R&D highlights edition 2019

Ecosystems and environmental quality 25 R&D Highlights 2019 T he clay found in large parts of the Netherlands is formed in a natural process in which sludge is deposited before ripening into clay. This natural process of clay formation is also seen on salt marshes in the Wadden Sea, the Eems-Dollard estuary and in the Province of Zeeland. The clay is traditionally used in a range of ways, for example as a building material for dikes. It is also possible to encourage the formation of clay. In recent decades, the Netherlands has gained experience in this field in places including Rotterdam (‘Euroclay’) but a similar process was also seen during the formation of the IJsselmeer polders. The Clay Ripening Pilot Project builds on this knowledge to see how sludge from the Eems-Dollard can be transformed as efficiently as possible into clay that can be used for dikes. There are two benefits if this can be done on a large scale: first of all, soft sediment volumes in the Eems-Dollard can be reduced, enhancing ecological quality. Secondly, a local material is created that can be used in the large numbers of dike-strengthening projects in the region. To produce usable clay from the Eems-Dollard sludge, the material has to ripen in a process during which the water content, salt level and organic matter content are reduced. Various ripening techniques are being tried out in test sections in order to identify the best approach. This involves varying the layer thickness, processing the clay by, for example, ploughing it and creating ridges, and introducing vegetation (oil radish and spring wheat). Ripening is monitored regularly in all these sections. All this information is being used to develop a business case for making dike clay. The clay that is produced will be used on the outer slope of an Eems-Dollard dike in the Broad Green Dike project. Deltares is coordinating the monitoring programme and the accompanying laboratory research in this project. In addition, numerical modelling is being used to facilitate the design work by monitoring the entire process from liquid sludge to solid clay. Deltares is executing the clay ripening project as part of Ecoshape, where we collaborate with Arcadis, Boskalis, HKV, RHDHV, Van Oord, Wageningen Marine Research and Witteveen+Bos. Ecoshape, in turn, is working with the Clay Ripening partners Groningen Seaports, the Groningen provincial authority, Rijkswaterstaat Noord Nederland, the Groninger Landschap Foundation and the Hunze and Aa’s water authority. The pilot project is being subsidised by the Dutch National Flood Risk Management Programme and the Wadden Sea Fund and it is one of the pilot projects in the Eems-Dollard 2050 programme. Contact: Ebi Meshkahti Shahmirzadi, Ebi.MeshkahtiShahmirzadi@deltares.nl , t +31 (0)88 335 7965 Wouter van der Star, Wouter.vanderStar@deltares.nl , t +31 (0)88 335 7269 Further reading : https://www.ecoshape.org/nl/projecten/kleirijperij/ CLAY RIPENING PILOT PROJECT: TRANSFORMING MARINE DREDGING SLUDGE INTO CLAY SUITABLE FOR BUILDING DIKES The Clay Ripening Pilot Project is studying the most efficient possible way of transforming salt dredging sludge into dike clay. The project will use two different sources of sludge from the Eems- Dollard estuary and it was launched in April 2018. Different methods are being tried out in 25 test sections. Deltares is involved in the project through the Ecoshape foundation. Suction induced consolidation (SIC) experiment Overview of the different processing methods Sampling at the Clay Ripening Pilot Project