Carte géologique de Corse.
BRGM set up its Regional Division in Bastia, Corsica, in1979. In addition to the director and an assistant, the team is made up of four engineers specialised in the fields of geology, hydrogeology and coastal conservation. The local team is also supported by various other BRGM regional divisions and the scientific and technical centre based in Orléans. Consequently, around ten engineers from mainland France regularly work on operations in Corsica.
A mountainous island in the Mediterranean
Corsica is the fourth largest island in the Mediterranean in terms of surface area (8,680km2) and has a population of 330,000 year-round inhabitants. Approximately 4.5 million tourists visit the island each year. The peak tourist period is during the first two weeks of August, when the island's population doubles. Urbanisation and tourism mainly affect the island's coastal areas.
Since 1 January 2018, pursuant to the NOTRe Act (Nouvelle Organisation Territoriale de la République) of 7 August 2015 concerning France's new administrative breakdown, Corsica has obtained a special status as a unique regional authority known as the "Collectivité de Corse", in accordance with Article 72 of the Constitution.
Corsica is a mountainous island, largely made up of granite (Hercynian Corsica) and metamorphic (Alpine Corsica) bedrock with some Tertiary sedimentary basins and Quaternary alluvial formations. The ophiolitic formations of Alpine Corsica are full of asbestos. The coasts are subject to coastal erosion and flooding. Groundwater is primarily exploited for drinking water. Although they cover a small area, the aquifers that have been the most exploited through boreholes are located in the Quaternary alluvial formations along the coast. Substantial water resources, exploited via springs, are in aquifers that are compartmentalised and poorly known, in metamorphic and granite formations. The mountain areas and coastal cliffs are subject to unstable ground movements (mainly rockfalls).
Public and private partners
In Corsica, BRGM works with various public and private partners:
- Prefectures, DREAL, DDTM, DIRECCTE,
- Rhône-Mediterranean-Corsica Water Agency,
- French Agency for Biodiversity,
- Collectivité de Corse, Corsican Office of the Environment, Corsican Office of Hydraulic Equipment,
- Bastia Conurbation Community Water Board (Aqua Publica), Ajaccio Community of Communes
- Municipality of Corte,
- Corsican Wine Research Centre (CRVI),
- Conservatoire du littoral (Coastal conservation agency)
- Société d'économie mixte Bastia Aménagement (Bastia spatial planning semi-public company),
- EDF-énergie nouvelle,
- European funds: INTERREG and ERDF.
What's new in Corsica?
In Corsica, around 50% of the drinking water supply comes from groundwater, half of which is extracted by drilling down into coastal alluvial water tables, with the other half captured by drilling and tapping into springs in granite or metamorphic formations. Water from certain aquifers in sedimentary formations is captured by drilling, such as in Bonifacio. Tapping rates in alluvial water tables are generally much higher than those in the granite or metamorphic aquifers.
The aquifers are generally small and therefore very sensitive to fluctuations in rainfall and the volume of water in rivers and streams. During periods when water flows are very low, the springs that supply the villages may dry up, water levels in boreholes may drop or even dry up, and salinity levels may also increase in boreholes along the coast. Since the aquifers and rivers are extensively interconnected, the water flows that can be mobilised for foreseeable periods of shortages need to be determined at the level of the hydrosystems.
Réalisation et instrumentation d’un forage artésien dans le cadre d’une caractérisation des ressources disponibles sur l’hydrosystème du Bevinco.
© BRGM - Marie Genevier
BRGM's involvement and responses
BRGM monitors the state of groundwater masses and publishes the recorded data via websites. This information is used in particular by the water management committees. The quantity of groundwater available is therefore monitored within the framework of a nationwide agreement with the French Agency for Biodiversity, or when providing technical assistance to the Corsican Office of Hydraulic Equipment in the Figarella catchment basin. Piezometers and boreholes are monitored within the framework of specific hydrogeological projects.
In conjunction with the Corsican Office of the Environment, BRGM also categorises the water resources available in the island's granite and metamorphic formations, through flow-measurement campaigns or the experimental study of catchment basins, in order to have a better understanding of the parameters that affect groundwater circulation in complex aquifers.
BRGM also develops hydrogeological models to improve our knowledge of the water resources available in order to manage them in a more sustainable way. To this end, it applies a multidisciplinary approach combining geological, geophysical, hydrological and hydrogeological surveys. The 3D dynamic models derived from these surveys are used to assess the hydraulic impact of different water-resource management scenarios. For example, this approach has been used to define the flows that can be drawn upon in the Bevinco hydrosystem, a water table used to supply drinking water to the Bastia conurbation and the Marana-Golo community of communes, as part of a project running from 2016 to 2019, in partnership with the Bastia Bastia Conurbation Community Water Board, co-financed by the Rhône-Mediterranean-Corsica Water Agency and the Corsican Office of the Environment.
Finally, BRGM is regularly called upon by various government departments to provide technical advice on certain public interest declaration files, as part of the project aimed at providing support to State administrative authorities.
Asbestos in the natural environment
A particular characteristic of the Haute-Corse département is that it has numerous outcrops of rock containing naturally-occurring asbestos. Due to natural erosion or human activities, these rocks may release the asbestos fibres they contain into the air. This release of fibres could be a health risk for the general population, as well as for workers who could inhale them, if exposed.
The implementation of prevention and protection measures that take this specific risk into account has greatly affected the organisation of civil engineering operations and management of the waste produced during works.
Veine de Chrysotile, Rutali (Corse,2020).
© BRGM - Anne Eléonore Paquier
BRGM's involvement and responses
Since 2010, BRGM has used its InfoTerre portal to publish maps showing the likelihood of naturally-occurring asbestos, based on geological knowledge of the terrain. As such, the Haute-Corse département has been fully mapped to a scale of 1:50,000. The mapping work is now being pursued to provide increasingly precise mapping details (on a scale of 1:5,000, such as the maps already produced for the municipalities of Greater Bastia, Nebbio, Murato, Corte and Bustanico).
Geological surveys and identification of areas that might release fibres into the air
As part of its 1:5,000 mapping campaigns, BRGM identifies the main outcrops that might release asbestos fibres and recommends measures to reduce the risk of fibre emissions.
BRGM sometimes works with public or private companies to carry out preliminary project studies whose main objective is to identify the occurrence of asbestos, as recommended for type A1 studies in the INRS guide.
As part of its mission to support government departments, BRGM can also be consulted by the DIRECCTE or the DREAL, for expert appraisals.
BRGM has provided government departments with support for studies into the management of excavated materials containing asbestos, notably working on "Technical recommendations for the transport and storage of excavated materials containing asbestos", and helping to find sites that could be used to store this type of asbestos waste.
Transmission of knowledge and training
All BRGM studies and maps are available on the InfoTerre portal, notably to facilitate surveys aimed at detecting asbestos.
A project is underway to set up a platform to centralise all the studies carried out in Haute-Corse; this will complement the sources of information available for future audits.
BRGM can, on request, provide specific training about the asbestos-bearing rocks found in the area and the types of formations that may be encountered.
The coastline: coastal erosion and coastal flooding
Corsica's sandy coastline is subject to natural shifts and changes due to the effect of waves, currents and wind. Human action aggravates these natural factors. Buildings or fixed structures that are erected within the beach and coastline area that is subject to movements are highly vulnerable to coastal erosion and flooding. It is recommended that these coastal hazards be addressed and the sediment cell studied to take into account the potential impact of any operations in terms of the different issues involved. Understanding the physical processes involved at the cell level at least is essential for ensuring integrated, concerted management of the coastal area.
The problem of coastal erosion affecting beaches is currently a burning issue along the Eastern Plain (from Bastia to Solenzara) and in the Bay of Calvi.
The problem of coastal flooding affects many low-lying areas of Corsica (Eastern Plain, "plages de poche" (beaches in small coves), bays).
Recul du trait de côte (Moriani, commune de San Nicolao) - impact de la tempête Adrian du 29 octobre 2018.
© BRGM - Thibault Laigre
BRGM's involvement and responses
Within the framework of the Corsican Coastal Observation Network (ROL: Réseau d’Observation du Littoral), measurements of the topography of the beach (area above sea level) and the foreshore (submerged area) (topo-bathymetric measurements) have been taken every year since the year 2000, in order to quantify changes to the beach (coastline and base of the dunes, sand-spits, etc.) and the foreshore (offshore bars, etc.). These recurrent systematic measurements contribute to local expertise concerning the vulnerability of sites in the short term (annual) and medium term (decade). These campaigns are mainly carried out within the framework of partnerships with the Corsican Office of the Environment (which receives European ERDF funding for this purpose), the Collectivité de Corse and the Ajaccio Community of Communes.
The seventeen sites concerned by these measurements represent a broad sample of Corsican beaches in terms of the topography and issues involved. They are located all around the island: the ROL monitoring programme includes beaches in small covers, the sandy beaches of the Eastern Plain as well as pebble beaches, ranging from areas of coastline that are wild to areas that have been shaped by human activity. The results of the campaigns are posted online on the ROL Internet portal.
BRGM is also developing innovations to improve how the coastline is managed and understand the potential effects of climate change. For example, the Franco-Italian cooperation programme INTERREG MAREGOT aims to identify best practices for managing cross-border coastal areas and reduce the risks linked to climate change; for this programme, BRGM is applying new observation methods based on the use of cameras and the coordination of a structured network for observing coastal flooding and erosion during storm surge events.
As regards coastal flooding, BRGM is working with government departments (DDTM and DREAL) to improve our understanding of high-risk areas. It is trying to identify low-lying areas that could be affected by flooding, as part of a forward-looking strategy that takes into account the rise in sea level due to climate change. We are also modelling these storm surge phenomena to better characterise their potential effects.
Climate change issues are also a central aspect of our partnership with the Conservatoire du littoral (Coastal conservation agency) as part of the Adapto programme.
The risk of ground movements
Because of its geology and topography, Corsica is subject to recurring ground movements. Large-scale collapses, rockfalls from escarpments, landslides, soil erosion and soil transported by torrential flooding: there are several types of ground movement, resulting from the various mechanisms involved as well as the geo-morphological contexts concerned.
These ground movements can have serious consequences for the safety of people and property, as well as significant economic impacts. With this in mind, it is essential to identify the spatial characteristics of the areas subject to these risks, especially in a context of global change, since the intensity of the factors triggering such events could increase.
Sur-aléa mouvement de terrain post incendie menaçant une habitation à Cervione.
© BRGM - Baptiste Vignerot
BRGM's involvement and responses
As part of its mission to support public policies, BRGM primarily works with government departments (Prefecture, DREAL, DDTM), and particularly closely with the local authorities concerned, in order to characterise and map the risk of ground movements and to provide the various departments with support in order to effectively take these phenomena into account in spatial planning. BRGM has therefore carried out several studies of the GR20 hiking trail in order to characterise any residual risks, particularly following the dramatic landslide of June 2015. In 2017, characterisation surveys were conducted following a major landslide in Ville-di Pietrabugno, which led to the temporary evacuation of several homes. In 2018, in conjunction with INERIS and CEREMA, BRGM began a complex study to assess the risk of a portion of the Bonifacio cliff collapsing, in response to questions from the French government and the Corsican authorities.
The fires during the summer of 2017 and the winter of 2018 also resulted in surveys being conducted to assess the risk of ground movements in the event of heavy rains, due to degraded soils that had been left bare by the fires. These studies made it possible to qualify the increased risk of ground movements linked to forest fires: they led to operational recommendations being made to government departments and local authorities so as to prevent potentially destructive events.