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Tunnels under the Atlantic connect the sea to the future Mamelles plant in Dakar, in a desalination project created to expand urban supply and transform saltwater into millions of liters of drinking water per day.
Senegal has advanced in the construction of the Mamelles desalination plant in Dakar, with the completion of microtunneling excavation of a 340-meter submarine pipeline intended for capturing water from the Atlantic.
The project, executed to reinforce the capital’s supply, foresees an initial production of 50,000 cubic meters of drinking water per day, with the possibility of expansion to 100,000 cubic meters daily.
The structure is presented by Eiffage as the largest desalination plant in West Africa when it becomes operational.
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Country ‘tears’ the sea with 340-meter underwater tunnels under the Atlantic to capture saltwater and build a megaproject capable of producing up to 100 million liters of drinking water per day in West Africa.
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Country ‘tears’ the sea with 340-meter underwater tunnels under the Atlantic to capture saltwater and build a megaproject capable of producing up to 100 million liters of drinking water per day in West Africa.
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The unit integrates a set of works on land and at sea to transform saltwater into drinking water, enhance Dakar’s water security, and reduce pressure on traditional supply sources.
The project has as its client the Société Nationale des Eaux du Sénégal, SONES, and is financed by the Senegalese government and the Japan International Cooperation Agency, JICA.
The project also involves companies such as Eiffage, Tsusho, and Wabag, in an engineering, construction, and initial operation contract for the future plant.
Submarine tunnels carry Atlantic water to the plant
The most complex part of the infrastructure is out of sight of those passing by the Mamelles coastline.
Under the coastal strip, tunnels and pipelines connect the ocean to the onshore station, allowing the entry of seawater and the controlled return of the brine generated in the desalination process.
According to Eiffage, the microtunneling excavation of the intake pipeline reached 340 meters and was completed in July 2025.
Soletanche Bachy, through Bessac Afrique, reported that the project includes two submarine outfalls of 340 meters each, with an internal diameter of 1.60 meters, intended for the intake of saltwater and the disposal of brine.
This type of work reduces the need for large open cuts in the coastal area and allows for the installation of large pipelines in sensitive sections.
Specialized equipment advances through the underground or submerged areas, opening precise passages to receive the ducts that will make the permanent connection between the Atlantic and the treatment plant.
The technical choice is decisive for the continuous operation of the unit.
The captured water needs to reach the station in a volume compatible with the planned capacity, while the saline waste must be taken to a discharge point defined in the project, with its own infrastructure for this flow.
Plant capacity may double in Dakar
In the first phase, the Mamelles plant will have the capacity to produce 50 thousand cubic meters per day, equivalent to 50 million liters of potable water.
The planned expansion will increase this volume to 100 thousand cubic meters daily, or 100 million liters, as the demand of the Dakar metropolitan region increases.
JICA describes the second phase as an expansion of capacity from 50 thousand to 100 thousand cubic meters per day, accompanied by improvements in distribution networks.
The goal is to diversify water sources and improve access to supply in an urban area that concentrates population, public services, and economic activities important to the country.
Eiffage states that the initial production could meet a significant part of the needs of the Dakar region.
In previous statements, the company associated the unit with the supply of about one million inhabitants and the diversification of Senegal’s potable water sources.
By July 2025, the Senegalese government reported that the advancement of the Mamelles desalination unit was estimated at 78%, with distribution network works underway in different areas of the capital.
No more recent official confirmation was found regarding the full operation of the plant.
Desalination strengthens water security in Senegal
Dakar faces increasing pressure on supply due to urban expansion and the concentration of residents and economic activities.
In this context, desalination has come to be treated as a complementary source, especially in coastal cities seeking to reduce dependence on aquifers, rivers, reservoirs, and water transfer systems.
The technology used in such projects separates the salts present in seawater to produce water suitable for human consumption.
The process generates two main streams: the treated water, which goes to the supply system, and the brine, which needs to be discarded by structures designed for this purpose.
Atlantic water, although abundant, cannot be consumed directly due to the high concentration of salts and other elements.
Therefore, the Mamelles plant relies on stages of capture, pumping, filtration, desalination, final treatment, and distribution before the water reaches the urban network.
The implementation of the unit also marks a change in Senegal’s water infrastructure.
Instead of relying solely on continental sources, the country begins to incorporate the sea as a technical alternative to complement the capital’s supply, even though the solution requires high investment, energy consumption, and strict environmental management.
Engineering at sea sustains urban supply
The construction of the tunnels helps to show that a desalination plant is not limited to the equipment installed on land.
Before the water reaches the treatment systems, it is necessary to create a resistant physical connection between the ocean and the station, capable of operating in a coastal environment and maintaining regular flow.
This network includes intake structures, pipelines, pumping systems, underwater outfalls, and discharge points.
Without this maritime stage, the plant would not be able to capture enough water or conduct the brine back to the ocean within the planned technical model.
The location in Mamelles reinforces the contrast between Dakar’s coastal landscape and the engineering installed below the surface.
While the coastal area remains an urban and maritime space, part of the capital’s supply solution advances under the Atlantic, connecting the sea to a treatment plant on land.
The project brings together civil engineering, maritime works, hydraulics, energy, sanitation, and environmental control.
This combination explains the high cost and complexity of a structure designed to operate daily, with the capacity to convert millions of liters of saltwater into drinking water.
The Mamelles plant also appears amid a broader debate about the role of desalination in coastal countries.
The technology can enhance water security, but it does not eliminate the need for efficient network management, protection of water sources, reduction of losses, and long-term planning for urban consumption.
In Senegal, the investment in the Atlantic aims to respond to a concrete demand from Dakar.
The water captured from the sea will be conducted through tunnels and pipelines to a station designed to increase the supply of drinking water, in a project that transforms an invisible infrastructure beneath the coast into an essential part of the capital’s supply.
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