Deltares has tested a new type of floating willow mattress. It keeps the reed marsh that develops on top floating for longer than the present ‘sinking’ reed marshes.
The new type provides better wave attenuation than the older structure. As a result, these floating reed marshes help to defend shores and therefore improve flood protection, ultimately generating savings for water management authorities. The wave attenuation of the new mattress was tested last week in a range of conditions and wave patterns in the Delta Flume at Deltares, The Netherlands.
Floating reed marshes are used throughout the world, primarily to improve biodiversity or water quality, but not for flood protection. Deltares initial attempt in 2010 to enhance flood protection using floating reed marshes partially failed because, in time, they sank.
A new type of willow mattress was developed for the current trial. It is expected to keep floating for a long period. Plastic floats and willow rolls have been attached to the mattress. The floats stop the mattress from sinking and the rolls provide additional wave attenuation.
Victor Beumer, an ecologist with Deltares and the project leader, said: “In a pilot setting the mattress can be designed to be between fifty and one hundred meters long. They can be used in front of the shores of lakes where management agencies want to improve the marsh habitat and improve flood defenses. But they can also be positioned in harbors, when there is enough room, to damp down waves generated by passing ships. We are also thinking about how to use them in rivers.”
Now that the trial has been a success, Rijkswaterstaat and Deltares hope that the new structure can be put into practice.