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An article about dam-induced flood danger in Mozambique. From The Cape
Argus (SA), March 4, 2000.
JOHN YELD
Environment Writer
Another potential flood catastrophe is looming in the floodplain of the
Zambezi River in Mozambique that could cost the lives of tens of thousands
of people without urgent international aid on a huge scale, one of southern
Africa's leading river ecologists has warned.
And there are some fears about the safety of the massive Cahora Bassa dam
on the Zambezi River in the Tete province of central Mozambique, following
unconfirmed reports of structural problems in 1998. The focus of the
flooding disaster in Mozambique to date has been in the south of the
country, caused by the swollen Limpopo and Save Rivers. Bryan Davies, an
associate professor in the Freshwater Research Unit at the University of
Cape Town who has been doing research on the Zambezi River ecosystem for
the past 25 years, said there was a growing danger that several hundred
thousand Mozambicans living in remote parts of the floodplain of the Lower
Zambezi would be exposed to "human-induced" flooding because of the need to
open the sluice gates of Cahora Bassa. "This will occur while
communications, air transport and aid infrastructures, and equipment are
tied up in the presently catastrophic floods from the Save and Limpopo
Rivers to the south," he warned. Professor Davies said he was "extremely
concerned" about the current situation in southern and central Mozambique.
"I predict that unless major international aid gets to the country within
the next day or so, we shall be seeing tens of thousands of dead by the
time we stop counting.
"And the situation is worsening by the hour," he said Thursday. Professor
Davies said he had learned during repeated visits to Cahora Bassa dam
between 1996-1998 that the Portuguese engineers controlling the massive
structure did not habitually practice pre-wet season drawdown (lowering the
level of the dam by releasing water) in order to receive floods from
upstream.
Also, in 1998, there had been a three-week delay in communications between
officials at Kariba Dam, further upstream, and their counterparts at Cahora
Bassa.
"If the same is still in operation, then we could be looking at another
flooding catastrophe in the making.
"And that seems to be at least partly the case, for Kariba has been
releasing for over a week and has now reached 3, 000 cumecs (cubic metres a
second) while Cahora Bassa only commenced releases a day or so ago, over
and above the standard single sluice gate release of around 850cumecs." But
there was still another major potential problem, Professor Davies added.
"In 1998 there were unconfirmed, but undenied, reports that when two
sluices of Cahora Bassa were opened during February of that year, the wall
- or gates - went into harmonic vibration, which is an extraordinarily
dangerous state of affairs.
"The result was the curtailment of releases and a resorting to turbine and
single sluice release in order to discharge surplus water." Professor
Davies said that because of the situation in Zimbabwe, where there were
continuous rains and the releases from Kariba, and the possibility of
Cahora Bassa lake being too high, emergency discharges from Cahora Bassa
dam could become necessary. "The lake must be drawn down to prevent
over-topping of the wall - the most dangerous event a dam wall can face."
In addition to the possibility of structural problems with Cahora Bassa -
"Hopefully they have been repaired now" - the situation was extremely
serious because of the number of people who had moved into the floodplain
of the Lower Zambezi River in the past two decades. "Because of tight
controls at the dam there has been an almost complete lack of flooding in
the past 25 years," Professor Davies explained. "Only three floods have
been released from the dam since 1975. "So the vast population of the
Lower Zambezi has moved on to the newly 'down-cut' floodplain in order to
be closer to the newly incised river channels.
"In other words, people now live on islands in the river which have formed
since flows were regulated by Cahora Bassa Dam from 1975 onwards." This,
combined with the lack of infrastructure in the Lower Zambezi River and the
lost "flood memory" of the culture, was a recipe for massive and
potentially catastrophic events, Professor Davies said.
Pointing out that Marienthal in Namibia had been flooded this week when the
nearby Hardap Dam had been opened "through failure to control inputs versus
outputs", Professor Davies said: "I think the situation in Mozambique could
be come very serious, which is why I am sticking my neck out a bit.
"My thesis is that, in the final analysis, dams do not control floods. They
may control small floods, but the real 'biggies' are utterly unstoppable.
"People and development have been allowed below dams because of a failure
to recognise that they are on a floodplain - a floodplain that has been
modified by 'flood control' for a long time until the big flood finally
arrives."
… The Zambezi is Africa's fourth largest river system, after the
Nile, Zaire and Niger Rivers. It runs through, or forms the border between,
six countries on its journey from central Africa to the Indian Ocean:
Angola, Namibia, Botswana, Zimbabwe, Zambia and Mozambique. Construction
of the massive Cahora Bassa Dam started in 1969 when Mozambique was still a
Portuguese colony, and it was completed in 1975.
South Africa had agreed to buy much of the 2,000 megawatts of electricity
which was to have been generated by the hydro-electric project. But in
1977 rebels of the Renamo movement, who were fighting Mozambique's first
post-independence Freelimo government, destroyed at least one third of the
pylons carrying the power lines from Cahora Bassa to South Africa.
Although the pylons were repaired after Mozambique's 16-year civil war
ended in 1992, there has been an on-going dispute between Hidroelecrica da
Cahora Bassa, the Portuguese operators of the scheme, and South Africa's
electricity parastatal Eskom.
The tariff dispute has now been referred for international arbitration, and
there is still no electricity from Cahora Bassa flowing into South Africa's
grid.
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Lori Pottinger, Director, Southern Africa Program,
and Editor, World Rivers Review
International Rivers Network
1847 Berkeley Way, Berkeley, California 94703, USA
Tel. (510) 848 1155 Fax (510) 848 1008
http://www.irn.org
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