New targets for water supply works
Ever since the establishment of modern waterworks in Tokyo a
hundred years ago, efforts have been made to secure water resources and to
maintain facilities. These efforts have brought results at last, but it is no
longer a question of just securing the necessary volume of water. A series of
new problems has surfaced. To cope with these problems, in 1997 the Tokyo
Waterworks Bureau proposed seven significant targets for the next
quarter-century.
Waterworks that are immune to shortages
In recent years, there has been no shortage as serious as that
of summer 1964. However, every few years, restrictions on water use have been
imposed in periods of low rainfall. Because water is used in many diverse
fields, the effect of water restrictions on citizens' lives and activities is
quite serious.
The goal for Japan's waterworks is a stable supply of water even
in times of great shortage that occur once every 10 years, but Tokyo's
waterworks have not yet reached that level. The waterworks of San Francisco and
New York in the United States have been designed to withstand the greatest
historical shortages, and in London they are designed to withstand the shortage
that occurs once in 50 years. The reservoirs on the Tone River and the Tama
River for Tokyo's waterworks hold about 30 m3 per person. In
comparison, the pondage per person is 520 m3 for San Francisco and
280 m3 for New York. The pondage is as low as 90 m3 per
person for Paris and 35 m3 for London, but the Seine River, as the
water resource for Paris, and the Thames River, as the water resource for
London, experience little fluctuation in discharges, which has made a stable
supply possible. Since the pondage per person for the Tokyo waterworks is quite
small, it can be said that the safety margin of the water supply is not high. It
is therefore important to establish a waterworks system immune from shortage.
Waterworks that can provide a constant water supply
Many disasters related to water quality have occurred in recent
years - there were 299 cases in 1995. About 60 per cent of cases of water
pollution are due to oil. In order to cope with the problem, channels for
emergency communications and information collection have been established by the
communications network through conferences held by related administrative
organizations.
Disasters related to waterworks facilities, in particular
purification plants, include pollution of water sources with toxic oils, ageing
of the facilities, and electricity failure caused by lightning strike or snow
fall. Disasters related to water pipes involve traffic vibration, ageing of
pipes, leaks caused by soil corrosion, and damage from construction works such
as road repairs or gas pipe works.
Even in times of disasters related to water quality or
facilities, systems to ensure a constant water supply must be established.
Preparation for a great earthquake
The Hanshin-Awaji earthquake of January 1995 should be
acknowledged as a precedent for epicentral earthquakes in Kanto urban areas. It
is clear that Tokyo's dilapidated water pipes would be devastated if hit by such
an earthquake. Since the Hanshin earthquakes, the Tokyo Waterworks Bureau has
been proceeding with the reinforcement of reservoir, intake, purification,
transmission, and distribution facilities against seismic shocks. In order to
secure potable water in the event of an emergency, it is planned to locate water
storage bases every 2 km. For this purpose, existing purification plants and
water stations will be used as water storage bases. For areas that are more than
2 km from these purification plants and water stations, emergency water tanks
are already in place; for example, there are 45 tanks in the Ward Areas and 7
tanks in Tama District. Each tank contains 1,500 m3 of water and is
placed in a park that has been designated as a refuge. Within the Tokyo area,
there are 169 emergency water supply points, and the total potable water volume
constantly stored is 910,000 m3. This is equivalent to the
consumption of Tokyo's 12 million citizens for three weeks, allowing 3 litres of
water per person per day.
Taking into account the worst possible scenario at the time of
an earthquake disaster, ways to secure potable water and water to extinguish
fires must be sought.
Maintaining water quality
As regards Tokyo's future water management, measures to maintain
the quality of the water must be seriously considered. The advanced water
treatment started at the Kanamachi Purification Plant should not be considered
as a temporary measure to cope with the contamination of water resources. It
should be seen as the forerunner of measures at a time when many new and
dangerous chemical substances are being developed.
Providing an impartial and efficient supply
In normal times, or even in times of disasters or shortages, the
purpose of the water service is to provide an impartial and efficient water
supply for users. Means of establishing such a system must be sought.
Waterworks that consider the environment
Waterworks must be designed to take into account energy saving,
the efficient use of energy, and the recycling of resources at all stages such
as purification treatment and the supply and operation of water services.
Waterworks that are familiar to users
In order to realize a peaceful life for the users, information
collection from users and a give-and-take two-way information system must be
encouraged. It is important for waterworks to become familiar and intelligible
to its
users.
