Underground tunneling works at the Lesotho Highlands Water Project (LHWP) site inside the two Polihali diversion tunnels are progressing well. Excavations of the outlets are reportedly advancing at a pace of about 6 meters a day per tunnel.
This will be followed by the tunnels’ concrete lining works that include concrete casting and reinforcement which have already started on tunnel one. Both tunnels’ intake and outlet portal drives have been reinforced with sprayed concrete and rock bolts, and preparatory works for the concrete inlet structure are also continuing.
The tunnels, one of which measures 7 meters in diameter and almost 1 kilometer in length while the second measures 9 meters in diameter and also almost 1 kilometer in length, run parallel to each other from the intake point to the outlet downstream of the Polihali dam.
Preparation for the construction of the Polihali dam
The tunnels are being excavated in advance of the construction of the Polihali dam in the second phase of the Lesotho Highlands Water Project in a bid to reduce the dam construction window.
The scope of the work for the Polihali dam according to the government of Lesotho mainly includes the construction of a concrete rockfill dam with a 165m wall. The Dam will be built downstream of the confluence of the Orange-Senqu and Khubelu Rivers in the Mokhotlong District of Lesotho. It will allow the formation of a reservoir on the Orange and Khubelu Rivers over an area of 5,053 hectares, with a total storage capacity of 2,325 million m³.
The dam will be supported by a saddle dam, which is an auxiliary reservoir built to confine the reservoir created by a primary dam, either to allow for higher water elevation and storage or to limit the extent of the reservoir in order to increase its yield.
Impoundment of the Polihali reservoir is expected to start in 2024, with water delivery planned to start in 2027.