Another milestone has been passed as the construction of the Lesotho Highlands Water Project (LHWP) Phase II continues.

Polihali dam has reached the rockfill placement milestone of elevation 1 977 m – 65 m above the river bed – following high rates of progress in 2025 that saw more than six-million cubic metres of rock placed by the end of November.

The main dam wall is achieving a rockfill placement of more than 22 000 m² every day – equivalent to nine Olympic pools of material daily, the Lesotho Highlands Development Authority said in a statement sent to Engineering News.

The saddle dam is also progressing steadily, with over 154 000 m² of rock placed.

In total, about 14-million cubic metres of rock will be required to complete the Polihali dam, which is a concrete faced rockfill dam larger than the 145-m-high Mohale dam built during LHWP Phase I.

This huge quantity of basal rock, weighing 3.5 t/m², is sourced from a quarry within the dam basin, which, when the dam is inundated, will be completely under water.

“Blasting at the quarry has to be done carefully in specific blasting patterns, to get the rock into correct sizes. That way, excavators can load it into dump trucks without the need to process the rock any further, and it is then transported directly to the dam where it is placed and compacted in layers up to 0.8 m thick.”

Working in two shifts, 2 700 truckloads of rock a day wind their way from the quarry to the rockfill site.

Mohale dam, at the time of its construction the largest rock-fill dam in Africa, is capable of storing up to 950-million cubic metres of water at full supply level.

The Polihali dam will surpass these dimensions, with an embankment that will rise to 166 m, and a crest spanning 921 m in length and nine metres in width.

At the base, the embankment will span about 490 m.

The Polihali dam appurtenant infrastructure includes a spillway, intake tower, bottom outlet, a compensation outlet structure and a small hydropower station.

It will create a reservoir on the Senqu and Khubelu rivers with a surface area of 5 053 ha and a full supply storage capacity of 2 325-million cubic metres at full supply level.

The Polihali dam is being constructed by the Sun joint venture (JV), comprising main partners China’s Sinohydro Bureau 8 and Sinohydro Bureau 14; South Africa’s Unik Civil Engineering and Lesotho’s Nthane Brothers.

Subcontractors include South Africa’s Melki Civils and Plant Hire and Mecsa Construction; as well as Lesotho’s Sigma Construction and China’s Kunming Engineering.

Construction is supervised by the Matla a Metsi JV, comprising South Africa’s GIBB and Mpamot Africa; France’s Tractebel Engineering SA/Coyne et Bellier; and Lesotho’s LYMA Consulting Engineers.

Phase II will increase the current yearly supply rate capacity from 780-million cubic metres to 1 270-million cubic metres, contributing towards meeting South Africa’s increasing water needs.

The additional flow of water from Polihali will simultaneously increase power generation within Lesotho, helping meet Lesotho’s domestic needs and reducing the country’s dependence on electricity imports.