Senqu River Bridge, Lesotho Highlands Water Project Phase II

A flagship extradosed bridge delivering long-term connectivity and water security through innovative design and close integration of engineering and construction excellence.

Client

Lesotho Highlands Development Authority

Project date

2026

The Lesotho Highlands Water Project Phase II is one of the most ambitious infrastructure programmes in Southern Africa, designed to strengthen regional water security while supporting long-term economic development.

The opportunity

Delivered by the Lesotho Highlands Development Authority on behalf of the governments of Lesotho and South Africa, the programme includes the Polihali Dam and extensive supporting infrastructure to maintain critical transport links.

At the centre of this network is the Senqu River Bridge, a landmark structure designed and supervised by Zutari. Spanning 825m across the Senqu Valley at heights exceeding 90m, the bridge forms a vital section of the A1 national route. Once the Polihali Reservoir is impounded, large sections of the existing road will be submerged, making the bridge essential for continued access between key regions, including Mokhotlong.

The project presented the challenge of delivering a long-span bridge in a remote, high-altitude environment characterised by steep terrain, extreme temperatures and limited access. Construction needed to be completed within a strict programme aligned with reservoir impoundment, while minimising risk, cost and environmental impact. There was also an opportunity to rethink conventional design approaches by integrating contractor methodologies, advanced analysis and digital tools to deliver a structure that was efficient, resilient and visually distinctive.

What we did

Zutari led the design and construction supervision, evolving the initial concept into an incrementally launched, extradosed stay cable concrete box girder bridge comprising 16 spans, including a central 100 m extradosed span. The removal of a central river pier reduced construction risk and cost, while introducing a structurally efficient hybrid solution combining prestressed concrete and stay cables.

Incremental launching from both abutments was adopted to accelerate construction and avoid extensive work in the valley below. Detailed analysis addressed temporary loading conditions, and a launching nose was introduced to reduce bending moments. Tall hollow hexagonal piers were constructed using continuous slipform methods, supported by carefully managed reinforcement detailing and 24-hour construction cycles.

Mass concrete foundations required rigorous thermal control strategies, including fly ash cement replacement, embedded thermocouples and extended curing regimes. Full-scale mock-ups validated mix designs and enabled single-pour construction. Deck and reinforcement detailing were refined in response to contractor and supplier input, reducing congestion and material quantities while improving constructability.

Digital 3D modelling was employed to resolve complex interfaces at pylons and stay cables, while structural health monitoring validated material behaviour and long-term performance assumptions during construction.
Incremental launching from both abutments enabled efficient construction across the deep Senqu Valley while minimising risk and environmental impact.

The outcome

The Senqu River Bridge stands as a benchmark for complex bridge delivery in challenging environments. Through close collaboration between designers and contractors, the project successfully integrated advanced construction techniques, material optimisation and digital tools to overcome logistical, environmental and structural constraints.

The bridge now provides a resilient and essential transport link that will remain operational long after the surrounding road network is submerged, supporting regional connectivity and economic development. The project demonstrates how integrated design and construction can deliver technically robust infrastructure that responds to both immediate constraints and long-term regional needs.


The Senqu Bridge demonstrates how engineering innovation, collaboration and technical excellence can deliver infrastructure that is both resilient and transformative.

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