Growing with the Sea: Testing Nature-Based Solutions for Climate-Resilient Dikes
How a pioneering Dutch project is turning harbor sludge into climate adaptation
Climate change is raising sea levels along Europe's coasts, and traditional approaches to dike reinforcement are reaching their limits. In the BONSAI project, partners across Northwest Europe are developing innovative solutions to make estuarine systems resilient against climate impacts. One of the most fascinating experiments of BONSAI is taking place in the Netherlands on the Westpolderdike along the Waddensea. At this location regional water authority Noorderzijlvest is testing whether a dike can literally "grow" to keep pace with sealevelrise.
A video explaining the experiments
Jan-Willem Nieuwenhuis of regional water authority Noorderzijlvest
From Concept to Reality
The "Meegroeidijk" (Growing Dike) represents an elegant idea: coat a dike frequently with sediment layers that gradually dry and compact into clay, incrementally raising the dike's height. But transforming this concept into practice requires careful engineering and continuous monitoring. One of the main questions is: How will the thickness of the layer develop during the time and how much will finally be ‘left over’? To be able to analyze this several types of instrument are used for monitoring. For example a drone but also a Sedimentation-Erosion Bar.
Jan-Willem Nieuwenhuis from regional Water authority Noorderzijlvest explains the evolution of their approach at the test site. The initial trials involved spraying sediment against the dike using standard slurry equipment. Now, the team has refined their technique significantly, employing a specialized manure injector mounted on a tractor that hovers just above the surface. This precision tool allows for much more controlled and even application of sediment layers.
The Critical Question: What Happens to the Grass?
While the concept may sound straightforward, the project's success depends on solving a critical puzzle: maintaining a healthy grass cover through multiple sediment applications. This grass layer serves as the dike's protective armor, preventing erosion and ensuring structural integrity during storms and high water events.
"The key question we're investigating is whether the grass can withstand being repeatedly covered with sludge (sediment) gained in the harbour of Lauwersoog," Nieuwenhuis explains. "Will the vegetation die under these conditions, or will it successfully push through each new layer?" This uncertainty is precisely why the experiment will continue gathering data through 2028. As an alternative gras seed mixtures are added to the sludge. How will the vegetation develop and will this be able to lock the different layers together?
To answer these questions, the projectteam regularly extracts cylindrical core samples from various sections of the test dike. These samples undergo rigorous testing, including pull-apart tests that measure the tensile strength of the grass cover. The critical factor is root interweaving—how effectively the roots of different grass species knit together to create a resilient, erosion-resistant layer.
International Climate Resilience
The BONSAI
project is taking this research one step further by testing how the seed
mixtures perform under different climate conditions. The same grass varieties
used on the Westpolderdike will be cultivated on a levee in France, where
they'll experience the warmer, potentially drier conditions that may become
typical in the Netherlands as climate patterns shift northward. These
comparative results will be crucial for long-term planning.
Nature's Blueprint, Human Precision
The sediment currently blanketing sections of the test dike arrives fresh from Lauwersoog harbour. As it dries and matures into clay, grass gradually colonizes the new surface. Eventually, sheep will graze these areas, trimming the vegetation while naturally fertilizing the soil. With each cycle, the dike rises slightly higher—a controlled recreation of the natural land-building processes that have shaped coastal regions for thousands of years.
A Future-Proof Approach
As sea levels continue their inexorable rise throughout this century and beyond, Northwest Europe's estuarine regions will increasingly need adaptive, forward-thinking solutions for coastal defense. The Meegroeidijk experiment represents a fundamental shift in philosophy—from static, resource-heavy engineering toward dynamic, nature-inspired solutions that embrace rather than fight natural processes.
The data emerging from this test site through 2028 will determine whether "growing dikes" can become a practical, scalable strategy for climate adaptation across the region. If the results prove positive, this approach could offer a truly sustainable alternative to conventional dike reinforcement—one that's less resource-intensive, more environmentally friendly, and flexible enough to adapt alongside our changing climate.
We will keep you updated with more information of the Meegroeidijk at this website.