The Johanna storm hits Le Conquet in Finistère (Brittany, France, 10 March 2008). © S. Lamarche

Preventing flood risks during tsunamis or hurricanes

02.04.2019
From upstream modelling and research on the origins of tsunamis to crisis management during hurricanes, the BRGM is involved in all phases of flood risk prevention and monitoring. Examples in 2017.

Surveying damage caused by Hurricane Irma at Sandy Grand on the island of Saint-Martin. © BRGM

Surveying damage caused by Hurricane Irma at Sandy Grand on the island of Saint-Martin. © BRGM

The Tandem project (ANR-Investing for the Future, 2014-2017) involved ten partners under AEC coordination. The aim was to estimate the effects of tsunamis along Atlantic and Channel coastal areas with civilian nuclear plants.

The project defined and adapted the numerical codes used for tsunami modelling, verifying them against the exceptional database produced in the wake of the Fukushima disaster in 2011. Numerous advances were made regarding the influence of the different parameters and the propagation of seismic triggering uncertainties, and on modelling buildings and tsunami interactions with coastal defences.

 maximum sea surface elevation simulated at very high resolution in the town of Kamaishi (Iwate province, Japan). © BRGM - projet Tandem

The 2011 tsunami in Japan: maximum sea surface elevation simulated at very high resolution in the town of Kamaishi (Iwate province, Japan). © BRGM - projet Tandem

The project also improved knowledge on the exposure of coastlines in mainland France by enriching the database on past tsunamis and characterising the seismic and gravity-related sources of tsunami generation that could come into play. Water heights along the coast generated by the potential sources investigated (Oléron fault in France, Lesser Caribbean and Canary Islands) are relatively low (1 to 2m), causing limited flooding.

Spicy project on preventing floods caused by hurricanes

The Spicy project (2014-2018) tested and further developed an experimental forecasting system for seawater and river flooding caused by hurricanes and its transposal into crisis management systems at the municipal and district scales. The project, conducted on La Réunion and involving five partners coordinated by the BRGM, was organised around improvements to weather forecasts and extending these to encompass marine and hydrological forecasts through to estimated flooding across given areas. The studies characterised forecasting uncertainties and proposed different flood estimation methods, subsequently developed as an atlas showing pre-calculated impacts or real-time calculations obtained with optimisation techniques based on statistical models.

An in situ crisis management exercise under the Spicy projet on La Réunion. © BRGM - S. Lecacheux

An in situ crisis management exercise under the Spicy project on La Réunion. © BRGM - S. Lecacheux

The exercises undertaken demonstrated the relevance of the project developments and their transposal to crisis unit operations.

Caribbean: hurricane crisis management

Irma, José, Maria: three hurricanes in succession hit the Caribbean in September 2017, causing major damage on Saint-Martin, Saint-Barthélémy and, to a lesser extent, on Guadeloupe and Martinique. The BRGM responded to this unprecedented situation with considerable efforts to support the prefectures in the French Caribbean and assist the Directorate-General for Civilian Security in crisis anticipation, management and recovery.

350 km/h wind speed recorded at Saint-Barthélémy during Hurricane Irma

Thanks to the combined expertise of our modellers and teams working on the spot, the BRGM helped the public authorities to anticipate both potential coastal flooding during the hurricane and their operational responses. These diagnoses were based on critical analyses of the real-time weather forecasts issued by national and international organisations, on the flood models produced at the BRGM (integrating specific hurricane parameters: trajectory and wind force and direction) and on data from previous studies (topography, bathymetry and land use).

The BRGM continued its support to the authorities during the crisis recovery period, particularly on aspects such as flood impacts, available water resources and soil salination.

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