Salt marshes protect our coast, but not where it is most needed

At its lowest level, the Netherlands is 6.78 meters beneath sea stage. With out dikes, dunes, waterworks and salt marshes we might by no means be capable of hold the water out. Researchers have now examined to what extent the salt marshes alongside the sides of the Wadden Sea are doing their protecting work sufficiently.

Scientists from the College of Groningen, in collaboration with the NIOZ analysis institute and the Noordzijldervest water board, have been monitoring the waves for 3 years. monitored that crash on the northern Dutch coast throughout storms. “After a storm, we shortly visited the analysis space to check the influence of the waves,” says ecologist Beatriz Marin-Diaz. That analysis space involved the coast of the Wadden Sea, the place mud flats and salt marshes are positioned. “Most data in regards to the safety of those salt marshes comes from fashions. There’s little or no information on what really occurs within the open air.”

Mapping the Wadden Sea Area
So she determined to go on her personal. She measured the peak and width of tidal flats and salt marshes, seemed on the vegetation that grew there and recorded the power of the waves and the peak of the tide line on the dikes. Marin-Diaz acquired information about wind pressure and wind path from the KNMI. Lastly, she charted the event of the salt marshes by trying again twenty years on the modifications in measurement. “Normally, the salt marshes have remained the identical measurement or expanded to 400 metres. They’ve shrunk in only some areas,” says the researcher Scientias.nl.

After three storm seasons, she was certain: the salt marshes certainly diminished the influence of the waves on the dikes. “The primary message is that the salt marshes are more practical in decreasing wave motion in opposition to the dikes than naked mud flats,” explains Marin-Diaz. “The wind path does not matter. Publicity to the Wadden Islands and vegetation additionally had no affect.” This shocked the researcher considerably. “It was stunning that the salt marshes that had been increased at all times resulted in much less wave motion in opposition to the dikes, whatever the wind path of the storm.”

Salt marshes present safety
What did matter was the peak of the shoreline and the width of the salt marshes: the upper and wider they had been, the extra safety they supplied in opposition to the waves. How precisely does that work? “The dykes in entrance of salt marshes have to resist much less excessive waves and the water additionally hits the dykes much less excessive throughout storms in comparison with dykes that solely have naked mudflats in entrance. In different phrases, these areas are higher protected in opposition to flooding. It’s because the salt marshes cut back the waves as a result of they’re increased up and comprise vegetation,” explains Marin-Diaz.

However the researcher found much more. For instance, it turned out that there have been no salt marshes in areas the place the tidal flats are usually not so excessive. The underside line is that the salt marshes increase in areas the place the tidal flats in entrance are increased (greater than half a meter above the typical native sea stage), whereas the salt marshes retreat the place the mud flats are eroding resulting from erosion. “The areas the place the salt marshes don’t develop want extra safety. Our conclusion is subsequently that different options are nonetheless wanted at some places, as a result of pure safety will not be efficient sufficient.”

Estimate the required dike reinforcement
That’s good to know for the water board. “The research gives information with which we will estimate the wave peak and the water stage in opposition to the dike, relying on the presence and properties of the salt marshes in entrance of it,” say Kornelis de Jong and Jan-Willem Nieuwenhuis of the Noorderzijlvest water board. “We will now decide what dyke reinforcement is required in locations with and with out salt marshes. That has an influence on future dyke enhancements and their prices.”

In areas the place the salt marshes don’t type naturally, human interventions might help to get them there. “You may create sediment fields or add sediment to stimulate the expansion of latest salt marshes, though there are additionally disadvantages to creating new salt marshes. That is on the expense of the mudflats, that are essential for wading birds, for instance. Furthermore, in some areas, salt marshes merely can not develop, even when we help. In that case, reinforcing the dikes could also be mandatory,” concludes Marin-Diaz.