Polihali Dam and Lesotho Highlands Phase II: A Mountain Water Lifeline for Southern Africa
High in the mountains of Lesotho, where rivers cut through deep valleys and cold highland water begins its journey toward Southern Africa’s economic centres, one of the continent’s most important water-transfer projects is taking shape. The Polihali Dam and Lesotho Highlands Water Project Phase II are not simply about building another dam. They are about connecting mountains to cities, valleys to industry, and one country’s water resources to a regional development system.
The Lesotho Highlands Water Project is one of Africa’s great transboundary water infrastructure systems. It is built on a simple but powerful geographical reality: Lesotho is a highland kingdom with abundant mountain water, while parts of South Africa, especially Gauteng Province, carry enormous industrial, urban, and economic water demand. Phase II continues this long-term partnership between Lesotho and South Africa by expanding the system’s capacity through the Polihali Dam, a major transfer tunnel, access roads, bridges, power infrastructure, and social-development works.
Unlike GERD, whose story is mainly about national hydropower transformation, or Julius Nyerere, whose story is built around large-scale power generation, Polihali is a water-security story. Its power is not only in turbines or megawatts. Its power is in elevation, gravity, tunnels, reservoirs, and regional cooperation. It is an engineering system that uses Lesotho’s mountainous geography to move water across long distances for the benefit of millions.
Project Snapshot
- Project: Polihali Dam and Lesotho Highlands Water Project Phase II
- Countries: Lesotho and South Africa
- Location: Mokhotlong District, Lesotho
- River system: Senqu and Khubelu Rivers / Orange-Senqu system
- Main purpose: Transboundary water transfer and regional water security
- Dam type: Concrete-faced rockfill dam
- Approximate dam height: About 163.5–165 metres
- Major tunnel: Polihali Transfer Tunnel
- Tunnel length: About 38–38.5 kilometres long and about 5 m in diameter
- Tunnel role: Transfer water from Polihali Reservoir to Katse Dam
Strategic value: Water supply to South Africa, royalties and infrastructure for Lesotho, mountain engineering, regional cooperation, and long-term water security
The Polihali Dam is planned as a major concrete-faced rockfill dam in the highlands of Lesotho. It will create the Polihali Reservoir by storing water in the valleys of the Senqu and Khubelu river system. From there, water will enter the Polihali Transfer Tunnel and move by gravity toward the existing Katse Dam system, linking Phase II to the earlier phases of the Lesotho Highlands Water Project.
This is what makes the project technically powerful. It is not only a dam wall. It is a connected hydraulic chain. The dam stores water. The tunnel transfers it. Katse Dam integrates it into the wider system. The Vaal River system receives the benefit. South Africa’s economic heartland becomes more secure. Lesotho earns royalties and receives infrastructure benefits. A mountain reservoir becomes part of a regional water network.
The Polihali Transfer Tunnel is one of the most important components of the project. At about 38 to 38.5 kilometres long, it is designed to carry water underground from the new Polihali Reservoir to the existing Katse Reservoir. In simple language, this tunnel is the hidden artery of Phase II. People may see the dam and the bridges, but the tunnel is the silent engineering work that makes the transfer system function.
The tunnel also shows the difficulty of highland infrastructure. Building underground across mountainous terrain is not easy. It requires geological investigation, tunnel boring, drill-and-blast works, lining, access adits, gate shafts, intake structures, outlet works, safety systems, ventilation, spoil management, and long-term maintenance planning. For engineers, this is a project of geology as much as hydraulics.
The project also includes major bridges and access infrastructure. One of the most visible achievements is the Senqu Bridge, built to cross the future reservoir area. It is not just a transport structure. It is a sign that engineers must think ahead: when the reservoir fills, old routes will be interrupted, communities will need new connections, and construction logistics must remain functional. Roads and bridges are therefore not secondary works; they are essential parts of the water project.
For South Africa, the project is strategically important because Gauteng Province is one of the country’s most important economic regions. Johannesburg, Pretoria, industry, mining, services, households, hospitals, schools, and businesses all require reliable water. A large share of Gauteng’s water security is connected to the Lesotho Highlands system. Phase II is expected to increase Lesotho’s water exports to South Africa significantly, helping reduce pressure on existing supplies.
For Lesotho, the project has a different meaning. Lesotho is not only a water supplier. It is a sovereign country seeking development benefits from its natural resources. The Lesotho Highlands Water Project brings royalties, roads, bridges, jobs, institutional experience, and infrastructure development. If managed wisely, Phase II can help transform mountain water into national revenue, local opportunities, and stronger public infrastructure.
But the project also carries responsibility. Large reservoirs change land, livelihoods, movement routes, grazing areas, cultural places, and local community life. The Lesotho Highlands Development Authority notes that Phase II requires land acquisition and that several thousand hectares will be affected by the Polihali Dam and reservoir. This means the human side of the project must remain central. Compensation, resettlement, livelihood restoration, local employment, communication, and long-term community support are not minor issues. They are part of the project’s real success.
This is why Polihali must be understood as both an engineering project and a governance test. A dam can be measured in metres. A tunnel can be measured in kilometres. But trust cannot be measured so easily. Trust is built when affected communities are treated fairly, information is shared clearly, commitments are honoured, and the benefits of the project are visible in people’s daily lives.
From a hydrological perspective, the project belongs to the Orange-Senqu river system, one of Southern Africa’s most important transboundary basins. Water stored and transferred from the highlands becomes part of a wider regional water balance. This requires careful planning, climate-risk assessment, reservoir operation, environmental flow consideration, and coordination between institutions in both countries.
From an engineering perspective, the project is a remarkable combination of structures. The Polihali Dam provides storage. The saddle dam and spillway help complete the reservoir system. The tunnel transfers water underground. Bridges maintain connectivity. Access roads support construction and future operation. Electrical and telecommunications infrastructure support project management. Each part is different, but the value lies in their integration.
From a regional development perspective, Polihali is one of Africa’s strongest examples of water interdependence. It shows that rivers do not stop at political boundaries and that water security often requires cooperation. Lesotho’s mountains and South Africa’s cities are linked by geography, history, economics, and infrastructure. Phase II makes that connection even stronger.
The project also offers a lesson for African water professionals: not every major water project must be judged only by hydropower capacity. Some projects are great because they move water. Some are great because they protect cities. Some are great because they connect regions. Polihali’s importance lies in its role as a mountain water-transfer system supporting one of Africa’s largest economic zones while also creating development opportunities in Lesotho.
African engineers should follow Polihali because it brings together dam engineering, tunnel engineering, road and bridge construction, transboundary water governance, community impacts, highland hydrology, climate resilience, water-security planning, and regional finance. It is a complete water infrastructure classroom built across mountains.
The project’s success will be judged by more than construction progress. It will be judged by whether water reaches where it is needed, whether Lesotho receives fair and visible benefits, whether affected communities are respected, whether the infrastructure remains safe and reliable, and whether the two countries continue to cooperate with technical discipline and political maturity.
Polihali Dam and Lesotho Highlands Phase II therefore deserve a central place in AquaLinked / Water for Africa Experts Media’s “Major African Water Projects” series. GERD showed Africa’s hydropower ambition. Julius Nyerere showed Tanzania’s national energy expansion. Mphanda Nkuwa showed Mozambique’s Zambezi power corridor. Polihali now shows another face of African water achievement: a highland transfer system where gravity, tunnels, bridges, diplomacy, and regional water security come together.
In the end, Polihali is not only a dam in Lesotho. It is a mountain lifeline. It is a reminder that water infrastructure can connect nations, support cities, generate revenue, and create long-term resilience. Its story is written not only in concrete and rockfill, but in valleys, tunnels, bridges, communities, and the shared future of Southern Africa.
The Polihali Transfer Tunnel is an excavated, concrete-lined underground water tunnel, not an ordinary pipeline. It will carry water by gravity from the Polihali Reservoir to Katse Dam as part of the Lesotho Highlands Water Project Phase II.
Sources
Official references used for this article.
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