Rapid urbanization and changes in water circulation

Urbanization affects water circulation. The spread of sewerage systems, as described previously, caused a deterioration in river and canal environments as a result of water flow loss. Other changes in water circulation are caused by the paving of roads and the conversion of farmland into housing.

The urbanization of Tokyo started in the 1950s. Tokyo's population increased rapidly from the latter part of the 1950s into the 1960s, and is now some 12 million, warranting the name "mega-city." Urbanization at such a pace has changed the water circulation of Tokyo drastically, and has become the cause of new urban flood hazards. The Kano River typhoon, on 26 September 1958, produced the highest recorded rainfall per day (392 mm) since 1875 in Tokyo, and caused great flood damage in the newly developed housing areas of the western part of Tokyo. Since then, damage caused by rainfall has increased in parallel with new housing developments. Changes in water circulation during heavy rains are the main cause.

The urbanization of Tokyo has been accompanied by the populace's desire for a higher standard of living, resulting in a heavy burden on rivers and water circulation. These burdens have involved the control of water, the utilization of water, the environment, and the landscape. Embankments became taller as a result of river improvement works undertaken to protect against water hazards, thus spoiling views along rivers and streams. The construction of highways to provide easy access to the areas alongside these rivers has also spoiled riverside scenery.

In today's Tokyo, projects that aim to restore the rivers and water circulation of the city are finally under way. They include advanced water treatment systems in purification plants, the discharge of treated sewage into rivers and streams, the utilization of treated sewage in high-rise buildings, the encouragement of urban renewal work, and river improvement work in the development of the Super Embankment along the Sumida River - a river that is emblematic of Tokyo.

The philosophy of recycling

Urban developments that contribute to the convenience of urban life and economic efficiency have altered the nature of water circulation in Tokyo. As a result, the populace has been troubled by new types of flood hazard since 1985, a decrease in water bodies, a decrease in the ability to control the temperature in the city, and the heat island phenomenon, which has become acute in recent years. Tokyo waterworks have eagerly sought to meet the increased demand for water and have developed water resources by means of dam construction. New technologies, based on visions worthy of the twenty-first century and not limited to conventional planning ideas, have been sought for the water management of the future.

This could be called the materialization of the philosophy of recycling. The characteristics of water as a natural resource are intrinsic in the meaning of the recycling of resources. The utilization of treated sewage in buildings and to recharge rivers since the latter half of the 1980s in Tokyo, no matter how limited, should be recognized as the forerunner of water recycling measures from the point of view of the history of technologies.

New technologies must be developed to cope with the utilization of treated sewage, which is expected to grow in volume in Tokyo in the future. In order to achieve this goal, it is important to offer water of acceptable quality at low cost. The administration that produces treated sewage and the administrative bodies for waterworks, rivers, and streams, and the environments expected to use the treated sew- age are related to each other. In order to realize the philosophy of water recycling, an all-around administration is a must. In order to achieve this academically, the development of interdisciplinary fields of studies and cooperation is required. At the moment, treated sewage is sent underground from treatment plants to buildings, rivers, and water channels. For the future, however, studies are already under way on numerous technologies for sending it back to the upper basins of rivers and streams supplying purification plants.

In this context, the utilization of treated sewage must be recognized as one part of water resource development. Water resource development for big cities in the future should be a combination of dams, the utilization of treated sewage, the use of rainwater, as is being done in Sumida District, Tokyo, the conversion of existing water rights, etc. The designers and the executors of development plans must recognize that projects that do not take recycling into account affect the natural circulation of water in that area. If this concept is not accepted, the philosophy of recycling will not be able to be applied to Tokyo as a basic element in city planning.

The concept of recycling should not be limited to the waterworks of Tokyo; it should be applied to the water management of any future megalopolis and especially to the future planning of water-related infrastructure. As water-related projects become bigger and more complicated, the concept will expand its influence beyond borders. Hence, the concept is undoubtedly the key to the global problems of water and the environment.