This file describes the relief of Vierville and gathers old maps on erosion, cliffs and natural hazards. The prescriptions and projects it reproduces correspond to their writing dates.
Relief and topography of Vierville-sur-Mer
Risk of landslides and rock falls
Risks related to swelling/retirement of clays
Seismic risks
The relief on the commune
Most of the territory of Vierville-sur-Mer is located on a plateau, whose altitudes vary little. This plateau is between 58 meters (in the southeastern limit of the territory) and 46 meters, along the RD 514. The edge of the plateau, along the cliffs is close to 30/35m.
The coastal facade is characterized by the presence of two cliffs, separated by a valley:
- a vertical and rectilinear cliff, 30 meters high, west of the valley,
- a dead cliff, with a softer relief, to the east of the valley.
This valley is developed and corresponds to the descent into the sea from the village of Vierville-sur-Mer.
At the foot of the dead cliff was created a coastal wet depression, in which a seaside urbanization developed. Some plots included in this wet depression are, in part, located below maximum sea level (the maximum difference between high tides and low tides is greater than 7m50).
A dike was built to protect the waterfront from the risks of marine submersion.
Extract from the IGN card at 1/25000
(details) IGN card at 1/25000, whole of the municipality
Map of the relief
details Hydrographic map of the SHOM -extract-
Risk of landslides and block falls
Under the action of marine erosion and continental erosion (action of frost, leaching of the rock face by rainwater, infiltration of runoff water), the coastal cliff is subject to ground movements (landslides and falling blocks).
The Omaha Beach campsite is located near an active landslide area. Especially in 1984, the cliff collapsed near the campsite, but the instabilities affecting the cliff to the right of the campsite do not directly threaten the areas reserved for campers.
The erodable sector has not been the subject of any opening to urbanization
On all the cliffs of the Bessin, and in particular in the municipality of Vierville-sur-Mer, the coastal path is no longer safe enough for pedestrians. His access was prohibited by prefectural order of March 30, 2001. The old file mentions the search, by the General Council, of a path layout set back from the edge of the cliff. (project registered in reserved locations).
2011 map
These maps are imprecise and the risks are sometimes overestimated. Only accurate and expensive studies could give valid information
Map of the exhibition to falling blocks (updated 2008)
Risk of landslides
Under the action of erosion (action of frost, leaching of the rock face by rainwater, infiltration of runoff water), the coastal cliff is also subject to landslides. This is particularly the case in the marly or clay areas of the dead cliff of Vierville.
Maps of these risk areas are provided by the administration (DTTM)
The map opposite of Vierville has been established at an insufficient scale to precisely define the risk areas. Significant positioning errors remain.
At least one of the houses located in the dead coastal cliff is subject to significant disorders due to these landslides of marly terrain.
Such landslides were also observed at the border of Vierville / St-Laurent, on the path that led to the monument of the Genie now displaced.
The risks of shrinkage-swelling of clays
The hazard is strong in the outcrop areas of the marls of Port-en-Bessin (J2a in the geological map at 1/50000). It is weak elsewhere, in the silt areas of the Plateaux (denoted LP on the geological map)
The map opposite is intended to delimit all areas that are a priori subject to the phenomenon of shrinkage-swelling and to prioritize these areas according to an increasing degree of hazard. Areas where the withdrawal-swelling hazard is
Qualified as strong, are those where the probability of a disaster will be the highest and where the intensity of the expected phenomena is the highest. A
The municipality of Vierville-sur-mer is part of an area where the hazard would be low, except on the southern part where the hask is considered strong.
The occurrence of disasters is possible in the event of significant drought but these disorders could only affect a small proportion of buildings (in
Priority to those with construction defects or an unfavorable local context, with for example nearby trees or a basement heterogeneity).
This knowledge does not lead to prohibiting or limiting new projects. However, builders must be encouraged to make a geotechnical reconnaissance on the plot, make appropriate foundations, consolidate the load-bearing walls, separate the adjoining buildings and avoid variations
Humidity near buildings
Seaside risk maps (Marnes de Port-en-Bessin, J2a)
Risk map south of Saint-Sever (south slope towards the Véret basin, Marnes de Port-en-Bessin, J2a)
Seismic risks, areas of seismicity
A physical zoning of France has been developed, based on 7,600 historical earthquakes and tectonic data for the application of earthquake construction rules.
This zoning is not only a seismic hazard map. It also responds to an objective of seismic protection within the economic limits that can be supported by the community.
The decree of October 22, 2010 determines 5 zones of seismicity: 1 very low --- 2 low --- 3 moderate --- 4 medium --- 5 strong.
Vierville is classified entirely in zone 2 of seismicity considered low.
Since June 1, 2006, the real estate concerned by these zoning has been subject to an information obligation for the buyer or tenant of these properties.
Seismic risk in Lower Normandy
Earthquakes are considered one of the major natural hazards worldwide given their deadly and devastating effects.
Lower Normandy is in no way exposed to this type of catastrophe, but it is not nevertheless free of seismic risk: the study of the archives shows that since the 9th century, more than 110 different seismic tremors have been felt in the region, including a major one in 1775 in Caen having caused significant damage.
Since May 1, 2011, the new French regulations on seismic risk management have come into force.
It provides for new seismic zoning as well as new earthquake rules for buildings.
The French regulations have been revised in particular to meet the requirements of the new European Code of Parasismic Construction: the Eurocode 8.
The new seismic zoning map (PDF format - 280.1 KB) was developed taking into account scientific advances in seismology.
The map opposite shows the new regulatory zoning of Lower Normandy pursuant to Decree No. 2010-1255 of 22 October 2010 delimiting the seismicity zones of French territory and to which Decree No. 2010-1254 of 22 October 2010 on the prevention of seismic risk applies.
More than a mapping of the seismic hazard, this zoning essentially responds to an objective of preventing the effects of an earthquake on the stability of buildings.
Application of seismic rules
The best prevention against seismic risk is the application of seismic rules during the construction of buildings. These "good construction" rules have been made mandatory since 1991 for all new buildings in areas defined as seismic. The revision of these rules by the decrees of October 22, 2010 makes it mandatory for certain new buildings a seismic design and construction on a large part of the municipalities of the Lower Normandy. These construction methods result in minimal additional costs, less than 5% of the cost of construction.
Seismic map (zone 2 "weak")
Seismicity of Normandy
Map of earthquakes observed for about 30 years