Uncertainty in open-channel discharges measured with the velocity–area method

Coz, Jérôme Le; Camenen, B.; Peyrard, X.; Dramais, Guillaume

doi:10.1016/j.flowmeasinst.2012.05.001

Cited by 65 publications

(34 citation statements)

References 9 publications

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“…Typical discharge uncertainties were assumed depending on the gauging procedure, and stage uncertainties due to varying flow were computed (cf. Le Coz et al, 2012).…”

Section: A3 Baratinmentioning

confidence: 99%

A Comparison of Methods for Streamflow Uncertainty Estimation

Kiang

Gazoorian

McMillan

et al. 2018

Water Resources Research

133

106

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Streamflow time series are commonly derived from stage‐discharge rating curves, but the uncertainty of the rating curve and resulting streamflow series are poorly understood. While different methods to quantify uncertainty in the stage‐discharge relationship exist, there is limited understanding of how uncertainty estimates differ between methods due to different assumptions and methodological choices. We compared uncertainty estimates and stage‐discharge rating curves from seven methods at three river locations of varying hydraulic complexity. Comparison of the estimated uncertainties revealed a wide range of estimates, particularly for high and low flows. At the simplest site on the Isère River (France), full width 95% uncertainties for the different methods ranged from 3 to 17% for median flows. In contrast, uncertainties were much higher and ranged from 41 to 200% for high flows in an extrapolated section of the rating curve at the Mahurangi River (New Zealand) and 28 to 101% for low flows at the Taf River (United Kingdom), where the hydraulic control is unstable at low flows. Differences between methods result from differences in the sources of uncertainty considered, differences in the handling of the time‐varying nature of rating curves, differences in the extent of hydraulic knowledge assumed, and differences in assumptions when extrapolating rating curves above or below the observed gaugings. Ultimately, the selection of an uncertainty method requires a match between user requirements and the assumptions made by the uncertainty method. Given the significant differences in uncertainty estimates between methods, we suggest that a clear statement of uncertainty assumptions be presented alongside streamflow uncertainty estimates.

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“…Typical discharge uncertainties were assumed depending on the gauging procedure, and stage uncertainties due to varying flow were computed (cf. Le Coz et al, 2012).…”

Section: A3 Baratinmentioning

confidence: 99%

A Comparison of Methods for Streamflow Uncertainty Estimation

Kiang

Gazoorian

McMillan

et al. 2018

Water Resources Research

133

106

View full text Add to dashboard Cite

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“…Based on the hydraulic regime in the surroundings of the stations, 2 and 3 segment rating curves are adopted at Agauntza and Lasarte, respectively; so that the 3 segment power law rating curve at Lasarte (and similarly the 2 segment rating curve at Agauntza) are:

q = ({|, \begin{matrix} \begin{matrix} a_{1} \cdot h^{b 1} \\ a_{2} \cdot h^{b 2} \\ a_{3} \cdot h^{b 3} \end{matrix} & \begin{matrix} h < {b r}_{1} \\ {b r}_{1} < h < {b r}_{2} \\ h > {b r}_{2} \end{matrix} \end{matrix})

where q denotes discharge in m 3 /s, h denotes water level in m, a i and b i are parameters, and br i are the breakpoints between the curves. RCU is estimated using the BaRatin, version 2.0, and the VPM with a ±7% Gaussian discharge measurement error that is typical for current meters and the velocity‐area method [ Le Coz et al ., ]. Both BaRatin and VPM use Markov Chain Monte‐Carlo algorithms to sample rating curve parameters representative of the available stage‐discharge gaugings.…”

Section: Methodsmentioning

confidence: 99%

The role of rating curve uncertainty in real‐time flood forecasting

Ocio

Vine

Westerberg

et al. 2017

Water Resources Research

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Data assimilation has been widely tested for flood forecasting, although its use in operational systems is mainly limited to a simple statistical error correction. This can be due to the complexity involved in making more advanced formal assumptions about the nature of the model and measurement errors. Recent advances in the definition of rating curve uncertainty allow estimating a flow measurement error that includes both aleatory and epistemic uncertainties more explicitly and rigorously than in the current practice. The aim of this study is to understand the effect such a more rigorous definition of the flow measurement error has on real‐time data assimilation and forecasting. This study, therefore, develops a comprehensive probabilistic framework that considers the uncertainty in model forcing data, model structure, and flow observations. Three common data assimilation techniques are evaluated: (1) Autoregressive error correction, (2) Ensemble Kalman Filter, and (3) Regularized Particle Filter, and applied to two locations in the flood‐prone Oria catchment in the Basque Country, northern Spain. The results show that, although there is a better match between the uncertain forecasted and uncertain true flows, there is a low sensitivity for the threshold exceedances used to issue flood warnings. This suggests that a standard flow measurement error model, with a spread set to a fixed flow fraction, represents a reasonable trade‐off between complexity and realism. Standard models are therefore recommended for operational flood forecasting for sites with well‐defined stage‐discharge curves that are based on a large range of flow observations.

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“…Les travaux concernant l'incertitude des jaugeages au courantomètres, qu'ils soient anciens comme la Norme Iso 748 ou récents comme les méthodes IVE [Kiang et al, 2009], Q+ [Le Coz et al, 2012] ou Flaure [Despax et al, 2016], montrent tous que la précision d'une mesure de débit par exploration du champ de vitesse repose essentiellement sur la finesse de la représentation de la bathymétrie et de la distribution des vitesses d'écoulement, c'est-à-dire le nombre de verticales de mesure. Le jaugeur doit trouver le compromis entre le nombre de verticales de mesure, la complexité de la section de jaugeage, et le temps de réalisation du jaugeage afin de rester dans des conditions d'écoulement permanent.…”

Section: Evolution Du Protocole De Mesure Au Courantomètre : Ajounclassified

Récentes évolutions sur les mesures de débit par exploration du champ de vitesse au courantomètre

Hauet¹,

Tornatore²

2017

La Houille Blanche

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RÉSUMÉ. -En hydrométrie, la mesure de débit par exploration du champ de vitesse au courantomètre reste une méthode très largement utilisée. A EDF-DTG, cette méthode représente environ 30% des 900 jaugeages réalisés chaque année. L'exploration du champ de vitesse est réalisée avec différents courantomètres, des historiques moulinets et micromoulinets mécaniques aux plus récents courantomètres acoustiques ou électromagnétiques. Les courantomètres acoustiques peuvent permettre de mesurer les trois composantes de vitesse, tandis que les courantomètres électromagnétiques sont peu sensibles à la végétation et peu invasifs dans l'écoulement. Alors que les appareils de mesure évoluent, les méthodes de déploiement et le système qualité associé à leur utilisation a subi peu d'évolutions ces dernières décennies. Cet article présente deux évolutions récentes mises en place de façon opé-rationnelles à EDF-DTG. La première concerne le protocole de réalisation de la mesure, avec ajout de verticales intercalaires où l'on mesure uniquement la hauteur d'eau. Cette évolution permet de diminuer notablement l'incertitude du jaugeage sas pénaliser son temps de réalisation La seconde concerne l'étalonnage et le contrôle qualité des moulinets. On constate qu'un étalonnage périodique en laboratoire avec une équation par hélice n'est pas nécessaire, et qu'une équation unique par type d'hélice avec un contrôle périodique suffit. Mots-clés : Courantomètres, Moulinets, ÉtalonnageMeasuring discharge using the velocity area method: recent evolutions.ABSTRACT. -Discharge measurements using the velocity area method with a current meter is widely used in river hydrometry. At EDF-DTG, this method represents about 30% of the 900 gaugings performed each year. Different current meters can be used: mechanical propeller, acoustic or electromagnetic current meters. Those current meters are in constant development, but the measurement methods and the quality insurance related don 't have undergone significant changes those last decades. This paper presents two recent evolutions developed and operationally used at EDF-DTG. The first one deals with the measurement protocol, by adding verticals for which only the water depth is measured. The second one deals with the mechanical current meters calibration.

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Uncertainty in open-channel discharges measured with the velocity–area method

Cited by 65 publications

References 9 publications

A Comparison of Methods for Streamflow Uncertainty Estimation

A Comparison of Methods for Streamflow Uncertainty Estimation

The role of rating curve uncertainty in real‐time flood forecasting

Récentes évolutions sur les mesures de débit par exploration du champ de vitesse au courantomètre

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