Engineering and environmental consulting firm Jeffares & Green’s (J&G’s) geotechnical division, in association with Lesotho-based consulting firm GWC Consulting Engineers, has been appointed to undertake the supervision of the geotechnical investigations for the Polihali dam and a 38.2 km transfer tunnel to the Katse dam, which form part of Phase 2 of the Lesotho Highlands Water Project (LHWP).
The construction of the dam and tunnel is expected to start towards the end of 2018, with water delivery and hydroelectricity generation expected to begin in 2024.
With Phase 2 still in the early stages, the 2015/16 focus of implementing authorities the Lesotho Highlands Development Authority and the Trans-Caledon Tunnel Authority will be on the procurement of consultants and contractors, such as J&G and GWC Consulting Engineers, for the advance infrastructure works and the main works of the water transfer component of the project.
The format and location of the hydroelectricity component of the project are to be confirmed pending the outcome of further feasibility studies, notes J&G, adding that the volume of work in Lesotho has been such that it has now registered an office in Maseru.
J&G’s geotechnical investigations will involve rock and soil extraction for testing purposes to provide comprehensive data for the dam and tunnel design consultants. The investigations will also identify the suitability, quality and quantity of construction material found at all investigated quarries.
The LHWP is a binational project being undertaken by the governments of South Africa and Lesotho. It is a multiphased project with the objective of transferring up to 70 m3/s of water from the Senqu river, in Lesotho, to the Vaal river, in Gauteng, South Africa, while using the water delivery system to generate hydroelectric power for Lesotho.
Phase 1 of the project, which was completed in 2004, was funded by a large number of cofinanciers, including South African money markets, multilateral agencies, export credit-backed commercial loans, and contributions from the governments of South Africa and Lesotho.
The World Bank’s involvement provided comfort for other lenders and assisted both countries’ governments by providing a monitoring and evaluation role. The first phase comprised the construction of two dams – Katse and Mohale – a hydropower station, an interconnecting tunnel between the dams and a delivery tunnel into South Africa.
Lesotho Lowlands Project
An increase in population numbers in the Lesotho Lowlands – which include the more populous, less mountainous western and southern third of the country, including the capital, Maseru – compounded by industrial development, has been putting pressure on the area’s limited groundwater and the available river-flow extractions.
J&G collaborated with UK-based consulting company Parkman in 2002 to undertake a feasibility study on how to improve the area’s bulk potable supply system. Completed in 2004, the study recognised that, in addition to constructing the Metolong dam as part of the LHWP, river-extraction systems should also be established to serve the Lowlands areas. This gave rise to the Lowlands Bulk Water Supply Scheme, with the Lowlands divided roughly into eight supply zones based on catchment areas.
In 2009, the Metolong Programme Implementation Unit signed a contract with the Lesotho Waterworks Joint Venture (LWJV) to undertake the master planning, detailed design, tender documentation, procurement and construction supervision for Phase 2 of the advanced infrastructure programme required to serve the Metolong dam, water treatment works and conveyance system works.
The LWJV comprised J&G, SSI Engineers & Environmental Consultants (DHV Netherlands), and GWC Consulting Engineers, of Lesotho. The project work was divided among the firms with shared responsibility for the design of river intakes, water-treatment works, pumpstations and civils designs. Bulk pipelines were designed for the eight supply zones, with J&G taking responsibility for the central zones and zones 4 and 5. These included the Metolong dam, on the Phuthiatsana river, with 20 large and 26 small reservoirs and 357 km of pipeline.