Phase 1A of the Lesotho Highlands Water Project includes the Katse and Muela Dams, a 45km Transfer Tunnel from Katse Intake Tower to the Muela Hydropower Station, which generates hydroelectric power for Lesotho, and a 37km Delivery Tunnel from Muela to Ash River outfall in Clarens, South Africa. This phase of the project (Phase 1A) was commissioned in 1988. Phase 1B consists of the Mohale Dam, a 32km Transfer Tunnel interconnecting the Mohale and the Katse reservoirs, the Matsoku Diversion Weir and 5.7km Tunnel from the Matsoku Diversion Weir to the Katse Reservoir; Phase 1B was commissioned in 2002.

The first Outage and inspection of the Transfer Tunnel was carried out in 2012, and second inspection and maintenance was carried out in October and November 2019. During this second outage inspection of the main tunnels was carried out together with inspection and repair of the hydro-mechanical equipment.

David accompanied the Lesotho team  which included members of the Lesotho Highlands Water Commission and members of the Operations and Maintenance from the Lesotho Highlands Development Authority.The team entered the Transfer Tunnel via the Muela Hydropower Station bypass on the morning of 8th October and travelled by inspection vehicles approximately 15km to exit at Hlotse adit.

On day 2 the team re-entered the Hlotse adit and exited at the Katse Intake Tower. The transfers Tunnel is excavated in Basalt and is lined with a cast in-situ concrete lining throughout with some sections of steel lining; the inspection found the Transfer Tunnel to be in good condition after more than twenty years of operation. 

On day 3 the team entered the Delivery Tunnel South via the Hololo adit and inspected over 15km of the tunnel to the Caledon South adit. The Delivery Tunnel is excavated in Sandstone and is only partially lined. Typically the tunnel is unlined open bore with occasional rockbolts with cast in-situ lining installed at major faults and joints. A steel lined syphon section traverses the Hololo, Ngoajane and Caledon Rivers. Again no major problems were identified during the inspection and upon refilling it is expected that the next inspection will not be required for another ten years.