The Civil Engineering Contractor July 2019

INFRA AFRICA The project is taking place in a pristine part of the Lesotho Highlands. LHWP II diversion tunnels construction underway The Lesotho Highlands Development Authority (LHDA) has awarded the R517-million contract for the construction of the Polihali diversion tunnels to SCLC Polihali Diversion Tunnel Joint Venture, marking another significant step in the implementation of Phase II of the Lesotho Highlands Water Project (LHWP). The contractor has been on site since April with the works expected to be completed in approximately 18 months. The project cost is estimated at R517-million. The SCLC Polihali Diversion Tunnel JV combines international, South African and Lesotho expertise: Salini Impregilo S.p.A (South African branch), Cooperativa Muratori Cementistri CMC di Ravenna (South African branch), LSP Construction (Lesotho) and CMI Infrastructure (South Africa). “The diversion tunnels are essential to facilitate the construction of the Polihali Dam. Their construction is an important element of the advance infrastructure works which started towards the end of 2018 with the awarding of the contracts for the Polihali North East Access road and the civils work at Katse and Mokhotlong. The advance infrastructure will largely be completed prior to commencement of construction of the Polihali dam and the Polihali to Katse water transfer tunnel,” says Tente Tente, the LHDA’s Divisional Manager, Phase II. Diversion tunnels divert water away from the natural river bed to create a dry foundation and work area needed for the construction of a dam. Their construction usually goes along with the building of cofferdams, one upstream and one 10 | CEC July 2019 downstream of the proposed dam, which together allow the river flow to bypass the dam foundation area. In the case of the Polihali Dam, two diversion tunnels will be constructed to divert the waters of the Senqu River. Building 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 7m in diameter and almost a kilometre in length, and the second, 9m in diameter and also almost a kilometre long, run parallel to each other from the intake point to the outlet downstream of the dam. The tunnels will be excavated by drill and blast method, and will be supported by rockbolts and shotcrete as required. The Metsi a Senqu-Khubelu Consultants Joint Venture (MSKC) which also includes a number of South African and Lesotho-based firms such as Aurecon (SA), Knight Piesold (SA), Hatch Goba (SA), SMEC (SA) and FM Associates (Lesotho), has designed the diversion tunnels and will also supervise the construction work. The LHWP delivers water to the Gauteng region of South Africa and utilises the water delivery system to generate hydro-electricity for Lesotho. Phase II will increase the current supply rate of 780 million m 3 /year incrementally to more than 1 270 million m 3 /year. At the same time, it will increase the quantity of electricity generated in Lesotho and is a further step in the process of securing an independent electricity source to meet Lesotho’s domestic requirements. nn www.civilsonline.co.za

The Civil Engineering Contractor July 2019 | Page 12