Taming the Scheldt
The Oosterweel Link project stands as one of Europe’s most ambitious infrastructure undertakings, designed to finally complete the Antwerp ring road and ensure unhindered road travel for Belgium. At its heart lies a feat of marine civil engineering: the construction, transport, and immersion of the massive Scheldt Tunnel. The client is LANTIS, and the contractor for this project is TM COTU (Combinatie Oosterweel Tunnel), which is a joint venture between DEME, Jan De Nul, BESIX and Stadsbader Contractors.
To understand the sheer scale of this operation and the digital intelligence required to pull it off safely, CEDA Industry News (CIN) spoke with two of the technical minds involved in the project: Brecht Devolder, Hydraulic Expert Engineer at DEME, and Boudewijn Decrop, Product Manager Water Computing & Monitoring at IMDC. These discussions followed Dredging Days, where the intensive sessions were coordinated by Freddy Wynants, Operations Manager at DEME.
The story of the Scheldt Tunnel begins not in Antwerp itself, but along the Belgian coast. Due to the immense space required to construct concrete structures of this magnitude, the project team looked beyond the immediate vicinity of the river and identified an ideal location in the port of Zeebrugge. There, an opportunity arose to integrate infrastructure needs with the harbour's expansion. The port authorities needed to excavate soil for their own development, creating a perfect synergy to construct a dedicated dry dock for the tunnel elements.
The dimensions of these elements are staggering. The tunnel comprises eight massive elements, each measuring 160 metres long and 42 metres wide. To put that into perspective, explained Decrop, “each block was roughly the size of one and a half football pitches, weighing a colossal 60,000 tonnes.” Constructing these giants on land was only the first phase of an extraordinary logistical chain.
From Zeebrugge to Antwerp
Once the concrete works in Zeebrugge were finalised, the massive building dock was flooded with water to float the structures one by one. The subsequent journey from construction to final placement was a carefully choreographed multi-stage maritime operation. The elements had to be towed out of the port of Zeebrugge and guided across a portion of the volatile North Sea, an environment known for its unpredictable weather and challenging marine conditions.
As Devolder explained, “because a transport of this size can only steer effectively by moving together with the natural flow of the water, the journey was strictly timed to coincide with the flood tide, using the massive natural push of the sea to transport the elements upstream towards Antwerp.”
To ensure maximum safety and operational control, the engineering teams wanted to completely decouple the long-distance sea transport from the delicate immersion process on the river. This required a strategic intermediate step by parking the elements temporarily in the Doel Dock in the port of Antwerp.
Once an element arrived safely in Doel, it would wait for the perfect operational conditions to proceed to the final site. This dual-layered logistics process meant that the marine teams could manage the workload efficiently, though it presented its own unique pressures.
Taming the river
The River Scheldt is a highly complex estuarine environment heavily influenced by the sea, experiencing strong tidal currents shifting flow direction four times a day with water levels fluctuating by up to six metres. This constant movement creates powerful, changing currents that pose a significant threat to floating infrastructure. Devolder explains, “In fluid dynamics, the physical forces at play do not scale linearly. If the velocity of the river current doubles, the physical force exerted on a floating tunnel element increases by a factor of four. When steering a 60,000-tonne structure into a precise location on the riverbed, guessing the current conditions is simply not an option.”
Decrop explains, “to eliminate variables and master the environment, IMDC brought 35 years of dedicated study of the Scheldt river to the table. We developed highly sophisticated mathematical representations of the entire tidal river network. This process relied on a meticulous, multi-tiered validation approach.”
As part of this, the team conducted extensive in-situ measurements directly in the river, which took place between 2019 and 2025. They recorded real-time data mapping water levels, flow velocities, and salinity levels across varying seasonal cycles to ensure the baseline mathematical models perfectly mirrored physical reality. This mathematical foundation allowed them to know the exact state of the river at any given minute and at any specific location.
Validation and the digital twin
To verify these digital calculations, the engineering teams took the scientific process a step further by conducting physical scale tests in a large laboratory environment. They built a precise, scaled-down replica of the Scheldt river and the tunnel elements, pumping water through the lab model to physically measure the hydrodynamic drag forces. This physical testing allowed them to cross-reference their data and guarantee that the computer simulations were predicting the forces with absolute accuracy. The combination of digital models and physical testing essentially created a highly accurate digital twin of the river.
This virtual reality setup allowed the engineers to safely play with different environmental scenarios, determining exactly what flow velocities were safe for immersion and what thresholds were too dangerous. Once perfected, these models were integrated into a live forecasting system that operated much like a highly advanced weather prediction model, but specifically tailored for water levels and flow velocities.
Environmental stewardship
This predictive engine dictated the project’s execution schedule, with the teams aiming for an immersion operation every two weeks to coincide with the neap tide, the period when tidal currents are at their weakest. Because the preparation for an immersion required three full days of work before the actual event, the team began analysing the five-day forecast well in advance.
Devolder explains, “If the predicted currents, water levels, wind, and weather conditions aligned with our strict safety parameters, we would issue a final go-ahead three days before the immersion date, initiating the intensive site sequence.” Interestingly, the natural elements proved remarkably cooperative throughout the process, and the team never had to issue a cancellation due to river conditions, though they did have to dynamically adapt to social factors, such as unexpected pilots' and lock operators' strikes.
With the forecasting model providing the perfect window, TM COTU’s marine teams executed the immersion sequences with extreme care. The process involved continuous, high-precision dredging to keep the immersion trench completely clear of the river silt that naturally accumulates in a tidal estuary before the immersion operation.
After the immersion, specialised vessels pumped a precise sand-and-water mixture underneath and alongside the element, creating a levelled, stable foundation that locks the tunnel into the riverbed permanently.
Engineering meets operations
While advanced software, digital twins, and heavy machinery were vital, the true catalyst for the project’s execution was human collaboration. The success of the Oosterweel tunnel elements proves that the line between theory and practice must be completely erased on a mega-project. The engineering team was deeply involved from the very early tender phase all the way through design, work preparation, and active execution, ensuring a continuous chain of knowledge. This close relationship between the engineering desk, the operational crew on the water and the client was the ultimate safeguard.
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