Salt marshes can help protect Dutch coast from storms
An experiment in Delft shows salt marshes survive extreme storm conditions and slow waves, knowledge a Frisian water board already uses in dike reinforcement.
Salt marshes (kwelders) withstand storm waves well and partly dampen them through their vegetation, Dutch researchers report in the journal Nature. Researchers from Wageningen University & Research, Deltares and the NIOZ sea research institute took part. Pim Willemsen of Wageningen is the first author.
The finding matters for how the Netherlands protects its coast. Wetterskip Fryslân, the water board in Friesland, already uses the knowledge in its dike reinforcement.
The team dug out blocks of salt marsh measuring 2 by 2 metres in the Peazemerlannen nature reserve in Friesland. Twenty lorries took them to Deltares in Delft. There the marsh was tested in the Deltagoot, a wave flume, under a simulated extreme storm of the kind that occurs once every few thousand years. Dutch dikes are designed for those conditions.
Under those conditions the marsh shrank by 7 millimetres on average and some plants were damaged. The ecosystem as a whole held, and the waves lost force.
Willemsen says salt marshes can help protect dikes by reducing the load from waves. Dikes will not be swapped for marshes any time soon, he says, because marshes do not stop extreme high water. He hopes the knowledge is now used in dike design, since dikes that need less reinforcement can save money.
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kwelder
A kwelder is a salt marsh: a low-lying coastal area, usually along the Wadden Sea, that is regularly flooded by seawater at high tide and overgrown by salt-tolerant plants. Its vegetation and sediment slow down and weaken storm waves before they reach the dikes behind it. This makes kwelders a natural coastal defence that the Netherlands takes into account in its flood protection.
Deltares
Deltares is an independent Dutch research institute for water, soil and infrastructure. It carries out applied research and advice on delta, coastal and river management, including flood protection, for the national government, water boards and other parties. Its work helps shape how the Netherlands designs and maintains its dikes and coastal defences.
Wetterskip Fryslân
Wetterskip Fryslân is the water board (waterschap) responsible for water management in the province of Friesland. Its tasks include regional water systems, water quality and the maintenance and reinforcement of dikes in its area. Because it manages sea and lake dikes in Friesland, its decisions directly affect how the coast there is protected from flooding.