Excavation works on Kariba Dam plunge pool complete

The Plunge Pool reshaping of Kariba Dam has been competed as rehabilitation works that will improve power generation and the bridge lifespan continue at one of the country’s main energy sources. 

The Plunge Pool reshaping sub-project of the Kariba Dam Rehabilitation Project (KDRP), has seen in total, about 750 000 tonnes of rock being excavated through meticulous drilling and controlled blasting, coupled with the stabilisation of 20,000 m² of slopes using anchors and shotcrete.

The rehabilitation project is expected to increase the longevity of the famous bridge by an extra 60 years and the successful completion of the excavation speaks positive news to Zimbabwe and Zambia energy production. 

Kariba produces at least 2 000 megawatts of clean electricity power generation to Zimbabwe and Zambia and is also a source of livelihood to many families through fishing and tourism. 

The dam wall which regulates water levels in Lake Kariba was under threat of collapse from increased swirling after the identification of scouring and preferential erosion along the weak fault zone towards the dam foundations. 

The objective of the plunge pool excavation works was to widen and change the shape of the 80m plunge pool which was created by the immense pressure of the ejected water jets during spilling episodes.

The overall rehabilitation works of the entire dam all comprise three main components, namely, the Reshaping of the Plunge Pool, the Refurbishment of the Spillway Upstream Control Facility, and Institutional Strengthening. 

Zimbabwe River Authority (ZRA) board co-chairperson Dr Gloria Magombo was earlier quoted saying an extra 60 years would be added to the gigantic infrastructure and uninterrupted power generation after completion of the rehabilitation works. 

Dr Magombo, the Zimbabwe Energy Ministry’s permanent secretary, co-chairs the board together with her Zambian counterpart. 

“The dam wall is a very critical infrastructure for energy development for Zimbabwe and Zambia. On either side of the countries, we have two power stations which have about a thousand megawatts each and are very critical to the energy security of our nations. 

“The work which is being done as part of the rehabilitation is aimed at improving the safety of the dam and the plunge pool had been affected over the years by the spilling water,” she said. 

ZRA’s director of projects and dam management services, Eng Sithembinkosi Mhlanga said the rehabilitation works at the plunge pool involved the use of concrete to strengthen the bedrock. 

“The works on the plunge pool involves the excavation of the rock around the pool’s walls. The 80-meter-long plunge pool is a hole that was dug by spilling water, and, during the works, we will put concrete to strengthen the bedrock that was affected by the spilling water,” he said. 

In a latest press statement released by ZRA this week, the authority’s chief executive officer, Engineer Munyaradzi Munodawafa said the works on the US$294.2 million-project were progressing well with the completion of the plunge pool excavation a huge milestone. 

“While the excavation works are now 100 percent complete, the overall project is now 93 percent complete. In total, 550,000m3 of water (99 percent of the plunge pool volume) have been pumped out of the 80m deep plunge pool. Of note is the fact that despite the high- risk nature of the project, no adverse environmental, health and safety standards have been violated, nor fatalities recorded thus far. 

“As 2023 draws to a close, we commence the final phase of this extraordinary engineering marvel and remain focused on the upcoming challenges related to the strengthening of the geological fault zone that is located immediately downstream of the dam. This will be achieved through constructing a reinforced concrete slab that will cover the weak-rock zone to protect it from possible future erosion. Upon completion of this concreting work, the plunge pool will be re-filled with water. This refilling will not in any way affect river levels downstream,” he said. 

Engineer Munodawafa also noted that the Spillway Refurbishment sub-project, was now at about 80 percent complete.


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