Everything you need to know about the Gariep Dam

For desert dwellers and drought survivors, seeing the Gariep Dam brimming over as it did in April this year, is balm for the soul, attracting water tourists from across the country. Seeing it overflowing is just one reason why water tourists are flocking there. Here are a dozen more reasons why Gariep is our Mother Dam.

The Gariep Dam, named the Hendrik Verwoerd Dam until 1996, was built between 1966 and 1972. Part of the Orange River Project (ORP), this was the anchor project in the most ambitious hydro-engineering endeavour this country has seen.

A budget of R300 million was committed to the ambitious Orange River Project, and aspects of it were planned to unfold over 30 years.

The dam wall was built at Ruigte Valley, very close to where Dutch explorer and soldier Colonel Robert Gordon became the first European to see and name the Orange River back in 1777.

It contains nearly two million cubic metres of concrete and weighs around four and a half million metric tons, resting atop a thick, geological slab of ironstone, its graceful double convex curvature arch spreads the tremendous pressure of the water towards the rocky abutments.

Atop the spillway at the dam wall, you might notice the Roberts Splitters. These are deceptively simple but carefully engineered ‘teeth’ projecting over the crest of the dam wall. They help dissipate the kinetic energy of the overspill water, making it tumble back and forth instead of falling in a steady scouring sheet that could eventually erode the rock at the foot of the wall.

The splitters are named after a South African engineer, Lieutenant-Colonel DF Roberts, who came up with the design in 1936, long before this dam was built. They’ve been used on 23 dams in South Africa, including Gariep, Vaal, Loskop and Vanderkloof, and their use has spread to dams around the world.

While a predominantly French company was occupied with building the dam, an Italian company began the intake tower that would divert a quarter of the dam’s water to the dry Eastern Cape Karoo’s fertile ground via a tunnel to the Teebus Spruit, Great Brak River and, finally, the Great Fish.

The 82,5 kilometre Orange-Fish Tunnel held the record for the world’s longest underground water aqueduct until fairly recently. It is now third on the honour roll. (COUNTRY LIFE featured an article on this engineering marvel in July 2017).

Thanks to the new constancy of river water flowing into a seasonally dry Great Fish from 1976, thousands of new farms and jobs were created. But that’s not all.

A secondary series of weirs, canals and smaller aqueducts guide the Gariep’s waters down to Somerset East and the Little Fish River to the Sundays River and onto the massive citrus orchards near Kirkwood and Addo, as well as dams for Port Elizabeth’s drinking water.

Four hydropower turbines at Gariep contribute 360 megawatts to the grid, enough to power 70 000 households.

British soldiers guarding the old blockhouse in 1914.

WORDS Julienne Du Toit

PHOTOGRAPHY Chris Marais

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