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Chapter 4. Japanese water transfer: a review

M. Okamoto
Faculty of Agriculture, Iwate University, Japan

IN JAPAN, Interregional Water Transfer (IWT) has been carried out since ancient times and has become increasingly important in recent years although the IWT projects that have been carried out so far or are now being considered are all relatively small in scale. Japan being an island country, the water transfer distances are shorter and yearly volumes of water transferred are smaller than those of IWT projects in many other countries. However, it can be said with some confidence that the IWT projects in Japan, though smaller in scale, face similar problems-technological, socio-economic, institutional and environmental-that need to be solved, and are also similar in terms of complexity. It seems that the problem of direct technology transfer does not so much depend on the scale of a project itself but rather on the political system (democratic or centrally planned), the state of economic development, and existing natural conditions.


First, geographical and hydrological characteristics of Japan and her socioeconomic and institutional structure, within which IWT projects are carried out, will be outlined.

Japan consists of four main islands. It is located in the Asian monsoon area where typhoons frequently occur. Therefore, the annual precipitation is abundant, but its monthly distribution is not uniform. Dry spells occur in some years in the rainy summer season, when irrigation is also necessary Thus, in spite of sufficient average annual precipitation, supplemental irrigation is essential, particularly for rice cultivation. There are few rain-fed paddy fields in Japan.

The catchment area of rivers tends to be small, i.e. 17,000 km at most, with steep banks which make for a large ratio between flood and low flow With the large yearly or seasonal fluctuations in precipitation, the volume of river runoff which can reliably be abstracted every year-irrespective of droughts or dry spells-is much smaller than the average flow rate.

Furthermore, due to the topography and compensation problems to be discussed later, it is difficult to construct large storage reservoirs which are necessary for increasing low flows during dry periods by regulating river runoff. Most reservoirs in Japan are of the month-to-month carry-over type, and not the year-to-year carry-over type, like the large storage reservoirs in other countries.

In Japan, rice cultivation has been conducted since ancient times, utilizing large quantities of river runoff, and currently reliable river runoff is almost totally taken into paddy fields. The development of cities and industries in recent years has increased domestic and industrial water demands, and has necessitated the construction of multipurpose reservoirs and execution of IWT projects.

Existing agricultural water rights are considered to be the traditional water rights, and have priority over newly developed domestic and/or industrial water rights. These existing traditional agricultural water rights have been guarded and exerted by the farmers' associations.

For scaling up IWT, the economic basis for completing the scaled-up projects as well as the technological advancement is necessary. Fortunately, in Japan, development of the required economic power and technology was synchronized with IWT during each historical period.


In Japan the river runoffs which can be steadily abstracted are taken even during a drought year, and all of it practically diverted into rice fields as mentioned earlier. Such a state of affairs has developed for historical reasons which will be briefly discussed now.

In Japan traditionally, feudal lords, landowners and farmers made efforts to expand their rice fields as much as possible. The rice fields must be prepared by levelling land surface, constructing earthworks such as levees for enclosing the land surface, diverting water from rivers and conveying it to the fields through irrigation canals. Rice grown under such arrangements is an excellent crop in many respects as compared with other upland crops. As is to be expected, the river flows in normal years are greater than in drought years.

Accordingly, during normal years or years with abundant flows, new rice fields are reclaimed. With the expansion of areas where rice is being cultivated, water available for irrigation during dry years is not enough. Consequently, further new water sources have to be developed by constructing tanks and diverting water from other rivers.

Therefore, when cities and factories need additional water, they have to construct reservoirs, which can release during dry spells water stored during average or above-average flow years, or divert runoff from other remoter rivers and convey it through canals and tunnels.

Thus, in Japan, IWT has been practiced over several hundred years to expand rice fields. During the past 100 years, especially after the Second World War, large multipurpose reservoirs were constructed for combined use of hydroelectric power generation and flood control. Large-scale IWT projects had to be constructed due to the remarkable expansion of cities and industries.

In most rivers, the low flow during dry periods is totally used in the existing agricultural lands. Thus for any IWT project, a reservoir or reservoirs must be constructed upstream where runoff is transferred.


Many alternatives are available in place of IWT. The first alternative is to reduce the water requirements. In Japan, there are many instances where water intake by factories has been reduced for many reasons, including easy availability of water, high water prices, extensive recycling, and more efficient use of water (see Chapter 1).

In cities, there are some cases where water consumption was reduced in of fice buildings and shops after a cumulative water price system was adopted. However, for the domestic water use sector, it is politically and socially difficult to increase the water price. Thus, reduction of water demand in this sector has not been successful. There are, however, some cases where water consumption was eventually reduced due to extraordinary droughts. Reduction in domestic use of water has not been successful in spite of various publicity campaigns.

The supply of water has to be increased when the demand cannot be restrained, or when demand increases in spite of all the restraining efforts. In Japan, the commonest method to cope with this situation is to construct reservoirs. Many of the recently constructed multipurpose reservoirs provide more reliable water supply, hydroelectric power generation and flood control.

If a lake is available at a suitable position, it can serve as a reservoir during dry spells, but its water level will be lowered. A freshwater lake, which can be developed by closing a bay by dikes and then gradually replacing sea water with fresh water from a river flowing into the bay, can be utilized in the same way as the aforementioned natural lake.

Another alternative is to divert the water used for other purposes. In Japan, a tremendous quantity of water is used for irrigating fields. It is possible to divert a part of this irrigation water for use by domestic and industrial sectors since irrigation area has decreased due to urbanization: rice fields have often become housing and factory sites. But this alternative has not produced the anticipated good results due to bureaucratic problems and inappropriate policies and technologies.


Recent technological progress has made it possible to carry out IWT which would earlier have been regarded as technologically impossible. Some of the technological developments in IWT during recent years in Japan will be briefly mentioned here.

The introduction of pumps first led to lifting a large quantity of water, and this has expanded the regions where IWT can be developed. Improvements in tunnel excavating techniques have also contributed to IWT.

IWT is often accompanied by the construction of a diversion dam or barrage. Construction of gates having larger spans has made it possible to enlarge the spacing between piers which hinder flood flow. Capacities of machinery used for civil engineering works have increased and new engineering techniques have been developed for underwater construction. As a result, construction of large barrages across major rivers has become possible.

Improvement in construction techniques for dams has also been remarkable. Since the earth dam was the only type of dam which could previously be constructed, the storage capacity of reservoirs was limited. However, improvement in design and construction techniques for concrete dams and rock-fill dams has made construction of high dams possible, which has significantly increased the storage capacities of reservoirs.


Generally, IWT is carried out as a public enterprise and requires large investment. Therefore, it is essential to have the backing of a financially strong government.

A short period after the Second World War, the Japanese government is said to have assisted an electric power company to produce hydroelectric power at a lower cost by controlling the interest rate and cost allocation, and thus provided stimulus to industries to grow. Further, in the agricultural sector, which has a low profitability, the government granted subsidies to farmers amounting to more than 75 per cent of the total construction cost for an irrigation project. The repayment conditions for the remaining 25 per cent share of the farmers were made favourable by providing a low interest rate (e.g 5.5 per cent per annum) and a long repayment period (e.g. 20 years).

In recent years, large-scale public undertakings have been welcomed in Japan partly due to the creation of effective demand for the business upturn.

Investments required have not been obtained from foreign countries for IWTs in Japan, with an exceptional case where a loan from the International

Bank for Reconstruction and Development was used to construct a multipurpose project to provide agricultural, domestic and industrial water supply.

Currently, the feasibility of a public undertaking is primarily determined by the benefit-cost analysis. Other analyses, such as internal rate of return, are not used. It should' however be noted that for benefit-cost analysis, benefits estimated often have political and other biases.

For large-scale IWTs, a system was developed where the facilities, particularly reservoirs and barrages, were made multipurpose, and the government paid a part of their construction costs because of their effects on flood control. This policy reduced the cost to be borne by each user sector, including electric power companies (hydroelectric power generation), and domestic, industrial and agricultural sectors.


The most important social obstacle in developing IWT in Japan today is the difficulty in obtaining planning permission to construct reservoirs. This is primarily due to the difficulty of obtaining the consent of the people who have to be resettled in other places due to inundation, some of whom have to even change their professions since their farms will be submerged.

In Japan, compensation has to be paid to the people whose houses and farmlands will be inundated. Except for large landowners, who own extensive rice fields, most people as a rule cannot maintain their living standard at the same level as before the inundation, even after compensation is received for the properties lost. Hence, the inhabitants whose houses and farmlands will be submerged by construction of reservoirs lobby against such schemes.

For these reasons, compensation that is currently to be paid must be adequate to ensure that the living standards of people affected remain the same as before. In addition to such compensation, provision has to be made for the construction and improvement of such social infrastructures as roads around the reservoirs.

Another important social obstacle to carrying out an IWT is the possible adverse environmental impacts of the project. For example, people oppose IWT because they are worried that groundwater under the alluvial fan may be depleted by the diversion of the river runoff to other basins, or that there will be adverse environmental impacts on fish, shellfish and plants.

It should be noted that a comprehensive and political judgement on these problems may be better than the monetary assessments that are currently conducted. It is difficult to assign monetary values to environmental impacts. Furthermore, uncertainties with the estimation of irrigation and hydropower generation costs introduce more problems in any economic analysis. The impacts of such issues should be judged scientifically and not evaluated purely on a monetary basis, which could price them somewhat arbitrarily.


According to Japanese law, river runoff is public property and not a private domain. In other words, the water rights must be granted by the government before river flow can be used. However, most agricultural water rights in Japan had already existed before the enforcement of the above law, which was instituted after European laws. This means many farmers are automatically entitled to the water rights.

Water laws further stipulate that any new use of river water must not do any damage to existing water rights. However, there are instances during extraordinary drought years when a party with a new water right upstream has infringed the long established water right of another party downstream, by simply taking the river flow. Based on such experiences, the parties that already hold water rights oppose any new plans to abstract water at any point upstream of their intakes. Such oppositions continue to be another important obstacle to IWT in Japan.

In order to solve this problem, parties acquiring new water rights should abstract at least at the same point as parties having prior water rights; alternatively, the new party could undertake to release a certain amount of discharge agreed to earlier. However, such undertakings have often broken down under severe drought conditions. Such problems led to the situation where an organization (e.g. the government) trusted by both parties undertook river operation.


IWT to Tokyo Metropolis

Tokyo, the capital of Japan, was a large city even as early as the 16th century, when the domestic water supply system was constructed. Due to a continuing increase in population, it became necessary to divert water from Tama River, which was far from the city of Tokyo, called Edo at that time. This was called Tama River water supply system, and was constructed at about the middle of the 17th century.

In the early 20th century, water had to be supplied to a population of about 1.1 million in Tokyo, and 50 million m were transferred annually. By 1935, the population had increased to 5 million, and the annual volume of transferred water exceeded 300 million m. In order to satisfy such rapid and massive increasing water demand, two tanks were constructed in the suburbs of Tokyo. They did not have their own catchment areas but stored water which had been diverted from the Tama River.

By 1960 the population was more than 7 million, and the annual transferred volume of water exceeded one billion m. In order to meet the increasing demands, a plan was made to increase the transferred volume of water remarkably by constructing a large reservoir at Tama River. Its completion, however, was delayed due to problems of compensation. The difference between supply and demand had to be made up by taking water temporarily from another river, Edo, and also by diverting water from the Sagami river.

These temporary solutions could not satisfy the water demands of the Tokyo metropolis. Consequently, it was decided to transfer water interregionally from the Tone River, which is the largest river in Japan and furthest away from Tokyo. Two reservoirs, Yagisawa and Shimokubo, were constructed for regulating the low flow. At the beginning of this plan, the location for diversion of water from the Tone River to Tokyo was planned to be further upstream than that of the former irrigation systems.

As the result of opposition by the farmers' association, whose members were irrigating rice fields by operating the former irrigation systems, a barrage to divert and transfer water to Tokyo metropolis was constructed midstream of the Tone River, so that both farmers' irrigation needs and water requirements of Tokyo metropolis could be satisfied by the water provided from this barrage.

The demand for water for Tokyo metropolis continuously and rapidly increased thereafter, and reservoirs were constructed at other tributaries of the Tone River. Thus, the distances of water transfer became greater with time. Moreover, as shown in Figure I, IWT projects from more remote rivers (Naka, Agamo, Shinano, Fuji, etc.) than the Tama or Tone are now under consideration.

Recently, people have begun to doubt the necessity for these large-scale IWT projects. This is because they suspect that the demand for water from cities and industry, which justifies these projects, is excessive and water is used inefficiently. In addition, there are other important reasons for opposition to such plans. Residents to be affected by the construction of reservoirs oppose the plan and so do people who fear further environmental disruption.

Figure 1. Tokyo Metropolis

Shin-Nippon Seitetsu Kabushiki Kaisha (Kitakyushu Area)

Shin-Nittetsu, which was constructed at Kitakyushu area as a governmentcontrolled iron works, has now developed into the largest iron-manufacturing company in the world. When the company was inaugurated, it constructed a small reservoir of about 250,000 m in a nearby small stream to start operations. However, after ten years, they began to withdraw water with pumps from the remote Onga River. Thereafter, they constructed reservoirs of about 1.5 to 7 million m to store water, after diversion from the Onga River.

In spite of improving the process for using water and the efforts made to reuse water extensively, the demand for water increased further. A larger storage reservoir was constructed upstream on the Onga River to increase the water available. Its point of water intake, that is the location of the diversion dam, caused similar problems to those experienced in the Tokyo metropolitan area and by the operators of earlier irrigation systems as at the Tone River.

Kagawa Irrigation Project

The northern region of Shikoku Island, where Kagawa prefecture is located, is the least rainy district in Japan. The area of Kagawa prefecture where rice is cultivated is about 37,000 ha, and there are 18,000 tanks whose total area is equal to about 5,000 ha. An IWT project from the Yoshino River, which flows in the centre of Shikoku to the east, was planned but it was not realized for a long time because of the opposition of Tokushima prefecture, which is located downstream of the Yoshino River. However, the project was realized after the Second World War, and a reservoir called Sameura was constructed upstream on the Yoshino River. At the Ikeda barrage, which was constructed midstream, some river flow was diverted and then transferred to Kagawa prefecture through the tunnel which passes through a mountain range.


In view of the development and results of IWT in Japan and in other countries, the following steps should be taken for the planning and execution of IWT projects:

(1) Firstly, fully examine all the possible alternatives to IWT in order to determine whether the IWT is necessary (See Chapter 1);
(2) If it is decided to carry out IWT, examine the advantages and disadvantages associated with various routes available;
(3) As a general rule the larger the IWT is in scale, the longer it will take to develop. It is desirable that the plan, survey, design, construction and operation be made ingeniously and by stages so that the IWT effects can appear, even if partially, before the entire IWT can be completed;
(4) The effects of IWT will become larger when the project encompasses a wider area, and the facilities become more multipurpose;
(5) Due care should be exercised in planning the operation of multipurpose IWT, since conflicts of interests between different sectors are likely;
(6) The positive effects are rarely overlooked. Carefully examine all potential negative effects, including environmental disruptions.

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