The Department of Water and Sanitation (DWS) has put measures in place for the release of water from the Sterkfontein Dam into the Vaal Dam to augment its 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 dam is currently sitting at 28.2% and has been on the decrease by 1.5 to 2% weekly primarily due to climatic factors including low inflows owing to lack of rainfall in the Vaal catchment and elevated temperatures which have led to increased evaporation losses. The surface area of 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 m3 from the normal annual transfer volume this year due to the shutdown.

The DWS analysis conducted to assess the risk of the IVRS performance as a result of the tunnel closure for duration of six months, from 01 Oct 2024 to 31 March 2025. The results of the analysis indicated the impact of the outage on the overall IVRS will be insignificant considering that dams in the IVRS such as the Sterkfontein Dam and others are relatively full. This means that the closure of the tunnel 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.

Water Releases from Sterkfontein to Vaal Dam

When the analysis was done in May 2024 there was a low probability for release from Sterkfontein Dam to augment Vaal Dam. This low risk was assessed at 5%. It is currently observed that this 5% probability has now materialised due to below normal rainfall and high evaporation rates.

Accordingly, the Department has since issued a notice to water users and the general public along the Nuwejaarspruit and Wilge rivers of possible release of water from Sterkfontein

Dam and has advised for removal of movable equipment such as irrigation pumps and to also avoid low lying bridges by 15 December 2024. It takes about three to four days for water released from Sterkfontein Dam to reach Vaal Dam.

The Lesotho Highlands Water Project Tunnel maintenance currently underway

The maintenance and the refurbishment of the LHWP Tunnel is still ongoing since its closure on 01 October 2024, and the repair work is on schedule.

The Trans Caledon Tunnel Authority (TCTA) is responsible for the maintenance work in South Africa while Lesotho Highlands Development Agency (LHDA) is focusing on the transfer tunnels at the Muela Hydro power station in Lesotho.

The DWS is monitoring the progress of the maintenance repair work and is satisfied that it will be completed within the scheduled time of six months.

The Department is also monitoring water supply to communities under local municipalities of Dihlabeng, Nketoane and Mafube, which are along the Liebenbergsvlei River and Wilge River. These municipalities benefit directly from the Lesotho Highlands Water Project (LHWP) and have adversely been affected since the tunnel closure.

Some towns in Setsoto and Mantsopa Municipalities in the Free State normally abstract water from Caledon River, while others abstract from the Vaal River and Rhenoster River. These municipalities benefit indirectly from the LHWP and the Department is also monitoring water supply to communities within these municipalities.

The Department has embarked on relief intervention programmes for the municipalities which includes the upgrading of water treatment works, upgrading of raw water pumps, upgrading of abstraction works, the construction of new reservoirs as well as the development of groundwater resources by drilling and equipping boreholes.

All of these projects are underway and are critical in ensuring sustainable water supply to communities during the tunnel system shutdown.

Municipalities had to implement water restrictions especially to regulate irrigation in their area of operation for the duration of the closure. The Department also Gazetted water usage by farmers in the area from 1 October till 31 March 2025, which stipulates that water users on the left bank of the Ash and the Liebenbergsvlei rivers may abstract water for agricultural purposes from 06:00 to 06:00 on Monday, Tuesday and Wednesday. On the right bank of the Ash and the Liebenbergsvlei rivers abstraction of water may be from 06:00 to 06:00 on Wednesday, Thursday and Friday.

These restrictions are necessary to ensure that there is enough water during the closure of the tunnel.

The DWS, together with the affected municipalities continues to engage with the communities through public education programmes, with the aim of encouraging responsible water usage and water conservation, particularly during the time of a tunnel closure.

For more information, contact 
Wisane Mavasa, Spokesperson for the Department of Water and Sanitation 
Cell: 060 561 8935 
E-mail: mavasaw@dws.gov.za

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