The outlet tunnel is 9.25m high, 6m wide and just under 500m long. Excavation of the top heading of the tunnel – the upper portion of the tunnel in cross-section – by drill and blast started earlier this year and advanced at approximately 2.4m per day.
The excavation of the bottom heading of the tunnel is expected to be completed in the next five weeks.
The bottom outlet tunnel will carry compensation water permanently to downstream users and generate hydroelectricity.
Ultimately, the Polihali Dam will create a 5,053ha reservoir on the Senqu and Khubelu rivers at full supply level and add 2.325 million m3 in storage capacity to the Lesotho Highlands Water Project.
