Water, Waler Everywhere . . .
97
The power it produces—more than a million kilowatts—will supply
homes and industry as well as the pumps pushing water into the
irrigation system. Another great dam, the Kariba, completed in
1960, has a total water capacity of some 180 million cubic metres.
This is enough water to supply a population of 50 million for fty
years at a rate of 200 litres per person per day without any relling.
These then are the giants of the water—supply and power—generating
business. In 1900 there were approximately 1,000 large dams in the
world. Since then the number has doubled every twenty years until
today there are over 8,000.
Dams are an obvious way of capturing and holding water until it
is needed; not so obvious is the use of porous rocks beneath the
earth’s surface as an underground reservoir. It is hoped that underground storage of water in the upper reaches of the Thames
catchment area will help to prevent future shortages anticipated for
south—east England. The water contained within the upper half mile
of the earth’s crust amounts to some 3,000 times that at any given time
in the world’s rivets. Compared with this largely untapped mass of
fresh water, the water stored in dams and reservoirs is comparatively
puny. Unfortunately it takes time to track down the hidden sub—
terranean supplies, and even when they are found the problem of
how they can be exploited remains. ln some cases removal of too
much water irreversibly damages the water—storing rocks, drastically
reducing their ability to soak up further supplies of ground water.
Even where there is little danger of altering the physical properties
of the underground storehouse, over—exploitation can lead to an
inux of brackish or salt water which contaminates the remaining
water. Some underground supplies in Israel, a country which relies
heavily on underground sources of water, are already in danger.
One solution may be to use desalting units along the coast like
kidneys, rejecting the unwanted impurities before feeding water
into the underground reservoirs. The Israelis have even considered
over—exploiting their subterranean supplies in order to stave off the
need for desalting plant. New developments in desalination might
occur in this interim period which would save them from having to
use present more expensive methods. However, the consensus of
opinion seems to be that waiting would be unwise; most experts do
not envisage any process which will replace present distillation
methods in the very large units.
Barragcs across rivers or hays provide another method of storing
4
97
The power it produces—more than a million kilowatts—will supply
homes and industry as well as the pumps pushing water into the
irrigation system. Another great dam, the Kariba, completed in
1960, has a total water capacity of some 180 million cubic metres.
This is enough water to supply a population of 50 million for fty
years at a rate of 200 litres per person per day without any relling.
These then are the giants of the water—supply and power—generating
business. In 1900 there were approximately 1,000 large dams in the
world. Since then the number has doubled every twenty years until
today there are over 8,000.
Dams are an obvious way of capturing and holding water until it
is needed; not so obvious is the use of porous rocks beneath the
earth’s surface as an underground reservoir. It is hoped that underground storage of water in the upper reaches of the Thames
catchment area will help to prevent future shortages anticipated for
south—east England. The water contained within the upper half mile
of the earth’s crust amounts to some 3,000 times that at any given time
in the world’s rivets. Compared with this largely untapped mass of
fresh water, the water stored in dams and reservoirs is comparatively
puny. Unfortunately it takes time to track down the hidden sub—
terranean supplies, and even when they are found the problem of
how they can be exploited remains. ln some cases removal of too
much water irreversibly damages the water—storing rocks, drastically
reducing their ability to soak up further supplies of ground water.
Even where there is little danger of altering the physical properties
of the underground storehouse, over—exploitation can lead to an
inux of brackish or salt water which contaminates the remaining
water. Some underground supplies in Israel, a country which relies
heavily on underground sources of water, are already in danger.
One solution may be to use desalting units along the coast like
kidneys, rejecting the unwanted impurities before feeding water
into the underground reservoirs. The Israelis have even considered
over—exploiting their subterranean supplies in order to stave off the
need for desalting plant. New developments in desalination might
occur in this interim period which would save them from having to
use present more expensive methods. However, the consensus of
opinion seems to be that waiting would be unwise; most experts do
not envisage any process which will replace present distillation
methods in the very large units.
Barragcs across rivers or hays provide another method of storing
4