Benthem Crouwel Reinforces Afsluitdijk Dam for One-in-10,000-Year Storms

Dutch studio Benthem Crouwel has completed an eight-year overhaul of Afsluitdijk, reinforcing the 32-kilometre dam so it can withstand a severe one-in-10,000-year storm.

The revamp equips the landmark flood barrier, built between 1927 and 1932, for increasingly extreme weather and rising sea levels while preserving its long, linear form. A quarter of the Netherlands sits below sea level, and Afsluitdijk remains one of the country's most critical pieces of water engineering, separating the IJsselmeer lake from the Wadden Sea.

"The Afsluitdijk is one of the Netherlands' most iconic waterworks and a landmark of Dutch water engineering," Benthem Crouwel partner Daniel Jongtien told Dezeen. "The significance of the Afsluitdijk is huge on many levels. It was built in the 1930s to close off the former Zuiderzee, creating the IJsselmeer and fundamentally changing how the country manages water."

"The brief was to strengthen the iconic and monumental character of the Afsluitdijk without losing sight of its primary function," Jongtien said.

What did the overhaul involve?

Benthem Crouwel has developed the project since 2018 with construction company BAM and contractor Van Oord, alongside investors Rebel and Invensis. The same group will maintain and oversee the dam for the next 25 years.

The physical works include:

• Reinforcement of the entire structure with 75,000 interlocking Levvel-blocs – concrete blocks arranged in a symmetrical, regular pattern
• A two-metre raise of the dam's height
• Additional pumping stations and discharge sluices, which regulate water flow
• Storm surge barriers
• A 15-metre-wide fish passage and a cycle path

The Levvel-blocs carry rough surfaces designed to let marine vegetation latch on.

How powerful are the new pumps?

Six new pumping stations, housed in four-metre-high domes, rank among the few deliberately visible architectural elements added to the dam. The almost 12-metre-high pumps beneath them push excess water from the IJsselmeer into the Wadden Sea.

"The almost 12-metre-high pumps beneath them discharge 275,000 litres of water per second, comparable to filling an Olympic swimming pool in nine seconds," the studio said.

Jongtien described the design approach as restrained. "The design is characterised by spectacular simplicity – abstract in form and minimalist in detail," he said.

"The architecture is restrained, allowing the function of the dike to remain visible while supporting technology is kept out of sight," he continued. "At the same time, where elements are made visible, they have a clear functional and architectural purpose."

The studio said its overarching goal was simplicity, with visible elements designed to "reveal how the infrastructure works and enhances the experience of the Afsluitdijk".

What does the fish passage restore?

A 15-metre-wide opening carved into the structure lets fish move between the IJsselmeer and the Wadden Sea. It reinstates a migratory zone between salt and fresh water that the dam blocked for almost a century.

"It represents a shift in thinking: from simply keeping water out to balancing flood protection with ecological connectivity," Jongtien explained.

A new cycle and pedestrian route runs along the Wadden Sea side, incorporating viewpoint platforms intended to give users "a more direct experience of the scale of the Afsluitdijk". An existing route on the IJsselmeer side was retained.

The overhaul positions a 1930s monument of Dutch water engineering as a model for combining hardened flood defence with ecological and public access — a balance the Netherlands will need to strike repeatedly as sea levels continue to rise.

Photography is by Jannes Linders.