Construction of the Polihali dam is now 50% complete and is on track for the start of impoundment in the 2027/28 rainy season.

The concrete-faced rockfill dam forms part of Phase II of the Lesotho Highlands Water Project (LHWP).

This milestone is accompanied by the construction of several elements of the Polihali dam infrastructure, including the main dam reaching an elevation of 2 020 m on the rockfill and upstream concrete curb in mid-May, slightly ahead of the construction programme timeline.

By the end of June, the upstream concrete curb and rockfill had reached an elevation of 2 024 m.

A total of 9.6-million cubic metres of rock placed at about 26 000 cubic metres a work day resulted in the rockfill on the 166-m-high dam reaching 67% completion.

The next step is to raise the rockfill on the dam’s downstream side to equal the upstream rockfill and concrete curb, the Lesotho Highlands Development Authority (LHDA) says in a statement.

“The concrete curb forms a competent clean surface for the face slab construction, and the casting of the starter slabs for the main face slab is under way,” the authority comments.

Starter slabs are initial reinforced concrete panels constructed immediately adjacent to the toe slab or plinth at the base of the dam’s upstream slope. Concrete works on the main dam internal and external plinths are complete.

Work on the 43-m-high saddle dam has progressed well, with 375 627 m2 of rock having been placed for the saddle dam wall by the end of June.

Further, the internal and external plinth concrete works have been completed, and the concrete curb on the upstream side of the dam wall has reached the 2 047 m elevation.

Construction of the intake tower – a hydraulic concrete structure 100 m high and 21 m across that is located upstream of the dam and dedicated to managing water flow – is also under way.

The bottom outlet tunnel with its embedded 2.2-m-diameter compensation pipe, the source of downstream releases to the river, will also feed a small hydropower station of 4.4 MW. It is also progressing well.

The spillway, another large concrete structure, continues to progress with both final excavation and concrete construction. Excavation of the plunge pool is also under way.

“While the physical construction progress is clearly visible, there are other achievements on the Polihali dam project which are a source of pride to the LHDA and the project team. These include its zero fatalities and high lost-time injury-free numbers, and that it has created employment for many people,” the LDHA highlights.

At the end of April, the project’s workforce stood at 2 709 people, with 2 062 being semi-skilled employees, 99% of whom were Lesotho nationals, contributing skills and hands-on learning in the country.

The Polihali dam is 1 km downstream of the confluence of the Khubelu and Senqu (Orange) rivers.

It will create a reservoir with a  2 235-million cubic metres storage capacity, enabling water delivery to South Africa to be increased incrementally from the current 780-million cubic metres a year to 1 270-million cubic metres a year.

“As construction progresses toward its expected completion in 2029, the Polihali dam is testament to what can be achieved through innovative engineering, international cooperation and a vision for sustainable development. It is not just a dam; it is a catalyst for regional transformation enhancing water and energy security and regional connectivity,” the authority states.