The Leyre Delta

Until the end of the 18th century, the Arcachon Basin consisted of extensive salt meadows, which were diked by large private landowners for productive purposes.

The Domaine de Certes et de Graveyron and the Île de Malprat, sites managed by the Conservatoire du Littoral in the heart of the Arcachon Basin, are influenced more or less directly by the Leyre Delta and provide a natural window into an urbanized area. These three sites are strongly linked to the territory’s identity, and the local population is very attached to them.

For both the Domaine de Graveyron and the Île de Malprat, the breaches observed in the dike system have been allowed to evolve naturally. The hydraulic compartments regularly flooded by the sea have changed configuration, transitioning into salt meadow areas.
After about twenty years, it is observed that the opening of the Graveyron breach has stabilized at a width of approximately 20 meters. Around this breach, the dike has transformed into a berm that has lowered and widened but has not completely disappeared.
Inside the hydraulic compartment, a salt meadow has established itself and has gradually elevated over time. This area now helps absorb wave energy through its structural characteristics (surface area, roughness, and absorption by salt meadow vegetation) and its altimetric profile.

Project actions and outcomes

Benefiting from flexible coastal management since 1996, the Leyre Delta site is an advanced location.

Numerous studies support the area, notably the multidisciplinary research program Liteau Barcasub from 2010 to 2013, which resulted in the proposal of several possible evolution scenarios for the diked areas of the Delta.

Adapto will build on the experience gained from sectors partially reconnected to the sea, which benefit from a large amount of data collected over the past 15 years.

The Adapto project at this pilot site will primarily focus on highlighting this data to share it with the public through the creation of educational tools and programs.

The landscape approach, to be developed in cooperation with the Council of Architecture, Urbanism, and Environment 33, will be a valuable tool, as will the historical analysis.

Chronology

• October 11, 2017: Spanish managers of the European Franco-Spanish cooperation project Txinbadia+ visit the Leyre Delta site.
• 2018: Photographic monitoring campaign, the results of which will be compared to those from 2007.
• May 30, 2018: The Adapto project is presented to DREAL Aquitaine, to the Sea and Coast service of DDTM33 in October, at the Rivages Council, and at the Coastal Dynamics Workshop of the Ministry in Capbreton.
• March 26, 2018: The Adapto project is presented to the management committee bringing together Gironde elected officials, the manager (Cd33), and the Conservatoire.
• October 2018: Meeting of Aquitaine Coast Guards on the theme of climate change adaptation, with the participation of Hervé Le Treut, Cyril Mallet from the Aquitaine Coast Observatory, the Director of GIP Littoral Aquitaine, the South Atlantic Botanical Conservatory, and Caue 33. Presentation of the Adapto project and the pilot site of the Delta.
• January 17, 2019: Presentation of the Adapto project to the management committee of the Domaine de Certes and Graveyron, involving Cdl and CD33, in the presence of departmental elected officials.
• February 7, 2019: Conference at the Aquaforum of the Terre et Océan Association in Bègles (33), presentation by the Aquitaine delegation of flexible coastal management actions and the Adapto project for pilot sites in Aquitaine (Leyre Delta – Ile Nouvelle).