Coastline Retreat : Challenges and Territorial Planning Strategies

By Julia Jordan, Deputy Director for Water and Marine Risks; Laura Dréan, Coastal Change Analyst; and François Hédou, Project Director for Coastal Knowledge and Management, Cerema.

The French coastline is a constantly evolving environment, with 20% of its natural shores currently retreating. As sea-level rise accelerates, planning strategies must adapt to ensure that today’s attraction to coastal areas is transformed into sustainable development projects rather than becoming an unsustainable burden for future generations.

The Coastline Is Not a Fixed Landscape

Developing robust planning strategies requires relying on objective and historical data. This is the purpose of France’s National Coastal Erosion Indicator (INEC), established under the Environmental Code and produced by Cerema since 2017, following a methodological process conducted under the guidance of the Scientific Committee of the National Strategy for Integrated Coastal Zone Management.

The methodology consists of comparing the position of the natural shoreline during a recent period with its position in the 1950s. This work is based on the digitization and comparison of shoreline positions observed along thousands of kilometres of mainland and overseas French coasts, using systematic analysis of historical and contemporary aerial photographs.

The results of the indicator provide a measure of coastal erosion: over the past 50 years, approximately 30 km² of land have been “returned” to the sea in retreating coastal areas. To put this into perspective, this represents roughly 4,200 football fields. While all French coastal departments are affected, significant differences exist. The low-lying sandy coasts of the Atlantic seaboard are far more vulnerable than the rocky shores of Brittany.

An updated version of the indicator will be released in 2026, incorporating, among other improvements, data collected by local shoreline observatories.

Coastal Attractiveness: Growing Challenges in the Face of Climate Change

Coastal erosion must now be understood within the broader context of accelerating sea-level rise and the increasing urbanisation of coastal areas over recent decades. Coastalisation is now well documented worldwide. In France, 8% of all housing units are located within the first kilometre of the shoreline. This concentration of people and activities, combined with projected shoreline retreat and the gradual inundation of low-lying areas, reveals the scale of the challenges facing society.

To support the National Shoreline Committee, particularly in assessing future financial implications, Cerema—the French public reference body for climate adaptation—published in 2024 an assessment of assets exposed to shoreline retreat by 2050 and 2100.

The 2050 horizon corresponds to a “likely” scenario that assumes the continuation of current shoreline retreat trends while maintaining and preserving existing coastal protection structures (seawalls, rock armouring, groynes) currently identified along the French coast. Under this scenario:

• 5,200 housing units could be threatened, including 2,000 second homes;

• 1,400 business premises would be exposed;

• The market value of these assets is estimated at €1 billion;

• 16 kilometres of major roads could be affected, creating significant challenges for transport networks and territorial accessibility.

Cerema also developed a “no-action” or “breakdown” scenario for 2100. This model assumes the loss of coastal protection structures combined with a one-metre rise in sea level. The scenario highlights the critical vulnerability of low-lying areas, often located behind the seafront, which could gradually become permanently inundated. Under this scenario, the scale of exposure increases dramatically:

• 450,000 housing units affected, including 300,000 primary residences;

• 55,000 business premises and 10,000 public buildings at risk;

• 1,000 campsites affected, including 640 losing more than a quarter of their surface area;

• 1,800 kilometres of roads and 240 kilometres of railway lines compromised;

• A potential financial cost estimated at €86 billion.

This work has also generated valuable new knowledge about French coastlines. For example, it enabled the mapping of low-lying coastal areas based on the level of the Highest Astronomical Tides (HAT), combined with an additional one metre of water corresponding to the IPCC’s most pessimistic sea-level rise scenario. It also led to the development of a database on “event-driven” shoreline retreat, documenting sudden coastal erosion associated with extreme events such as storms. All these results are available through the Géolittoral portal.

These scenarios help raise awareness among national stakeholders about coastal issues, climate change, and their consequences. They highlight not only the potentially enormous cost of inaction but also the need to begin preparing responses today.

Integrating Shoreline Retreat into Urban Planning: A Major Shift

The transition from a model centred primarily on hard-engineering coastal defences to a more integrated and adaptive approach to coastal management through local strategies represents a significant cultural shift in France. The 2021 Climate and Resilience Act now requires the preparation of local shoreline retreat exposure maps, incorporating development restrictions in areas at risk. To date, 371 municipalities have voluntarily committed to this process.

The national assessments described above do not replace local shoreline mapping studies. These local analyses rely on a more detailed understanding of site-specific coastal processes and are intended to inform spatial planning documents. Their purpose is to identify areas exposed to shoreline retreat over two key time horizons:

• 0–30 years: Within these zones, a principle of non-development applies in order to avoid placing new assets in the path of foreseeable short-term risk.

• 30–100 years: Development remains possible but is subject to requirements for reversibility or removability of structures, allowing for future relocation if necessary.

To support local authorities and ensure greater consistency across territories, the Ministry for Ecological Transition has published national guidance prepared by Cerema and BRGM (the French Geological Survey). The document provides a structured methodological framework, including analysis of historical shoreline dynamics, consideration of local erosion processes, and integration of local adaptation strategies.

These recommendations are not strictly prescriptive, allowing them to be adapted to local circumstances. However, they provide the essential technical foundation needed to improve the reliability and consistency of studies. The French government supports this effort by subsidising up to 80% of study costs. A model terms-of-reference document is also available to help local authorities manage these complex assessments.

Avoiding the Growth of Ecological, Economic and Social Debt

Anticipation is the cornerstone of resilient coastal planning. Questions relating to the maintenance, design and cost of shoreline protection infrastructure will play a determining role in selecting the most appropriate approaches, both spatially, according to local contexts and challenges, and over time. Cerema continues to work on these issues, but evidence already shows that waiting for a crisis before acting will prove far more costly than planning the transition today.

The preparation of local exposure maps represents only a first step. The integrated shoreline management strategies developed by local authorities will help clarify future trajectories and management approaches.

The challenge is to avoid passing on three forms of debt to future generations:

• Ecological debt, by preserving healthy coastal ecosystems capable of playing their full role in buffering the impacts of the ocean;

• Economic debt, by anticipating change and supporting the sustainable development of activities that are essential to the vitality of coastal territories;

• Social debt, by fostering a shared culture of risk awareness and preparedness.

Successfully adapting our coastlines requires more than legal and technical tools; it demands a transformation in the way we relate to the sea. Transparent information is the first lever of resilience. By inventing a new way of inhabiting coastal areas—one that is more humble in the face of natural forces, more supportive of communities, and more respectful of coastal dynamics—we can ensure that these territories remain places to live, work, and dream for the generations of 2100.

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Further Information :

• Consult the Géolittoral Portal to access data (Géolittoral) from the National Coastal Erosion Indicator (INEC) and the associated methodological guidance documents.