Climate change and sizing of the Itezh-itezhi Dam reservoir capacity

Thu, 01 Dec 2016 10:17:09 +0000

By Ronald Lwamba

The ZESCO spokesperson, Mr. Kapata, complained that not all the water being released from Itezhitezhi Dam is reaching Kafue Gorge Power Station, which is affecting the amount of power generated. Indeed, this is true because by the time it reaches Kafue Gorge Power Station there are two major water consumers, namely Zambia Sugar Company and Lusaka Water and Sewerage Company.  The subtraction of water by Kafue town although insignificant at the moment is likely to grow with the town being declared as a steel economic zone. The Lusaka Water and Sewerage Company is also expanding its water treatment plant. Zambia Sugar is likely to have plans on its drawing board to expand its irrigation scheme. These activities are likely to result in even further reduction in water reaching the Kafue Gorge Power Station. It is therefore imperative for all the stakeholders to increase the Itezhitezhi Dam reservoir capacity which is currently at 5.7 billion cubic metres.

The Itezhitezhi Dam on the Kafue River was built between 1974 and 1977 at the Itezhitezhi Gap, in a range of hills through which the river had eroded a narrow valley, leading to the broad expanse of the wetlands known as the Kafue Flats. The initial purpose of the dam is to store water for the Kafue Gorge Power Station more than 270 kilometres downstream. (I am not aware of any provision of water usage by other water consumers in the design). There was a provision of constructing a 120 MW power station in future when the power demand increases. The Kafue River has a very high seasonal variation, flooding in the rainy season and slowing to perhaps a twentieth of the peak flow rate at the end of the dry season. Power generation, however, requires a steady flow, which can only be achieved by having a reservoir large enough to store the rainy season flood for use in the dry season. At the Kafue Gorge the topography does not allow a large enough reservoir to form. The designers of the dam therefore had the idea of siting the main reservoir at Itezhitezhi, and releasing the water in a steady flow down the river along the Kafue Flats to the Kafue Gorge Dam.

The idea of increasing the reservoir capacity at Itezhitezhi Dam is not new. The Itezhitezhi Dam and Kafue Gorge Power Station were designed by SWECO, the Swedish consultants, in the early 1970s. The optimum reservoir capacity is based on the record of water flows in the river to be impounded and the longer the record of measurement the less likely the reservoir will fail. A reservoir fails when it cannot meet the required release of water.

The Itezhitezhi Dam reservoir has failed in the past because the period on which the designed capacity was based was not long enough to capture some water flows of very dry years. In 1991 when I worked at Itezhitezhi Dam as Resident Engineer the Itezhitezhi reservoir ran almost dry and we could not release water through the usual main spillway and had to release the water through the low level outlet to Kafue Gorge. Zambia has again experienced a drought in the 2015/16 rainy season.

The record of measurement of water flows on Kafue River started in 1905. The period of records from 1905 to 1923 was removed in the design of the reservoir capacity resulting in a smaller reservoir. SWECO, the Swedish consultants, argued that these water flows were too low and must have been as a result of errors in their measurement. The World Bank gave Watermeyer, Legge and Piésold, the British consultants, to review the design.

They argued that the low water flows were also observed on other rivers in the region such as the Shire River in Malawi. They also argued that the high water flows from 1923 onwards could be as a result of seeding of the clouds from the pollution from the mines which had become operational at about this time. The design capacity based on the Swedish design was 5.7 billion metres, the current capacity. The British design was some 7 billion cubic metres. Unfortunately the Swedish design carried the day. However a compromise was reached that in future the dam capacity could be increased to some 7 billion cubic metres by heightening the dam by a metre or so and by constructing a saddle dam to prevent the water from spilling from the reservoir. I am therefore convinced that climate change is not a new phenomenon as the drought period we are now experiencing is similar to the one where the low water flows were observed but wrongly attributed to faulty measurements and discarded by the Swedish consultants. The British consultants rightly argued, with the benefit of hind sight, that the water flow measurements were not faulty but were a true reflection of the climate of the time. Itezhitezhi reservoir capacity should be, therefore, increased as soon as possible based on the period of measurements from 1905 to date and it should take into account the increased water usage by other users. The raising of the dam and the resulting head behind the dam will also result in increased power generation at the power station at the Itezhitezhi Dam

The Kafue Flats is an amazing wetland landscape of grasslands, lagoons and reed beds, covering about 6500 km2 of the Kafue River Basin. They are home to more than 470 species of birds and a wide variety of mammals, including the endemic Kafue lechwe, a rare species of antelope. The ecosystem has been heavily influenced by natural cycles of floods and droughts, but this changed radically after the construction of the itezhitezhi dam in 1977. Although in the sizing of the Itezhitezhi reservoir there was an allowance of 300m3/s to be released every March to simulate the natural flooding, power generation has taken precedence over the releasing of these environmental flows. Such water releases may be seen as a waste, yet their impacts on people’s livelihoods can be dramatic. This is why it is important to increase the reservoir capacity to also take this into account.

Looking at the diagram prepared by the International Energy Agency, the countries that have produced the highest amount of energy-related Carbon Dioxide from 1890 to 2014 are the USA and the Western World to sustain their industrialization.

The countries that will produce the highest number of energy-related Carbon Dioxide in the projected period of 2015 to 2040 are China, the USA and India. Africa’s contribution and in particular Zambia’s contribution with its 600 MW thermal (coal) power station is negligible. While it is laudable to have a more sustainable greenhouse gas (GHG) inventory management system in Zambia, it is quite evident that unless the big emitters such as China, USA and India come to the table Zambia’s efforts will not make any impact on climate change. If China, India and other developing countries were allowed to consume as much energy as rich ones did during their own industrial revolutions and the rise in global temperatures is limited to two degrees this would allow developing-country emissions to rise by 200% whereas rich-country emissions would have to fall by an amount that is politically inconceivable.

Pope Francis has added his voice on climate change. The encyclical about climate change has aroused a lot of interest from the general public with some saying that let him stick to religion and leave science to scientist forgetting that he was a chemist before being ordained. Former Florida Gov. Jeb Bush, a Catholic convert, said, “I don’t get economic policies from my bishops or my cardinals or my Pope. I think religion ought to be about making us better as people and less about things that end up getting into the political realm.” Donald Trump thinks that climate change is a hoax perpetrated by China. But while more than 80% of Catholic Democrats say there is solid evidence that the Earth is warming, just half of Catholic Republicans agree. And less than a quarter of Catholic Republicans believe that global warming is a man-made or poses a very serious problem.

“The Earth, our home, is beginning to look more and more like an immense pile of filth,” Pope Francis said. “The rich and powerful shut themselves up within self-enclosed enclaves, Francis argues, compulsively consuming the latest goods to feed the emptiness within their hearts, while ignoring the plight of the poor.

The problem is “aggravated,” the Pope said, “by a model of development based on the intensive use of fossil fuels.”  If present trends continue, Francis argued, the changing climate will have grave implications for poor communities who lack the resources to adapt or protect themselves from natural disasters.

That is the dilemma of climate change. A substantial number of people, especially in the USA who are the biggest emitters in the world, do not believe that climate change is manmade despite such evidence as our own drought in Zambia, in California and Brazil, water reservoirs ran dry and yet the rainy season was four months away, heat waves in India and Pakistan, extreme floods elsewhere, the shrinking of the Arctic ice cap and so on.

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