eBusiness Weekly
Golden Sibanda
TWO earth tremors were reportedly recorded in parts of the mid-Zambezi Valley area this week, near Zimbabwe’s biggest source of hydro power, Kariba Dam, is located.
Under normal circumstances, Zimbabwe draws most of its power from the 1 050 megawatts Kariba South hydropower plant, which is situated on the Kariba Dam, the world’s largest inland dam shared with Zambia.
Like its neighbour, Zambia also relies on the Kariba Dam for most of its electricity, generated on northern bank of the dam.
Authorities confirmed this week that the earthquakes, a common feature in the area since 1963, were caused by the heavy load of water filling into the humongous water body.
Kariba Dam, which has faced the threat of depletion since last year due to drought in its catchment, receives the bulk of its water between April and June each year, as flows from its major source, the Barotse Plains of northern Zambia, hit its shores.
“The two earth tremors or earthquakes with magnitude 4.0 were recorded in the Zambezi Valley around the Kariba Dam on the 1st and 2nd of this month at 19:29 hours and at 17:31hours respectively,” the Zambezi River Authority (ZRA) said.
The epicentre of the first earthquake was approximately 27 kilometres south of the Kariba Dam, while the epicentre of the second earthquake was estimated to have occurred 65km east of the Kariba Dam wall.
According to ZRA, such tremors are a common occurrence in the area around the Kariba Dam.
“The tremors are referred to as load- induced tremors or specifically reservoir- induced tremors in the case of the Kariba Dam and are a result of the earth crust’s response to the water load or weight of water given the size of the dam,” ZRA.
These reservoir induced tremors have been occurring since 1963 when the Kariba Dam started filling. ZRA said over 1 000 tremors of magnitude 4.0 as the most recent tremors have occurred since filling of the dam in 1963.
The tremors of this magnitude do not affect the structural integrity of the giant dam, which sits on the 2 700-kilometre- long Zambezi River.
However, as a precaution, the Kariba Dam is inspected after each event and the instruments records analysed for any anomalous behaviour irrespective of the magnitude.
The dam was inspected soon after the tremors and the dam instrumentation data was analysed. No damages were reported.
Analysis of instrumentation data showed that the dam wall was not affected which was also corroborated by the visual inspections and its appurtenant structures, which showed no structural damage to the wall and its related structures.
Kariba is Zimbabwe’s biggest power plant ahead of the only other major plant, Hwange Power Station, which is a 920MW rated power station but can now only manage just over half its capacity due to age.
With Kariba’s water level still critically low, ZRA has allocated Zimbabwe just 20 billion cubic feet per month, which sees the plant generate only 200MW at any given moment.
