Lesotho Highlands Tunnel to close for maintenance

The works is scheduled to run for six months, from October to March next year.

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.

Tunnel inspections and maintenance are conducted every 5-10 years. The Department of Water and Sanitation said during the last work, in 2019, the steel liners in the tunnel urgently need extensive maintenance on both the Republic of South Africa and Lesotho side.

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

The work will include 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 maintenance 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, from which Rand Water draws water to supply its customers,” the department said.

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

“After the shutdown period, the water transfers will be increased to enable the shortfall in transfers to be recovered,” the department said. 

To secure water supply for users along the Liebenbergsvlei River and its tributaries, which receive outflows directly from the tunnel, the department will fill a reservoir at the start of the shutdown.