22 Hydropower

22 Hydropower Beneath the cover of water, deep deposits of silt have reduced the capacity of the Collywobbles dam. Sue Matthews Sue Matthews visited Collywobbles in the Eastern Cape and explores ways of mitigating its impact on the surrounding environment. he Mbhashe River rises in the Gariep (360 MW) and Vanderkloof Of course, there’s a higher demand mountains of the southern (240 MW) schemes on the Orange for electricity in winter, so enough water TDrakensberg, and then snakes east- River. (This excludes the Drakensberg must be stored to see the power ward across the coastal plateau, a gentle and Palmiet pumped storage schemes, station through the dry months. But landscape of undulating grassland. where water is pumped during off-peak the Collywobbles dam was only Shortly after flowing beneath the N2, the periods to generate electricity during designed to provide an effective storage river encounters the more rugged terrain peak demand.) of 2,5 GWh – equivalent to 60 hours of of the Wild Coast, and – as if in shock or operation with all three turbines gen- confusion – it suddenly flails into a series Like many conventional hydropower erating at maximum capacity. Water is of violent contortions, before seemingly schemes, Collywobbles has a storage therefore diverted from the Ncora Dam getting a grip on itself and continuing dam and a penstock to pipe water down on the Tsomo River in the neighbouring more sedately to the Indian Ocean. to the turbines, which drive the genera- Greater Kei catchment, taking about two tors. What’s amazing about this scheme days to reach Collywobbles. This interba- This convoluted section of river course – though is that the penstock tunnels sin transfer of water has ranged between viewed on Google Earth as a squiggle of straight through the mountain spine about 115 and 150 million m3 annually loops and bends – is known as separating two bends of the river. This over the last four years. Collywobbles, and is the site of a hydro- means the water takes a direct shortcut electric power station of the same name. of a little over a kilometre to skip the “In summer we generally have enough It was commissioned in 1985 by TESCOR, 34 km ‘by the river’ meander between run-of-river yield, so most of the water is the former Transkei Electricity Corpora- the dam wall and the power plant. As transferred in winter,” explains Monique tion, and is now operated by Eskom. a result, this stretch of river barely flows Klopper, Network Optimisation Analyst With three generating units of 14 MW unless water overtops the dam wall for Eskom’s southern region, based in each providing a total maximum output during the summer months, when the East London. “The valve at Ncora Dam is of 42 MW, it ranks as Eskom’s third larg- Mbhashe catchment gets most of its controlled by the Department of Water est hydroelectric power station after the rainfall. Affairs & Forestry (DWAF), so we monitor The Water Wheel November/December 2008 Hydropower 23 the levels at Collywobbles and then put effects. That’s why we can’t scour as determined using the Rapid Simulation in requests to DWAF to release water to much as we’d like,” says Klopper. Model is 67 million m3 per year – about us. There’s an agreement that the level half the amount of water transferred of the Ncora Dam cannot drop below Yet the presence of the dam and the from Ncora Dam. 50%, and the valve can only be opened interbasin transfer of water in winter 20-35%.” completely alters the flow regime of the The relationship between freshwater river, which contributes to the siltation flows and the state of the estuary, as A complicating factor, however, is that problem and also affects the system’s well as the consequences for its habitats the Collywobbles dam has silted up to ecological functioning. According to and biota, will be examined in a desktop such an extent that only about 10% of DWAF’s Internal Strategic Perspective assessment that form part of a project to its original 9 million m3 capacity remains. of the Mzimvubu to Mbhashe ISP Area develop an estuary management plan for The soils in the Mbhashe catchment are (2005), the natural run-of-river yield the Mbhashe River. naturally prone to erosion, but overgraz- ing exacerbates the problem, with the result that more than 60% siltation had already occurred. Clearly, somebody didn’t do their homework properly in the planning stages of the scheme. “At least once a year we’ll open the scour- ing gates at the dam to try and scour out some of the silt, but it doesn’t have much effect,” says Klopper. “Since we’ve lost so much of the dam’s holding capacity, we can’t get the generation out of the station that we’d like.” The upshot of this is that while the power station may run round-the-clock during summer, in winter only two of the three units run for a few hours per day over peak demand periods in the morning and evening. “The operators at the power station check the level of the dam, and if it’s overflowing they’ll generate more, and stop if it drops too low. We monitor from East London as well to check what’s going on,” confirms Klopper. “Flow meas- urements taken by gauging weirs in the river are also fed back to us in East Lon- don so we can instantaneously see what the river level is, and generate depend- ing on the rise and fall of the river.” Apart from reducing the dam’s capacity, the silt load in the water causes increased wear and tear to the turbine parts. It is also silting up the Mbhashe River estuary, which separates the Dwesa and Cwebe Nature Reserves and forms part of the adjoining marine protected area. “The amount of silt going down the river Sue Matthews is a big concern for us, and we’re always The machine floor at Collywobbles hydroelectric power station, showing the three on the lookout for ways to mitigate the 14 MW generating units. The Water Wheel November/December 2008 24 Hydropower The Eastern Cape Parks Board has commissioned the study, under the auspices Plant operator of the CAPE (Cape Action Plan for People Lucas Ngqata and the Environment) Estuaries Manage- (seated), electri- ment Programme. Options for rehabilita- cal officer Fundile tion of the estuary are to be identified, Mgulugulu (left) and perhaps some operating rules for and mechanical the Collywobbles scheme can be sug- officer Lungile gested to reduce its impact. Because Madlolo (right) in despite all its problems, Eskom is not the Collywobbles likely to give up on the scheme in the control room. near future – especially in the current era of countrywide power shortages and the Sue Matthews looming threat of rolling black-outs. on tribal land. In the gaily painted bun- crop irrigation is limited due to the area’s “Collywobbles is important in terms of galows scattered throughout the coun- poor soils and steep terrain. electricity supply, but more so in terms tryside, people burn paraffin, candles, of the stability of the network, as it can wood and gas – or even cow dung and A bit further north, however, the twin keep the network running during high maize cobs – for cooking, light and benefits of irrigation and hydroelectric- demand periods or temporary short- warmth, but more than 25% of villages ity are being touted as the main motiva- ages,” explains Klopper. “The return we have electric power. Indeed, accord- tion to dam the Mzimvubu River, which get on it is enormous, plus it’s a clean ing to the Mbhashe Municipality’s draft flows into the sea at Port St Johns. This source of energy.” Integrated Development Plan for 2008- is South Africa’s largest remaining unde- 2009, about 60% of all households now veloped river, but the massively ambi- Electricity generated at Collywobbles have access to electricity, and Eskom is tious Mzimvubu Basin Development is distributed remotely from East Lon- extending its reach little by little. Project is set to change this. The num- don, with most directed to Mthatha bers being bandied about are that some (formerly Umtata) and other towns and Water services are the more pressing 897 000 jobs would be created through villages in Transkei – some quite close problem, since only 0,63% of house- forestry and agricultural expansion, and to the point of origin. The Mbhashe holds have access to water inside the as much as 2 000 MW of hydroelectri- River flows through one of the poorest home, while 67% rely on streams and city generated for the national grid and most undeveloped areas of the rivers for their water requirements. through a network of large dams. Eskom country, where 77% of the inhabitants DWAF’s ISP report indicates that rural has reportedly identified nine possible earn less than R800 per month. Census people in the upper catchments must hydropower sites on the Mzimvubu 2001 revealed that there were 253 372 deal with annual water deficits during River and its main tributaries. people (53 199 households) living in the dry season, limiting their domestic the Mbhashe municipal area, which uses and stock watering. The situation Apart from Collywobbles, Eskom inher- includes the towns of Dutywa, Gatyana is exacerbated by the 24 600 ha (246 ited three other small hydropower sta- 2 (Willowvale) and Xhora (Elliotdale), but km ) of forestry plantation here, which tions from TESCOR. The smallest is Ncora 95% of residents live in rural settlements reduces annual runoff by an estimated (2 MW), situated alongside the dam 19 million m3.

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