The Department of Water and Sanitation has put measures in place for the release of water from the Sterkfontein Dam into the Vaal Dam to augment water levels when it reaches 18% in volume.

The standard operating rule for releases of water from Sterkfontein into the Vaal Dam is when the Vaal Dam reaches 18% of its full supply capacity.

The department said the Vaal Dam is currently sitting at 28.2% and has been on the decrease by 1.5 to 2% weekly, due to climatic factors, including low inflows owing to the lack of rainfall in the Vaal catchment and elevated temperatures which have led to increased evaporation losses.

“The surface area of the Vaal Dam is wide and shallow and is therefore susceptible to high evaporation losses. Another cause for the drop in levels is due to low inflows into the Vaal Dam as a result of the Lesotho Highlands Water Project (LHWP) tunnel closure for planned maintenance work currently underway.

“The tunnel transfers 780 million cubic metres of water per annum into the Integrated Vaal River System (IVRS). However, there was a shortfall of 80 million cubic metres from the normal annual transfer volume this year due to the shutdown,” the department said in a statement.

An analysis conducted by the department to assess the risk of the IVRS performance due to the tunnel closure, indicated the impact of the outage on the overall IVRS will be insignificant considering that dams in the IVRS, including the Sterkfontein Dam and others, are relatively full.

“This means that the closure of the tunnel (from 01 October 2024 to 31 March 2025) for maintenance, will not result in any disruption of water supply to Rand Water, and to the municipalities in Gauteng and other provinces which are customers of Rand Water,” the department said.

The department said when the analysis was done in May 2024, there was a low probability for release from Sterkfontein Dam to augment the Vaal Dam.

The low risk was assessed at 5% and it was observed that the percentage probability has now materialised due to below normal rainfall and high evaporation rates.

The department has since issued a notice to water users and the public along the Nuwejaarspruit and Wilge Rivers of possible release of water from the Sterkfontein Dam and has advised the removal of movable equipment, including irrigation pumps and to also avoid low lying bridges by 15 December 2024.

The department explained it takes about three to four days for water released from Sterkfontein Dam to reach Vaal Dam.

Originally posted on SAnews.gov.za.