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Adaptation et évaluation d'un système d'anticipation de crues éclair sur des bassins de montagne non-jaugés

Abstract : In Europe, flash floods primarily occur in the Mediterranean and mountainous areas. The concerned basins are often small and ungauged with a short lag time. Anticipating such events is a tricky task with many difficulties. The AIGA method (Adaptation d'Information Géographique pour l'Alerte en crue), initially developed for the Mediterranean area, aims in real-time to locate floods and to evaluate their danger in terms of return periods. This method is based on a hydrological model and on the accumulation of rainfall estimated by ARAMIS radar network. This thesis is part of a common project between Irstea and Météo-France (RH YTMME project) with two objectives: - the adaptation of the hydrological model of AIGA method to the mountainous areas, taking into account the environment characteristics ; - the evaluation of the new model on small basins, which are actually ungauged. To achieve the first objective, the model is complicated by the integration of a snow modelling on 118 basins from HYDRO database in Rhône-Alpes and Provence-Alpes-Côte-D͛azur areas. Then the model is regionalized. The second objective is to use flood reports from the mountain area restoration services database (services de Restauration des Terrains en Montagne (RTM)). The model is evaluated with these reports on 123 very small basins under conditions as close to as possible the reality. On the gauged catchment, the original model of the AIGA method is improved step by step. Nash and Sutcliffe criterion increases about 40% during this development phase. These improvements are mainly significant in mountainous areas and they are less consistent in the Mediterranean area. On the real ungauged catchments from the RTM services, proving the benefits of the new model is difficult because of the lack of observed flow data. To overcome this problem, an evaluation method is developed, based on contingency statistics, illustrating the coincidence between observed damages and threshold crossing by simulated flows. A graphic with the probability of detection (POD) according to the success rate (SR) is introduced for different thresholds. Thereby, a multi-threshold approach is used to compare hydrological models like ROC-curves. With this technique we show bestperformances with the new model developed in the previous step. However, this performance can be further improved by a calibration integrating directly the damage information. This final step allows to overcome the limitations of classical hydrology. An evaluation matter of the flash flood warning systems is highlighted by t his thesis: an evaluation on gauged basins is a necessary first step but not sufficient. Indeed, the works illustrate that the decided compromises on the large gauged basins do not lead automatically to the best performances on the small basins occurring flash floods.
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Dimitri Defrance. Adaptation et évaluation d'un système d'anticipation de crues éclair sur des bassins de montagne non-jaugés. Sciences de l'environnement. Thèse de doctorat en hydrologie, 2014. Français. ⟨tel-02606141⟩

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