 45 46 47 48 49 50 5 52 53 54 55 56 57 58 59 60 6 62 63

平 平 平 平 平 平 平 平 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 昭 平1 平11 平1 昭 昭 平元 (4 ) (3 ) (2 ) (1) (5 )(5)) 主 Major Typhoon July downpour Typhoon No.17 Downpour 水害 第二 七月 台風17号 豪雨 Tokai東洊東洊東洊 cause of Daini-muroto (collapse長良川 of embankments in (flood damage in 豪雨 原因 室戸台風 豪雨 the 長崎水害 downpour豪雨豪雨 flood 堤防決壊 ) damage N注1ote 1:成 Final確定値成 data are shown up to速報値あ 1999. Data for 各水害被害額成2000 are preliminary. Amounts価格実質化したもあ of flood damage have actually been presented in 注2昭和200036公益事業等被害い調査さ price. いい N注ote3 2:グラ中 No investigations各カッコ書数値水害被害総額大い順位位 were made of the damage to public utilities services付与し in 1961.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 N注ote4 3:昭和 Figures36～成11均値 in the parentheses 7,indicate143億円 うtheち ranks一般資産等 in total 2,3 flood10億円公共土木施設 damage amount 4,720 (top億円公益事業等 five in the des 11cending3億円 order). Encircled figures indicate 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)

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

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 . 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.

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 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 . 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 Plains in several threads toward . After , a warlord, moved to (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 the Open cut of Shinkawadori in Kaino River in 1594 Open cut of the Akahori River since 1621 (water discharge in 1654) Coffering of the Moto-ara Open cut of the Sakase River in 1641 River in 1629 Open cut of the in 1635-1641 period Open cut of Ohki hills along the Kinu River in 1629

Tone River Kokai River

Kinu River Ara River

Relocation of the Kokai River in 1630

Legend Present alignment Alignment in the Edo Era 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

Notes: Source :MLIT

Figure. 5 Eastward relocation of Tone River

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 , 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 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 Floodway the Meiji Era built groups of cement, shipbuilding and fertilizer plants near the mouth of the 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. Notes: Source: MLIT The large scale project to excavate the floodway Figure .6 Construction of floodway of the Ara River 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 , 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)

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.

Legend From 1882 From1910 1920-1932 1933-1954 From1955 From 1971 Up to 1881 From 1988 Urbanized Ara River before completion Urbanized after completion of floodway

Notes: Source :MLIT

Figure. 7 Phases of urbanization

(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.

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.

Phase 1: The area was constantly hit Paddies existed in by floods floodplains

Flood control project Phase2: Creation of usable land Increase of safety of land Creation of usable land

Road improvement Railroading Phase3: Development of infrastructure Land rearrangement and other two-dimensional improvement

Concentration of population Start of business (development of Phase4: (creation of residential area) commercial and industrial areas) Urbanization

Construction of sewerage Construction of system waterworks

Phase5: Expansion of economic activities Expansion of economic activities

Increase in Increase in Increase in Increase in tax Rise in land manufacturers' commercial income revenue price shipment value sales value

－ 治水事業効果波及プロセス Figure. 8 How the effects of flood control project spread

(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

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 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

河道改修Channel modification 分水路放水路Construction [of河川水道 diversion ]channels and floodways (in rivers and sewerage works) Construction of flood 治水施設整備 Installation調節地整備事業旧 of detention 治水緑地防災調節地流域調節地 area (former flood control green area, disaster control facilities control detention area and detention area in the basin) Water detention in 河川域貯留 river basin Installation雨水貯留施設設置 of rainwater[河川 detention] facilities (in rivers) 総 Installation計画調節地設置 of planned[河川水道 detention] area (in rivers and sewerage works) 合 的 Maintenance 市街化調整区域保持 of urbanization control areas Total Installation暫定調節地設置恒久化 and permanent use of temporary detention flood area by developers control Maintenance of water 治 保水遊水機能保全対策detention and retardatio n Rainwater開発者実施すも detention and infiltration projects in the basin (rainwater detention facilities, infiltration pits or other 水 facilities流域貯留洋透事業雨水貯留施設洋透す等各戸貯留 for household-based rainwater storage) 対 Restriction盛土抑制 on filling works 策 Measures 流域対策 take n in the basin Restriction土地利用規制盛土規制開発規制 on land use (restriction on filling and development) 水害強いちくFlood-resistant 洋水実績予想区域公表等住民意識向Public awareness programs by publicizing areas actually inundated community planning or expected to be inundated Enhancement予警報ステム避難対策充実 of forecasting and warning systems and evacuation practice Promotion耐水化ロティ式建築等促進 of flood-resistant structures (e.g. buildings on pilotis)

Figure.10 System for 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.

＜ Before constructionSlope behind of the supeembankmentr ＜After constructionEffective of super use embankment of slope behind the embankment bk t＞ ＞ Height of embankment

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

Figure. 11 Construction of super embankment 3.3 Promotion of development of flood control software

The Tokai disaster in 2000 made the threat clearly understood that people became less Flood洪水ハド hazardマッ mapプ 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 水想定区域 heavy rains, risk management for mitigating disasters is also being demanded. For the rivers for which flood Potential inundation forecasts were made mandatory, dissemination area of information by flood forecasts or other 避難方向Shelter 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 Potential避難対象施設 inundation was revised to enhance flood fighting efforts. area Hazard maps should be prepared in coordination with municipalities so as to encourage residents to take appropriate action in emergencies. Figure. 12 A hazard map