Tunnel Drilling Marks Progress of Lesotho Highlands Water Project

Last week, government officials representing South Africa and Lesotho were at the Polihali construction site, in Mokhotlong, Lesotho, to unveil the Tunnel Boring Machine (TBM), a state-of-the-art tunnel boring machine that will drill the 38.5 km long tunnel connecting Polihali and Katse Dams. This is a significant milestone in Phase 2 of the Lesotho Highlands Water Project – a powerful symbol of progress as the project transition from preparation to full scale tunnelling along one of the region’s most ambitious water transfer routes. 

The first TBM was launched in Katse Dam in February 2025 and has started the tunnel drilling at the Katse site.

Measuring roughly 423 metres in length and featuring a 5.38-metre cutterhead and engineered to work continuously even in the toughest underground conditions, the two TBMs will excavate the belly of the Maluti mountains that will connect Polihali and Katse reservoirs, advancing simultaneously from each end of the alignment to create a tunnel.  

During this process, the machine will also install precast concrete lining segments, seamlessly transforming raw rock into a completed structure in one uninterrupted process.

Once completed, the Polihali Tunnel will facilitate the transfer of significantly larger volumes of water, thereby enhancing regional water security and bolstering hydropower generation in Lesotho.

The Polihali Tunnel is one of the major components of LHWP2 and currently under construction. Other components include an approximately 165m high concrete faced rockfill dam at Polihali downstream of the confluence of the Khubelu and Senqu-Orange Rivers and the 800 metres long Senqu Bridge, as well as other assorted infrastructure such as feeder roads, resettlement and environmental, social and public health programmes etc.

The LHWP aims to harness the Orange–Senqu River system through the construction of major dams and transfer tunnels in order to augment supply to South Africa’s water-stressed Integrated Vaal River System, thereby supporting the economic hub of Gauteng, while concurrently generating hydropower for Lesotho. Through the new Polihali reservoir, which will have the capacity of 2322 million cubic metres (mᵌ) of water storage, this phase will progressively increase the current water supply rate by adding 490 million mᵌ/a to the existing 780 million cubic metres per annum (mᵌ/a) to 1 270 billion mᵌ/a transferred to South Africa.  

For more about the Lesotho Highlands Water Project keep reading …