Excavated by drill and blast and supported by rockbolts and shotcrete, the tunnels will run parallel to each other from the intake point to the outlet downstream of the dam. Both will be around 1km long but have different diameters – one 7m, the other 9m.

SCLC Polihali Diversion Tunnel Joint Venture – comprising Salini Impregilo, CMC di Ravenna, LSP Construction and CMI Infrastructure – was awarded the construction contract in April 2019. According to Lesotho Highlands Development Authority, the tunnels will take around 18 months to complete.