Vaal dam
| Vaal Dam | |
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 Location of Vaal Dam in South Africa
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| Official name | Vaal Dam |
| Country | South Africa |
| Location | Border Gauteng and Free State |
| Coordinates | 26°53′41″S 28°08′44″E / 26.89472°S 28.14555°ECoordinates: 26°53′41″S 28°08′44″E / 26.89472°S 28.14555°E |
| Purpose | Domestic and industrial water |
| Opening date | 1938 |
| Owner(s) | Dept of Water Affairs |
| Dam and spillways | |
| Type of dam | Gravity dam |
| Impounds | Vaal River |
| Height | 54.2 m |
| Reservoir | |
| Creates | Vaal Dam |
| Total capacity | 2,609,799,000 cubic metres (9.21642×1010 cu ft) |
| Surface area | 320 square kilometres (120 sq mi) |
 Vaal Dam from the South African Department of Water Affairs
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Vaal Dam from the Department of Water Affairs
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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.
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 (3.51×1010 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).
The dam was subsequently raised in the early fifties to a height of 60.3 metres (198 ft) which increased the capacity to 2,188,000,000 cubic metres (7.73×1010 cu ft). A second raising took place in 1985 when the wall was raised by a further 3.05 metres (10.0 ft) to 63.4 metres (208 ft) above lowest foundation. The capacity of the dam is currently 2,609,799,000 cubic metres (9.21642×1010 cu ft) and a further 663,000,000 cubic metres (2.34×1010 cu ft) or 26% can be stored temporarily for flood attenuation.
The flood attenuation properties of the dam were severely tested in February 1996 when the largest flood ever recorded at the Vaal Dam site was experienced. An inflow of over 4,700 cubic metres per second (170,000 cu ft/s) was measured into the Vaal Dam which was already at full capacity due to good rains and it was only through the expert management of the Hydrology staff at DWAF that the maximum flood released from the dam was limited to 2,300 cubic metres per second (81,000 cu ft/s). Flows above 2,300 cubic metres per second (81,000 cu ft/s) would have caused serious damage downstream of Vaal Dam and the situation during the 1996 flood became extremely tense as the storage in the reservoir peaked at 118.5% of Full Supply Capacity on 19 February 1996 i.e. only 194,000,000 cubic metres (6.9×109 cu ft) of flood absorption capacity remained before the full inflow would have been released causing massive damage.
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Wikipedia