GARIEP DAM

The Gariep Dam (formerly known as the Hendrik Verwoerd Dam) forms the largest storage reservoir on South Africa with a total storage of approximately 5 500 million m3 and a surface area of more than 370 km2 when full. The dam is the central structure of the original Orange River Project which involves the supply of water to parts of the Vaal, Fish and Sundays catchments as well as to irrigation along the Orange river itself.

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Water from the Gariep Dam is released downstream into the Vanderkloof Dam through four generators which are each capable of producing 90 MW of electricity at a flow rate of approximately 200 m3/s. The hydro-power plant can therefore provide up to 360 MW of electricity at a flow rate of 800 m3/s.

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The Gariep Dam is 88m high (90.5m above foundation level), with a crest length of 914m and contains approximately 1.73 million m3 of concrete. It is situated in a gorge at the entrance to Ruigte Valley some 5km east of Norvalspont. It is a combined gravity and arch dam built entirely of concrete. Since the gorge at the dam site is too wide to allow a complete arch, only the central portion is arched. The two concrete flank walls were needed to form artificial gravity abutments for the main arch. The dam is a double curvature structure i.e. it is shaped like an egg shell making it one of the most impressive and aesthetically appealing dams in South Africa.

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The dam wall incorporates two huge outlet structures on the upstream side of the wall. The one on the left flank supplies water under pressure to the hydro-electric power station while both can be used for controlled release of water into the river. There are also six enormous radial gates, three on each side of the dam which form a striking feature of the dam. These gates are used to discharge floodwaters into six concrete chutes which lead the water away from the base of the dam wall into the downstream flow of the river. In this manner the risk of erosion to the base of the dam wall is minimised. The radial gates are rubber sealed and faced with stainless steel which provide a life expectancy of three centuries - well in excess of the design life of the dam itself.

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Gariep Dam was the first dam where the construction was put out to tender by the DWAF who had previously planned, designed and constructed all major water works commissioned in South Africa. The tender was awarded to Union Corporation/Dumez Borie Dams in 1966 and it was commissioned in 1971.

Water from the Gariep Dam is transferred to the Fish and Sundays basins via the Orange/Fish Tunnel which was until recently the longest continuous water transfer tunnel in the world with a length of more than 82km.