1959 1.05gw+1.08gw Kariba Dam on Zambezi River at Zimbabwe+Zambia

(Satellite, 1,809 photos)

RhodesianStudyCircle
"The Kariba Dam is a double curvature concrete arch dam in the Kariba Gorge of the Zambezi river basin between Zambia and Zimbabwe. The dam stands 128 metres (420 ft) tall and 579 metres (1,900 ft) long. The dam forms Lake Kariba, which extends for 280 kilometres (170 mi) and holds 185 cubic kilometres (150,000,000 acre⋅ft) of water."

nsenergybusiness, also e360.yale.edu
Kariba Dam is the largest in terms of water storage capacity. Kariba South has a capacity of 1.05gw and belongs to Zimbabwe while Kariba North has a capacity of 1.08gw and belongs to Zambia. "Although the Kariba South power station typically accounts for more than half of the country’s electricity, low dam water levels due to the prolonged drought in the region since May 2019 has led to trimming down the facility’s electricity output to almost one-fourth of its design capacity as of December 2019." Both of these countries were part of Rhodesia, which was created by Britain. "The Kariba Dam has been undergoing a £235m ($294m) rehabilitation project since 2017, in order to fix the deformities on the structure that were figured out in a series of assessments. The Kariba Dam overhaul project involves the reshaping of the plunge pool and the refurbishment of the spillway gates."

FLY HAC posted
At HAC, you always get the bird's eye view, including a sneak peak of the Kariba Dam wall rehabilitation program.
Zambia - The Real Africa posted

The access road to the bottom of the plunge pool is nearing completion.

FLY HAC posted
The views at HAC continue! With an update aerial of the Kariba Dam wall rehabilitation program from a recent fly by.

I zoomed out to see where we are in Africa, and you can clearly see Lake Kariba.

Road Map

RhodesianStudyCircle
"The double curvature concrete arch dam was designed by Coyne et Bellier and constructed between 1955 and 1959 by Impresit of Italy at a cost of $135,000,000 for the first stage with only the Kariba South power cavern. Final construction and the addition of the Kariba North Power cavern by Mitchell Construction was not completed until 1977 due to largely political problems for a total cost of $480,000,000. During construction, 86 men lost their lives."

All six of the floodgates are open.

ZimFieldGuide
"On the rare occasions that all six flood gates have been opened, over 9,500 cubic metres (300,000 cubic feet) of water surges into the river below each second!"
[To put that in perspective, the design capacity of the Oroville Dam is 160,000 cfs.]

Two of the flood gates are open.

ZimFieldGuide

The commercial fishing of kapenta, the size of sardines, in the lake has been decimated by the red claw crayfish. "Even crocodiles don't eat crayfish." The crayfish are a threat to other species as well.

Feb 24, 2023      

voanews
"Zambians and Zimbabweans have been suffering long hours of power loss since water levels at the Kariba hydropower dam plunged to an all-time low in December. Columbus Mavhunga reports from Zambia, which plans to build a $2 billion solar power project to alleviate the situation."

There is a paywall, but I was able to read that the lake is down to less than 1% of its usable water in Dec 2022. [Bloomberg]

The dam has not been at full capacity since 2011. [EnergyPolicy]

"Building the dam and its reservoir forced the resettlement of around 57,000 Tongan people living along the Zambezi in both Northern Rhodesia and Southern Rhodesia." [ice]

"When the floodgates were opened in 2010, 6,000 people had to be evacuated....Its plunge pool is now a 266-foot-deep crater. As the stony facade continues to crumble, the likelihood rises that the Kariba Dam will not just fail but fall. If the dam collapses, the BBC reported in 2014, a tsunami would tear through the Zambezi River Valley, a torrent so powerful that it would knock down another dam a hundred miles away, the Cahora Bassa in Mozambique — twin disasters that would take out 40 percent of the hydroelectric capacity in all of southern Africa." [nytimes]

The nytimes talked about the impact on hydroelectricity, but not on people's lives. Is it such a wilderness that there are no people in the river valley?

No, there are 3.5 million people. [e360.yale.edu]

2009: The dam "has been a cause for concern on a number of safety issues, including from its earliest days when the filling of its reservoir caused earthquakes, to more recent times when rumors began to surface that the huge dam had structural problems and suffered from poor maintenance. Kariba has also worsened the region's floods in recent years." After bad floods in Mar 2000, the US Army Corps of Engineers (USACE) was requested to inspect the river's dam. They were given full access to Cahora Bassa and Kafue dams, but not Kariba.  "Kariba, like many dams, has been affected by a condition that mars its concrete, known as “alkali-aggregate reaction.” " But the dam operators are keeping the amount of degradation a secret! [InternationalRivers_1]

2012: The plunge pool is deeper than expected. It is not the eroded depth of 90m (300'), but the proximity of the hole to the foundation of the dam. In fact, the preferred solution is to widen the hole.

InternationalRivers_2, Source ZRA ppt, 2012
Multi-beam bathymetric photo of the Kariba Dam plunge pool.

This diagram provides the cross-section I need to illustrate why this is a double-curved arch dam. A normal arch dam looks curved when you view it from above. A double-curved dam also looks curved when you view it from the side.

InternationalRivers_2

2018: The budget to repair the dam is US$294m. "According to the Zambezi River Authority’s KDRP Project Manager, Eng. Sitembinkhosi Mhlanga,  the existing pool will be widened from bank to bank and will also be extended in the downstream direction. The result will be an enlarged pool with an increased volume. The enlarged shape will create a water cushion which will improve the capacity of the pool to absorb the potential energy from spillage, thus reducing the development of the pool, and ensuring the stability of the dam foundation....Over time, alkali aggregate reaction can occur in concrete exposed to water causing the concrete to swell. This causes distortions to the steel-lined guides of spillway flood-gates, affecting the spillway functionality....The spillway refurbishment is part of this dam safety assurance process." They are studying two more dam sites on the river. [zambezira] They make a big deal about having a lot of instrumentation to monitor the performance of the dam. But they don't mention if they are still keeping the data a secret.