Adapto: towards a flexible management of the coastline - Orne Estuary

Orne Estuary and Cagny Marsh (Cities of Sallenelles, Amfreville, Ranville) – France

Project leader: Conservatoire du Littoral

Dates : 2018-2022

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, this project is being implemented in 10 pilot areas, including the Orne Estuary site in Normandy. The creation of the canal in the 19th century and the damming of the river have considerably modified the morphology of the Estuary, leading to the disappearance of the salt marsh over most of the site. In 2011, the dike of the Cagny marsh broke down, causing the flooding of low-lying areas. During high tides, the sea occasionally overtakes the top of the dike. In this situation, combined with the prospect of adapting to climate change, a joint reflection is being conducted with all the local players to find solutions. In addition to decompartmentalising the adjoining polders and marshes, the aim is to conserve the qualities of natural maritime areas. Indeed, the recovery of salt marshes’ vegetation in some zones presents economic, biodiversity and landscape interests.  

The actions carried out are as follows: (1) Historical and prospective analysis of landscape evolution; (2) Hydraulic study of the saltwater wedge; (3) Mapping of natural habitats and analysis of their possible evolution; (4) Establishment of an ecological quality indicator; (5) Economic evaluation of the different scenarios for managing the coastline; (6) Analysis of the social perception of users and residents of the site; (7) Development of decision-making tools (multi-criteria analysis) and consultation on possible development scenarios; (8) Educational activities with schoolchildren, elected representatives, users and coast guards; (9) Exchange of experience with other sites and capitalisation on the adopted approach.

Actions

The Adapto project is conducting territorial planning actions relative to the approval of the Multi-Risk Prevention Plan (PPR). The planning activities also include the Local Urbanism Plan (PLU) revision as part of a relocation project of a bicycle path.  

Finally, this action is deployed in the context of a local strategy for integrated management of the shoreline at the hydro-sedimentary sub-cell level. It is carried out by three Public Establishments of Intercommunal Cooperation (EPCI): Intermunicipalities of the Nacre coast; Urban Community of Caen la Mer and intermunicipalities of Normandie Cabourg Pays d’Auge.

The knowledge available on this site shows that maintaining these polders in their current condition is not the only way to approach the future of this land. The recovery of salt marsh vegetation in the Terrains François area encompasses several economic, biodiversity and landscape interests. The Orne, heavily channelled, lacks flood expansion space, thus bringing up the possibility of decompartmentalizing the adjacent polders and marshes to adapt to climate change.

The project foresees the creation of a gutter in a first rank dike. This environmental compensation for the extension of the port of Ouistreham should help restore estuarine habitats by depoldering, thus controlling the volume of incoming water while maintaining the continuity of the coastal path on the Terrains François land (Sallenelles). 

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 department’s rangers
  • Creation of an exhibition on the evolution of the Orne Estuary by 2100

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. Consultative workshops are regularly held among the population. 

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

The Conservatoire du Littoral is carrying out on-site research actions such as historical and prospective analysis of the evolution of the landscapes; hydraulic studies on the saltwater ridge; mapping of the natural habitats and their prospective evolution; economic assessment of the different coastal management scenarios; updated analysis of the social perception of the users; as well as developing decision-making tools (economic and multi-criteria analyses) around possible long-term evolution scenarios.

It 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 qualification of the impact of reconnection projects 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

As there are still relatively few depoldering initiatives in France, the 10 Adapto program sites offer great potential for feedback.

The Conservatoire du Littoral owns the entire site currently being reconnected in the Terrains François polder, and a large section of the submersible zone in the Cagny marsh. 

Support from the Conservatoire du Littoral and the site manager over a long period, which aims to set up more resilient agriculture that is favourable to biodiversity (cultivation of permanent grasslands with extensive grazing), to initiate renaturation actions and to reduce the economic and human stakes to allow the free evolution of the site towards a maritime marsh and finally the development of the ecotourism and cultural potential around these new landscapes.

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 policies.

Partners

Technical partners: sites’ users, Conservatoire du Littoral, Department of Calvados, Bureau de Recherches Géologiques et Minières, Muséum National d’Histoire Naturelle, CPIE Vallée de l’Orne, Maison de la nature et de l’estuaire, State services, Chamber of Agriculture, Urbanism agency, cities and inter-municipalities, economic actors 

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

Resources