They are researchers Jim van Belzen, Gerlof Rienstra and Tjeerd Boum from the NIOZ Royal Netherlands Institute for Sea Research and van Rienstra Policy Research and Policy Advice BV. Their report will be presented today at the Climate adaptation summit. It was written on behalf of the World Wildlife Fund.
The hinterland continues to decline and become salty
The crux of the matter is that, according to the researchers, lifting the dikes over and over again is no longer a good long-term solution, as it means the hinterland continues to decline and become saline. In addition, according to the report, switching polders offer prospects for new economic functions, which means that this option ultimately costs less than reinforcing dikes.
The principle of an alternating polder is based on a double dike. An opening will be made in the current sea wall, which will allow free flow and ebb in the land behind. The sea is then stopped by a second dike: an old existing sea dike, a dormant dyke or a new second dike to be built. This may be slightly lower and cheaper than the current dike, as the worst force will already have been removed from the water behind the first dike.
Three to five inches per year
The land between the dikes will then rise gradually due to the silt that remains after each flood. Along the Western Scheldt, according to the researchers, this will be done with an increase of about three to five centimeters per year. After half a century, the land between the dikes is thus up to three meters higher.
In the meantime, aquaculture can be practiced on the growing land, saline crops can grow, and normal agriculture can later be practiced again on the fertile marine clay. In addition, part of the alternating polder can also be converted into a nature reserve for waders and other plant and animal species depending on tidal zones.
Researchers also know that ceding land to sea in Zeeland is a sensitive issue. But according to the report’s first author, environmentalist Jim van Belzen, their proposal is different. “Unlike the previous stripping, the double dykes with reversible polders have the main purpose of water security; something that is deeply rooted in the soul of Zeeland.” He therefore expects much less opposition to the implementation of this plan than, for example, the skinning of the Hedwig.
In addition, the switching polder can also be used, which is generally popular with many Zealander. “You can get a lot of value out of it, for example through mussel culture or samphire. And through nature, which is good for tourism. Because of these returns, the cost-benefit analysis of an alternating polder is also very important. more favorable than continuing to raise it. existing sea walls. “
‘Not just in thirty years’
The authors argue that the Western Scheldt, which will deposit a relatively large amount of silt in exchange polders, will produce the fastest return in terms of coastal defense. In the Oosterschelde, where less silt floats in the water, it will take longer before the earth behind the dike is sufficiently raised. “Considering the approach to sea level rise, therefore, it is absolutely important to implement these kinds of measures on time and not just thirty years from now,” says Van Belzen.