Radix - Mozambique floods

 

This page carries links and material on the flooding in Mozambique, 2001.

bluesquiggle.gif (968 bytes) Go here for Gavin Andersson, CEO of the Leadership Regional Network for Southern Africa (LeaRN), requesting advice on disaster prevention.

bluesquiggle.gif (968 bytes) Go here for Floods in Mozambique, 2001: Act of God or Human Act, Act II, Scene I....? By Bryan Robert Davies


Gavin Andersson

I am CEO of the Leadership Regional Network for Southern Africa (LeaRN) working across 6 countries of the region including Mozambique. In our Public Policy Dialogues program we seek to help bridge the gap between local level concerns and issues and the deliberations and influence of policy makers and the general public. Right now, as Mozambique is flooded for the second year in a row, we need to start raising discussion about the possibility of disaster revention. Is there any advice RADIX is able to give about this? So far we have only heard non-expert opinions that it would be possible to keep Cahora Bassa at fairly low levels through the year, pumping water into smaller dams across the missle of the country, so that when heavy rains occur anywhere from Angola through to Mozambique an early warning system will allow for regulated outflows from Cahora Bassa, and so additonal capacity to take in flood waters. This sounds plausible to a novice, but of course we need to start a serious research process if we are to be at all useful. Any pointers, or insights please?

Best wishes
Gavin Andersson


Floods in Mozambique, 2001: Act of God or Human Act, Act II, Scene I....?
By Bryan Robert Davies, Associate Professor, Freshwater Research Unit, Zoology Department, University of Cape Town, South Africa, 7700 [brdavies@botzoo.uct.ac.za]

I hate to say "I told you (them) so" and take no pleasure from it but the recent and continuing flooding of the Lower ambezi was predicted and predictable. The pre-dam Zambezi has two flood peaks - one November through December and a second usually much larger in February and March. Last year I expressed the view that central Zambezi reservoirs and Cahora Bassa in particular appear to be held too high during early summer to absorb mid - to late summer floods. This was certainly the case during my visits there in 1996 and 97 and I have been in correspondence with the engineers at Hidroelectrica da Cahora Bassa through last year about the issue.

Their thesis is that the dams are good for the people and stop the old flooding problems. I contend that no dam no matter how large can ever stop the big flood and that people grow accustomed to lack of flooding, settling in areas that they would not normally have done so. We now see the bitter harvest.

Last year in March Kariba was "forced' to release 2000 cumecs (tonnes per second) whilst Cahora Bassa made no changes to its releases. The result was that Zumbo at the upper end of Cahora Bassa lake was flooded and flooding took place along the Zambian shore of the Zambezi between Kariba and CB simply because of backed-up water.

Exactly the same thing has taken place now, but worse because Kariba has been discharging for ten or so days whilst heavy rains in Zambia have also forced releases from the Kafue system dams - Kafue Gorge and Ithezhitezhi - the water enters CB reservoir.

Last Friday a radio report (I have not been near a TV since last Thursday and have not seen any footage yet) indicated that between 7500 and 10 000 cumecs were being released by CB at the critical time when heavy rains were already flooding the delta and Marromeu areas coupled with heavy flooding in southern Malawi which feeds the Shire River, the only major northern confluent of the lower Zambezi. Both Malawi and Mocambique now urgently need aid.

My thesis is that large dams DO NOT AND CANNOT prevent large floods particularly if they are insufficiently drawn down to absorb flood events.

The Zambezi is a natural floodplain river - the largest in the sub-continent, but which for decades has had no major floods - 1978, 1989 and 1997 were big events, but essentially between times the people below the dam have been forced to move closer to the over-regulated river in order to fish and to farm. I have footage and stills showing the vastly altered geomorphology of the river caused by low releases from CB....people now have to move into the old flood plain in order to feed themselves. Unused to regular natural flooding people's reluctance to believe authorities exacerbates efforts to evacuate them when the 'big one' comes. This is the case in the Marromeu area with radio reports of people refusing to be moved - the same thing occurred during the Limpopo floods of last  year, for exactly the same reasons and people died in their hundreds because of it! Now we have Zumbo underwater, a flood pulse has inundated the city of Tete and is moving down stream over an area already badly flooded locally and via the Shire River.

What is really scary are radio reports (yesterday, 5pm bulletin on SAFM pm live.......not repeated thereafter) that officials are asking Zambians not to release more water from Kariba because CB cannot cope, and the Zambians arguing that they must because Kariba has a crack in the wall! Jeeezzzus! If that is the case then God help the people in the valley.

Some statistics - Kariba holds back some 80 billion tonnes at full supply - CB some 65 billion! Present reports indicate that the CB reservoir is rising by 5cm per day despite releases and that it is less that 1 metre from the crest. Overtopping of dams is the most dangerous because water over the wall hits the toe of the dam and erodes it (this is a poor design feature of Kariba which has top release sluice gates with no throw out mechanism). Cahora Bassa is a deep release dam with shute discharge well away from the toe of the dam. Overtopping is a frightening scenario.

With climate change throughout the world, weather patterns are shifting; I said last year that if cyclonic systems coming in from the Indian Ocean shifted more northerly and westerly then the Zambezi would be hit hard. Given the present state of affairs I am very upset to say the least that people have already died, that vastly expensive rescue systems have had to be set in train and that some people are refusing evacuation, simply because of a history of flow release mismanagement over the past 25 years. When I visited the site in 1996 I was informed that there was no direct communication between Kariba and Cahora Bassa! Extraordinary in an age of network cell phones and email.

I have video and still pics of people living on islands in the newly carved downcut channel of the river (caused by no regular flood releases over years). The floods that are now affecting some 400,000 people are about equal to the historical MEAN annual peak flood flows - in other words, in the past this magnitude flood occurred relatively regularly but because of past "trapping" of such floods we are faced with an extremely dangerous human settlement patterns across the valley and the loss of the cultural "flood memory".

If Cahora Bassa goes to maximum discharge (13 800 cumecs) + turbine discharge (a total of about 17 500 cumecs) this coupled to the flooding of the Shire from Malawi will lead to massive damage over an area that will become virtually inaccessible.

I am more than worried!

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