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International audience; Proposed topic: Models for coastal areas management Coastal flooding by wave overtopping is quite regular at Reunion Island, in particular during cyclonic events. Given the limited geographic scale of this phenomenon, the municipalities are often in first line to assure the protection of the population. Current operational forecasts provide nearshore marine conditions of waves and water levels but this information is not directly usable to estimate the flood extension and anticipate operational measures. Thus, there is a crucial need for the municipalities to have flexible and practical tools at their disposal to interpret the marine forecasts in terms of flooding impact on their territory and enhance their capacity to anticipate and organize their operational response. Here, we propose a framework to design a GIS-based decision support tool based on both feedback analysis, field observations and state-of-the-art coastal hydrodynamic modelling. The method notably relies on a pre-calculated database of 500 synthetic events simulated with a complete chain of models: (1) WW3 for waves (2) MARS-2DH for water levels and surge (2) SWASH for wave overtopping. The analysis of the relationship between marine conditions, overtopping discharge volumes and flooded areas led to the constitution of inundation maps, delimiting the extension of impacted areas given different levels of exposure. It is coupled with a graduated response plan, defining a list of operational actions associated to each level (water level monitoring, alert, roads closure, evacuation, etc.). The criteria of transition between the different levels connect marine forecasts with field observations and historical landmarks, thus enabling different levels of use and anticipation. This tool was constructed in a collaborative manner with the municipal services of Sainte-Suzanne city (northern coast of Reunion Island) and tested during a crisis exercise on site. During the exercise, it allowed the municipal services to project into the future of the event, and thus to adapt to the situation and to anticipate the actions to be implemented. The appropriation of this GIS-based decision support tool must continue for the municipal services to gain in efficiency.

International audience; Proposed topic: Models for coastal areas management Coastal flooding by wave overtopping is quite regular at Reunion Island, in particular during cyclonic events. Given the limited geographic scale of this phenomenon, the municipalities are often in first line to assure the protection of the population. Current operational forecasts provide nearshore marine conditions of waves and water levels but this information is not directly usable to estimate the flood extension and anticipate operational measures. Thus, there is a crucial need for the municipalities to have flexible and practical tools at their disposal to interpret the marine forecasts in terms of flooding impact on their territory and enhance their capacity to anticipate and organize their operational response. Here, we propose a framework to design a GIS-based decision support tool based on both feedback analysis, field observations and state-of-the-art coastal hydrodynamic modelling. The method notably relies on a pre-calculated database of 500 synthetic events simulated with a complete chain of models: (1) WW3 for waves (2) MARS-2DH for water levels and surge (2) SWASH for wave overtopping. The analysis of the relationship between marine conditions, overtopping discharge volumes and flooded areas led to the constitution of inundation maps, delimiting the extension of impacted areas given different levels of exposure. It is coupled with a graduated response plan, defining a list of operational actions associated to each level (water level monitoring, alert, roads closure, evacuation, etc.). The criteria of transition between the different levels connect marine forecasts with field observations and historical landmarks, thus enabling different levels of use and anticipation. This tool was constructed in a collaborative manner with the municipal services of Sainte-Suzanne city (northern coast of Reunion Island) and tested during a crisis exercise on site. During the exercise, it allowed the municipal services to project into the future of the event, and thus to adapt to the situation and to anticipate the actions to be implemented. The appropriation of this GIS-based decision support tool must continue for the municipal services to gain in efficiency.

SHF : Société Hydrotechnique de France; National audience

International audience; Forecasting cyclone-induced inundations in the French Overseas Territories raises specific issues, as most of them are steep volcanic islands with a complex orography and presenting (1) very dense water systems with numerous gullies and potential intense water flows (2) a lack of continental shelf that leads to an important exposure of the coast to high waves and overtopping despite the presence of fragmented barrier reefs (3) complex interactions between marine and river water supplies in river inlet environments. To date, there is no forecasting system taking into account all these specificities.This presentation gives an overview of the research project SPICy that aims at tackling the issue of cyclone-induced marine and river floods forecast in the French Overseas Territories through the realization of a demonstrator for the pilot site of Réunion Island. To reach this objective, the project addresses various challenges, focusing on : (1) the assessment of meteorological forecast uncertainties with the development of ensemble tracks generation techniques (2) high resolution meteorological modelling taking into account orography and real-time data assimilation to improve local rainfall predictions (3) the extension of meteorological forecast information to marine and river floods through the development of dedicated modules, notably in urban areas (4) the consideration of marine/river interaction (5) the management of computation times and the investigation of optimization techniques including the use of meta-models (6) the development of users interfaces to provide relevant information to emergency managers. The originality of the project is the interdisciplinary approach that enables to build a comprehensive strategy to holistically address cyclone-induced inundations forecast issues for this type of Territory. Beyond the development and combination of physical models, the novelty of SPICy also lies in the consideration of crisis operators’ needs at an early stage of the project and the realization of crisis exercises. This work is supported by the French National Research Agency (ANR – 14 – CE03 – 0013). More details on the project are available at http://spicy.brgm.fr.

International audience; This paper presents the development, validation and performance of a modelling chain dedicated to cyclone-induced coastal hydrodynamics and marine inundation forecast for Reunion Island (Indian Ocean). Usually, cyclone-induced inundation forecasting systems concern generalized overflowing, for which broad low-lying areas are affected and waves can be neglected (as for the US east coast). Reunion Island presents specific issues: (1) it is surrounded by fragmented fringing reefs that can generate considerable wave-induced setup (2) local marine inundations are due to overtopping only. Thus, it demands the development of dedicated models requiring limited computing resources in order to give results for different scenarios in a delay compatible with crisis management. Beyond the implementation and optimization of classical wave and surge models (Wavewatch3 and MARS2DH) from 10km to 100m resolution, a method was developed to compute efficiently wave-induced setup and overtopping at the scale of the island. It is based on (1) a delimitation of homogeneous coastline segments regarding on morphological and exposition criteria (2) simulations of setup and overtopping for each segment with 1D cross-shore profiles of SWAN and SWASH models. For a pilot site at local scale, marine inundation is also calculated with a high resolution Non Linear Shallow Water equations model, comprising an explicit representation of the buildings and integrating overtopping discharge from SWASH profiles. This chain was extensively tested for historical cyclones with high resolution analysed cyclonic wind and pressure fields from Meso-NH (with bogussing) atmospheric model. Comparisons were made against buoys, altimetry and tide gauge measurements as well as inundation extent observations. First results show that this chain can provide meaningful