<Tr> <Th> Total capacity </Th> <Td> 2,609,799,000 cubic metres (9.21642 × 10 cu ft) </Td> </Tr> <Tr> <Th> Surface area </Th> <Td> 320 square kilometres (120 sq mi) </Td> </Tr> <P> The Vaal Dam in South Africa was constructed in 1938 and lies 77 km south of OR Tambo International Airport . The lake behind the dam wall has a surface area of about 320 square kilometres (120 sq mi) and is 47 meters deep . The Vaal Dam lies on the Vaal River, which is one of South Africa's strongest - flowing rivers . Other rivers flowing into the dam are the Wilge River, Klip River, Molspruit and Grootspruit . It has over 800 kilometres (500 mi) of shoreline and is South Africa's second biggest dam by area and the fourth largest by volume . </P> <P> The construction of Vaal Dam started during the depression of the early thirties and the dam was completed in 1938 with a wall height of 54.2 metres (178 ft) above lowest foundation and a full supply capacity of 994,000,000 cubic metres (3.51 × 10 cu ft). The dam is a concrete gravity structure with an earthfill section on the right flank . It was built as a joint venture by Rand Water and the Department of Irrigation (now known as the Department of Water Affairs). </P>

Where does the vaal dam get its water from