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Suivi sismologique de l'impact des cyclones sur la charge de fond de la Rivière des Pluies et de la Rivière du Mât à La Réunion

Abstract : Tropical cyclones can generate huge precipitation rates leading to torrential floods. The consequences for civilian infrastructures and population can be significant as phenomenal amounts of sediment are transported to the ocean. Direct measurements of sediment transport are impossible to implement under these extreme hydrodynamic conditions. To overcome these experimental limitations, previous studies have shown that seismology can be an excellent tool for an indirect access to information on the dynamics of a flooded river: turbulent flow and solid transport. Reunion Island is an ideal place to make such observations because its relief, its latitude, and therefore the climatic aspects favour the generation of potentially devastating torrential floods. We have deployed a temporary seismological network of ten three-component, brodeband seismic stations (http://dx.doi.org/10.15778/RESIF.ZF2015) dedicated to studying signals associated with the activity of the rivers Rivière des Pluies and the Rivière du Mât. Data from these seismic stations during several cyclonic floods (Bejisa, Carlos and Dumazile) were analyzed. For a better understanding of the seismological signal of fluvial origin, one of the key points was to compare it with hydrometeorological data and punctually with granulometric and photogrammetric observations. We show that it is possible to use high-frequency seismic observations (> 1 Hz) to monitor the variation in water level during such episodes in Reunion Island and thus estimate a flood wave velocity. We distinguish the seismic signature of the flow and sediment transport and show that these two seismic sources are distributed throughout the entire river segment near the seismometers.
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Alicia Gonzalez. Suivi sismologique de l'impact des cyclones sur la charge de fond de la Rivière des Pluies et de la Rivière du Mât à La Réunion. Sciences de la Terre. Université de la Réunion, 2019. Français. ⟨NNT : 2019LARE0018⟩. ⟨tel-02468230⟩

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