#6- In danger of collapse?

Figure 1. Kariba dam, 1965

Having moved through the timeline of the Kariba dam, we have now reached current times where the dam is facing two big problems: climate change and collapse. If this was a sensationalist blog I would definitely milk the idea of its crumbling, but that’s not the case. Instead I want to find somewhat of a middle ground between disaster and denial. 

However, this doesn’t change the fact that what once was a dream of secure energy supply has turned into a threat to over 30 million people’s basic needs. Unsurprisingly the collapse of the world’s largest reservoir would be an ‘epochal event in the history of energy development- the dam industry’s Chernobyl’. With its destruction, a tsunami-like event (4 times bigger than the largest on record) would rush over the basin, creating a domino chain reaction of events, including the destruction of the Cahora Bassa dam in Mozambique. 

The problem

Firstly, the dam’s construction was based on only three decades worth of river discharge data, which is much too little, especially for such a grand scheme. This mistake was soon realised when in 1957 the construction site was overrun by a much bigger flood than any predicted worst-case scenario, and again in 1958 when an even greater flood occured. Sloppy planning if you ask me. 

Furthermore, the dam has become one big contradiction due to climate change. Ongoing droughts have made it difficult for the dam to reach its minimum capacity to produce energy, all whilst extreme rainfall is threatening the dam’s collapse and causing flooding. This is because Southern Africa is highly susceptible to climate change, which is indicated by the rising temperatures (0.5% increase over the last 100 years) and changing rainfall patterns; rainfall periods are becoming longer and more extreme, putting extra stress on the Kariba dam. Hence, when combining poor planning, a lack of maintenance and climate change Kariba’s plunge pool ended up deepening to a shocking 90m (Figure 2). As a result, the water started to erode the softer rock strata towards the dam, ultimately risking its base from becoming unstable. 

Figure 2. Diagram of Kariba dam’s plunge pool.

So, what to do?

In order to minimise the plunge pool from increasing, operators have started to ‘open only three of the dam’s six floodgates at a time’. However, during events of heavy rainfall these three floodgates become quite limiting, leaving the operators with two options: letting the water flow over the dam wall and damaging its foundation or opening more floodgates and risking the enlargement of the plunge pool. Thus, due to the lack of management options the ZRA introduced a Rehabilitation Project in 2014, supported by a $300 million loan from the World Bank. It involves reshaping the plunge pool by using a cofferdam, so the water can be pumped out in dry seasons and allow the construction of a bigger pool that directs the force of water away from the dam. Additionally, the floodgates will be repaired over an 8-10 year period, since they can only be restored individually. 

Yet, despite all these efforts, there are contradicting statements from countries in the north and south of the Zambezi basin in terms of the urgency of this project. For example, the Zambian government seems to have more of a disaster mindset, while Zimbabwe's government takes a rather relaxed stance (some might even say its denial). This might be because Zimbabwe is one of the world’s poorest states with many other dams that require their attention. Juggling all at once as well as having to fund and carry out a massive project such as this can become quite challenging. In Zambia’s case it might be because they are in charge of collecting investments for the project, which becomes much easier when the situation is described as a disaster rather than under control. That being said, it’s best to move away from the notion of disaster or being overly optimistic, as they’re both too extreme. Instead governments should find a middle ground in which they can be vigilant and urgent, but also remain level-headed.

Finally, the Kariba dam makes one thing abundantly clear: development projects cannot be taken on a light shoulder and need to be done with proper planning. Ideally future projects will take an IWRM approach, but even those have flaws and need to be carefully thought-through.