The tender for the construction of the largest of three bridges that will span the Polihali reservoir and that will be built as part of the Lesotho Highlands Water Project (LHWP) Phase 2 – the Senqu River bridge – was released on March 4.

The bridge will be the first extradosed bridge, which combines pre-stressed box girder and cable-stayed elements in an efficient design, in Lesotho.

The bridge will be 825 m long and almost 100 m high. Work on the bridge design started in 2018, led by Zutari, formerly Aurecon Lesotho. Zutari also designed the Mabunyaneng and Khubelu bridges and will supervise the construction of the three bridges.

The tenders for the construction of the major bridges is an important step preceding the imminent tenders for the construction of the Polihali dam and the Polihali transfer tunnel, the Lesotho Highlands Development Authority (LHDA) notes in a March 20 statement.

Interested construction firms have up to June 18 to submit tenders. Specific information on the requirements and conditions of the tender is available on the LHDA website.

Construction of the Polihali dam will form the Polihali reservoir in the valleys and tributary catchments of the Senqu and Khubelu rivers, which will have a surface area of about 5 000 ha.

Owing to the depth of the valley and the inaccessible nature of the area where the Senqu Bridge will be built, the deck of the bridge will be built incrementally from both abutments. An in-situ segment midspan of the centre span will connect the two parts to form a continuous deck.

This construction method will minimise disturbance to the surrounding area and increase workers’ safety. It is envisaged that a steel launching nose will not be required.  The pier shape is ideal to be constructed with sliding formwork, the LHDA says.

“Experience and expertise are crucial in delivering a sophisticated, technically challenging project of this kind, which will be one of the few for the LHWP and Lesotho. Based on our experience with other major works tenders, we are confident that our call for tenders will attract the right mix of expertise and experience,” comments LHDA CE Tente Tente.

Besides the three major bridges, the restoration of access across the reservoir also necessitates the construction of new approach road sections to the bridges that tie into the existing A1 road. The A1 is the main road between the Mokhotlong district in the north-east of the country and the capital Maseru.

The LHWP Phase 2 entails construction of the Polihali dam, a 38-km-long transfer tunnel and the associated infrastructure and hydropower component.

It builds on the successful completion of Phase I in 2003. LHWP delivers water to the Gauteng province in South Africa. Phase 2 will increase the current supply rate of 780-million cubic metres a year incrementally to more than 1.27-billion cubic metres a year.

The Phase 2 water transfer component comprises a dam at Polihali and a gravity tunnel that will connect the reservoir at Polihali with the Katse reservoir. It will also increase the electrical energy generated in Lesotho, using the delivery system to generate hydroelectric power.

This is a further step in the process of securing an independent energy source to meet Lesotho’s domestic requirements, the LHDA notes.

Further feasibility studies for the hydropower component of Phase 2 have concluded that conventional hydropower is the more feasible option to meet Lesotho’s energy needs.

Three potential sites were identified: two on the Senqu river and a third site at Oxbow on the Malibamatso river. The plan is to commission the selected option at the same time as the water transfer component in 2027.