PRINCIPAL POLICIES OF THE TOKYO METROPOLITAN GOVERNMENT

Maintaining the Sewerage System

The Bureau of Sewerage is a local, publicly-run company. In order to support the cycle of water use in the capital and to ensure that we are able to lead healthy, civilized lives and engage in the activities associated with a city, the Bureau disposes of and treats sewage and performs all the other essential tasks required of public sewerage services. In the Tama district the Bureau is responsible for the treatment of sewage emitted by the public waterworks in the district's municipalities.

Reconstruction of Deteriorating Facilities

Tokyo's sewerage facilities have been gradually built up over an extended period of time dating all the way back to 1884. As a result, approximately 13% (around 2,000 kilometers) of all the sewerage pipelines in the 23 special-ward area is older than the 50 years stipulated as the legal limit for durability. This is particularly true of pipelines in the central area, where more than 80% of the lines exceed their legally defined service lives. In fact, various problems - among them road collapses - have resulted from sewerage line deterioration and breakage.

This problem also extends to treatment plants, pumping stations and other sewerage facilities, some 45% of which are similarly beyond their legal lifespan. The consequences include structural deterioration, functional decline and other critical conditions. To deal with this situation, sewerage facilities are being reconstructed in a systematic and efficient fashion to ensure that they adequately fulfill their functions in maintaining and improving safety and comfort for Tokyo residents.

Flood Countermeasures

In Tokyo, a city distinguished by a high degree of urbanization, it is now difficult for rainwater to be absorbed into the ground, with the great majority of storm water flowing into the local sewerage systems over short periods of time. This has increased the incidence of flooding even in districts served by sewer lines.

Steps taken to resolve this problem include raising the handling capacity of sewer pipelines, pumping stations and other storm water and wastewater facilities, making improvements in rainwater overflow control facilities and other measures.

Improvements in Combined Sewerage Systems

In Tokyo, 82% of the 23 special-ward area is served by combined sewerage systems in which both wastewater and storm water are channeled through the same pipelines. The problem with this approach is that heavy rainfall causes the wastewater to become diluted with storm water, with a portion of the dirty water eventually released into rivers or the ocean via storm water spillways or pumping stations.

To preserve water quality in public water areas, large pipelines are being installed to carry wastewater to treatment plants during the initial stages of rainfall, while reservoir facilities are being constructed to store sewage that cannot be fully treated during heavy rainfall.