Bereng Mpaki
OPERATIONS at the Polihali Dam construction site recently kicked off with the excavation for two diversion tunnels.
The two tunnels will divert the water from the Senqu River away from the natural river bed creating a dry foundation and work area needed for the construction of the Polihali Dam.
The works are part of the Lesotho Highlands Water Project (LHWP) Phase II advance infrastructure. The works had temporarily been suspended during the Covid-19 lockdown period which ran from 30 March to 19 May 2020.
According to the Lesotho Highlands Development Authority (LHDA) chief executive officer, Tente Tente, the resumption of the advance infrastructure works will be gradually increased based on the lifting of travel restrictions and meeting of Covid-19 safety precautions by contractors.
Mr Tente said the construction of the two diversion tunnels was an important element of advance infrastructure works of phase II of the LHWP.
Phase II builds on the successful completion of Phase I in 2003. It delivers water to the Gauteng region of South Africa and utilises the water delivery system to generate electricity for Lesotho. Phase II will increase the current supply rate of 780 million cubic metres per annum incrementally to more than 1 270 million cubic metres per annum.
At the same time, it will increase the quantity of electricity generated at the Muela Hydropower Station. This is expected to help Lesotho produce adequate electricity to cater for its domestic requirement.
“We are pleased to see construction works restarting, including the work on the diversion tunnels,” Mr Tente said.
“However, particularly at this time, the LHDA’s priority is the safety of its employees and the project-affected communities. Full resumption of the Phase II advance infrastructure construction works and the projects social and environmental programmes will be incremental as consultants and constrictors meet their Covid-19 mitigation obligations and travel restrictions are lifted.”
He said the diversion tunnels would take about 18 months to complete.
“Building the two tunnels will increase the capacity to carry floods and will provide flexibility to work in one tunnel while the river flows in the other one. The tunnels, one seven metres in diameter and almost a kilometre in length, and the second, nine metres in diameter and similar length, run parallel to each other from the intake point to the outlet downstream of the dam. They will be excavated by drill and blast method, and will be supported by rock bolts and shotcrete as required.”
The SCLC Polihali Diversion Tunnel Joint Venture was awarded the diversion tunnel construction contract in April 2019. It comprises South African and Lesotho expertise; Salini Impregilo S.p.a (South African branch), Cooperativa Muratori Cementistri CMC di Ravenna (South African branch) and LSP Construction (Pty) Ltd.
The tunnels were designed by the Metsi a Senqu-Khubelu Consultants Joints Venture (MSKC), which also includes a number of South African and Lesotho-based firms, Aurecon (SA), Knight Piesold (SA), Hatch Goba (SA), SMEC (SA) and FM Associates (Lesotho). The joint venture is also supervising the construction work.
