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Spécificités des systèmes d'endiguement et de l'analyse de risque en contexte torrentiel

Abstract : When located along torrents or torrential rivers, embankment systems experience violent natural hazards characterized by intense sediment transport (bedload or even debris flows). These torrential phenomena are likely to cause significant morphological evolutions of the bed during the floods - and of the river banks in case of overflows. The latter are related to streambed displacements, accretions, erosions or/and woody debris which strongly modify the flow conditions. Conventional hydraulic approaches and the use of 2D numerical models are often inoperative because they do not take into account these evolutions. Expert approaches based on historical, geomorphological analysis and lessons learned from past disasters, are essential to understand phenomena and qualify the related hazards, taking into account: analysis of bed longitudinal profile(s) and field reconnaissance. The most proven methods for assessing flow conditions in embanked channels are presented, as well as current limits for assessing hazards outside of the regular bed. The different dike failure modes are reviewed. External erosions and scouring of structures remain by far the predominant degradation mechanisms of torrential dikes. Finally, the specificities of the hazard potentials of torrential dikes compared to river dikes are presented, as well as elements on risk analysis and assessment. To assess the consequences of overflows towards the protected area, a "safe" approach is proposed. It consists in delimiting maximum areas of flood extension based on an approach similar to the one described in the guide on "torrential stream" natural hazard prevention plans.
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Submitted on : Saturday, May 16, 2020 - 5:23:08 PM
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Y. Queffelean, S. Carladous, Guillaume Piton, D. Kuss, M. Fouquet, et al.. Spécificités des systèmes d'endiguement et de l'analyse de risque en contexte torrentiel. Digues maritimes et fluviales de protection contre les inondations - 3e colloque - Digues 2019, Mar 2019, Aix-en-Provence, France. pp.11, ⟨10.5281/zenodo.2531314⟩. ⟨hal-02609199⟩

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