Map of rock-fall and rock-slide risks in the municipality of Ivry-la-Bataille; close-up of a highly-vulnerable sector with buildings and infrastructures
© BRGM
The need
The Eure département has been carved out by the Seine, Eure and Risle valleys, which all have urban areas of various sizes at the foot of their slopes. However, because the chalky slopes of these valleys have distinct geological, geotechnical and geomorphological features, certain weather events can make them unstable, resulting in rock falls and, more rarely, rock slides. Due to the recurrence of these phenomena, the Eure Departmental Authority for Inland and Marine Areas (DDTM27) carried out a preliminary study to identify sensitive cliff areas, which could represent risks. Following this work, BRGM launched a campaign of surveys, carried out over several years in all the sensitive areas identified, in order to assess and map these risks in detail. The aim of the campaign was to identify which areas were really at risk, to determine which buildings and infrastructures would be most affected in the case of rock falls or slides, and to provide relevant recommendations concerning the appropriate safety measures to be implemented.
All the cliff areas mapped as part of the survey of rock-fall and rock-slide risks in the Eure département
© BRGM
The results
The programme was carried out in four phases, according to sector-based priorities. Between 2017 and 2023, a total of 86 sectors, representing around 30 linear kilometres, were mapped. These surveys identified just over 700 buildings and 75 sections of roads that were exposed to risks (including departmental and municipal roads and footpaths). During the final phase, a total of 15 sectors were surveyed (around 4 km of linear rock faces) in the municipalities of Cailly-sur-Eure, La Vacherie, Normanville, Saint-Philbert-sur-Risle, Saint-Samson-de-la-Roque and Port-Mort. Each site was assessed, modelled and mapped for rock-fall and rock-slide risks. Exposed buildings and road sections located in areas with low, medium and high vulnerability were identified for each site. Ultimately, this work identified:
- 14 buildings and 4 road sections in highly vulnerable areas;
- 13 buildings and 5 road sections in moderately vulnerable areas.
Indicative safety recommendations based on different safety objectives were proposed for the sites located in highly vulnerable areas, in which buildings or infrastructures are present. The recommendations mainly concerned managing visitor numbers and implementing hazard-reduction or protection measures.
Using the results
The maps produced during the campaign will be attached to local inter-municipal land-use plans in order to regulate urban development in the areas that could be adversely impacted in the event of rock falls. Specific design and structural studies will be carried out prior to future development projects in zones that are highly vulnerable to rock falls and slides, in line with the required safety objectives.
The partner
- Eure Departmental Authority for Inland and Marine Areas (Direction Départementale des Territoires et de la Mer de L'Eure - DDTM27)
