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Pyrénées-Orientales/Sainte-Marie-la-Mer: underwater nets to fight against beach erosion

This Thursday, May 19, 2022, in the coastal waters of Sainte-Marie-la-Mer, the company S-Able has installed an unprecedented device aimed at creating an underwater dune in order to prevent erosion from nibbling the beach. Supported by the urban community of Perpignan, this experiment also benefits from co-financing from the Occitanie region and the Bureau of Geological and Mining Research (BRGM).

This is a great first in the Mediterranean. This Thursday, May 19, the S-Able company installed at sea, north of Sainte-Marie, about 280 meters from the shore, a system of experimental nets intended to fight against coastal erosion by creating an underwater dune. protective.

The operation of the device is very simple. It is a structure extending over a line of 200 meters and composed of four to six superimposed green nets. Weighted on its sides by chains, it is raised on its central axis thanks to buoys, in order to create a slope on a little more than one meter in height. All submerged at a depth of between three and five meters.

We use the energy of the sea to capture the sand

Inventor of the system and manager of the company S-Able, which manufactures and installs it, Dominique Michon, originally from Loire-Atlantique, says he designed this system based in particular on the observation of beaches, where the preservation of dunes helps prevent the escape of sand. “There, it’s the same thing, but under water, sums up this former fisherman with training in the French Navy. When the swell rises, the sand it carries passes through the mesh and is captured inside the net. We use the energy of the sea to capture the sand and create an underwater dune to prevent beach erosion.”

The sector chosen to install these first experimental nets in the Mediterranean was not chosen by chance. Located not far from the first groyne to the north of Sainte-Marie-la-Mer, opposite the Le Spot beach club, this is a red zone in terms of erosion in the resort. “Since last summer, we have lost between seven and eight meters of beach in this sector”, deplores the mayor of the town, Edmond Jorda.

An innovative, natural and gentle solution

It is in this context that the urban community of Perpignan launched this experiment. “Beyond the sand refilling that we carry out each year at this location, we were looking for an innovative, natural and gentle technical solution to fight against erosion and trap the sand over the long term”explains the head of the major works department of the intercommunality, Aurélien Querbes.

Wishing to extend the project to its entire coastline if the test is conclusive, the Occitanie region also participated in the financing of the test. “Scientists predict a sea level rise of between 70cm and one meter by 2100, recalls regional councilor Christophe Manas. We have a responsibility to find ways to either adapt or limit this phenomenon.”

The objective of setting up these experimental nets, which have already been successfully tested in the laboratory and in the northern bay of Authie, subject to tides, is to see if they work as well in the Mediterranean. The services of the Agglo and the Bureau of Geological and Mining Research (BRGM), which also co-financed the test, will be responsible for ensuring follow-up over one year. “And if it works, we will put otherspromises Dominique Michon, who specifies that being green and therefore clearly visible, his nets are harmless to fish. To have convincing results, for this to regain beach, I think it would be necessary to put three lines of nets in parallel over a length of 600 to 800 meters.

The project in numbers

200 meters of nets installed this Tuesday and 200 others announced for the next few months.

€130,000 excluding tax invested in making and laying the nets.

13 months of experimental follow-up.

€95,425 investment excluding taxes for the monitoring program, which will notably include camera monitoring, bathymetric processing and hydrodynamic monitoring/modelling.

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