The Polihali Dam will create a 5042ha reservoir at the confluence of the Senqu and Khubelu rivers. The Polihali Dam and the Polihali to Katse Transfer Tunnel are the main water transfer infrastructure works of Phase II of the Lesotho Highlands Water Project.
Phase II adds 2,325 million cubic metres in storage capacity to the LHWP enabling an incremental increase in the volume of water to be transferred to South Africa from 780 to 1,270 million cubic metres per annum, while simultaneously increasing power generation at ‘Muela by 40%.
New roads and bridges are required to restore access across the reservoir and connectivity to the national road network.
Three major bridges are being built under Phase II along the Maseru to Mokhotlong A1 road at the Mabunyane, Khubelu and Senqu rivers.
The three major bridges will provide access to Mokhotlong town across the reservoir even at full supply and retain connectivity to the national road network along the A1, the main road between the Mokhotlong district in the mountainous north-east of the country and Maseru, the capital of Lesotho.
The major bridges programme is complemented by the construction of four pedestrian bridges and six vehicle bridges under the feeder roads and bridges programme to maintain connectivity and ensure mobility for communities in the reservoir area. This programme is currently under procurement.
About the Senqu Bridge
The Senqu Bridge is the largest of the three major bridges under construction to span the Polihali reservoir.
Almost a kilometre long (825m) and at a height of 90m, it will be the first extradosed bridge in Lesotho and is larger than the Mphorosane Bridge on the Malibamats’o River which spans the Katse Dam and was constructed under Phase I of the Lesotho Highlands Water Project. The bridge design has taken into consideration the Mokhotlong highlands’ long, cold and harsh winter conditions.
Due to the deep valley and the terrain of the area, the deck will be constructed incrementally from both abutments. This construction method will minimise disturbance to the surrounding work area and increase workers’ safety. An in-situ segment midspan of the centre span will connect the two parts to form a continuous deck. The pier shape is ideal to be constructed with sliding formwork.
Work on the bridge design started in 2018, led by Zutari, formerly Aurecon Lesotho. Zutari also designed the Mabunyaneng and Khubelu bridges, the other two major bridges to be constructed under Phase II.
The Lesotho Highlands Development Authority awarded the Senqu Bridge construction contract valued at approximately M2 billion to the WRES Senqu Bridge Joint Venture in August 2022.
The WRES Joint Venture includes South African, Lesotho and international companies as per the requirements of the Phase II Agreement. The primary partners are: Webuild S.p.A. (Italy); Raubex Construction (Pty) Ltd (South Africa); Enza Construction (Pty) Ltd (South Africa) and Sigma Construction (Pty) Ltd (Lesotho). Sub-contractors include: EXR Construction (Pty) Ltd (South Africa; Gleitbau-Geselschaft (Austria); Post Tensioning and Structural Solutions (Pty) Ltd (South Africa) and Freyssinet International et Cie (France).
The Senqu Bridge is expected to be completed in early 2026.
Pictures above – Left: View of the massive construction site dwarfed by the majesty of the landscape; Right: The sliding formwork for Pier 10 (the second highest pier) under assembly. Starting the week of 19 February 2024 and rising slowly and continuously at a rate of 4m/day the entire 84 m high pier will be cast over 22 days working 24/7 with only one pause at around 60m which will be required to extend the tower crane.
Photo shows how the sliding formwork looks when the contractor slid the first pier (Pier 1) late last year. Top platform is for fixing steel, 2nd platform for casting concrete and lowest platform for finishing the concrete.
Pier 9 foundation casting. The 20x20x3 m foundation contains approximately 1000m3 of concrete and 150 m3of reinforcing steel. The concrete was placed in one continuous pour of 28 hours (so as to avoid having a cold joint within the foundation if it were cast in 2 or more pours). Both 40 m3/h concrete batch plants on site, two truck mounted concrete pumps, numerous concrete trucks and three shifts of approximately 40-50 persons each were involved.
Pier 9 foundation casting. In the background one can see pier 1 which is at the height of the underside of the future deck, Pier 9 will have the highest of the 15 piers reaching approximately 88m in height.
