VOL.3

Vol.3

Ensuring stable supplies of water

The development of water resources in the Prefectures of Tokyo and Saitama is in accordance with the criteria laid down in the "Basic Water Resources Development Plan (Full Plan)", which is itself based on the Water Resources Development Law of 1961. The Plan designated seven major rivers, the Tone, Ara, Toyo, Kiso, Yodo, Yoshino and Chikugo, in whose basins live some 65 million people - 51.3% of Japan's total population.

Of that total population, one quarter inhabits the basin of the Tone and Ara rivers, which flow through the two Prefectures. The Plan has set the target rate of flow of the water to be supplied by these two rivers at 257.4m3/second, although this figure is currently the subject of a thorough revision.

The Plan's output target for the water resource development facilities, namely the reservoirs and dams, on these two rivers, was 204.5 m3/second; whereas the actual output at the end of 2002 was 166.4 m3/second, or 80% of the target figure. Since the Japanese population figures are expected to fall from 2006 onwards, the inhabitants of the basin can be adequately supplied with water if the rate of flow can be increased to the target figure.

However, the safety factor (probability of water shortage in terms of years) of these water utilities has been set at 1/5 (probability of water shortage once in 5 years), as compared with the national standard of 1/10, with the aim of satisfying the pressing need for the water.

Moreover, data for the past 100 years show that rainfall has been declining since 1960, with eight of the ten driest years falling within the last thirty-five. If rainfall is low, the volume of water that can be stored in a dam is obviously smaller. Evidence shows that the stable quantity of water supplied from the dams on the Tone River has been about 20% less than that for which they were designed. Because of the decreasing rainfall and of the granting of provisional water rights that have not been backed by the necessary water resources, water intake restrictions are being applied as often as once every two to three years.

The water quantity supplied by the existing water resource development facilities (dams and reservoirs) in which the Tokyo Metropolitan Government has invested is 56.96 m3/second. Since the average water supply in Tokyo is approximately 540,000 m3/day ( 52.5m3/second, the demand for water in Tokyo can be met with water from the Tone and Arakawa systems. The supply will be increased by 6.08 m3/second by water from Takizawa and Yamba dams, currently under construction, and from the Ogochi dam, which is a reserve facility.

Tokyo was transformed from a water-based to a land-based capital through the process of the city's development, which led to the loss of waterways and paddy fields. However, although it lost this "natural water", it secured "urban water" instead.

Let us examine another Prefecture, Saitama. The rapid increase in its population began during the high economic growth period of the 1960's. This increase began 5-10 years later than that of Tokyo and because of its excessive dependence on supposedly abundant groundwater, Saitama was tardy in securing water resources.

The quantity of water required by Saitama Prefecture was calculated to be 28.84 m3 /second on the basis of a daily per capita water consumption of 356 liters (0.356m3/second) in 2001 and a total Prefectural population of 7 million. However the stable water rights (as expressed by the quantities freely available from the river any time to those who hold water rights) granted to Saitama Prefecture and to its municipal governments total approximately 15m3 /second. This shortage is made up by the water acquired under provisional, but not stable, water rights. This is one of the reasons for the frequent restrictions that have been imposed on the intake of river water in the surrounding Prefectures, including Tokyo. It is expected, however, that it will not be necessary to make use of groundwater once the Takizawa and Yamba dams are completed.

Nevertheless, society cannot run the risk of being without safe supply networks of water and/or electricity. How can people living in Saitama be assured of having water? Well, there is water in the paddy fields.

The volume of agricultural water which leaked from the agricultural irrigation systems, moistened the earth and was continually recycled, decreased as a result of urbanization. An abundance of water is said to be a measure of civilization. However, a civilized society absorbs as much water as it can be supplied. If agricultural water is made available for industrial and residential use, it will be completely used up.

If this remaining water is lost as the amount of agricultural land progressively decreases, then Saitama will lose this last safety reserve. The paddy field water that remains, which is vital to agriculture, should be preserved.

There is another important reason for preserving agricultural water. Because their waters are protected by traditional water rights (granted to farmers for agricultural use), both the Ara and the Tone can survive as rivers, not just as aqueducts whose role is to transport and supply water. Unless agricultural water is preserved, all Japan's rivers will become nothing more than aqueducts and will lose their many other functions.

Minumadai Field Preservation Tamenaga Shinden

The Minuma paddy field, located in the eastern part of Saitama City, dates from the middle of the Edo Period (1603-1868), when the area of Minuma, between today's cities of Saitama and Kawaguchi, was developed by Izawa Sobei Tamenaga on the orders of Tsunayoshi, the Eighth Shogun, as was the construction of a 60-kilometer agricultural irrigation channel from the River Tone.

Today, only 1,263 hectares of paddy field remain in Minuma. The field has been preserved not only as a rice paddy, but also for flood regulation and environmental protection purposes. However, because of various reasons, less and less land is being cultivated. There may be sufficient residential and industrial water in Saitama Prefecture once the Takizawa and Yamba dams are completed. However, water for use as a last resort in the event of a serious shortage will not be supplied by these dams.

Hitherto in Saitama Prefecture, agricultural water has been used as residential and industrial water. However, urban society has grown accustomed to using as much water as is available. This is why we need to increase the size of the paddy field and to preserve agricultural water which may help the city in the event of a water shortage. In return, we city dwellers will help to conserve both the field and the water. For these reason, our NPO organization, Forum Aquarium, has established the Minumadai Preservation Club.

Our first project is the Tamenaga Field, named after Izawa Sobei Tamenaga, who developed the Minuma region. The cultivation of the fallow field began with weeding, followed by exterminating noxious insects and unwanted millets. This year's exceptionally cold summer also adversely affected the rice plants. Nevertheless, we really are enjoying growing rice in the sun, with the help of farmers and of our wonderful friends.