Clay Ripening Pilot


To goal of the clay ripening project is to find out with which innovative methods sludge on land can be converted into clay in a useful and cost-effective way. In the pilot multiple stakeholder objectives are merged effectively. As part of the project a business case for a scenario of large scale implementation of the concept is evaluated.

Project goal

The Clay Ripening Pilot is part of the subprogram ‘Useful apply of fine silty sediment’ of the so-called EemsDollard 2050. This is 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.

More specifically, the goal is:

To find out with which innovative methods sludge on land can be converted into clay in a useful and cost-effective way, whereby an economic basis can be laid under the desired sludge extraction from the Eems-Dollard.”

Stakeholder involvement

Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and Water Management), the Province of Groningen, Groningen Seaports, Water Authority Hunze en Aa’s, nature conservation organization Het Groninger Landschap and EcoShape team up in the Clay Ripening pilot to look at different ways of transforming dredged fine sediment into clay soil, applicable in dike reinforcement operations. EcoShape researchers are engaged in practical experiments to investigate which approaches to clay ripening performs best.

This pilot forms a good example of how intensive and constructive stakeholder involvement can lead to a unique project, in which multiple stakeholder objectives, gathered around the reduction of freely moving silts in the estuary, can be merged effectively.

Research questions

The questions below will be answered in the Pilot project:

  • Can clay-ripening through land farming contribute to a (feasible) solution for the turbidity problems in the estuary?
  • How can silts properly be extracted from the Eems-Dollard estuary for efficient clay-ripening?
  • Which clay quality will clay-ripening produce?
  • How can ecosystem services contribute to clay-ripening? For instance, by growth of vegetation to enhance evapotranspiration.
  • How can clay-ripening contribute to ecosystem services? For instance, by producing clay: a natural material for embankments
  • Will clay-ripening provide a positive business case?

Business case clay ripening

The business case evaluates a scenario of large scale implementation of the concept. It takes into account the need for clay to strengthen dikes and the value of the quality improvement of the estuary. In addition, knowledge is lacking about the ripening process of clay. Although clay ripening itself is well known (with a lot of experience in the mid to late 20th century, in the Netherlands, but also especially on the German Eems-Dollard estuary), monitoring a (large-scale) ripening processes of marine sludge and methods to influence this ripening process (i.e. by removal of salt and organic matter) have barely been systematically researched.

The aim of the pilot is to convert 290,000 m3 of silty estuary sediment into roughly 105,000 m3 of clay which meets the requirements of clay for dikes. “Water Authority Hunze en Aa’s” will be using 70,000 m³ of the produced clay to transform/strengthen one kilometer of dike into a Wide Green Dike, in a subsequent pilot project. This is a dike with a shallow slope covered by grass. If the produced clay proves to be successful in this test section, the remaining section (about 11.5 kilometers) of the flood defense structure it forms part of may also be strengthened with this method. In addition, the ripened sediment may be suitable as a raw material for the brick industry and for raising agricultural land.

Movie explaning clay ripening (English with Dutch subtitles).

Scaling up

If successful, future scale up of clay ripening on land could significantly reduce the amount of sediment, freely moving with the tides, in the Eems-Dollard estuary. The aim regarding the ecological rehabilitation is to sustainably extract 1 million tonnes (dry mass) of sediment from the Eems-Dollard annually by 2022 and clay ripening on land could contribute to this goal by offering a suitable material application. This is expected to have a positive effect on the unique ecological value of the estuary.

The pilot will generate knowledge about transforming dredged material into clay soil and the usefulness of this process. This knowledge could also be very valuable elsewhere, where building materials are scarce and intensive flows of fine sediment lead to high dredging costs and/or loss of ecological value, such as in Singapore or the Western Scheldt estuary (NL).