9 March 2009
While the recently opened R1.5-billion Berg River Dam in the Western Cape province is expected to augment Cape Town’s water supply by almost 20%, the government is still calling on the city’s residents to use water sparingly.
The project, a partnership between the Department of Water Affairs and Forestry, the City of Cape Town and the Trans-Caledon Tunnel Authority, comprises a dam with a storage capacity of 130-million cubic metres, a supplement scheme, two pump stations and 12 kilometres of pipeline.
The dam, which started storing water in July 2007 and was full a year later thanks to good rainfall, and will increase Cape Town’s total water supply from 668 to 898 cubic metres per year.
Reducing demand
The conditional go-ahead for the project from the department was dependent on the city reducing its water demand by 20%. In response, the city implemented a water conservation strategy aimed at reducing the use of water by using treated sewage effluent instead of fresh water for irrigation and industrial purposes.
As a result of this strategy, and because people have become more aware of the value of water and are trying harder to conserve it, the council is experiencing a 25% saving.
“Although the dam will alleviate immediate water shortages, it is imperative that Cape Town residents continue to use water sparingly and that, in a relatively arid province, we continue to develop a culture of saving water,” Cape Town Alderman Clive Justus said in Franschoek last week.
South African first
The Berg River Dam was the first dam in South Africa to be designed, constructed and operated in accordance with the guidelines of the United Nations World Commission on Dams.
The concrete-faced, rock-fill dam, located in the upper reaches of the Berg River catchment area, is 250 metres above sea level. It consists of an embankment of rock mined from the river bed and surrounding area, with an impermeable 300mm layer of concrete on the upstream side. The dam wall is 68 metres high and 929 metres long.
The civil engineering and operational design of the dam and the downstream supplement ccheme was predicated on the need to maintain the ecological integrity of the river.
The operating rules provide for specific volumes of water to be released from the dam to maintain the flow and integrity of the Berg River downstream of the dam.
Supplement scheme
In addition to the dam itself, the project entails a supplement scheme located 10 kilometres downstream of the dam, alongside the Drakenstein (formerly Victor Verster) prison.
The function of the supplement scheme is to divert winter high flow, entering the Berg River from the Franschhoek, Wemmershoek and the Dwars River tributaries, to supplement water stored in the dam. Water from the scheme is pumped via the Drakenstein pump station, along a 9.5km pipeline, back up to the Berg River Dam.
Indigenous plants have been planted on the downstream face of the dam wall, which is visible from the main road into Franschhoek, ensuring that the dam and associated structures blend with the surrounding landscape.
At the start of the contract, the Working for Water Programme was awarded a R21-million, eight-year contract by Trans-Caledon Tunnel Authority to remove alien vegetation from the Berg River catchments, significantly increasing the amount of water available for storage in the dam and for indigenous plant species.
After completion, the dam was transferred from tunnel authority to the department, who operate and maintain it as part of their Western Cape water supply systemid.
Source: BuaNews
