Incertitude des mesures de débit des cours d’eau au courantomètre. Amélioration des méthodes analytiques et apports des essais interlaboratoires

Abstract : During crisis (droughts or floods) hydrometric data are essential for decisions, in real-time, related to water resource management but also afterwards in cases of disagreement. Discharge measurements are the first step to produce such data and associated uncertainty has to be estimated in order to make coherent decisions. Although discharge measurements techniques have improved in recent years, uncertainty analysis is still a challenge in hydrometry.This study aims to estimate uncertainty in discharge measurements using the velocity-area method with potential perspective of ISO 748 standard updating. Different analytical methods, that follow the guide to the expression of uncertainty in measurement, are available in the literature, all with their own limitations and drawbacks. To address the limitations of existing methods, this study presents a new methodology, called FLAURE, to estimate the uncertainty components. Special attention is given to the estimation of u’m component related to cross-sectional interpolation errors. High-resolution reference gaugings are used to assess the uncertainty component through a statistical analysis. The method then establishes an explicit link between the estimation of cross-sectional interpolation errors and a sampling quality index.It is a challenging task to assess which analytical method provides the best uncertainty estimation due to the lack of streamflow measurement reference standards in natural streams. A useful tool to empirically estimate the uncertainty of a gauging method is the field inter-laboratory experiments. This study presents a comparison between analytical methods and two field inter-laboratory experiments. The comparison has shown the limits of these two approaches and has not highlighted the best analytical method. However, further comparisons, with various site conditions, between the two approaches will probably consolidate analytical methods and improve the reliability of discharge uncertainty estimates.
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Aurélien Despax. Incertitude des mesures de débit des cours d’eau au courantomètre. Amélioration des méthodes analytiques et apports des essais interlaboratoires. Ingénierie de l'environnement. Université Grenoble Alpes, 2016. Français. ⟨NNT : 2016GREAU009⟩. ⟨tel-01496704⟩

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