A quarter of the world’s beaches are narrowing down, according to Delft PhD research in the Netherlands. Other beaches remain fairly stable in size, or are even growing.
The recent study analysed millions of satellite images of some 300,000 km of sandy coastline around the world. When compared to 1984, the study shows that beaches have narrowed down at about 70 thousand kilometres of coastline, or nearly 25%. What’s more, approximately 12 thousand kilometres of beach erodes with more than 5 meters per year.
“Grains of sand are carried along by the water flow at those places and blown away by wind, without returning,” says Arjen Luijendijk of TU Delft.
What is causing the narrowing of beaches?
While raising sea levels speed up coastline erosion, a more important cause is the blockage of the supply of fresh sand from rivers. Indeed for tens of thousands of years, rivers have been carrying rock breakdown from mountains which eventually ends up on beaches after being broken down into sand. The construction of dams and ports for increasingly larger ships have hampered the supply of sand in many places. On the contrary, in places where rivers are unaffected, beaches actually grow.
In his research, Luijendijk combined millions of satellite images with (new) calculation models in order to monitor the movements of beach sand. The study aims to help look ahead:
“We are working on a calculation tool that will allow us to determine how much sand we need to put in at crucial places in order to keep things safe.” Often in such cases, the content of a football stadium full of sand would mean that the coast is safe for another twenty years.
How can countries keep their coastline from narrowing down?
According to Luijendijk, sand suppletion is a proven way for more and more countries to keep their coastline in order.
‘‘Small sand nourishments and large-scale, natural-based sand motors should certainly be placed in the coastal guard’s toolbox”, says Gerd Masselink, professor of coastal geomorphology at the University of Plymouth. Elsewhere dams, dikes and sometimes breakwaters are necessary.
Other glaring cases of narrowing beaches
Famous beaches such as Copacabana and Ipanema in Rio de Janeiro have a solution in place already. Sand is actually deposited regularly at these beaches; with plenty of money being spent to do so. On the contrary, for example, is the case of Negril beach in Jamaica, for which a similar fate awaits as with Hellshire Beach years ago. Without adequate resources for such small-scale tourism spots, beaches fall prey to the sea. According to researcher Luijendijk, it can even form a danger for coastal residents.
Click here for a world map with a complete overview of long-term shoreline changes.