Lancieux Bay

The Lancieux Bay is an area gradually reclaimed from the sea by humans (polder). Over the centuries, the successive construction of dikes (such as the Dike of the Monks, the Roche Dike, or the Beaussais Dike) and irrigation canals has made it possible to develop agriculture.

The landscape has thus been shaped according to human needs, alternating between salt meadows, vegetable farming, bocage pastures, apple orchards, cereal crops, and wet meadows.

The Conservatoire du littoral’s land ownership of the polder has made it possible to initiate a transition of agricultural land. By establishing permanent grasslands without inputs, the aim is to improve water quality and reduce economic pressures in a sensitive area.

The Lancieux Bay has retained a wild character, with a great diversity of natural landscapes, while still being inhabited and used by humans.

Between the 13th and 16th centuries, the Benedictine monks of the Abbey of Saint-Jacut built a dike, now known as the “Dike of the Monks.” It enabled the draining of the coastal marshes for agricultural use. Later, the Roche Dike (18th century) marked the extension of the polder to its current boundaries. The Beaussais marshes (Ploubalay polder), separated from the Lancieux polder by a watercourse, were drained through the construction of a dike in the early 19th century. These two adjacent polders form a coherent unit within the Lancieux Bay.

The Dike of the Monks is the oldest heritage feature of the site and represents a valuable testimony to the development of the land-sea interface over past centuries.

Project actions and outcomes

Climate change and rising sea levels are causing changes along the coastline. During high spring tides, the sea now reaches the tops of the dikes and sometimes overflows them during storms.

Since 2015, new approaches to land management have been explored in order to anticipate the effects of rising sea levels. A strategy of planned dike retreat over time is gradually giving back to the sea what humans had reclaimed.

Accepting the maritime nature of the bay means shifting the perspective of users—allowing the sea to reclaim some space and creating new areas for walking and recreation.

Allowing saltwater to enter the low-lying inland marshes in a controlled way provides a new area for sea expansion. This helps absorb part of the sea’s energy during storms and reduces the cost of building and maintaining protective infrastructure. The bay offers favorable conditions for this flexible approach to coastal management.

Several reconnection scenarios have therefore been evaluated for the Lancieux polder:

• Dike removal
• Creation of breaches
• Installation of water control structures (sluices)
• Natural (uncontrolled) tidal flooding

Thus, in the municipality of Lancieux, this transitional area makes it possible to envision a layered protection system based on:

• The restored historic Dike of the Monks, repurposed as a walking path;
• A new, limited-length dike providing protection for people and property between the Dike of the Monks and the urbanized areas;
• The controlled intrusion of saltwater into the area returned to the sea, creating a new salt meadow marsh that helps dissipate wave energy.

The aim here is to balance heritage, environmental concerns, and the use of natural spaces through a strategy of gradually supporting the landward retreat of the coastline.

Chronology

• July 27, 2011: Resolution by the Lancieux municipal council proposing a system of successive defense layers: relying on the Dike of the Monks and, if necessary, implementing a third dike to protect the campsite and nearby homes.
• 2015: Hazard study – Assessment of the dike’s condition and maintenance recommendations. Definition of the vulnerable area.
• 2016: Meetings with mayors and intermunicipal officials – concerns about how residents might receive the project. Desire to highlight the benefits of the project for local residents as well as for tourism. Growing awareness of the emerging challenges related to climate change, which the Community of Municipalities will have to address within the GEMAPI framework (flood risk and aquatic environment management).
• November 4, 2016: Presentation of the results of geomorphological and landscape university studies to elected officials of the Côte d’Emeraude. Questions raised about project funding and the interest in a reconnection initiative rather than simply allowing nature to take its course. Desire to include cost estimates and assess technical and legal feasibility for each scenario.
• November 15, 2016: Exchange day between elected officials from Val de Saire (Licco site, Normandy) and those from the Bay of Lancieux on adapting coastal territories to climate change.
• 2017: Studies on “Ecosystem services of a Slikke-Schorre complex” and “Biogeomorphology and evaluation of the storm attenuation service of the Lancieux Bay salt marsh” (EPHE study).
• November 21, 2016: Discussions with the municipality of Lancieux on establishing a DUP (Public Utility Declaration) to secure land control—key to advancing the Adapto project.
• November 6, 2017: COPIL (steering committee) meeting for the implementation of GEMAPI.
• July 11, 2018: Site management committee for Tertre Corlieu and Beaussais Marshes.
• August 8, 2018: Meeting with the mayor of Lancieux about land acquisitions and water management in the Lancieux marsh.
• November 2018: Acquisition of parcel AH 238.