Excessive levels of sediment in the Eems-Dollard area are having a negative impact on water quality and biodiversity. Large amounts of sediment accumulate in ports, making regular dredging necessary.
On the other hand, clay soil is needed in the area to strengthen dikes and to raise farmland. Collecting sediment from the Eems Dollard and converting it into clay soil creates a win-win situation: the water quality improves and there is more clay soil for reinforcing dikes and raising farmland. There are plans for more dike upgrade operations in the future on the Eems-Dollard coast, and clay soil will be needed there, too.
Rijkswaterstaat, the provincial authority of Groningen, Groningen Seaports, the Hunze and Aa’s water authority, nature conservation organisation Het Groninger Landschap and EcoShape have teamed up in the Clay Ripening pilot project to look at different ways of transforming sediment into clay soil. EcoShape researchers are engaged in practical experiments to see which approach to ripening works best.
In 2018 we filled the first sediment depot with dredged material from the Havenkanaal, the canal leading to the port of Delfzijl. A second depot will be filled in 2019, with sediment from the Breebaart polder near Termunten. The sediment is transformed into clay soil in the clay ripening site by means of processes such as dewatering, desalination and oxidation. The site includes several sections that allow us to test different ripening approaches. It is expected that the clay soil will have ripened enough by 2021, at which time it will be suitable for application.
The central focus will be on the following questions:
• Is making clay on land a cost-effective solution for the sediment problem?
• What are the best ways of extracting sediment from the Eems Dollard area and ripening it efficiently?
• What quality of clay can clay ripening deliver?
• Which ecosystem services can clay ripening deliver?
• What is the business case for clay ripening?
The Hunze and Aa’s water authority will be using 70,000 m³ of ripened clay to strengthen a one-kilometre section of dike in the ‘Broad Green Dike’ pilot project. This is a dike with a shallow slope covered by a relatively thick layer of clay and grass. If the Clay Ripening pilot project is successful, the idea is to strengthen the remaining section of the dike (measuring about 11.5 kilometres) on the banks of the Dollard.
Scaling up could significantly reduce the amount of sediment in the Eems Dollard. The aim is to extract 1 million tonnes of sediment from the Eems Dollard annually by 2022. This will have a positive effect on the unique ecological value of the estuary.
The pilot will generate a lot of knowledge about transforming dredged material into clay soil and the usefulness of this process. This knowledge could also be very valuable elsewhere in the Netherlands, for example in the Western Scheldt as well as in the rest of the world. As a dredging country, the Netherlands can use this knowledge internationally: estuaries elsewhere in the world have problems with sediment, too.