Orne Estuary

The morphology of the Orne estuary, from Caen to the sea, was significantly altered following the construction of the canal in 1857. After passing through Caen, the Orne River splits into two straight lines that structure the surrounding landscape. These two watercourses—the Orne and the canal—flow between two agricultural and urban plateaus, shaping a variety of evolving landscapes. The western corridor, guided by the canal, conveys an industrial and port-related character. To the east, the river changes with the tides, feeding a rich natural heritage: the Bay of the Orne.

The river’s embankment led to the disappearance of salt marshes (schorre ) over much of the site. The banks of the Orne were reclaimed (polderized) all the way to its mouth. The Cagny marsh dike was built in the 18th century, transforming the former meander and its salt meadows into grazed wet grasslands. The François Fields polder is the result of more recent embankment works (1960s) on a tidal flat. As a result, downstream from the Montalivet dam (in Caen), the lateral expansion zone for natural habitats and tidal flooding now remains along only about one-fifth of the river’s length.

In 2011, the Cagny marsh dike failed, causing flooding in low-lying areas. During high spring tides, the sea occasionally overtops the dike, forcing the temporary closure of the cycle path built along its crest. This calls for a reassessment of the dike’s future—and more broadly, of the land behind it.

Today, available data on this site indicate that maintaining these polders in their current state is not the only possible vision for the future of the area. In fact, the return of salt meadow vegetation in the François Fields sector offers clear benefits in terms of economy, biodiversity, and landscape.

On the Cagny marshes, the LiCCo program (Coastal and Climate Change), carried out from 2011 to 2014, provided valuable insight into the evolution of the Orne estuary. A collective reflection was launched with all local stakeholders on what the coastline of tomorrow could look like. Adapting this estuary in the context of climate change and rising sea levels is based on:

• A vision for 2050: the development of a larger, deeper estuarine area to increase climate resilience;
• A trajectory to 2025: implementation of concrete, localized projects to re-establish lateral floodplain connectivity and promote coastal mobility.

The Orne, heavily canalized, lacks sufficient space for flood expansion—raising the issue of opening up the polders and affected marshes.

Project actions and outcomes

At Sallenelles, the approach involves working with local stakeholders to define public access facilities during the re-flooding of the François Fields.

Regarding the Cagny marsh, a process of reflection and project definition needs to be initiated, starting with historical and landscape analyses, followed by the development of prospective scenarios. In a scenario involving sea level rise, erosion, and rising groundwater levels, the current Cagny marsh dike would become obsolete and lose its protective function. Based on this analysis, the Conservatoire du Littoral and the Calvados Departmental Council, which manages the natural areas, are working on an alternative to the existing cycle path.

If the maritime character of the marsh is restored, new walking, cycling, and boating routes would offer visitors new experiences. Starting from the Nature and Estuary House, these paths contribute to maintaining the site’s appeal at the heart of the bay. At the same time, a consultation process should be conducted with Normandie Cabourg Pays d’Auge, the Chamber of Agriculture, Safer, the Conservatoire du Littoral, and local farmers to plan the gradual adaptation of their working tools over the coming years for this scenario.

Preliminary Study for 2050: Download now

Furthermore, addressing climate change requires a broader perspective than just the mouth of the Orne estuary (the intervention area of the Conservatoire du Littoral). Restoring the maritime character of the Orne demands a well-considered strategy at the scale of the entire Orne River—from Caen to the sea. Planning adaptation through different stages up to 2050 involves the participation of various stakeholders:

• The Calvados Department (greenways, sensitive natural areas, etc.), the CPIE
• The City of Caen, the Communauté de commune Caen la Mer, the Communauté de commune Normandie Cabourg Pays d’Auge, and the municipalities located downstream of the estuary (GEMAPI, urban planning documents, urban development of the peninsula…)
• Ports of Normandy (master plan for port development)
• State services (Risk Prevention Plan).