Geological map of La Réunion.
BRGM has its offices in Saint-Denis de La Réunion, as well as an archive/Subsurface database (BSS) area which is open to the public, a rock-sample collection (lithothèque) and an instrumentation facility. The team is made up of a dozen people, specialising in natural hazards (geotechnology, coastlines), groundwater resources (quantity and quality) and the environment (polluted sites and land, waste, circular economy). BRGM Réunion also provides its expertise to several other island nations in the Indian Ocean.
In the middle of the Indian Ocean
Located in the south-west of the Indian Ocean, La Réunion is the only European Union region in the southern hemisphere. Covering a surface area of 2,520km2 – more than three times smaller than the smallest regions in mainland France – it is the third most densely populated region of France, with 840,000 inhabitants (2014). Despite enjoying economic growth that is much higher than in the rest of France (3.1% in 2015), La Réunion's economy remains fragile, with a high unemployment rate (around 25%).
The island is made up of two volcanic mountain ranges, the Piton des Neiges, which became inactive about 12,000 years ago, and the Piton de La Fournaise, a highly active volcano with one eruption every nine months, on average. The island has a tropical climate characterised by high rainfall, but with great variability in terms of both season and location (the west is arid, whereas the east is very wet), leading to intense erosion and a very rugged, abrupt topography. The island is also subject to regular cyclones.
La Réunion requires geoscientific expertise to address several challenges: demographic pressure and limited available land, the globalisation of trade, natural hazards and climate change, the management of natural resources and waste, the island's dependence on imported fossil fuels, etc.
Public and private partners
BRGM has extensive experience of both public and private partnerships. We work on projects to help shape public policy, or for public and private research in response to industrial requirements, as well as training projects aimed at every level of spatial planning and decision-making in the region: Prefecture, DEAL, DAAF, Regional or Departmental Councils, Water Office, ADEME, AFB, University of la Réunion, CIRAD, ONF, Météo-France, Piton de la Fournaise Volcanic Observatory (OVPF), La Réunion Nature Park, ARS, EPCI, Municipalities, etc.
BRGM also occasionally works with private companies to develop methodologies for Research, Development and Innovation aimed at supporting their various fields of activity.
References and projects
Natural hazards: improving knowledge, preventing various risks, proposing solutions and managing crises
More than 125,000 inhabitants on La Réunion (16% of the population) are affected by the risk of major natural hazards, with consequences on agricultural activity, regional development policy, housing, biodiversity, etc. Climate change exacerbates the existing natural conditions and risks.
Preventing these risks and their impact on people, economic activity and biodiversity is a key issue, which needs to be taken into account more effectively in national and European policies.
Rockslide on the coast road (RN1) in La Réunion on 14 November 2016.
BRGM's involvement and responses
Improving the knowledge base
Since 2004, BRGM has been carrying out morphodynamic monitoring of La Réunion's coastlines ("Observation and management of coastal erosion in La Réunion" programme), in partnership with the DEAL and the Réunion Regional Council. These observations form the basis for recommendations to the public authorities concerning the management of coastal erosion.
Since 2002, BRGM has been managing a major research project devoted to understanding and monitoring large-scale ground movements in the cirques and large ravines on La Réunion: the MvTerre-1, MvTerre-2 and RenovRisk Erosion programmes (launched in 2018). Indeed, the Salazie cirque is subject to one of the world's largest landslips involving inhabited land.
La Réunion was chosen as the pilot site for the Spicy research programme, the aim of which is to develop an experimental forecasting system for cyclone-driven marine and river floods in the French Overseas Territories. The Spicy system integrates the entire forecasting chain, from weather models to flood models.
For nearly fifteen years, BRGM Reunion has been working on a mission for the DEAL to help establish Natural Risk Prevention Plans (land movements, flooding and coastal erosion and submersion). The team is helping to adapt the national Risk Prevention Plan (PPR) methodology to the local context and to draw up best practice guides ("Management of coastal erosion in La Réunion").
Expertise and crisis management
BRGM Réunion intervenes in crisis situations (expertise, recommendations) to support government departments, local authorities and the National Forests Office (ONF).
This is particularly true as regards the road networks: post-incident geological advice (essentially rock falls, landslides); risk assessment for unstable and dangerous features exposing users to potential danger; technical advice on projects or works (planned or in progress).
BRGM Réunion is on call every weekend during the 6 months of the cyclone season in order to respond to urgent requests.
- Provision of know-how and expertise to several countries in the Indian Ocean to support local authorities: in Madagascar, the GRIMA project (Antananarivo/ground movements) and a project concerning the management of the Morondava coastline; technical expertise for the Seychelles, Mauritius, etc.
Natural resources: groundwater protection
There are abundant water resources in La Réunion but they are unevenly distributed. Moreover, the quality of the water distributed is a concern. The challenge is to promote the sustainable, balanced management of these resources while meeting the dual objective of protecting the environment and providing water for all uses.
The Grand-Galet waterfall pours out of volcanic rock left by lava flows (Saint-Joseph, La Réunion, 2005).
© BRGM - Pierre Vassal
BRGM's involvement and responses
Understanding saltwater intrusion
The island setting means the groundwater resources are highly vulnerable in the coastal areas. Most coastal aquifers are in fact hydraulically connected to the ocean: salt water penetrates inland due to the effect of density.
Salinisation in coastal aquifers can be due to several things: upward or downward vertical leakage, residual soil salinity, influence of surface water salinity, etc. There is therefore a real need to improve our understanding of the phenomena involved in order to adopt management measures that are suited to each groundwater salinisation process.
Several projects are currently under way, notably on the Gol and Pierrefonds aquifers. The aim is to develop new methods for characterising salinisation dynamics in order to define monitoring indicators and reduce the impact of exploiting such aquifers on water resources.
Aquifer potential and water resource management
In the high-altitude areas, where very little drilling has been done, the groundwater resources have not been fully quantified. However, based on studies into the potential quantities available, it would appear worthwhile to pursue the work in this area.
The Hauts de La Réunion (high-ground region) have real water supply problems, particularly in the West. The municipalities in the east receive a significant amount of rainfall but encounter recurrent problems in terms of drinking water resources (turbidity linked to the exploitation of surface water during periods of heavy rainfall; presence of phytosanitary products).
The potential resources available at altitude would have certain key advantages such as gravity-driven distribution towards coastal areas (Plaine des Palmistes towards the east coast), and good water quality (since they are upstream of agricultural and urban catchment areas).
The study of the hydrodynamics of the Hauts de La Réunion should also make it possible to improve knowledge about how the coastal aquifers recharge.
A programme in favour of hydro-thermal resources
Cilaos (at an altitude of 1,220m) is the only active spa resort on La Réunion. Spa therapy is an undeniable economic asset, with some 800 people staying at the spa every year. Programming work and studies on the thermal spa resource contributes to effective regional planning and the sustainable development of the activity. The aim is to equip the spa sector with every possible innovation to improve knowledge about the resource and ensure it is protected effectively.
BRGM is also conducting a research project on hydrothermal circulations, particularly in the Salazie cirque.
- A study of the processes that transfer contaminants to groundwater (nitrates, phytosanitary products, industrial effluents, emerging pollutants, etc.): programmes to identify and understand the mechanisms involved, development of predictive models, remediation solutions, etc.
- Methodology for estimating the widespread pressure linked to non-collective sanitation: MicroReuse project.
- Process to reduce micropollutants released by sewage treatment plants with a view to reusing treated waste-water for agriculture (context: waste-water treatment plant of Grand-Prado/sugar cane irrigation).
Environment: quality of the natural surroundings and circular economy
Waste recycling is a major issue in La Réunion, from an environmental point of view but also in terms of reducing dependence on raw material imports.
Past and current industrial and agricultural activities have created risks that may impact the quality of natural environments, sites, soils and groundwater.
Non-hazardous waste storage facility (ISDND) of the Saint-Etienne River in La Réunion.
BRGM's involvement and responses
Management of waste, polluted sites and soils
BRGM provides government departments with its expertise concerning the recovery/recycling of certain waste. For example, it has published a "Guide to using recycled waste in the construction industry in La Réunion". Aimed at companies and contracting authorities in the construction sector, it aims to take full advantage of these alternative materials (inert waste, asphalt aggregates and used tyres).
BRGM helps the Inter-municipal Public Cooperation Organisations (EPCI) to design and operate storage centres for household and assimilated waste in their areas.
BRGM provides project management assistance to EPCIs and local authorities for the rehabilitation of former landfill sites in their areas, as part of the national policy aimed at cleaning up these former operational sites that could have an impact on the environment.
BRGM carries out studies to identify potential new storage sites.
- Support for government departments, local authorities and companies on the issue of polluted sites and soils. For example: provision of project management assistance for a municipality dealing with lead pollution in soil.
The circular economy
BRGM is part of the Green Cluster, which brings together companies from several industries as well as public and private organisations that want to use environmental issues as a means to leverage economic, ecological and societal development on La Réunion.
The aim is to promote environmentally-friendly and eco-responsible companies and to develop synergies around projects linked to sustainable development and the circular economy.
BRGM has launched a research project, named "Insularity and the circular economy", aimed at demonstrating the feasibility of using the "Input-Output Table" (IOT, a national mapping system for monetary exchanges between economic sectors of activity) on a regional scale.
The project aims to define a methodology for creating a regional IOT based on data from La Réunion, with a view to transposing it to other French Overseas Departments, Regions and Local Authorities. The IOT is in fact used as the basis for a large number of studies on the circular economy and for the environmental assessment of material flow management (recycling).
Geology: knowledge base and derivative applications
Improving geological knowledge is essential for BRGM's research work and application development, and the fact that La Réunion is an island region makes the issues encountered even more acute: mineral resources (building material requirements, etc.), energy resources (development of geothermal energy), natural hazards (large-scale ground movements, volcanic activity, coastal erosion, etc.), sustainable management of groundwater resources.
The ReunEM heliborne geophysical survey of La Réunion (2014).
© BRGM - René Carayol
BRGM's involvement and responses
In 2014, BRGM, in partnership with Europe (ERDF fund), the French government and the Region, conducted a programme named REUN_EM (a heliborne magnetic and electromagnetic survey La Réunion). This complete geophysical survey of the territory made it possible to create a 3D visual model of the first 200 metres down into La Réunion's subsurface, providing new knowledge in terms of the geometry and physical properties of the soil and the upper subsurface.
This survey resulted in several other research projects, including:
- Mapping of material resources: identification of potential hard rock deposits on the surface and at depth, determination of the thickness of loose weathered formations (sterile or exploitable clays, etc.);
- Prospecting for new groundwater resources: imaging of the deep geometry of aquifer rocks, location of aquifer sectors and main recharge zones, characterisation of saltwater intrusions, etc.
- Imaging of sensitive areas prone to landslides and study of the slides, etc.;
- Geothermal energy: re-assessment of the island's potential.
This work will also contribute to updating the geological map of La Réunion.
The last geological map of the island to a scale of 1:50,000 was completed in 1974. Since then, numerous studies have improved our knowledge of the subsurface: drilling campaigns, water transfer projects, mapping of the La Fournaise volcano, mapping of the cirques (MVTerre programme).
All this new data needs to be integrated into the new harmonised geological map in order to produce a vectorised, geo-referenced and upgradeable product, incorporated into a GIS with an interoperable database.
The new geological map will have several applications: projects concerning regional spatial planning, water resources, environment, infrastructure layouts, regional planning schemes, and so on.