The ‘Berg’s new pumped storage scheme will massively boost SA’s peak power. And even the environmental watchdogs are happy…
Striking a balance between the needs of a modern, power-hungry society and the constraints of environmental responsibility has never been easy. But our much-maligned power utility has managed to do just that with the development of its latest underground pumped storage scheme in the Drakensberg, showing even the most sceptical of critics that it’s possible for mega-engineering projects and the environmental lobby not only to co-exist, but actually thrive while they go about their business.
Reality check: when the grid crashes at supper time, or as we’re about to watch our favourite detective series, human nature kicks in and we curse Eskom with an abandon that’s only slightly softened by the gentle glow of candlelight. In fact, grumbles about load shedding have become part of our national discourse – a discourse that generally fails to acknowledge the regular appeals on television and other media to turn off our geysers, stoves and lights when the national grid starts buckling under the strain. Let someone else do it, we tell ourselves.
Blame games aside, common sense suggests that the only sensible solution is to ramp up our electricity generating capacity. This, it need hardly be said, takes a long time, a great deal of forward planning (something that critics say has been severely lacking for a number of years) and huge dollops of money, generally measured in the billions.
Construction began on Eskom’s Ingula Pumped Storage Scheme, located in the Little Drakensberg on the provincial boundary between the Free State and KwaZulu-Natal, in 2006. When it officially comes on line in 2016, its 1 332 MW of extra generational capacity will undoubtedly help lighten the load, especially during high electricity demand periods.
It comprises an upper reservoir (Bedford) – perched on the edge of the escarpment near the small village of Van Reenen – and a lower reservoir (Braamhoek) in the rolling hills of KZN, some 4,6 km distant and 470 metres lower down. All inner workings are hidden in a cavernous powerhouse complex carved out of the escarpment deep (the equivalent of 116 storeys) underground. Twin headrace (entrance) waterways, consisting of concrete- and steel-lined headrace tunnels, pressure tunnels and shafts, link the upper reservoir with the pump-turbines. Draft tubes, concrete-lined surge shafts and a single concrete-lined tailrace (exit) tunnel connect the pump-turbines to the lower reservoir.
Here’s how it works: when the national grid requires extra capacity, water is released from the Bedford dam (both dams are named after the streams that feed them) to spin the turbines and give the grid a much-needed boost. Then, when our coal-fired power stations – which provide most of our base load but cannot respond to quick fluctuations in demand – are producing excess capacity late at night (remember, if you don’t use it, you lose it), the entire process is reversed. Water is then pumped back to the upper level to be used again as required.
Avi Singh, power station manager for Peaking Generation, elaborates: “Because we’re a peaking station, we can respond to demands on the national grid very quickly. Our four 333 MW turbines will be able to generate electricity within two and a half minutes, and be in sync with the grid in five.”
This is welcome news, but it gets even better. Since Ingula straddles the escarpment – the continental watershed between the Vaal River catchment, flowing into the Atlantic Ocean, and the Thukela River catchment, flowing into the Indian Ocean – it was in everyone’s best interests to keep the area as pristine as possible.
The upper site incorporates sensitive wetland and mountainous grassland biomes – two of the most threatened habitats in the world. Both are home to four of South Africa’s critically endangered bird species, all of which appear on the Red Data List: the white-winged flufftail, wattled crane, rudd’s lark and eurasian bittern. The vulnerable Southern bald ibis (there are about 8 breeding pairs) and all three species of crane are regularly spotted in the area. And let’s not forget the indigenous escarpment forest. Altogether, over 280 bird species have been recorded in the area, making it a twittering mecca for birdwatchers the world over.
Right from the start, environmental objections to the planned scheme were strong. The main concern was for the affected wetland area where the white-winged flufftail, an elusive little bird not much bigger than a Cape sparrow, spends part of the year. Little is known about it other than its preferred habitat (it lives in mountainous wetland areas above altitudes of 1 700 metres), that it appears in Ethiopia between July and September and spends time in South Africa between November and March. It’s estimated that only 300 and 400 of these birds exist globally.
Middelpunt Wetland Trust’s Malcolm Drummond says they have no idea where it goes in between. “We assume that it migrates but we haven’t been able to prove that yet. We also have no reliable recordings of its calls and know little about its breeding habits, either. In many ways, we see this bird as a flagship species for threatened wetland habitats. So many have been destroyed over the last 300 years, and they are critical from an environmental standpoint for the purification of water.” To everyone’s amazement, the Minister of Public Enterprises listened to the critics, then stopped the scheme, mandating that Eskom purchase 8 000 hectares of land, turn it into a protected area in perpetuity and form a partnership with BirdLife South Africa and Middelpunt Wetland Trust. Eskom was also instructed to build artificial nesting sites for the Southern bald ibis, as their natural sites would be submerged once the Bedford reservoir had filled. From that point on, a constructive relationship began to develop between the various parties concerned.
This partnership was formalised in 2004 to ensure the integration of environmental factors in the planning and implementation phases of the project. Although still elbow-deep in the project, all parties are now beginning to set their sights on their next shared goal: setting up a world-class, sustainable conservation area that incorporates walking, hiking, cycling and river trails, campsites and other non-consumptive ecotourism opportunities.
Says Singh: “There were many disagreements in the beginning, but all of our initial objectors have become partners, which is really satisfying. Together, we’ve come up with a great model for managing mega-engineering projects such as this.”
The already established Ingula Conservation Area, which Eskom manages, currently incorporates about 14 000 hectares of grassland, including around 250 hectares of wetland. Everyone’s hoping to have it officially declared a nature reserve sometime next year – it does, after all, span two provinces. Plans are also in the pipeline to incorporate the project and neighbouring cattle farms into a massive 65 000-hectare conservancy area over time.
Getting down to business
Carving out large chunks of mountain to accommodate the machine hall, transformer hall and 16 km of accompanying tunnels, 8 km of them waterways, was a mammoth undertaking. To provide some idea of the challenges involved, we learn that a staggering 3 million cubic metres of rock was eventually excavated from the site. This was achieved by first digging a level service tunnel large enough to accommodate construction vehicles in the side of the escarpment. That accomplished, construction teams began to dig in earnest, starting at the top of the machine hall’s cathedral-like ceiling and working their way down, carving out the required spaces and tunnels as they went. Fortunately, the mud rock – originally thick sediment at the bottom of an ancient lake system – was relatively easy to work.
The machine hall, which houses the four massive turbines, is 175 metres long, 45 metres high and 25 metres wide. The two high-pressure tunnels, linking the upper reservoir to the machine hall 2 km downhill, have a diameter of 6 metres at the headrace. Constructed at a steep incline of 24 degrees, they narrow down to a mere 2,5 metres before entering the plant. The end result: serious water pressure. As a consequence, their lower sections had to be clad with thick steel bands to withstand the huge stresses. Each tunnel then splits in two, creating four branches to feed each turbine individually.
Abruptly shutting off such a massive flow of water when it’s no longer required can be problematic, to say the least; after all, the accumulated energy has to go somewhere. To prevent damage to the plant when turning off the taps, huge surge chambers – measuring 200 metres deep – were incorporated into both tunnels near the surface, giving the massive redirected pressurised flow somewhere to dissipate. The single 2,3 km-long, 8 metre-diameter tailrace tunnel, connecting the plant to the Braamhoek reservoir, also has two surge chambers. Situated underground near the transformer hall, they’re significantly smaller, as pumping water uphill requires much less pressure.
When Ingula comes online, it will draw water only from the Braamhoek catchment area. This makes sense because it covers an area of 64 km², which is considerably larger than the catchment area available on top of the escarpment. The dam itself holds 26 million cubic metres of water, of which only 19 m³ will be used as “live volume” – that is, moved up and down the mountain.
Singh explains: “We keep the remaining 7 million cubic metres aside to maintain a minimum water level; otherwise, we’ll suck air when pumping everything back uphill.” This is probably good news for the fish, too.
For more information, visit www.eskom.co.za