Six-month planned maintenance of the Lesotho Highlands Tunnel

Water users of the Vaal River System have been reminded about the upcoming six-month closure of the Lesotho Highlands Tunnel for planned maintenance work.

The planned maintenance work on the transfer and delivery tunnels of the Lesotho Highlands Water Project (LHWP) is scheduled to start from 1 October 2024 to 31 March 2025.

The tunnel system consists of a Transfer Tunnel, linking Katse Dam with Muela Power Station and Muela Dam, and a Delivery Tunnel, linking Muela Dam with the Ash River Outfall Works between Clarens and Bethlehem.

The Department of Water and Sanitation said the inspections and maintenance of the tunnels are conducted at intervals not shorter than five years and not exceeding 10 years. 

“The last maintenance was conducted in 2019. During the shutdown of 2019 it was found that the steel liners in the tunnel urgently need extensive maintenance on both the Republic of South Africa and Lesotho side,” the department said. 

It noted that this process cannot be done in a shorter period than six months. 

The planned maintenance work is being overseen by the Lesotho Highlands Water Commission, a joint governance body between South Africa and Lesotho and will be jointly undertaken by the Lesotho Highlands Development Agency (LHDA) and the Trans Caledon Tunnel Authority (TCTA). 

The work required to be undertaken during the period includes grit-blasting the steel-lined section around the entire circumference and re-applying corrosion protection on the tunnel lining, as well as other maintenance and repair work identified during the 2019 maintenance shutdown. 

The work to be undertaken requires lot of time as it is expected to protect the infrastructure for another 20-30 years. 

“This much-needed maintenance is critical to maintain the integrity of the delivery tunnels as a tunnel failure will risk the transfer of the 780 million m3/annum to the Integrated Vaal River System (IVRS), from which Rand Water draws water to supply its customers. The six months period required to conduct maintenance is thus crucial to avoid any catastrophic event which may result from lack of maintenance,” the department explained.

As a result of the tunnel shutdown, the department said 700 million m3 per annum will be transferred in 2024, and only a shortfall of 80 million m3 from the annual transfer volume will be impacted.

“After the shutdown period, the water transfers will be increased to enable the shortfall in transfers to be recovered. It must be noted that for the IVRS, transferring the full volume (780 million m3) on an annual basis from Lesotho (regardless of the status of the IVRS) does not yield the most efficient use of the system yield,” the department said. 

An analysis was undertaken in May 2023 to assess the risk to the IVRS’ performance because of the outage and to determine the impact of the shutdown on water availability to users in South Africa. 

The results showed that 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. 

The standard operating rule is that Sterkfontein Dam releases water to the Vaal Dam when the Vaal Dam reaches a minimum operating level of 18%. 

The department’s analysis indicates that this is unlikely to occur at any probability level in the 2023-2024 operating year (1 May – 31 April). 

The department said further analysis will be undertaken in May 2024 to ensure that there are also no likely risks to water supply from the IVRS in the 2024-2025 operating year. 

However, the department warned that the shutdown will have implications of water supply to users along the Liebenbergsvlei River and its tributaries during that period, as the river directly receives outflows from the tunnel. 

“The towns of Bethlehem, Reitz, and Tweeling as well as licensed irrigators will be affected. The reason for these users being affected is that there will be a significantly reduced amount of water in the Liebenbergsvlei River and its tributaries, from which these users draw their water. 

“In order to secure water during the shutdown for these local users, the Saulspoort Dam will be filled up at the commencement of the shutdown period. DWS analysis indicates that a full Saulspoort Dam will be able to provide water for local requirements including those of Bethlehem, Reitz, and Tweeling for a period of up to nine months which is more than the six months tunnel outage,” the department said. – SAnews.gov.za