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Theses

Prévisions d'ensemble hydrologiques et hydrauliques pour la vigilance crues

Abstract : This PhD originates from a cooperation from CEREMA (Centre for Studies and Expertise on Risks, the Environment, Mobility and Urban Planning), EDF R&R, CERFACS (European Center for Avanced Research and Training in Computational Sciences) and SCHAPI (French national service for flood forecasting). In order to realize the twice-daily vigilance maps, the SCHAPI and the 19 SPC (Services de Prévision des Crues) distributed on the territory, use, among others, the results of numerical models generally launched with a deterministic approach (meteorological forecasts, hydrological and hydraulic modeling). The objective of the thesis is the implementation and evaluation of hydrological and hydraulic ensemble forecasts within the framework of the flood surveillance and forecast carried out by the governmental agencies in order to identify and reduce uncertainties for short to mid-term forecasts (24 hours). The originality of this work lies in the hybrid use of physics-based models and learning models on a large volume of data. For this purpose, meteorological forecasts are used to force a hydrological-hydraulic chained model to provide discharge and water level forecasts. In order to take into account the various sources of uncertainty related to the numerical models, model parameters and associated data, the limits of the deterministic are overcome by an ensemble approach; an ensemble of flow and water level forecasts is thus generated.The study basin is the Odet watershed located in Finistère (France, Brittany). The upstream part of the basin is represented by a hydrological model (GRP or MORDOR-TS). It provides a forecasted inflow for the 1D hydraulic model MASCARET that represents the dynamics of the river, and represents water heights at the downstream observing stations.First, a global sensitivity study (GSA) is carried out for the hydrological and hydraulic models. This is a prerequisite for the generation of ensemble forecasts. The GSA allows to identify the main sources of uncertainty and to perturb the significant uncertain parameters for the generation of an ensemble of forecasted discharges and water levels. The propagation of these uncertainties results in the generation of a raw ensemble for both hydrology and hydraulics, with the hydrological ensembles used to force the hydraulic ensembles. Two methods of ensemble correction are then investigated in the PhD: statistical calibration via the Quantile Regression Forest method and data assimilation calibration via an ensemble Kalman Filter (EnKF). It was shown that both approaches significantly improve the performance of the ensemble in terms of reliability and resolution. Finally, the performance of ensemble forecasts is compared for hydrology and hydraulics and recommendations are made for the operational generation of ensemble flow forecasts within SPCs
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Submitted on : Thursday, February 3, 2022 - 2:54:10 PM
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Anne-Laure Tiberi. Prévisions d'ensemble hydrologiques et hydrauliques pour la vigilance crues. Ingénierie de l'environnement. Université Paris-Est, 2021. Français. ⟨NNT : 2021PESC2031⟩. ⟨tel-03539466v2⟩

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