A bit of Vaal Dam History

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.

The Lesotho Highlands Water Project feeds water into the system by gravity contributing to a stable supply of water to the people and industrial complex of Gauteng. This water is piped from Lesotho into the Liebenbergsvlei and Wilge Rivers.

The Sterkfontein Dam forms part of the Tugela-Vaal water transfer scheme for the interbasin transfer of water from the Thukela River in KwaZulu-Natal to boost the levels in the Vaal River System. Water from the Sterkfontein Dam is released once the Vaal Dam drops to below 16%.

The dam has its own island some 5 km (3 mi) long. The island was used as a secret meeting place by the apartheid government but now hosts the annual Round the Island Yacht race, a Guinness Book of World Records title of the largest inland yacht race.