Adapto: towards a flexible management of the coastline - Polders of Mortagne-sur-Gironde

Mortagne-sur-Gironde, Chenac-Saint-Seurin-d’Uzet – France

Project leader: Conservatoire du Littoral

Dates : 2017-2022

Classification

Risks

Solutions

Actors

Costs

Summary

The Adapto project seeks to demonstrate by example the value of flexible management of the coastline as a solution for adapting coastal territories to climate change.  It is a project financed by the European Union’s Life programme and supported by the Conservatoire du Littoral and the Bureau de Recherches Géologiques et Minières. 

In France, it is being deployed in 10 pilot areas, including the Mortagne-sur-Gironde polders, located in the Gironde Estuary. These polders were created between 1960 and 1970 to install intensive agricultural production on estuarine salt meadows that used to be unexploited and regularly covered by brackish water. Following the Martin storm in 1999, this site was reconnected to the estuary, and the Conservatoire du Littoral acquired the agricultural plots located in the former dyked area. Throughout the 20 years of site depoldering, several lessons were drawn. The objective of the Adapto project is to carry out a multidisciplinary assessment of this reconnection, to share and launch reflections concerning a potential reconnection of the upstream polder. 

The actions carried out are as follows: (1) A mapping of natural habitats; (2) Diagnosis of the agricultural activities in the area; (3) An assessment of sedimentary, fauna, flora and landscape changes following the depoldering of the downstream polder; (4) Educational activities for schoolchildren, elected representatives, users and coast guards; (5) The development of decision-making tools (multi-criteria analyses) and consultation on possible development scenarios; (6) An analysis of the social perception of users and residents; (7) The implementation of an ecological quality indicator; (8) Exchanges of experience with other sites and capitalisation on the adopted approach.

Actions

Following the Martin storm in 1999, the site was reconnected to the estuary while the Conservatoire du Littoral acquired the agricultural parcels located in the former diked area. Since then, the area has been left to evolve freely and is subject to scientific monitoring regarding the fauna, flora and landscape evolutions.

As part of the Adapto project, the Conservatoire du Littoral is deploying a series of educational actions:

  • Development and deployment of an educational programme for primary and secondary school classes 
  • Raising awareness and developing tools for the regional rangers

The project is also committed to organising events to report and communicate the results of the project to practitioners, elected officials and the general public at the local and regional levels. 

It also participates in national actions to capitalise on and put into perspective the other Adapto sites’ experiences.

As part of the Adapto project, the following studies are being conducted:

  • Historical and prospective analysis of landscapes’ evolutions
  • Diagnosis of the agricultural and shellfish farming activities carried out in the area. 
  • Modeling of submersion risks according to different scenarios of coastal management
  • Mapping of natural habitats and analysis of their possible evolution 
  • Assessment of the sedimentary, faunistic, floristic and landscape evolutions following the depoldering of the downstream polder
  • Analysis of the users and residents’ social perception 
  • Development of decision-making (multi-criteria analysis) and consultation tools on possible evolution scenarios 

The Conservatoire is also working on the implementation of an ecological quality indicator. This research project, carried out in partnership with the National Museum of Natural History as part of the Adapto project, aims to develop an ecological quality indicator tailored for natural coastal environments. This indicator should allow the description of the reconnection impacts on the ecological quality of natural coastal areas and the monitoring of their evolution. It is pivotal for the Conservatoire du Littoral and its managers that intend to improve the environmental quality of the coast. It also entails the provision of answers to the concerns expressed by various environmental stakeholders about the potential negative impacts of marine reconnection on species relying on these ‘soft’ environments.

Outcomes

Since the reconnection of the downstream polder, the sedimentation rates observed on this site are exceptional. In 15 years, the initial topographic level has been regained, and a gradual reclaiming of vegetation typical of estuarine marshes has begun. In addition to the intrinsic qualities of these environments, the reedbeds and salt marsh habitats act as a buffer by absorbing part of the wave incident energy, thus reducing its impact on the coast and protecting the dike built in the hinterland.

  • The Conservatoire du Littoral entirely owns the site. The Conservatoire and the manager have been supporting the area over a long period, focusing primarily on the implementation of renaturation actions and the free evolution of the site that has been made easier by the absence of significant economic and human stakes. 
  • A specific estuarine context, with a high sedimentation rate.

Importance of popularising and widely disseminating the results of the monitoring carried out on the site to local stakeholders, in order to strengthen the social acceptability of management choices.

Partners

Technical partners: Conservatoire du Littoral, Conservatoire d’espaces naturels Nouvelle-Aquitaine, Bureau de Recherches Géologiques et Minières, Muséum National d’Histoire Naturelle, CPIE Marennes-Oléron, state services, municipalities and inter-municipalities, economic actors, local communities. 

Financial partners: European Union, Region of Nouvelle Aquitaine, Office Français pour la Biodiversité, Fondation de France, Total Foundation

Resources