Willow Woods as Breakwaters

A three-month ‘Building with Nature’ study has been launched by Ecoshape, Deltares and Witteveen en Bos in the channel to the south of the Ridderkerkse Griend nature reserve in the Netherlands.

The study will look at two types of willow woods – pollard willows and an osiery – to see whether it is possible to confirm what models and laboratory experiments have already indicated: can willow woods improve local flood risk management? In other words: are they good breakwaters?

In late September, the willows will be taken out of the water and the results will be presented. It is expected that this type of solution has the potential to make a genuine contribution, both in the Netherlands and in other countries, to improving flood protection.

‘Building with Nature’ assigns a central role to flood risk management against the backdrop of climate change, and to solutions that draw on nature.

It is thought that using willow woods as breakwaters could mitigate the impact of the waves generated by shipping on the River Noord. The exact level of mitigation will be assessed: pressure sensors measure the height of the waves four times a second over the entire length of the section with willows.

They also establish a picture of the extent to which the willows lower the waves, and therefore reduce the height and force of the wave impact, improving protection against floods.

Field research

Models and laboratory experiments have already shown the effect that willows have on waves but this is the first field study of willows.

“We selected this location because the willows here can be located at some depth in the water. That means that we can take good measurements of how the willows work as breakwaters in extreme conditions, such as the submergence of the floodplains, when the water gets as far as the winter dike,” said Wouter van der Star, a project manager with Deltares.

The idea is that the results should produce guidelines.

“On that basis, you can make calculations for other locations in the Netherlands and in other countries showing the potential of willow woods.”

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