Learning From the Kariba Dam
The Kariba Dam is failing. Since the late 1950s, it has sat on the Zambezi River, on the border between Zambia and Zimbabwe, in one of the zigzagging gorges that ripple the land there. It provides 1,830 megawatts of hydroelectric power to both countries and holds back the world’s largest reservoir. For the last decade, scientists and reporters have issued warnings about the dam’s potential to cause ecological disasters — of opposite kinds. On one hand, low rainfall has yielded water levels that barely reach the minimum necessary to generate electricity. On the other hand, heavy rainfall has threatened to flood the surrounding areas. When the floodgates were opened in 2010, 6,000 people had to be evacuated.
Climate change catastrophizes the weather — and when it comes to such extremes, dams are, well, inflexible. They cannot be narrowed enough to eke more force from less water during droughts, and far worse, they cannot be expanded enough to accommodate floods. The only other ways to handle floods are to let the water flow over the top of the dam or to open up a spillway for controlled release. Neither of these measures is foolproof at the Kariba Dam because of how the passage of time has worn it down. The dam was built on gneiss and quartzite and is made of concrete — 80 feet at its thickest point. But over six decades of the waters’ rushing through it, tumbling over it and crashing down on its other side have eroded the dam’s foundations and carved a pit at its base. 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. At the same time, longer hot seasons have drained the reservoir to record lows, and drought-induced power cuts have become a daily reality for homes and businesses. The World Bank is supporting efforts to secure the Kariba Dam, but any attempts to fix or expand it risk weakening it further, which would be disastrous in the event of a flood.
Whether the water is too high or too low, the lives of millions of people are at stake, to say nothing of the natural ecosystem. It’s a familiar, seemingly inevitable tale of human folly: One of our most ambitious efforts to harness the power of nature has left us exposed to nature’s vagaries.
Is this just a failure of our power of prophecy? When we talk about climate change, we talk about our inability to predict and control what’s coming, to step into the same river twice. We’re out of time, in more than one sense: We’ve fallen out of rhythm with the circulatory relations between sun and rain and earth. We’ve damned ourselves, foreclosed some of the future’s forking paths — this is the aspect of time we call the subjunctive, the grammatical mood for what is imagined or wished. A river’s branches suggest to us what could, would, should be. But the subjunctive mood — when it comes to rivers, when it comes to time — doesn’t move in only one direction. If we look back, it’s clear: It didn’t have to be this way.
The history of the Kariba Dam is the story of a war over the past and the future of a river. That war was fought in the 1950s between European colonial powers and the local people in a place then called the Central African Federation or the Federation of Rhodesia and Nyasaland. The federation was a short-lived colonial experiment — or fiasco, depending on your perspective — that merged three adjacent territories with historically disparate relationships to the British Empire. Southern Rhodesia (now Zimbabwe) was a self-governing colony founded by the British South Africa Company; Northern Rhodesia (now Zambia) and Nyasaland (now Malawi) had been demarcated as British protectorates. The decision to conglomerate the three territories into one came from the colonialists, whose motivations were exploitatively economic and crudely economical.