Coastal erosion risk and impacts on populations

Based on concrete examples, this activity aims to argue and quantify the potential retreat of the coastline by exploiting geographic data to determine the existence of a risk due to coastal erosion, and to propose measures to limit this risk for populations.

The lesson begins with a report on a demolition of a seafront house ordered by authorities , thus pupils could establish a link between global warming, the rising sea level, and the risk for the inhabitants who live near the coast.

One might then ask whether all coastal populations are subject to the same erosive risk?

To answer this question, the students are divided into groups to work on different locations with various geomorphological properties (Normandy’s chalk cliffs, Gironde’s sandy dunes, Brittany’s granite coasts…).

First, it involves determining the importance of natural hazard for the studied area. Students use the online government mapping tool Geolittoral, available at https://geolittoral-data.cerema.fr/portal/apps/experiencebuilder/experience/?id=4b570eb445ca4041ac605c615b5f2a60 to identify the evolution of the coastline over a few decades. Using image processing software (Mesurim), they can then measure the average rate of coastline retreat at a given location.

Next, they will be able to identify buildings located on the coast, corresponding to the vulnerability factor of the studied area. They can then assess the associated risk by estimating the time remaining before the natural destruction of these buildings if erosion continues to progress at the same rate.

The comparison of the results obtained by the different groups highlights the impact of local geomorphology and the nature of the subsoil on the erosive hazard and therefore the risk to populations.

The activity finally allows questioning the measures to be taken to limit this risk: fighting the retreat of the coastline (strengthening dykes, breakwaters, planting on dunes…) and/or prohibiting construction in erosion zones or even proceeding with expropriations? Numerous concrete examples can be consulted by students on the Surfrider Foundation website: https://fr.oceancampus.eu/cours/les-strategies-de-gestion-du-trait-de-cote/.