THE Lesotho Highlands Development Authority (LHDA) has awarded SCLC Polihali Diversion Tunnel Joint Venture a M517 million contract for the construction of the Polihali diversion tunnels under Phase II of the Lesotho Highlands Water Project (LHWP).
The LHDA this week told the Lesotho Times that the diversion tunnels are part of the advance infrastructure works which also include the construction of roads ahead of the construction of the Polihali Dam.
The LHDA further said that the awarding of the contract for the construction of the Polihali diversion tunnels “marks another significant step in the implementation of Phase II of the LHWP”.
The LHWP is a multi-phase, bi-national initiative established by a 1986 Treaty between Maseru and Pretoria. It involves the construction of dams and water-transfer tunnels in the two neighbouring nations and the generation of hydro-electric power in Lesotho.
South Africa seeks to augment its water-supply for both domestic and industrial use through the project while Lesotho expects to benefit from infrastructure such as roads as well as royalties and electricity from the initiative.
Phase I of the LHWP, consisting of the Katse and Mohale dams, the ‘Muela hydropower station and associated tunnels was completed in 2003 and inaugurated in 2004. Phase II of the LHWP is currently in progress. It consists of two separate but related components: water transfer and hydropower generation.
The bilateral project which is estimated to cost at least M23 billion, is expected to provide about 3000 jobs at the peak of its operations.
The water transfer component of Phase II comprises an approximately 165m high concrete faced rock fill Dam at Polihali downstream of the confluence of the Khubelu and Senqu (Orange) Rivers and an approximately 38km long concrete-lined gravity tunnel connecting the Polihali reservoir to the Katse reservoir.
Other Phase II activities include advance infrastructure (roads, accommodation, power lines and telecommunication) and the implementation of environmental and social mitigating measures.
The hydropower component of Phase II, which is currently under further feasibility studies, may include a pumped storage scheme, conventional hydropower such as the expansion of the ‘Muela infrastructure or new greenfield sites.
Its exact form will be determined on completion of the further feasibility studies. Phase II is expected to be substantially complete by the end of 2024.
The LHDA is the implementing and management authority of the LHWP on behalf of Lesotho, while in South Africa, the project is governed by the Trans-Caledon Tunnel Authority.
This week, the LHDA told this publication that “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.
“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 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 seven metres in diameter and almost a kilometre in length, and the second, nine metres in diameter and almost a kilometre long, run parallel to each other from the intake point to the outlet downstream of the (Polihali) dam.”
The LHDA further said that the contractor (SCLC Polihali) would be on site before the end of this month and the work is expected to be completed in 18 months.
The SCLC Polihali Diversion Tunnel Joint Venture comprises of the following local and South African companies: Salini Impregilo, Cooperativa Muratori Cementistri CMC di Ravenna, CMI Infrastructure Ltd (all South Africa) and LSP Construction (Pty) Ltd. (Lesotho).
The Metsi a Senqu-Khubelu Consultants Joint Venture (MSKC), which includes Aurecon, Knight Piesold, Hatch Goba, SMEC (all South African companies) and FM Associates (Lesotho), designed the diversion tunnels and will also supervise the construction work.