Aida 204 Kariba
AFTER the recent torrential rains experienced over much of southern Africa, there is some concern about one of Africa's greatest monuments to the White man's genius: Kariba Dam, linking Zambia and Zimbabwe and at the time of construction in the late 1950s the biggest man-made lake in the world. Built on the Zambesi River 385 km downstream from Victoria Falls, the huge concrete double-curve arch dam is bracing for what could prove to be unprecedented flood levels.
Exceptionally heavy rains have fallen over Barotseland, one of the Zambesi's main collection areas. When this flow, from above the Falls, joins the Zambesi's feeder tributaries below the Falls, including the sizeable Sanyati River which combines with the Zambesi at the entrance to the gorge, the flow could become massive. The threat of the Sanyati is that it may peak at precisely the same moment as the Zambesi goes into full spate.
As the concentration period with run-off from rainfall in the main catchment area is fairly long, the flood could peak sometime in May. A German engineering contractor tells me that there is some uneasiness about the level of care and maintenance on the Zimbabwe side.
"The dam was placed in its present position
because of politics. A better site would have been in the same
gorge, but five or six km further east. During construction a
fault was discovered on the right (south) bank. While most of
the dam wall
- 131 metres high and 633 metres along the crest
- stands on mainly sound granite stands on mainly sound gneiss (granite), on the south bank the granite was overlain by broken and weathered quartzite. Hundreds of tons of concrete were poured to stabilise the formation.
"The Kariba project was designed and constructed by some of the world's very best engineers. Every possible safety factor was built in to ensure there would be no breakthrough of water in flood periods. But sustained skilled care and maintenance are obligatory. Kariba engineers must brace for possible extreme fluctuations as the wall of water hits. Because the six sluice gates are so high, the water falls close to the wall, setting up great vibration. In the past they have always used teams of highly skilled SA divers to map out the movement below the water, putting in various reinforcements over the years. Special care also must be applied to the tunnels in the dam wall.
"Earlier, dam maintenance on the Zimbabwe side was always very good, but it is not known whether such expertise is still in place. It is understood there has been some breakdown in cooperation between the various control authorities. The Zambians are said to be most clued up, having maintained their advisers. Zimbabwean expertise has certainly declined. The bulk of their maintenance money seems to have been diverted to the Wankie coal-fired power station."
The Batongas have always maintained that one day,
the river god Nyaminyami will take his revenge for the building
of this vast project on his domain. Let's hope that this time
too Nyaminyami will be defeated once again.
|Cycad Web Works Sun Jul 22 06:42:50 EDT 2018
: # 1 : last modified 8/4/97 |
The Aida Parker Newsletter viewed by firstname.lastname@example.org