DROUGHT looms over Britain once more. A year of exceptionally dry
weather has
left the reservoirs in much of northern and western England and Wales emptier
than ever before at the start of the summer. Despite plenty of summer showers
since, a fifth of the country still has hosepipe bans. And a repeat of last
year鈥檚 hot August could yet bring draconian restrictions on water use
across the
country.
The 10 regional water companies of England and Wales blame the weather for
their repeated failure to meet the nation鈥檚 demand for water. But some
hydrologists say that the real reason for the shortage is Britain鈥檚 reliance on
rivers and surface reservoirs where the supply is notoriously fickle. 鈥淲e are
virtually alone in Western Europe in our heavy dependence on surface water,鈥�
says hydrogeologist Michael Price of the University of Reading. Meanwhile,
larger and arguably more dependable reserves lie untapped underground in the
pores and fissures of chalk and sandstone hills.
At present, Britain taps only 28 per cent of its supply from groundwater.
Most countries in Western Europe use them to supply at least half of their
water
[see
Table]. The only countries that extract
less are Norway, whose
rain-soaked mountains provide huge amounts of water, and Spain, which has
rivalled Britain in the 1990s for drought headlines.FIG-20414202.gif
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Britain is 鈥渙ne of the wettest countries in Europe,鈥� says Terry Marsh of the
government鈥檚 Institute of Hydrology. Average rainfall, at more than a metre a
year, is almost 50 per cent higher than that in France and Germany. And
allowing
for differences in evaporation, says Marsh, the amount of water that flows into
British rivers and groundwaters from every square kilometre of land is double
that in France and Germany.
Lowland England, where almost half the population live, has the least
rainfall. But curiously supplies are threatening to run out in the wetter north
and west. The reason, says Price, is that these regions rely on water collected
in surface reservoirs filled from 鈥渟hort鈥� rivers鈥攔ivers that quickly lose
most of their flow during prolonged dry weather. In the south and east, where
groundwater sometimes accounts for more than half the supply, the water
authorities cope with drought much better.
The events of 1995 exposed the flaws in British water supply
planning鈥攁nd explain why water planners are so nervous about this summer.
Ironically, last year began with widespread floods. The River Ure in Yorkshire,
for instance, exceeded its previous maximum level, according to the
Institute of
Hydrology which measured national flow rates in rivers draining the Pennines.
鈥淢ost reservoirs are at or near capacity and the water resources outlook
is very
healthy,鈥� the institute concluded.
Fateful words. Seven months later, most Pennine reservoirs were all but
empty, water tankers plied the streets of Yorkshire and, it later emerged,
secret plans were prepared for the evacuation of up to a million people from
several Yorkshire towns. This year, with a dry winter following the summer
drought, the situation threatened to be even worse. What has gone wrong?
Part of the problem is that Britain鈥檚 weather does seem to be changing.
Drought is becoming more common. In the past 20 years, says Price, 鈥渕ost parts
of Britain have had three droughts which we might expect only once in 200 years
or more鈥�. Rain is also falling at different times. According to Marsh, in the
mid-19th century equal amounts of rain fell in winter and summer. But now
summers have become drier, and there is typically 30 per cent less rain in
summer than winter. The Climatic Research Unit at the University of East Anglia
predicts that by 2030, annual flow in British rivers could fall by between
4 and
8 per cent, and up to 20 per cent in summer.
Winter water
These changes mean the country needs to increase water storage
capacity鈥攂oth to save excess winter water for the long, hot summers, and
to increase reserves for use in dry years. But national planning has been at
odds with these needs. The National Rivers Authority and its successor the
Environment Agency are legally charged with ensuring Britain鈥檚 water supply.
Last summer, the NRA鈥檚 published policy for meeting rising water demand was to
move 鈥渟urplus鈥� water along a network of canals and pipes 鈥渇rom the wetter north
and west to the drier south and southeast of the country鈥�. The plan was
misconceived, says Price. Fortunately it was not carried out.
So what is to be done? All parties are now agreed that water demand has
to be
reined in: first by plugging leaks in water mains that lose up to a third
of the
nation鈥檚 water, and second by reducing domestic demand. Demand, however,
continues to rise. Earlier this year the Department of the Environment
predicted
it will increase by 18 per cent in the next 25 years. 鈥淯ntil last summer the
regulators believed that demand management and some water transfers could solve
water supply problems,鈥� says Brian Connorton, groundwater resource manager at
Thames Water, the country鈥檚 largest water supplier. 鈥淏ut now the climate of
opinion is changing. The new Environment Agency, unlike its predecessor the
National Rivers Authority, is looking favourably on developing new water
蝉辞耻谤肠别蝉.鈥�
The conventional solution to water shortages is to build more surface
reservoirs supplied by rivers. But many hydrologists now believe that tapping
more of the underground reserves is the only real solution. Earlier this year,
Price told a meeting at the Institution of Civil Engineers that the chalk
downlands on the east side of the country and the Permo-Triassic sandstones of
the west 鈥渃ontain absolutely huge amounts of water, much more than we
would ever
need鈥�. When full, says Price, all the surface storage reservoirs available for
public water supply in England and Wales contain about 1800 million cubic
metres
of water鈥攅nough to supply the nation for about a hundred days. But the
main groundwater reserves contain at least three times as much accessible
water,
depending on how deep companies are prepared to sink boreholes.
Three years ago, the British Geological Survey concluded that the chalk
strata alone contain up to 2400 million cubic metres of pumpable
飞补迟别谤鈥拢辞迟
more than 10 metres below the lowest recorded level of the water table.
Although
some of this water is already tapped, Price believes there is plenty more to be
had. And, he argues, the potential supply from sandstones is even higher.
Sandstone has been little used for public water supply, but 3000 million cubic
metres of easily accessible water lie not more than 2 metres below the lowest
recorded water table.
And some of the largest sandstone outcrops are close to last year鈥檚 centres
of greatest water shortage. 鈥淭he potential to develop groundwaters in the north
and west of England is much greater than most water companies have realised,鈥�
says Price. Indeed, in many parts of the country groundwaters are so
little used
that rising water causes flooding. The high water table is corroding
foundations
of buildings in central London and Birmingham, and has to be pumped out of the
Mersey tunnel. Of the 10 water regions of England and Wales, only Wessex and
Southern鈥攕erving the region from Somerset to Kent鈥攖ap more
groundwater than river water.
So why isn鈥檛 groundwater widely used? One reason is contamination.
Increasingly, underground reservoirs are becoming polluted by nitrates washing
down from over-fertilised fields and by industrial chemicals. In mildly
contaminated areas this could be overcome by diluting groundwaters with
cleaned-up river water until pollution levels are low enough to make it
acceptable for drinking. This is the way water managers deal with the
problem in
continental Europe. But it will not work in areas such as the West Midlands,
where pollution is particularly bad.
Environmentalists have erected another barrier to the exploitation of
groundwaters. They claim that it threatens rivers. The NRA identified 40 chalk
streams in lowland England that dry up in some years, partly because of low
rainfall and partly because water is pumped from the hills from which they take
their water. But critics in the water industry say that the NRA and
environmentalists have exaggerated how much water abstraction dries up rivers.
Connorton claims most would probably not be damaged by more abstraction. Last
summer, for example, most chalk streams maintained high flows because
groundwaters had been topped up by the wet weather in early 1995.
But groundwater levels don鈥檛 hold up so well under conditions of prolonged
drought. They were very low at the end of 1992, for example, after four years
when the amount of rainwater recharging the chalk hills of eastern England had
been less than half normal levels. Water tables fell to levels 鈥渨ithout
parallel
this century鈥�, says Helen Jones of the British Geological Survey鈥檚 hydrogeology
group, who studied that drought鈥檚 impact below ground. But, during the next wet
period they refilled quickly and without problems. Now the BSG has begun
work on
a National Groundwater Survey, the first complete study of the country鈥檚
aquifers and how quickly they fill.
Some people say that Price exaggerates the amount of water that underground
reserves can yield without being drained, but Jones鈥檚 results confirm his
optimism. 鈥淭here could still be considerable quantities of water available for
abstraction from the chalk,鈥� she says, if resources are managed properly. It鈥檚
not simply a matter of sinking boreholes and pumping. The position of boreholes
is crucial because the complex geology in chalk means that water has to be
coaxed through often narrow fissures.
Price鈥檚 plans are more sophisticated than simply pumping more water out of
the hills. He wants to put more water down there too. He believes porous rocks
should store water in the same way as surface reservoirs do, by pumping
water in
until it is needed, a technique known as artificial recharge. In this way, some
excess rainwater that would normally run out to sea during a wet period
could be
redirected underground.
One project opened for business last autumn in north London. Parts of the
chalk aquifer beneath the boroughs of Enfield and Haringey had been
鈥涣惫别谤辫耻尘辫别诲鈥�
in the past, lowering the water table. 鈥淥ver-exploitation has created empty
storage, a reservoir waiting to be used,鈥� says Price. Thames Water has invested
拢7 million in sinking new boreholes and building 15 pumping
stations. Last
winter, the company started pumping excess water from the Thames down into the
chalk via the water mains.
In dry years, when water from other sources is short, the pumps will be put
into reverse and the stored water will be used to keep the capital鈥檚 water
mains
full. This and another recharge scheme in the Lee valley in east London could
supply 60 million cubic metres a year for the London area. A similar project is
planned for south London.
And what works for London would work elsewhere, says Price. If more aquifers
were recharged with river water in winter, they would greatly increase the
nation鈥檚 water reserves, without flooding farmland or causing ecological havoc
on rivers. 鈥淲e should be examining potential for recharging aquifers now,鈥� says
Price.
Britain already lags behind. A recent review by Eureau, a club of Europe鈥檚
water utilities, found that artificial recharge is widely used in Europe.
Sweden
has thousands of small schemes that provide a fifth of all its tap water. In
Germany, France and the Netherlands between 10 and 20 per cent of all tap water
is stored by artificial recharge. Many of Paris鈥檚 western suburbs, as well as
Dijon, Dunkirk and Lyon use recharge water.
Artificial recharge
Price says: 鈥淭here is no geological reason why Britain should not develop
artificial recharge as much as the Germans have.鈥� In the 1970s the government鈥檚
Water Resources Board researched several recharge schemes, beneath Birmingham
and Nottingham for instance, before being disbanded. The Severn Trent Water
Authority developed a pilot project at Norton near Stourbridge in the 1980s
which came to a stop with privatisation. But work is set to resume on a
national
level. 鈥淲e [BSG] are about to start a new assessment of the potential of
recharge, together with the Environment Agency,鈥� says Jones.
The British water industry has written off further development of its most
valuable water resource because it has not taken the trouble to investigate it
properly, Price believes. The engineers who have traditionally dominated the
British water industry prefer building reservoirs. 鈥淭hey don鈥檛 understand
hydrology,鈥� says Price. Engineers mistrust water they cannot see, agrees
Connorton. Water below ground is out of sight and out of mind. And geologists
are the Cinderellas of the industry. But perhaps now they shall go to the
ball.
