Global first in Groningen: sea dike made from salt dredged material

A sea dike in Northeast Groningen has been strengthened with clay made from salt dredged material. That has never been done before. The sediment was ripened into firm dike clay over a period of three years, a process that takes decades in nature. The special clay was used to widen and raise a 750-metre-long section of the dike. From 2025 onwards, the Hunze and Aa’s water authority plans to strengthen the remaining 11.5 kilometres of the Dollard Dike with this local clay as well.

The idea for this innovation emerged ten years ago. The Delta Programme looked at new and sustainable approaches to upgrading dikes that are appropriate for the Wadden Sea World Heritage Site. The Hunze en Aa’s water authority has to strengthen the dike bordering the Dollard, and the National Delta Programme provided an opportunity to explore the idea of the Wide Green Dike. The idea is simple: remove excess silt from the Ems-Dollard, dry it into clay and use it to strengthen the adjacent dike. This improves water quality by reducing the levels of suspended sediment in the water, and results in a safe and green dike that blends in well with the surroundings.

First step towards strengthening the entire sea dike

Project manager Erik Jolink: “This 750-metre-long Wide Green Dike is the culmination of research into the use of sediment for strengthening dikes. As a result of extensive research, we now know how to make clay from sediment in a short time and how strong this clay is. Using this knowledge, we plan to upgrade the remaining 11.5 kilometres of the Dollard dike from 2025 onwards. The plan is to build clay ripening plants right next to the sea dike so that we can make ‘local clay’, eliminating the need for long-distance transport with lorries.”

Smarter and more sustainable

Delta Commissioner Peter Glas: “The wide, green sea dike is a magnificent example of Dutch innovative hydraulic engineering. We have to upgrade a lot of dikes in the years ahead. This project shows that we can meet that challenge in smarter and more sustainable ways. It is a green dike that blends in well in this Natura 2000 area. Because we are strengthening the dike with local clay, we don’t need to transport soil, we are cutting carbon emissions from transportation and, at the same time, we are improving water quality by using material from the Ems Dollard. For me as the Delta Commissioner, it is also important that this sea dike can be adapted easily in line with sea level rise. You don’t have to remove a layer of asphalt first before applying sand and then covering the dike again with asphalt. You can just put extra clay on top.”


A lot has now been learnt about the clay in extensive research. The 750-metre-long dike will be monitored over the next three years to gather information about things like the development of the herb-rich grass, drainage and the required management. The knowledge generated by this project will be useful in other projects in the Netherlands and internationally.


The Hunze and Aa’s water authority commissioned the project. EcoShape built the dike and is running the monitoring activities. The provincial authority of Groningen, Rijkswaterstaat, Het Groninger Landschap and Groningen Seaports are partners. The project is part of the Ems Dollard 2050 programme and the Dutch Delta Programme. Financing comes from the Wadden Fund and the Flood Protection Programme. The water authorities and Rijkswaterstaat are working together in that programme on the largest dike upgrade operation since the Delta Works: over the next 30 years, 1,500 kilometres of dike will be upgraded.