ECOPLAGE in Les Sables d'Olonne

La grande plage des Sables d’Olonne – France

Project leader: ECOPLAGE

Dates : 1999-2021

Classification

Risks

Solutions

Actors

Costs

Summary

In the 1990s, several studies established that the Sables D’Olonne beach showed a clear trend towards erosion. This erosion is leading to a lowering of the beach profile, reducing its width and weakening the embankment. To protect the beach, the municipality of Les Sables d’Olonne turned to the Ecoplage® system. The objective was to stop the beach erosion, stabilize its profile and improve the process of beach accretion. 

The Ecoplage® system consists of several drains positioned underneath the beach, parallel to the coastline, and connected to a pumping station whose action creates a dry zone facilitating the infiltration of waves and the deposition of suspended sediments. At the same time, part of the wave energy is absorbed and the erosive effect is attenuated. Dryer sand facilitates sediments’ wind transport, which supports beach accretion. 

Actions

Healthy beach and dune systems are one of the best solutions to protect the shoreline. When the sand level is insufficient, or when the dune and/or the beach are urbanised, sediment flows essential for adaptation are no longer possible. The drainage system allows the beach – particularly at the top – to reconstitute a sufficient sand stock serving as a buffer during storms. The drainage helps the beach to recover better after a storm, acting as a crutch. This system does not block sedimentary transits, it therefore has no negative impact on neighborhood coasts.

The system consists of several drains positioned underneath the beach, parallel to the coastline, and connected to a pumping station whose action creates a dry zone facilitating the infiltration of waves and the deposition of suspended sediments. At the same time, part of the wave energy is absorbed while the erosive effect is attenuated. Dryer sand facilitates sediments’ wind transport, which supports beach accretion. Regular ecological monitoring allows the city of Les Sables d’Olonne to measure the effects of the ECOPLAGE system on erosion.

Outcomes

Following the installation of the first section in 1999, the satisfying results highlighted by the beach scientific monitoring entrusted to the University of Nantes (A. Miossec, P. Fattal, S. Pacaud) encouraged the town to install the second section in 2002.

Monitoring between 1999 and 2005 revealed that the beach had stabilised. Despite the erosion occurring during storms, the Ecoplage® system allows the beach to recover its balanced level more quickly. At the top of the beach, the profile variation is less drastic since the system installation. The supervision and monitoring of the beach highlight an increase in the beach altitude between April 1999 and June 2005. Indeed, studies showed a 10-metre seaward shift in the slope break between the top (dry zone) and the middle sections of the beach as well as a recovery of the rocky bed. 

During the winter of 2013/2014, the beach level dropped drastically subsequently to a series of storms. ECOPLAGE decided to measure the beach recovery following these storms and concluded that the variations are fewer on the drained zones than on the non-drained zones. 

These observations confirm that since the installation of the drainage system the beach of Les Sables d’Olonne has been stabilised. Winter erosion continues to impact the beach but to a lesser extent in the drained area as it is balanced by the accretion favoured by the drainage in the summer season. Today, the system seems to give satisfaction to the elected representatives, technical services and beach users. 

Partners

Technical partners: City of Les Sables d’Olonne, Institute of Geography  and Regional Planning of Nantes University, DDE85 Maritime Service, CETMEF

Financial partners: Conseil Général de Vendée, Conseil Régional des Pays de la Loire, City of Les Sables d’Olonne, D.R.A.S.T.

Resources