R1.5bil Berg River Dam to supply 20% of Cape Town's water

Friday, March 6, 2009

Franshoek - The R1.5 billion Berg River Dam, opened on Thursday, is expected to augment Cape Town's water supply by almost 20 percent.

The project, which was opened by President Kgalema Motlanthe, is a significant triumph for stakeholders who were able to complete it on time and within budget.

Alderman Clive Justus, Mayoral Committee Member for the Utility Services Portfolio, which includes the Water and Sanitation Department, said the project would increase Cape Town's total water supply from 668 to 898 million cubic metres per year.

Central to the success of the project, was the partnership between the Department of Water Affairs and Forestry, the City of Cape Town and the Trans-Caledon Tunnel Authority (TCTA).

The project comprises the dam with a storage capacity of 130 million cubic metres, a supplement scheme, two pump stations and 12km of pipeline. It started storing water in July 2007 and, a year later, was full, due to good rainfall.

The concrete-faced, rock-fill dam, 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 conditional go-ahead for the project from department was dependent on the city reducing its water demand by 20 percent.

In response it implemented a water conservation and Water Demand Strategy which is 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 percent saving, Mr Justus said.

"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."

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 civil engineering and operational design of the dam and the downstream Supplement Scheme 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.

In accordance with the National Water Policy, which stipulates that, where possible the end user should pay for the development of water infrastructure, the city pays a raw water tariff.

The tariff, paid to the department, is used by the TCTA to repay loans secured through local and international financial institutions to fund the project.

In addition to the dam itself, the project entails a Supplement Scheme located 10km 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 flora has been planted on the downstream face of the dam wall which is visible from the main road into Franschhoek. This ensures that the dam and associated structures will blend with the surrounding landscape and thus be environmentally friendly.

At the start of the contract, the Working for Water Programme was awarded a R21 million, eight-year contract by TCTA to remove alien vegetation from the Berg River catchments. This significantly increased the amount of water available, for storage in the dam and for indigenous plant species.

After completion, the dam was transferred from TCTA to the department, who operate, and maintain it as part of their Western Cape water supply system, Mr Justus said.