With the construction of multiple elements of the Polihali dam infrastructure underway simultaneously, the site is characterised by extensive activity and significant construction progress.
Recent construction milestones on the main dam include reaching el. 2020 on the rockfill and upstream concrete curb in mid-May, slightly ahead of the construction programme timelines. By the end of June the upstream concrete curb and rockfill had reached el. 2024. With a total of 9.6 x 106m3 of rock placed at an average of 26 000 m3 per work day, the rockfill on the 166-m high CFRD is now 67 per cent complete. The next step is to raise the rockfill on the downstream side of the dam to equal the upstream rockfill and concrete curb, thus achieving the third milestone.
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 underway. The 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. They serve as the starting point for constructing the main concrete face. Concrete works on the main dam internal and external plinths are complete.
Work on the saddle dam, which is a 43-m high CFRD, and is in itself a large dam, has progressed well. At the end of June, 375 627 m3 of rock had been placed for the saddle dam wall; the internal and external plinth concrete works were complete and the concrete curb on the upstream side of the dam wall had reached el. 2047.
The intake tower, which is a massive concrete structure 100 m high by 21 m across, and similar to the one at Katse, is underway. The intake tower is a hydraulic structure located upstream dedicated to managing water flow.
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 4.4 MW hydropower station. It is also progressing well.
The spillway, another extremely large concrete structure, also continues both with final excavation and concrete construction. Excavation of the plunge pool is also underway.
While the project’s physical construction progress is clearly evident, the Polihali dam project has also achieved significant milestones in terms of health, safety and socio-economic development. These include maintaining a zero-fatality record and high lost time injury-free numbers. In addition, the project has created substantial employment opportunities. By the end of April that figure stood at 2709 people. Of these, 2062 are semi-skilled employees, 99 per cent of whom are Basotho nationals, contributing to enhancing skills and hands on learning in the country.
The Polihali dam is approximately 1 kn downstream of the confluence of the Khubelu and Senqu (Orange) rivers. It will create a reservoir capable of storing 2 325 x 106m3 of water and will enable water delivery to South Africa to be increased incrementally from the current 780 to 1 270 x 106m3 annually.
