Development of water resources in the upper Tone River basin

Development of the water resources of the upper basin of the Tone River system to serve Tokyo had been proposed to Tokyo City Council in 1926. Concrete discussions in the Council started in 1936, but it was not until after World War II that the actual plans were approved for execution. In March 1963, a plan to bring water from the Tone River to Tokyo was decreed by the Cabinet as the "Water Utilization Plan of Tone River Systems." Based on the plan, the development of water sources has become a part of the National Water Resource Development Plan, and many of its projects have been executed by the Water Resources Development Public Corporation that was established in 1962. The Tokyo Metropolitan Government was to take partial financial responsibility for the costs of the water supply, including industrial water, by way of multi-purpose dams. The Akigase Intake Weir and Asaka Canal had been built as emergency measures during the "Tokyo Water Famine" of 1964 as described earlier. The Musashi Canal was also constructed by the Public Corporation. Thus it became possible to get water from the Tone River systems when there was some spare volume, until the completion of dams in the upper basin of the river. Water from the upper Tone River basin was planned to flow through the Musashi Canal, via Tone Oseki (Tone Grand Diversion Weir), to the Ara River, with purification occurring at the Asaka Purification Plant, and sent from there to Tokyo by way of water pipes. The Asaka Purification Plant was completed in 1966. (Prior to that, in 1965, the Yodobashi Purification Plant, which had played an important role as the largest plant in Tokyo, ceased to exist. The site occupied by the plant was taken over for the development of the Shinjuku Suburbanization Plan, and became a town of high-rise buildings, such as the Tokyo Metropolitan Government Centre, hotels, and offices.)

The volume of water supplied to Tokyo increased by 1,200,000 m³/day after construction of the Asaka Purification Plant (900,000 m³/ day) and the Higashi-Murayama Purification Plant (300, 000 m³/ day). All planned construction was completed by 1968, including the Yagisawa Dam in the upper basin of the Tone River in August 1967 and the Shimokubo Dam in the basin of the Kanna River, a branch of the Tone River, in November 1968. As a result, the volume of water supplied to Tokyo increased dramatically. Furthermore, the Tone River water resource development projects were completed one by one, and after 1965 the water supply operation expanded to serve not only the urban areas of Tokyo but also Tama districts. Construction of the Tone Estuary Barrage was completed in 1971 and dams in the basin of the Watarase River, the Kinu River, etc. and expansion of the Asaka Purification Plant were undertaken in the 1960s and 1970s.

Since the 1970s, however, it has become increasingly difficult to get agreement on dam-site areas. Difficulties in balancing water demands in the future have been anticipated. The Tokyo Waterworks Bureau made a public announcement in 1973 on "Statements Concerning Water Conservation" and, for the first time, appealed to citizens regarding the need for control over water demand and the saving of water. At about the same time, the state government began to propose a "water conservation conscious society." Furthermore, the 1973 "Act of Special Measures for Reservoir Areas," a measure to cope with the difficult situation of upstream reservoir areas, was passed by the Diet. Great progress has been made, by making a differentiation from money compensation-type measures. This was one of the turning points in the history of dam construction policy.

Criticisms about dam construction were originally based on the shortcomings of the measures for the reservoir areas of the upstream basin. Eventually, the effect of dam construction upon the environment has begun to be taken into account, with the cost of environmental measures being added on. The cost of construction has thus risen considerably. Although the Yanba Dam and other dams along the Agatsuma River (a branch of the Tone River) are already on the government's construction list, potential dam sites are in general decreasing and it is gradually becoming difficult to secure future water resources for Tokyo by means only of dams.

Tokyo's waterworks, having experienced a century of many complications, have fulfilled their mission well. Now there are new problems: environmental problems such as pollution of water at intake points on rivers, etc., further upgrading of service to inhabitants, and earthquake measures.