Polihali tunnel completion marks LHWP milestone
After seven months of tunnelling on the Polihali transfer tunnel construction site, the Lesotho Highlands Development Authority (LHDA) has achieved the successful breakthrough of the upper intake tunnel into the lower intake tunnel.
The successful completion of the intake tunnels brings the LHDA one step closer to realising the full potential of the Polihali dam: boosting water transfers to South Africa, increasing the volume of hydropower generated in Lesotho, enhancing the livelihoods of Basotho and contributing to the economies of Lesotho and South Africa.
The intake tunnels will allow water from the 5 042 ha Polihali reservoir to enter the transfer tunnel for delivery to the Katse reservoir, the centre point of the Lesotho Highlands Water Project.
The authority will now embark on the next two critical phases of the project, including the safe start of the impoundment of the Polihali reservoir, made possible by the collapse of the upper tunnel into the lower one.
The process allows for a controlled and secure increase in water levels up to the lower tunnel, which can then be temporarily sealed.
The second phase enables continuous debris removal from the remaining tunnel works.
As construction progresses towards its connection with the access adit, debris can be efficiently cleared through the upper intake tunnel without interrupting the impoundment process, the LHDA said in a statement to Engineering News & Mining Weekly.
“This efficient operation is crucial for maintaining project momentum while ensuring the structural integrity of the tunnels.”
Key milestones in the Polihali transfer tunnel works include the excavation of the 450 m long tunnel, which started on January 16 and was completed on August 19; the completion of the 370-m-long lower intake tunnel on August 5 and the ongoing excavation of the connecting tunnel.
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