Bay of Lancieux-Beaussais. Flooding caused by a 100-year event. Hypothesis of a 250m breach in the Ploubalay dyke with the La Riche dyke left intact. © Adapto
Outstanding result / Life Adapto project: flexible solutions to erosion and coastal flooding
BRGM and the Conservatoire du Littoral are stepping up their cooperation to protect and promote the French coastline, based on a partnership agreement for the period 2022-2026. An interface between land and sea, the coastline is undergoing major transformations as a result of climate change. The consequences are already visible and will certainly be of huge importance in the future. The issue here of course is not only rising sea levels, but also the impact on human activities.
In response, BRGM and the Conservatoire du Littoral are combining their knowledge and expertise in order to contribute to efforts to manage, protect and promote the French coastline.
Flexible management of the coastline
The first partnership, which was signed in 2015 for 5 years, paved the way for the joint development and implementation of the Life Adapto project, for flexible management of the coastline. The aim of this recently completed project was to test and demonstrate the effectiveness of new nature-based solutions (NBSs) to erosion and coastal flooding.
Adapto’s objective was to explore new solutions to erosion and coastal flooding on natural coastlines, taking particular account of the growing impact of climate change, which results in more frequent extreme climate events, as well as rising sea levels.
Ten pilot coastal sites of natural and agricultural land were chosen to test this management method: the Bay of Authie and the Bay of Lancieux, the Orne estuary, the Moëze-Brouage marsh, the Gironde estuary, the Leyre delta, the Petit and Grand Travers, the Vieux Salins site in Hyères, the Golo delta and the Mana rice fields. These experimental sites, nine of which are in mainland France and one in French Guiana, represent a range of different coastal environments, from the low-lying, sandy coasts and low-lying coastal polders of the Atlantic, to the lidos and salt flats of the Mediterranean as well as mangroves.
On each site, the Adapto project encourages local authorities, managers and users to build their own local project. Adapto implements an interdisciplinary approach, encompassing coastal risks, landscapes, economics, sociology, biodiversity, and other aspects.
An original approach
An original approach was implemented to test flexible management solutions to coastal erosion, and to compare the results with other development scenarios, such as dykes made of earth or bricks.
In this way, polders can be reconnected to the sea, creating more space for seawater (expansion zones for coastal flooding) and taking advantage of the capacity of marine habitats to mitigate hazards. This is a new approach in that it does not necessarily seek to protect absolutely everything. In the Bay of Lancieux for example, and more specifically the Beaussais polder, the protective dyke was in poor condition along one section in particular, and breaches were already visible. It was therefore reconnected with the sea. In the case of the Moëze-Brouage marsh, a breach has been made in the dyke on the boundary of the land belonging to the Conservatoire du Littoral. For both sites, studies are under way on the choice of project (landscaping, natural hazards, biodiversity, social and economic perception). This could change mindsets and convince regional stakeholders – elected representatives, professionals and the general public – of the merits of reconnecting the land with the sea and of accepting this reconnection without repairing the dyke. Another example is Hyères, where most of the existing rockfill has been removed from the old salt farms of Vieux Salins.
This type of initiative is starting to become more common. Further, these solutions are also useful for carbon treatment: environments such as mudflats and salt meadows are recognised for their high rates of carbon capture and sequestration. Solutions of this type also help to change the mindsets of local stakeholders (general public, elected representatives, users, professionals, etc.).
In this way, the new agreement signed in January 2022 aims to go one step further, by defining the areas and conditions of the cooperation between the Conservatoire du littoral and BRGM. Work will involve nature-based solutions (NBSs), the national bodies overseeing coastline management strategy, and overseas cooperation.
Saltmarshes in the Bay of the Somme. © Adobe Stock