Lesotho Highlands tunnel ‘good for 25 more years’

The tunnel is critical to delivering water from Lesotho to South Africa. 

The 38-kilometre tunnel, part of a vital regional water transfer system, was shut down in October for structural maintenance. 

Water flow to South Africa was temporarily suspended to allow for detailed assessments and repairs to the tunnel’s ageing steel lining.

Following months of work by engineering teams and contractors, the Department of Water and Sanitation expressed confidence in the tunnel’s lifespan. 

The tunnel officially reopened on Sunday.

"We used 43,000 litres of paint to recoat this steel. That’s 19,000 square metres of steel that we had to sandblast, clean, repaint and test before we could allow the water to run," said Teboho Nkhahle, South Africa’s project representative. 

"One thing we can assure you is that this steel is going to last another 25 years.”

The tunnel was first commissioned in 1998 and underwent maintenance in 2003 and 2012. 

The latest round was the most extensive to date, involving over 2,200 tonnes of sand for sandblasting and paintwork on more than two kilometres of steel lining.

Nkhahle detailed the scale and difficulty of the operation, noting that some sections of the tunnel posed physical and environmental challenges.

"There was an area inside the bypass, for instance, where they have this butterfly valve, where you had to crawl underneath. Literally crawl on our knees.

"The sandblasting equipment had to be carried into confined spaces, with some sections only about two metres wide."

Environmental conditions during Lesotho’s summer months, including high humidity, low tunnel temperatures, and frequent rainfall, also hindered work.

"For the paint to dry, you need the humidity below 80%. Many times, the moist air was coming into the tunnel, making it difficult for the paint to cure. Inside the tunnel, temperatures were so low they fell below the dew point — difficult to work in," Nkhahle explained.

In addition to weather, the project faced delays due to contract negotiations, labour issues, and community-related concerns, ultimately pushing the completion beyond the original 30 March deadline.

Despite the setbacks, the department hailed the operation as a success and confirmed that future maintenance will occur every five years, with the next shutdown scheduled for 2030.

The tunnel feeds into the Vaal River Integrated System, a key water source for five South African provinces. 

The refurbishment secures continued water delivery and reflects the importance of infrastructure resilience in an era of growing climate and supply pressures.

"We are here, the water is running — so we have delivered, finally," Nkhahle said.

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