THE floodwaters that have driven tens of thousands of people from their homes
in Mozambique are a 鈥渉uman-induced tragedy鈥�, hydrologists are claiming. People
are having to flee a surge of water flowing towards the Indian Ocean after heavy
rains. But the crisis has been exacerbated by two giant hydroelectric dams on
the Zambezi river upstream of the flooded area, says Bryan Davies of the
University of Cape Town in South Africa.
The amount of water flowing down the river is no greater than the volume that
flowed before the two dams were built. It 鈥渋s about equal to the historical mean
recorded in pre-dam times鈥�, says Richard Beilfuss of the University of Wisconsin
in Madison. 鈥淭he difference is the dams.鈥� The Kariba dam, on the border between
Zambia and Zimbabwe, and the Cahora Bassa dam, just inside the Mozambican
border, have a combined capacity of 220 cubic kilometres.
Davies claims that, both this year and last, managers did not partially empty
the reservoirs before the rainy season to make room for floodwaters
(快猫短视频, 25 March 2000, p 16).
They wanted to keep them full to maximise
electricity production. 鈥淭hey have ended up being forced to release water at
critical times,鈥� says Davies.
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Beilfuss says a further problem is that in recent years of low rainfall, the
managers of the Cahora Bassa have held back natural river flows during the rainy
season. This has often harmed farmers downstream who need the water to irrigate
their crops. 鈥淟arge dams do not stop large floods,鈥� concludes Davies. 鈥淭hey
exacerbate them鈥攑eople below them move closer to the river. But when the
big one comes, God help them.鈥�
At the weekend, the floodgates of the Cahora Bassa dam were releasing 8000
cubic metres of water a second into the lower Zambezi, which had already flooded
an estimated 80,000 people from their homes. Silvano Langa, director of
Mozambique鈥檚 National Disasters Management Institute, said that even though
rains have eased in the region, the dam鈥檚 releases will cause water levels in
the river鈥檚 lower reaches to continue rising for several days.
Concerns are also being raised about the stability of the Cahora Bassa dam.
When gates were opened during floods in 1997, a series of vibrations ran through
the dam, says Beilfuss. But last week Fernando Cunha, general manager of
Hidroelectrica de Cahora Bassa, the Portuguese company that operates the dam,
denied that it was in any danger. 鈥淭his is just speculation,鈥� he told the
English-language service of the Mozambique News Agency. 鈥淭here are over a
thousand sensors in the dam wall that alert us to any problem.鈥� Cunha also
claimed that a study by US Army engineers last year gave the dam a clean bill of
health.