3D clay reefs should create a more sustainable home to flora and fauna

Ensuring the flow of water, even at high water levels, and improving the ecological quality of water and rivers go hand in hand at Rijkswaterstaat, the executive agency of the Dutch Ministry of Infrastructure and Water Management, that is dedicated to promoting safety, mobility and the quality of life in the Netherlands. This is also the case when 3D-printed clay reefs are used to stop riverbank erosion, also known as ‘tidal reefs’, before it becomes a full-scale flow slide.

In a new pilot project, Rijkswaterstaat is placing 'tidal reefs' developed by Urban Reef, a Dutch organisation, at a riverbank located in Boxmeer, to the south east of Oeffelt, to restore the habitat of riverine plants and animals in the Meuse River and along its course. The agreements in the European Water Framework Directive (WFD) are important starting points for this project.

The WFD has been the main law governing water protection in Europe since its adoption in 2000. It entails an integrated and river basin district approach to water management to ensure that neighbouring countries cooperate to manage the rivers and other bodies of water they share.

Bank restoration and protection

The riverbank at Oeffelt was created a few years ago and forms a gradual transition from water to land. The bank contains shallows that create a good habitat for many plants, fish and other aquatic life.  According to Esther Stapper, Sustainability Advisor at Combinatie Maaskracht, “Erosion in this kind of riverbank is a natural process. However, the process can become so serious that it requires intervention and we will do this in the near future.”

As part of the pilot, banks that incurred excessive flow slides will be restored and defences to protect restored banks will be created. In addition, a slope to break the wave action that would otherwise erode the bank will be created a few metres from the riverside. “We can then prevent new flow slides occurring again almost immediately,” adds Stapper.

Open stone structure full of microhabitats

“Under normal circumstances, we would build a dam at the riverbank by placing rocks and stones”, continues Stapper. “The purpose would be to break the wave action and ensure a safe habitat and spawning ground for a wide range of species. Rather than placing rocks and stones, we are now using 15 tidal reefs.”

Urban Reef in Rotterdam designed these tidal reefs. They are made from 3D printed clay and are then baked in an oven to give them a ceramic finish. “Other than the rocks and stones that are placed in the river, these tidal reefs are a complex network of hollows with a rough surface,” explains Stapper. 

The hollows in these tidal reefs enable all sorts of river life to nestle in and around them. They then live in a sheltered environment, despite the Meuse’s strong current. This is good for biodiversity, for the ecological water quality and for the riverbank.

“We monitor the situation to see how well the reefs work as a dam, whether they are resistant to the current and the conditions, and, above all, whether they support biodiversity. After all, the aim here is to provide a home to as many species as possible,” says Stapper.

The next step: making tidal reefs with materials obtained locally

The clay that is currently used to build the reefs is not from the local Maasheggen area, but sourcing locally is the way forward, Stapper concludes. “We are trying to make our work more sustainable on all fronts. For instance, by working towards using zero-emission materials.”

Reusing materials that become available at high tide and in the side channels is also part of the project. The ideal future scenario is to reuse 100 percent of the regionally available biomass and dredging spoils. Stapper says that “The dream for the future is that we create these types of reefs with material from the area where they will be placed.”