Dependence on the Zambezi River

The Zambezi River rises in the Congo, curves through the top of Zambia into Angola and then traverses Zambia from north to south until it hits a basalt barrier at Kazungula where the boundaries of Zimbabwe, Zambia, Botswana and Namibia meet. At that point it turns east and cuts across Zimbabwe and Zambia until it exits Zimbabwe at Kanyemba and enters the Cahora Bassa Dam and then down to the Indian Ocean.

It is not a long river by international standards or a very big river, but it is one of the cleanest and most important rivers in the world. Its not navigable like the Rhine or the Congo, but it supports two of the larger hydro electric power stations in the world and serves six southern African States. In a region where fresh water is going to be very short the Zambezi is a system that everyone is looking at and wondering how do we get access to this resource?

The elephant in the room is South Africa already a largely arid or semi arid country where a third of the GDP of Africa is generated in the Gauteng Province. By this year, Gauteng will have largely exhausted its traditional sources of water from the Vaal River, the Highlands Water Scheme in Lesotho and the rivers of Natal. Further growth in this Province is going to be dependent on sources outside the traditional supply zone and the Zambezi or the Okavango River systems offer one major possibility.

For many years, the South Africans have planned and pondered on a scheme to take water from the Zambezi River system probably in northern Botswana and then run it through a system of pipelines and open canals past Francistown to Gauteng. An offtake to Bulawayo has even been considered. Those who think that such schemes are farfetched need to appreciate that Windhoek, the Capital of Namibia already moves water from the north and after moving it for 800 kilometers dumps it into underground aquifers for recovery when needed.

The Zambezi is famous for the spectacular gorges it is cutting back through a vast sheet of volcanic rock basalt and the cutting edge is the Victoria Falls. But in winter the Falls are often reduced to a few isolated falls along its front and in summer you often cannot see the Falls for heavy spray. This mighty river is now captured in two of the largest dams in the world, Kariba and Cahora Bassa.

Zambia and Zimbabwe plan a further dam below the Falls in the Batoka Gorge and Mozambique plans another at a site below Cahora Bassa. These four dams coupled with perhaps two on the Kafue, a tributary in Zambia, would then complete a system that will be capable of producing nearly 15 000 megawatts of electricity for regional consumers. The particular value of this capacity is that its clean, sustainable and cheap and it can be used to meet peak demands from regional grids.

There is potential to raise even more power from the river by harnessing the now controlled flow of water in the middle and lower sections of the river for river flow hydroelectric systems that do not require dams but simply use low profile barrages to harness the river through river flow turbines.

This potential is dwarfed by the potential of the Congo, but that is many years into the future even though the approvals for the first 5000 megawatt station at Inga has been given and a transmission system across the Congo to Zambia and then south to Gauteng, is planned.

But the Zambezi River system is limited in its potential Kariba Dam has only spilled 5 or 6 times since it was completed in 1958, suggesting that its originally installed capacity of 1400 megawatts was about its capacity. The two States are in the process of upgrading and expanding the capacity at Kariba with Zambia already over 1100 megawatts and Zimbabwe shortly to follow suit. The problem is that this is in excess of the capacity of the river and the dam and right now the water level in the dam is well below safety levels for the power plant. So much so that the operator the Zambezi River Authority has issued an instruction to cut throughput to preserve water levels.

I was on the river last week at Chewore and saw no signs that the river flow is down in fact to my mind, its about 1,5 meters above last year on average. This suggests that the dam is operating over capacity for the size of the lake. I have asked the Authority for data relating to rainfall and river flow records for the upper Zambezi and have received a letter from the Chief Executive saying that they are reluctant to release such information. Why I have no idea as they are a publicly funded entity and I would have thought that this sort of information should even be available on their website. I have gone back to them and am waiting for a response.

However I have the records for one measuring station on the upper river and this shows that there has been very little run off this year in fact it looks like an all time low. This is confirmed by reports from the Falls where water levels are well below normal. Is this due to climate change?

A good friend of mine is Professor Euan Nisbet of London University who is a world renowned expert on atmospherics. He says that the specialists he confers with say the Inter Tropical Convergence Zone is shifting northwards by 18 degrees. You can watch this system moving every day on satellite images as it is the main rainfall system of the continent. This winter I have been surprised by how far into the Sahara Desert the rains have reached, perhaps Euan and his colleagues are right. (Euan comes from Mberengwa in Zimbabwe.)

If that is true, it has profound implications for southern Africa and the whole Zambezi system. Ever since I went on a short fishing trip on the flood plains of the Caprivi Strip, I have been concerned that the Hippo populations in the floodplains of the upper Zambezi are being shot out or dying of disease. I saw not a single Hippo in the flood plains I was fishing in even though we penetrated them for 35 kilometers.

Ever since, I have been pointing out to anyone who will listen, that if the Hippo populations in the flood plains of the upper Zambezi are wiped out, there is no one to maintain the drainage channels that feed the water back into the main river system in winter. Such a development would create vast swamps of stagnant water and deny the Zambezi of its life blood with dire consequences for all who depend on the river downstream.

The Zambezi cuts through the center of the five Nations wild life conservation area that joins Angola, Zambia, Namibia, Botswana and Zimbabwe in the largest contiguous conservation Park in the world. When fully functional it will contain over 70 per cent of the wild life of Africa and be a massive draw card for tourists.

We need to ensure that we do not take the Zambezi for granted or over exploit its resources. The natural systems that make it such a special and spectacular river must be preserved for future generations. Competition for its water is going to be intense and we need to know what we are doing and its implications for the whole system before we agree to any developments that might harm the system as a whole.

E G Cross
Bulawayo 28th July 2015