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 Building with Nature Guideline > Projects > Clay Ripening Pilot Project, Delfzijl - NL

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Clay Ripening Pilot Project, Delfzijl - NL


Location: Eems-Dollard Estuary – Delfzijl (The Netherlands)

Date: 01-01-2018 - (expected) end date: 1-1-2022

Involved parties: Rijkswaterstaat, Province of Groningen, Groningen Seaports, Water Authority Hunze en Aa’s , Het Groninger Landschap and EcoShape. The project is financially supported by the Waddenfonds and the Dutch national flood protection program HWBP.

Technology Readiness Level 3: Proof-of-Concept Demonstrated, Analytically and/or Experimentally

Environments: Estuaries, Ports & Cities

Keywords: soft sediment, sludge, clay, ripening, desalination, dike reinforcement, water quality, ecology, economic basis

Building with Nature designTraditional design

Collecting fine silty sediments from the estuary and converting this into clay soil creates a win-win situation: the water quality improves and more clay becomes available for reinforcing dikes, and raising land behind the dike.

In traditional dredging, fine sediments dredged from an estuary are disposed at sea or stored in large (land) disposal sites, without further application or use. (picture: Slufter disposal site – NL).




Excessive levels of sediment in the water column in the Eems-Dollard estuary have a negative impact on water quality and thus also on biodiversity. Large amounts of sediment accumulate in ports, making regular dredging necessary.

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Initiation Phase

The Clay Ripening Pilot is part of the subprogram ‘Useful apply of fine silty sediment’ of the so-called Eems-Dollard 2050, a program aimed at improving ecological values by reducing the turbidity in the Eems-Dollard estuary. All projects within this adaptive program share the same goal: “Balancing ecological values and economical advantages”.

The pilot is based on collecting silty sediments from the Eems-Dollard estuary and converting it into clay soil creating a double win situation: the water and ecosystem quality in the estuary improves, and more clay soil is available for reinforcing sea dikes along the Eems-Dollard estuary. The material may also be used for raising agricultural land to compensate soil subsidence.
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Planning and Design Phase

Activities in the field started in 2018 by setting up two depots and filling these with fine sediments by pumping of dredged material (see figure 2 in section 'Operation and Maintenance Phase'). One depot is for ripening dredged sediments from the Zeehavenkanaal, the channel leading to the port of Delfzijl. This depot is located just behind the sea dike (figures 1.1 and 1.2). The other depot is located further east, outside the sea dike on the salt marsh, and will be filled with sediment dredged from the Breebaart polder near Termunten (figures 1.1. and 1.3), a polder that inundates with the tides and is thus filled with sediment continuously, as a kind of silt-trap. The sediments in both depots are transformed into clay soil by means of processes such as dewatering, desalination and oxidation of residual organics.

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Construction Phase

The construction of a depot for clay ripening can roughly be distinguished in six steps:

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Operation and Maintenance Phase

The marine sediments are dredged relatively close to the depot location and are brought into the depots by pressure pipes (Figure 2). The location of the dredging is chosen carefully based on exploratory research of the seabed, relating to the environmental quality and physical characteristics of the sediment (high density, suitable for future application).

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Lesson Learned

As of end 2018, the project is expected in the next 2-3 years to show valuable information regarding the transformation of clay-water mixtures into clay soil. The following lessons have so far been learned from clay ripening in the first depot, at location Delfzijl.

It is possible to create a pilot which investigates estuary quality improvement, production of geo-technically suitable construction materials as well as economic stimulation. By tackling those goals simultaneously, a diverse group of stakeholders can participate.

Other findings are:

  • Ripening of dredged fine sediment mixtures on land does not need to be associated with environmental pollution if sufficient care is taken in the choice of the sediment dredged.
  • Transforming marine fine sediment into clay soil requires removal of water and salt, oxidation of organic matter as well as enough time for the relevant processes to occur.
  • The depots have been filled in two rounds: a first batch is placed in April 2018, followed by a second batch on top in July 2018 (in most of the compartments). One of the advantages of working in two rounds is the possibility to adjust the volume, for example when expected fill densities are not reached. Consolidation takes place during the two filling rounds resulting in a higher (dry) soil storage volume.




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