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GROOTDRAAI DAM

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Grootdraai Dam is situated in the upper reaches of the Vaal River less than 10km upstream of Standerton. It has a catchment area of 8 195km², a mean annual precipitation of approximately 750mm, a mean annual potential evaporation at the dam site of 1 400mm and a natural inflow of 580 million m³/a. The full supply capacity of the reservoir is 364 million m³, making it a 0.7 MAR dam.

Grootdraai Dam is a composite structure comprising a central concrete gravity section 360m long and two earthfill flanks giving a total crest length of 2 180m and a maximum wall height of 42m above lowest foundation level. The dam was completed in 1982 and was built primarily to support the water needs of the SASOL I, II and III coal to petrol plants at Secunda, ESKOM's, Tutuka Power Station as well as the Matla, Duvha, Kendal and Kriel power stations located on the coal fields in the adjacent Olifants River basin.

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The dam also provides some flood attenuation for Standerton and stores up to 100 million m³/annum pumped into the upper reaches of the Vaal River basin from Heyshope Dam in the Usutu basin.

During the serious drought of 1983, the water resources in the adjacent Komati and Usutu basins were badly depleted, leading to serious concerns that the water supplies to various power stations could be affected. Any water shortages to the power stations would be disastrous for South Africa since 80% of the country's electricity is dependent on water from the Komati-Usutu-Vaal system. It was estimated that the newly completed (1982) Grootdraai Dam would empty within a matter of months and an emergency scheme was therefore initiated to pump water upstream over a distance of 202km to Grootdraai Dam from Vaal Dam. The emergency scheme involved constructing 7 weirs, each with numerous pumps capable of pumping a total of 1 million m³/day. Although the emergency scheme was never used, it was completed and received an award for the Most Outstanding Civil Engineering Achievement of 1983 from the South African Institute of Civil Engineers.