News · Published 28 February 2017
Experts have warned that without urgent repairs the Kariba Dam risks collapse, unleashing a ‘tsunami’ of water through the Zambezi Valley, reaching the Mozambique border in just eight hours where it would overwhelm the Cahora Bassa wall, in so doing eliminating 40% of the region’s hydro-electric capacity and putting an estimated 3.5-million human lives at risk. Overlooked, perhaps inevitably, amidst the hyperbole of collapse, destruction and loss of life, is the cost of the poor management of the asset, and the water resource, something that can be relatively easily fixed and where the failure to do so is less dramatic but no less costly.
Fifty years ago the Kariba Dam was the centrepiece of collaboration of the Central African Federation. Built in just four years, it was opened by the Queen Mother in 1960 in front of a crowd of 3,000 onlookers, reported by British Pathé at the time, in black and white of course, “as one of the wonders of the world”, an “£80-million masterpiece of engineering skill”. In the Queen Mother’s words, it marked “a new era in the economic life of the Rhodesias”, generating “power for the rapidly growing industries for this potentially enormously rich territory”.
Mention the facility today, and the talk is about the potential for catastrophic failure of the 128-metre dam wall on account of the erosion of its basalt foundations. Experts have warned that without urgent repairs the dam risks collapse, unleashing a ‘tsunami’ of water through the Zambezi Valley, reaching the Mozambique border in just eight hours where it would overwhelm the Cahora Bassa wall, in so doing eliminating 40% of the region’s hydro-electric capacity. According to the Zambezi River Authority (ZRA), which operates the dam, aside from the devastation of wildlife in the valley, the lives of an estimated 3.5-million people would be at risk from this calamitous event.
The Kariba Dam, the world's largest man-made reservoir, supplies water to two hydropower stations: that on the north bank, operated since 1976 by the Zambia Electricity Supply Company (Zesco), with an installed capacity of 1,080 megawatts (MW); and the south bank, operated by the Zimbabwe Power Corporation (ZPC), with 750MW currently and projects to increase this to 1,050MW by 2018. Cahora Bassa’s installed capacity is 2,060MW, much of which is transmitted to South Africa. A further two dams, Itezhi-Tezhi and Kafue Gorge, are on the Kafue River, a tributary of the Zambezi, with a combined capacity of a little over 1,000MW once Itezhi-Tezhi is completed.
Kariba requires rehabilitation, especially to the plunge pool into which the water from the sluices is discharged at a peak of 8,000 tonnes per second. Along refurbishment to the spillway, rehabilitation is expected to cost $300-million over 10 years, seemingly cheap at the price when considering the cost of a new Kariba at around $5-billion. Emergency spilling over the years has scoured a plunge pool to a depth of about 80 metres around 50 to 75 metres downstream of the dam wall. The emergency spilling is itself a result of a lack of turbine capacity.
Many of the issues are, in the words of one specialist engineer, “fairly predictable 50-year maintenance works”. Moreover, “the growing installed turbine capacity at Kariba makes it less likely that substantial spilling will be required going forward”. There is a view that the sense of ‘crisis’ is seriously trumped up – and for good reasons: 300-million of them, in fact.
Overlooked, perhaps inevitably, amidst the hyperbole of collapse, destruction and loss of life, is the cost of the poor management of the asset, and the water resource, something that can be relatively easily fixed and where the failure to do so is less dramatic but no less costly. The answer to this crisis is, however, at least as political as it is technical, in Zambia as elsewhere.
Today there are chronic power shortages in both Zambia and Zimbabwe, attributable only in part to lower than normal reservoir levels, particularly at Kariba.
Zimbabwe’s power demand is some 2,200MW. Its supply is usually around two-thirds of this. In April 2015, for example, Harare, Bulawayo and Manyati stations were producing a combined output of 78MW against a capacity of 265MW. With problems afflicting Hwange Thermal Station, with an installed capacity of 920MW, pressure for continued production has been placed on Kariba to deliver close to its 750MW.
In Zambia, the electricity shortage is a result of some good news – an increased demand for electricity – and some bad, in the form of delays to new generation projects and overuse of newly-installed ‘peaking’ turbines at Kariba.
Demand for electricity has grown very rapidly in Zambia as new customers have been connected to the grid. These have included residential, commercial, agricultural, industrial, and mining customers. Demand has increased from around 1,600MW in 2008 to about 2,200MW in 2015. Ultimately this is a good thing as it represents economic growth and progress for the country. The challenge has been bringing in new generation projects on time to keep up with the growing demand.
This has been compounded by delays to new generation projects in Zambia.
Long before the current shortages, Zesco recognised the growing electricity demand and began to contract for new generation. Notable recent additions to Zesco’s generation capacity have included 50MW from a new Ndola-based fuel oil generation plant, and the 360MW (2x180MW) Kariba North Bank Expansion to meet peak evening demand.
Zesco has also contracted an additional 120MW of hydro power from Itezhi-Tezhi and 300MW of coal-fired power from Maamba Collieries. Delays to these two projects are a key reason for the current energy shortages in Zambia. Both were planned to be online in 2014, but have been delayed due to financing issues and the slow completion of powerlines to connect these projects to the national grid. If Itezhi-Tezhi and Maamba had been finished on time, there would be no power supply problem this year.
Zambia’s total installed generation capacity is currently just over 2,200W and will grow to over 2,600MW once these new schemes are connected by 2016. Other new projects are at various pre-development stages, but timeframes continue to drift and financing requirements cast uncertainty over further projects. For instance the 750MW Kafue Gorge lower hydro project would greatly increase power supply availability in Zambia in perhaps the 2020 timeframe, but financing for this $2-billion project is not yet secured. There is, as an illustration, a proposal for a 600MW solar power project currently, though this would, as the US Energy Administration notes in its chart, below, an expensive (and inconsistent) option, especially for a country with an abundance of hydro and coal.
Like this? Subscribe for free to receive the latest.
Cost of Electricity for New-Build Power Plants
- Plant Type | Average Tariff (USc/kWh)
- Coal-fired: 9.5
- Gas-fired: 7.5
- Nuclear: 9.5
- Geothermal: 4.8
- Biomass: 10.1
- Wind: 7.4
- Wind (offshore): 19.7
- Solar PV 12.5:
- Solar Thermal: 24.0
- Hydroelectric: 8.4
Kariba has been used to meet this growing demand, requiring more water to drive the turbines, pushing the volume of water use for generation to levels unsustainable by regular annual rainfall and inflows. Both Zesco and ZPC have been using more water than they are supposed to during 2015.
Following the completion of the 360MW Kariba North Bank Expansion project in 2013/2014, Zesco has been generating a lot more electricity at Kariba than in previous years. The new turbines are being run much more than they were originally intended to. It seems that Zesco has been operating the intended peaking units much more than the planned three to four hours a day. This means they’ve needed to use more water, resulting in low reservoir level.
As a result, ZRA reduced the water allocations for Zesco and ZPC by 12% in March 2015. Instead of reducing their water use, both Zesco and ZPC substantially increased the amount of water used. Between March and June 2015, Zesco overused its water allocation by 39%, while ZPC overused by 16%. If the utilities complied with the allocations from ZRA, there would have been some load-shedding required beginning in March this year, but it would have been minor in comparison with current cuts. This would also have provided more time to source electricity imports and pursue other mitigation strategies prior to the situation becoming a crisis.
Some of the additional power generated from the overuse of the new 2x180MW turbines has been used to meet the growing electricity demand within Zambia. There has been speculation that extra power generated is being exported, a situation not helped by Zesco’s unwillingness to publish daily statistics on power production, and its imports and exports.
So just how serious is the current situation?
It has been widely reported that water will run out at Kariba in October. In fact, this refers to the timing when Zesco is likely to reach 100% of its 2015 water allocation. This is not the moment, however, when the Kariba reservoir levels would physically reach the minimum operating level and thus force the turbines to be shut down. There will be enough water for Zesco to continue operating its power plant at Kariba beyond October; it will just have to exceed its total allocation from ZRA for the year (as it has done every month of 2015 thus far). At current generation levels, by end of 2015, Kariba would potentially reach a low point of 477 metres, which is 1.5 metres above the minimum operating level. At this level, there would still be about seven billion cubic metres of water in Kariba available for generation, or around 10% of the ‘live capacity’ of the reservoir. Assuming rains in the catchment arrive at the normal time, this would be the minimum drawdown level, and allow Zambia to make it through without more severe load-shedding.
It’s a difficult juggling act. The impact of a shortage of power on business would be devastating to Zambia’s economy. Should, for example, the power be cut by one-third (or 115MW) to the country’s largest copper producer, First Quantum, as many as 500 jobs and as much as $140-million in annual government income would be at risk. According to the Extractive Industries Transparency Initiative, in 2013 Zambia’s mining sector contributed 68% of export revenue, 30% of government revenue and 9% of gross domestic product. One mine, First Quantum’s Kansanshi, alone contributed 27% of all revenue from mining.
In the short-term this demands keeping the lights on, in spite of the risk of drawing down the level in Kariba, not ideal of course if there are delays to the seasonal rains, or if the work on the new power plants at Itezhi-Tezhi and Maamba are further delayed. But between increasing imports from the Southern African Power Pool and conservation through load-shedding, Zambia should manage to get through the worst.
In the longer-term, a solution to Zambia’s power woes stresses both the importance of water management at Kariba on the one hand; and the imperative of continuing to grow power supplies, including by soliciting private capital. The same rule applies across the region. Indeed, Zambia, like South Africa, is not alone in confronting, simultaneously, governance and growth in dealing with its electricity problems.
The real emergency over Kariba has less to do with undermining its basalt foundations but with the destabilising of economic growth caused by cutting off its electrical supply. Zambia’s overall problem is that, in the Queen Mother’s words, for all its abundant natural resources, its potential has not been realised. Switching off Kariba would simply confirm this status and the reasons behind it.
Dr Greg Mills heads the Johannesburg-based Brenthurst Foundation.
This article was originally published in The Daily Maverick.