2024-01-19 17:17:53
No more than 390 brisk steps. That is the distance you have to walk on average, anywhere in the world, to walk from the high tide line on the beach to the first buildings you see. If you’re on your way to an ice cream from a warm beach, those 390 meters may feel quite far, agrees coastal ecologist Eva Lansu. “But if you consider that this is the average distance for all sandy beaches in the world, then the buildings are very close to all our coasts.”
Lansu published the results of an extensive calculation in the scientific journal last week Nature Communications. Together with colleagues from the Netherlands Institute for Sea Research, the University of Groningen, Utrecht University, TU Delft, Deltares and Staatsbosbeheer, she examined all the sandy beaches of the world. She was able to build on the work that coastal researcher Arjen Luijendijk had previously done for TU Delft and Deltares. It had already built up a huge stock of all the sandy beaches in the world, minus the sandy coasts of Antarctica and other beaches that are permanently under the ice.
Self-written mathematical program
Lansu projected the publicly available OpenStreetMap maps onto those mapped sandy beaches. She then had a self-written mathematical program on her computer draw a line at every kilometer of the coast, perpendicular to the high tide line, and then measured when that line crosses the first infrastructure. The result: on average, a paved road or building is located 390 meters from the high tide line. Not only in Scheveningen or Zandvoort, but also at a beach on the edge of the Amazon rainforest, the west coast of Namibia or the desolate coasts of Australia.
“In summary, it sounds very simple,” Lansu protests with a wink. “In reality, it was a huge job even for a computer. My laptop has been pounding away at these calculations for days.”
The researcher also had to make the necessary corrections. “We didn’t just exclude the icy coasts of Antarctica and the Arctic. We have also excluded small, uninhabited islands, such as Griend in our own Wadden Sea. If my imaginary line met another coastline within 25 kilometers of the coast, without crossing any infrastructure along the way, it would disrupt our measurements too much.”
Waves that swallow entire houses
With a total of more than 235,000 measurements, Lansu and colleagues’ research ultimately covered regarding a third of the world’s ice-free coasts.
The mere 390 meters of undeveloped coast that separate our roads and buildings from the sea is problematic, says Lansu. “Beaches and dunes form a natural and, above all, very good coastal defense. They are a buffer between the sea and habitation. In more and more places you can see what happens when that buffer becomes too narrow or disappears completely. You really don’t have to search long on the internet to find images of waves swallowing entire houses or roads.”
But it is more than just coastal defense, the researchers say. A lot of drinking water also comes from the buffer between the sea and buildings. And, certainly not last, the researchers emphasize the natural values of the dunes. “When we also include biodiversity in our analysis, we see that natural wealth decreases extremely when the buffer between the sea and habitation becomes too narrow.”
The distance between the coastline and buildings is especially short in countries with more inhabitants per square kilometer and with a higher gross national product. “A bit of an open door perhaps,” admits Lansu. “People like to live near the coast, most of the fertile land is located in deltas and the more people, the busier it becomes on the coast.”
Pick up Scheveningen and move it inland
There is also a partial solution to the problem, the researcher thinks. “With global warming and sea level rise, you will see problems arise along more and more coasts. And then countries with a high GDP, such as the Netherlands, with many inhabitants close to the coast, can absorb that for a while. For example, we are very good at expanding the beach. Nowadays we also do this with enormous nourishments such as the sand motor at Monster. This allows us to move the coast seaward for several decades in one fell swoop.”
Yet that solution cannot continue forever, Lansu thinks. “At a certain point we can no longer supplement once morest the rising sea. In our article we say that moving infrastructure is the best solution. That may sound a bit naive; as if you pick up Scheveningen and move it inland. But there comes a time when the tide turns. Then a disaster strikes and we have no choice.”
Until then, the researchers emphasize that it would be good to preserve what we still have in the way of natural buffers. “Fortunately, our analyzes show that coastal protection works well. In protected beach and dune areas, the average distance to infrastructure and buildings appears to be four times as great.”
Hondsbossche dike and dunes
“The increasingly trapped coast, or coastal squeeze in the jargon of international coastal science, is a hot topic among my colleagues.” This is what professor of coastal ecology Tjisse van der Heide of the University of Groningen and the Netherlands Institute for Sea Research says, who is also the scientific supervisor of the research of PhD candidate Eva Lansu. The history surrounding the Hondsbossche and Pettemer Sea Defenses is a famous case study, Van der Heide knows. The dunes there had been too narrow for good coastal defense since the Middle Ages, following which a dike was finally built in 1880.
“A natural coast is dynamic, such a dike is obviously not,” emphasizes Van der Heide. Because the dike was also in danger of becoming detached from the retreating first row of dunes, it was decided at the beginning of this century to create a completely new beach and dune area in front of the dike, which resulted in the Hondsbossche dunes in 2015.
“A beautiful piece of engineering work,” says Van der Heide. “But if you look closely, you will also see how little we actually know regarding natural coastal dynamics. The dunes laid in front of the dike ultimately do not really resemble natural dunes, which are so flexible that they can grow with sea level rise. You cannot simply recreate real, natural dune areas. It’s better to just protect them properly.”
Also read:
Dunes instead of dikes: the success of a revolutionary experiment near Petten
God created the earth, except for a stretch along the coast of North Holland. There a new dune landscape has been created by human hands. With a lot of help from the wind, that is.
Climate change, law reform and ‘tourismophobia’, the battle for the Spanish coast rages on
A 1988 coastal law was intended to provide clarity regarding housing construction and activity along the Spanish coast. But the application of this law often causes uncertainty. With climate change threatening the coasts, further legal reform seems necessary.
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