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By Eddie Cross 85 per cent of the Zambezi's catchment is in tropical forest. The balance of the water comes from major rivers in Zambia (the Kafue and Luangwa), and in Zimbabwe (the Gwaai, Sanyati, Hunyani and Mazowe). The other major downstream source is the drainage from Lake Malawi via the Shire River system. The importance of this great river basin is that it draws most of its water from reliable rainforest areas, which are likely to become wetter, not drier as a long-term consequence of global warming. Its role as a source of hydro-electric power is already well established with the Kariba dam producing a third of the power needs of Zimbabwe and Zambia, and Cahora Bassa producing 5 000 megawatts – enough to supply electricity to the whole of Mozambique as well as South Africa and Zimbabwe. This role is bound to increase when the planned extension to the power station at Cahora Bassa is implemented and other projects on the river are undertaken. But, compared with the use of Zambezi water to quench the thirst of regional cities, the role of the river as a power source is likely to be much less controversial in the long term. For over 60 years Zimbabwe has talked about the need to draw water from the Zambezi for the City of Bulawayo. Already an extraction system takes water from the river for Victoria Falls, Livingstone and Hwange. But it is the plans for a system to take water from the Zambezi at Kazungula for delivery into the massive Gauteng urban conglomerate in South Africa that must raise concern within the region. By 2015, the Gauteng area will have run out of new raw water sources. This area generates 60 per cent of South Africa’s GNP and is already drawing water from Lesotho and all the rivers within a 500 kilometre radius. This is likely to be made much worse by global warming which, in South Africa, is expected to make the semi-arid regions of the country even drier.
If 85 per cent of the river flow emanates from the central African rainforest zone, then over 80 per cent of that flow must be generated by rainfall from October to April each year, with peak flow in January and February. The river is unusually flat through a 300 kilometre stretch from Lokulu to Kazungula. At Kazungula the river hits the edge of a massive, volcanic, basalt ledge and when it floods, the water backs up this section of the river, flooding both banks. In the centre of this stretch are the Bamamgwato floodplains – famous because of the people who live there and the way they have adapted their lives to the cycles of the river. In the south the river spills over into a vast reed bed that runs into the Caprivi Strip, down into the Chobe River and back into the lower Zambezi just above Victoria Falls. It is these vast floodplains, covered in sedges and reed beds that absorb the peak river flows and absorb much of the silt carried down the river from its sources. This means that the flood peak at Victoria Falls actually occurs in April and May – some three months later than the actual peak in river flow from the sources of the river. This time delay is critical for two reasons – it means that the river has a much more constant flow of water through the year than otherwise possible based on rainfall alone, and it also explains why the river is so clean when it reaches Victoria Falls. Lower down, the seasonal rains in Zimbabwe and Zambia render the river dirty and muddy, and also give rise to mini peaks in river flow in January and February when the main rains occur in these countries. It is vital for those who wish to exploit the river lower down for either power generation or water extraction, that these features of the river should be maintained. To do so they must start to pay closer attention to just what is happening in these floodplain regions and the implications for the river system in the long term. Of critical importance to the whole system is its wild heritage, in particular the role of the hippo. It is The hippo is a favorite for poachers who shoot them to obtain meat for human consumption as well as hippo hides for tanning. Poaching is already a major problem in Namibia and in Zambia. Only Botswana and Zimbabwe have effective anti-poaching activities and systems in place. In the Caprivi Strip – the hippo population has been virtually shot out and a similar situation must be developing in parts of Zambia. It is an urgent requirement that these trends be monitored and effective action taken to protect the remaining hippo populations. Where the hippo have been virtually wiped out they might have to be re-introduced from areas where there are adequate stocks and, once established and protected, their numbers should rise quite rapidly. It makes absolute sense to pursue these floodplain management strategies in conjunction with the region's plans for trans-frontier wildlife parks or nature reserves. In this way the region can extend management systems across national boundaries and ensure that key populations of wildlife are protected. It would also make it possible to then exploit these vast natural regions for eco-tourism and other forms of economic activity. But the goal must be to protect what nature has already created for Southern Africa – a natural water system that uses its strengths and weaknesses to best advantage and which can be used to support economic and industrial life in the arid south. |
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western Zambia to Kazungula. From there it runs over a basalt volcanic screed, across Victoria Falls and down along the Zambia/Zimbabwe border to Mozambique. In the process it flows through two of the great dams of the world – Kariba and Cahora Bassa. 
the hippo which maintain the drainage systems of the floodplains by eating back the growth in the reed beds and sedge banks. Without this network of channels the surplus water of the seasonal floods cannot penetrate the interior of the floodplains as easily, and the drainage back into the main river in April and May is also hindered.