WHEN devastating floods engulfed the lowlands of Mozambique over the past
month, the rains were blamed. But matters weren’t helped by the operators of
dams upstream of the flooded areas in neighbouring countries such as South
Africa. Having kept dams on the Limpopo and Zambezi almost full at the start of
the rainy season, they were forced to release massive amounts of water through
the spill gates, claim scientists who know the rivers well. The flood waters
came as a surprise to people downstream because there were no agreements in
place on how to manage the dams during a flood or alert them to the imminent
danger.
At the Second World Water Forum in The Hague this week, scientists and
environment ministers are discussing fears that inept dam management will
contribute to similar catastrophes around the world. The Mozambique disaster
followed a spate of major floods in Mexico, Venezuela and India. These disasters
have heightened the diplomatic pressure for better management of the 261 rivers
and numerous underground water reserves that cross national boundaries.
Already, the World Bank has said that dozens of large Indian dams do not have
sufficiently large spillways to cope with flood flows down their rivers. The
result, says a leaked internal memo, is that the dams could be breached, causing
catastrophic floods downstream and possibly thousands of deaths. Anti-dam
campaigners such as Anil Agarwal, director of the Centre for Science and the
Environment in New Delhi, warn that the major new Indian dams under
construction, such as the Sardar Sarovar on the Narmada River and the Tehri Dam
on a tributary of the Ganges, pose major threats to people downstream.
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“The threat from the Tehri Dam is accentuated by its being constructed in a
seismically active zone that was shaken by a major earthquake in 1991,” says
Agarwal in the runup to the forum this week. “If a future quake breached the
dam, tens of thousands would die.”
In the last decade, “over-topping” (when dams overflow) has killed more than
100 people in the US, Russia and Romania. According to Patrick McCully of the
International Rivers Network in Berkeley, California, many major dams worldwide
have been responsible for increased flooding downstream and they continue to
pose a risk to their neighbours whenever it rains. They include the world’s
largest hydroelectric dam, the Itaipu Dam on the River Parana between Paraguay
and Brazil, as well as the Hirakud Dam in India’s Orissa state and the Folsom
Dam in California, which came close to flooding half a million people in 1986
after emergency releases.
Warnings
The 1998 floods in Tegucigalpa, the capital of Honduras, during Hurricane
Mitch were seriously exacerbated when engineers made an emergency release of
water from the Concepción dam 10 kilometres from the city up a narrow
gorge. Shortly afterwards, survivors describe seeing a “wall of water” rush into
the city.
In Mozambique, the thousands of people killed and half-million left homeless
emphasise the urgent need for the international community to impose tough laws
on the people who manage rivers. But to draw up the necessary regulations,
engineers need to understand how dam management can contribute to severe
flooding.
It is frighteningly clear what went wrong in southern Africa in the past two
months. First, there was heavy rain, about five times as much as normal for the
wet season, which runs from January to March. The effect of the rains was
worsened by changes in land use in the past 50 years, such as deforestation,
soil erosion due to farming and the drainage of swamps, all of which reduce the
land’s ability to soak up and store heavy rains. Finally, and most lethally, it
appears that many dam operators ignored warnings from meteorologists that the
rain this year was likely to be heavy. To varying degrees, scientists think such
factors play a part in dam-related floods around the world.
“After more than 20 years of low rainfall and droughts in the region, people
had forgotten the devastation that floods can cause,” says Mark Jury, the
climatologist at the University of Zululand who warned of a “wet, wet” start to
2000 as early as September
(91av, 11 March, p 21).
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managers try to hang on to their precious water at all costs,” says Jury. On the
Limpopo in South Africa, they were keeping their reservoirs 80 per cent full at
the start of the wet season. This, he says, is contrary to good engineering
practice on a river where 85 per cent of the annual flow occurs during the short
rainy season. Some of the water should have been released before the rains.
Even after rains began to swell the rivers, the dam managers kept their spill
gates shut. Only when the reservoirs were full to bursting did they begin
massive emergency releases. “Late releases from dams on the Limpopo
significantly added to the flooding in Mozambique,” claims Jury. However, a
spokesman for South Africa’s Department of Water Affairs denies this. “Even if
the dams had been empty, there would still have been floods,” he said. But he
admitted better dam management could have held back two days’ worth of
rain.
Now scientists fear the mistake could be repeated on the Zambezi further
north. The river is barred by two massive hydroelectric dams: the British-built
Kariba Dam on the border between Zimbabwe and Zambia, and the Cahora Bassa Dam
in Mozambique, conceived in colonial days to generate power for South Africa and
still 80 per cent owned by the Portuguese government.
The operators of Kariba came perilously close to causing a disaster this
year. On 26 February, they began emergency releases of water from the reservoir,
which is 280 kilometres long, for fear the dam would break under the crushing
weight of water behind it. People from miles around rushed to see the spectacle.
Meanwhile the water surged through fields, grain stores, schools and villages
occupied by more than 12 000 people on the river’s Zambian shore. And the
Mozambique border town of Zumbo remains flooded as a result.
Though the Cahora Bassa did not cause flooding this rainy season, Bryan
Davies of the University of Cape Town, an expert on the ecosystems of African
rivers, believes it, too, is a disaster waiting to happen. Not only is the
reservoir kept too full, there may also be major structural problems with the
dam itself.
“In 1998 there were unconfirmed—but also undenied—reports that
during the February rainy season, when two sluice gates were opened, the walls
went into harmonic vibration, an extraordinarily dangerous state of affairs,”
says Davies. “They had to shut one of the sluice gates. If it is managed as I
saw in 1998, and if it is also structurally challenged, then sooner or later I
fear the worst.”
What are the chances of that being averted? The Hague conference this week
delivered a global declaration calling for “effective water governance”. But
rather than proposing a world water body, it wants countries that share rivers
to get together to draw up or toughen agreements to manage the rivers better, to
conserve water in times of scarcity as well as to prevent floods. In the event
of such agreements breaking down, leading figures at the conference suggested
setting up an “independent international corps of conflict mediators” to be made
up of former heads of governments. The idea was presented by the former Soviet
president Mikhail Gorbachev, who is now president of the Swiss-based Green Cross
International and clearly sees himself as a future world water
troubleshooter.
Recent events show there’s an urgent need for action. Without it, experts
warn, things can only get worse. The greatest disaster as a result of
mismanagement occurred at the Banqiao Dam on the Yangtze River in China in 1975
when emergency releases got out of hand and the dam was partially destroyed.
About 85 000 people died in the flooding that followed. Philip Williams,
president of the International Rivers Network in Berkeley, California, warns
that a similar failure on China’s latest project on the Yangtze, the Three
Gorges Dam, would result in “history’s worst man-made disaster”.
