Netherlands' 9km flood barrier triggered "sand hunger," shrinking tidal flats

The Netherlands built one of the world’s most ambitious flood defences after the devastating North Sea flood of 1953. Completed in 1986, the 9-kilometre Eastern Scheldt Barrier was designed to protect hundreds of thousands of people while keeping the estuary open to tides and saltwater.

But the engineering solution created an unexpected environmental consequence. By reducing tidal currents, the barrier disrupted the natural movement of sand across the Eastern Scheldt. Decades later, tidal flats and shoals are steadily shrinking in a process known as “sand hunger”.

The Eastern Scheldt Barrier was built after the 1953 flood

The Eastern Scheldt Barrier was built as part of the Netherlands’ Delta Works, the huge national programme created after the catastrophic North Sea flood of 1953.

Construction began in 1976 and took 10 years to complete. According to Rijkswaterstaat Ministry of Infrastructure and Water Management, the barrier stretches 9 kilometres between Schouwen-Duiveland and Noord-Beveland in Zeeland, with 3 kilometres containing movable floodgates.

Unlike a conventional dam, it normally remains open so that tides can continue flowing through the Eastern Scheldt. The decision preserved the estuary’s natural environment and helped protect the region’s fishing industry while providing a powerful defence against exceptionally high water.

The barrier changed how sand moved through the estuary

Keeping the Eastern Scheldt open preserved tidal exchange, but it did not leave the estuary’s natural processes unchanged. The official data explains that the barrier reduced the volume of tidal water moving through the system, weakening the currents that previously transported sediment. As a result, less sand returns to the tidal flats, mudflats and salt marshes during the ebb-and-flow cycle. A report, ‘Oosterschelde Storm Surge Barrier: development of scour pits and stability of seabed protection’, by Rijkswaterstaat Waterdienst researchers from Deltares found that the morphological situation after construction was no longer in equilibrium, with the remaining channels becoming relatively too large while tidal-flat and mudflat areas experienced erosion.

This sediment shortage became known as “sand hunger”.

Tidal flats began disappearing as sand was carried away

The consequences are particularly visible on the exposed tidal landscapes of the Eastern Scheldt. During storms, large quantities of sand can move from the flats and mudflats into deeper channels, while the weaker tidal currents are unable to return enough sediment. These areas are therefore becoming progressively smaller. Its 2012 morphological report recorded average erosion of roughly 1 centimetre per year on the Eastern Scheldt’s tidal flats and mudflats.

Rising sea levels add another long-term pressure. Without intervention, the shrinking areas could gradually disappear beneath the water, reducing important habitat for wildlife and changing the shape of the estuary.

The Netherlands is now adding sand to restore the lost habitat

Rijkswaterstaat is responding by deliberately putting sand back onto vulnerable areas. A current project at the Galgeplaat tidal flat and the Slikken van den Dortsman is scheduled to run from 2022 to 2027, with sand nourishment taking place during 2026 and 2027.

The aim is to keep these landscapes above water for longer and maintain their ecological functions. The tidal flats provide feeding grounds for wading and migratory birds, while seals use them as resting places.

The Slikken van den Dortsman also helps reduce wave energy before it reaches nearby dikes. After the nourishment work, there are plans to monitor the results for at least five years.The Eastern Scheldt Barrier therefore illustrates an unusual challenge in environmental engineering, solving one problem can create another. The structure remains a crucial part of Dutch flood protection, but by altering tidal currents, it also changed the sediment balance that maintained the estuary’s shallow landscapes. Now, decades after the barrier was completed, the Netherlands is using carefully placed sand to compensate for that change and keep the Eastern Scheldt’s tidal flats, wildlife habitat and coastal defences functioning.