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Until work started on the Gariep Dam in 1966, Pongolapoort was the largest dam under construction in South Africa. It is a medium thin, double curvature arch dam with a gradual transition towards a gravity thrust block on the left flank. It has a maximum height of 89 m and a crest length of 515 m. The dam has a controlled and an uncontrolled spillway. The gross capacity of the reservoir is 2 500 million m3, which is more than twice the mean annual runoff. The chute spillways have a combined capacity of 2 010 m3 at high flood level. The thickness of the wall above the cushion is 18,3 m tapering to 8,2 m at the spillway and then flowing to 11 m to carry a road across it. (Ref: The Water Wheel May/June 2009)