That decision to leave it alone is the entire point of the project. Dutch coastal defence has traditionally relied on beach nourishment: adding one to five million cubic metres of sand every three to five years to counter erosion along a coastline that sits well below sea level in places and depends on artificial reinforcement to exist at all. The Zandmotor, commissioned jointly by Rijkswaterstaat, the Dutch government agency responsible for infrastructure and water management, and the province of South Holland, tested a different idea: put a much larger volume of sand in one place and let wind, waves, and longshore currents redistribute it naturally over roughly two decades, rather than repeating a smaller, more disruptive intervention every few years.
The idea behind letting the sea do the work
The project is often described as an application of “Building with Nature,” an approach to coastal and hydraulic engineering that tries to work with natural sediment transport processes rather than fight them with rigid structures like sea walls or repeated dredging cycles. Marcel Stive, a coastal engineer at Delft University of Technology, is generally credited as the originator of the sand-engine concept behind the project, and TU Delft researchers, including coastal engineer Stefan Aarninkhof, have been involved in analysing its performance since construction finished. The project cost approximately €70 million, a substantial upfront figure, but one framed against the cumulative cost and ecological disruption of repeated smaller nourishments over the same period.
Monitoring has been coordinated primarily by Deltares, the Dutch applied research institute for water and subsurface issues, with ecological and visitor-experience research contributed by Wageningen Marine Research and Wageningen University. The scale of monitoring involved is itself unusual for a coastal engineering project: from the outset, the Zandmotor has functioned as much as an open-air, decade-plus field experiment in how a coastline redistributes an artificial sand surplus on its own as it has as infrastructure.
What has actually happened to the sand
A formal ten-year evaluation, presented at an international conference in July 2021, offers the clearest picture so far of whether the bet is paying off. The peninsula’s width more than doubled over that first decade, expanding from roughly two kilometres to about five kilometres as the initial hook shape flattened and spread along the coast, exactly the redistribution pattern the design intended. Researchers traced roughly 60 per cent of the sand that has moved to nearby beaches and dunes, with the remaining 40 per cent found further along the coast in both directions, suggesting the currents are carrying material somewhat more widely than the immediate project area.
Dune formation, which depends on wind picking up dry sand from the beach and depositing it further inland, was slow in the project’s early years and has accelerated more recently, with dunes reaching up to three metres in height on the peninsula’s southern section. A December 2025 paper in the journal Discover Geoscience, examining the dynamics of the engineered dune landscape at the site, continues to document ongoing dune growth and sediment transport consistent with the project’s original ten-year findings, suggesting the process is still tracking roughly as planned at its informal midpoint. The Zandmotor’s full twenty-year design horizon runs to around 2031, so a comprehensive final assessment is still several years off.
What it has become besides infrastructure
Along the way, the Zandmotor has turned into something its planners did not need to engineer directly: a popular recreational destination. Its exposed, wind-swept shape has made it a well-used spot for kitesurfing, along with walking and running, and a 2020 Wageningen University visitor survey recorded an average satisfaction rating of 8 out of 10 among people using the area. Ecological monitoring has also recorded higher bird and benthic, or seafloor-dwelling, biodiversity at the site compared with an ordinary managed beach, an outcome linked to the varied, evolving mix of wet and dry sand, shallow lagoons, and early dune vegetation that a static, regularly renourished beach does not develop in the same way.
What this project can and cannot tell other coastlines
The Zandmotor is a single, large-scale field trial, run in a specific tidal, wave, and current environment off the Dutch coast, and its results should be read as evidence about that environment rather than a universal formula for coastal defence. Whether a similarly sized mega-nourishment would redistribute the same way, or at all, on a coastline with different wave energy, tidal range, or sediment supply is a separate question the Dutch results do not answer on their own. What the project has demonstrated, roughly at its halfway point, is that a single large deposit of sand can behave the way its designers modelled — spreading gradually along a coast, feeding dune growth, and functioning as usable habitat and recreation space in the years between deposits, not just sitting inert as an engineering curiosity. Whether that holds through to the full twenty-year mark, and whether the approach gets repeated elsewhere in the Netherlands or exported to other countries facing similar erosion pressures, is what the next several years of monitoring will settle.