Application de la méthode LSPIV pour la mesure de champs de vitesse et de débits de crue sur modèle réduit et en rivière

International audienceLSPIV technique enables the measurement of surface flow velocities using image sequence analysis. EDF and Irstea partnership made possible the development of Fudaa‑LSPIV freeware by DeltaCAD Company. Two software applications at flume and field scales are detailed: (i) bed shear stresses were calculated owing to LSPIV velocities, water depth and bathymetry for a physical model of the Old Rhine; (ii) the software was used to optimize the calculation parameters of LSPIV flood discharge measurement stations in Mediterranean rivers.La technique LSPIV (Large Scale Particle Image Velocimetry) permet de mesurer les vitesses de surface d'un écoulement par analyse de séquence d'images. Pour faciliter l'application opérationnelle de la méthode, un logiciel, Fudaa-LSPIV, a été développé par la société DeltaCAD dans le cadre d'une collaboration entre EDF et Irstea. Deux applications en laboratoire et en rivière sont présentées : (i) couplée avec des mesures de hauteur d'eau et de bathymétries, la LSPIV a permis d'estimer des paramètres de Shields sur le modèle physique à fond mobile du Vieux-Rhin ; (ii) le logiciel a été utilisé pour procéder à des analyses de sensibilité pour paramétrer ainsi au mieux les stations LSPIV de mesure de débit en crue de rivières cévenoles

Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies

The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cut-off meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava river (Slovakia). Field measurements were performed in the exit of the Port-Galland cut-off meander, Ain river (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cut-off meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel

Emploi des profileurs acoustiques à effet Doppler (aDcp) pour étudier la structure des écoulements en rivière

Depuis une quinzaine d'années, les profileurs de vitesse acoustiques à effet Doppler (aDcp) sont de plus en plus employés par les équipes hydrométriques pour le jaugeage des cours d'eau. Ces appareils offrent la possibilité d'investiguer la bathymétrie et les vitesses d'écoulement tridimensionnelles rapidement, de manière peu intrusive, sur de vastes domaines et pour une large gamme de conditions de terrain. Le principe de fonctionnement, les stratégies de déploiement et de traitement des données mises en oeuvre sont exposés en s'appuyant sur un cas d'étude expérimental: la station hydrométrique "Saint-Georges" sur la Saône à Lyon

Quantifier l'effet de choix du site dans l'incertitude des jaugeages ADCP par transects

HMEM, Durham, New Hampshire, USA, 09-/07/2017 - 12/07/2017International audienceStage-discharge rating curves are used to relate streamflow discharge to continuously measured river stage readings to create a continuous record of streamflow discharge. The stage-discharge relationship is estimated and refined using discrete streamflow measurements over time, during which both the discharge and stage are measured. There is uncertainty in the resulting rating curve due to multiple factors including the curve-fitting process, assumptions on the form of the model used, fluvial geomorphology of natural channels, and the approaches used to extrapolate the rating equation beyond available observations. This rating curve uncertainty leads to uncertainty in the streamflow timeseries, and therefore to uncertainty in predictive models that use the streamflow data. Many different methods have been proposed in the literature for estimating rating curve uncertainty, differing in mathematical rigor, in the assumptions made about the component errors, and in the information required to implement the method at any given site. This study describes the results of an international experiment to test and compare streamflow uncertainty estimation methods from 7 research groups across 9 institutions. The methods range from simple LOWESS fits to more complicated Bayesian methods that consider hydraulic principles directly. We evaluate these different methods when applied to three diverse gauging stations using standardized information (channel characteristics, hydrographs, and streamflow measurements). Our results quantify the resultant spread of the stage-discharge Quantifying the uncertainty of discharge measurements (or "gaugings") is a challenge in the hydrometric community. A useful tool to empirically estimate the uncertainty of a gauging method is the field inter-laboratory experiment (Le Coz et al., 2016). Previous inter-laboratory experiments conducted in France (in 2009, 2010, 2011 and 2012) showed that the expanded uncertainty (with a probability level of 95%) of an ADCP gauging made of six successive transects is typically around 5% under optimum site conditions (straight reach, uniform and smooth streambed cross-section, homogeneous flow, etc.) and may be twice higher under poorer site conditions. In practice, the selected cross-section does not always match all quality requirements which may result in larger uncertainty. However, the uncertainty due to site selection is very difficult to estimate with predictive equations. From 9 to 10 November 2016, 50 teams from 8 different countries, using 50 ADCPs simultaneously, conducted more than 600 discharge measurements in steady flow conditions (~14 m3/s released by a dam). 26 cross-sections with various shapes and flow conditions were distributed over 500 meters along the Taurion River at Saint-Priest-de-Taurion, France. A specific experiment protocol, which consisted of circulating every team over half of the cross-sections, was implemented in order to quantify the impact of site selection on the discharge measurement uncertainty. Beyond the description of the experiments, uncertainty estimates are presented. The overall expanded uncertainty of a 6-transect ADCP gaugings (duration around 720 seconds) is estimated to be around 6%.The uncertainty of the discharge measurements varies among the cross-sections. These variations are well correlated to the expert judgment on the cross-section quality made by each team. First results seem to highlight a relation between uncertainty computed for each cross-section and criteria such as flow shallowness and measured discharge ratio. Further investigations are necessary to identify the criteria related to error sources that are possibly meaningful for categorizing measurement conditions and site selection. Moreover, experimental uncertainty and the uncertainty predicted by analytical methods such as QRev, QUant, OURSIN, RiverFlowUA or QMSys software will be compared

The AVuPUR project (Assessing the Vulnerabiliy of Peri-Urbans Rivers): experimental set up, modelling strategy and first results

International audienceLe projet AVuPUR a pour objectif de progresser sur la compréhension et la modélisation des flux d'eau dans les bassins versants péri-urbains. Il s'agit plus particulièrement de fournir des outils permettant de quantifier l'impact d'objets anthropiques tels que zones urbaines, routes, fossés sur les régimes hydrologiques des cours d'eau dans ces bassins. Cet article présente la stratégie expérimentale et de collecte de données mise en ½uvre dans le projet et les pistes proposées pour l'amélioration des outils de modélisation existants et le développement d'outils novateurs. Enfin, nous présentons comment ces outils seront utilisés pour simuler et quantifier l'impact des modifications d'occupation des sols et/ou du climat sur les régimes hydrologiques des bassins étudiés. / The aim of the AVuPUR project is to enhance our understanding and modelling capacity of water fluxes within suburban watersheds. In particular, the objective is to deliver tools allowing to quantify the impact of anthropogenic elements such as urban areas, roads, ditches on the hydrological regime of suburban rivers. This paper presents the observation and data collection strategy set up by the project, and the directions for improving existing modelling tools or proposing innovative ones. Finally, we present how these tools will be used to simulate and quantify the impact of land use and climate changes on the hydrological regimes of the studied catchments

Rapport d’essai : Comparaison de mesures du débit des petits cours d'eau par courantomètres sur perche. Journées d'intercomparaison des 15, 16 et 17 octobre 2013

In addition to the uncertainty propagation method provided by the GUM (Guide to the expression of uncertainty in measurement) witch requires the modelling of the measurement process, the inter-laboratory experimental method is a good solution to deal with the uncertainty of a measurement technique, in given conditions. This method is commonly frequently used in some fields (eg. in chemistry); it is managed with ISO standards and technical notes or specifications. Thus, inter-laboratory comparisons in hydrometry allow the quantification of uncertainty due to errors that will be expressed in repeated simultaneous gauging operations. These repetitions have to be done by different teams, at the same time, in stable flow conditions, under repeatability and reproducibility conditions. Simple formulae with repeatability variance and the inter-laboratory variance results assessed to evaluate the gauging technique uncertainty, supposed to be unbiased. The bias or systematic error is linked to the gauging technique; it could be evaluated by comparison with an independent flow measurement technique with a known uncertainty.En parallèle de la méthode de propagation des incertitudes, méthode de référence (GUM - Guide pour l'expression de l'incertitude de mesure) qui nécessite de modéliser l'ensemble du processus de mesure, la méthode expérimentale des essais interlaboratoires présente un grand intérêt pour quantifier les incertitudes d'une méthode de mesure, dans des conditions données. Cette méthode, très utilisée dans certains domaines (chimie, biologie, essais mécaniques, etc.), est encadrée par des normes ISO compatibles avec le GUM décrivant la méthode de référence. Ainsi, les comparaisons interlaboratoires hydrométriques permettent de quantifier l'incertitude résultant des erreurs de mesure qui s'expriment lors de la répétition de jaugeages simultanés par plusieurs équipes en conditions de répétabilité et de reproductibilité, et en particulier pour une plage de débit constant. Des formules simples permettent de quantifier, à partir des résultats expérimentaux de variance de répétabilité et de variance interlaboratoire, l'incertitude de la méthode de jaugeage testée, supposée non biaisée. Cette étude présente des essais réalisés a Nant en octobre 2013 avec des courantomètres sur perche dans le cadre des travaux de l'atelier débitmétrie du réseau mesure Irstea

Hyperhomocysteinemia in type 2 diabetes: relationship to macroangiopathy, nephropathy, and insulin resistance.

OBJECTIVE: The aim of this study was to determine the distribution of plasma total homocysteine (tHcy) concentrations in type 2 diabetic patients and to assess whether high tHcy values were related to chronic complications (particularly macroangiopathy and nephropathy) and/or the degree of insulin resistance. RESEARCH DESIGN AND METHODS: Fasting tHcy levels were measured in 122 type 2 diabetic patients in whom the presence of chronic complications (e.g., macroangiopathy, microalbuminuria, macroproteinuria, decreased creatinine clearance, hypertension, retinopathy, and neuropathy) was recorded alongside an assessment of insulin resistance by the homeostasis model assessment (HOMA). RESULTS: We found that 31% of the cohort (group 1) had raised tHcy (mean +/- 1 SD) values (20.8 +/- 5.1 micromol/l), whereas 69% (group 2) had normal values (10.2 +/- 2.0 micromol/l). The prevalence of macroangiopathy was higher in group 1 than in group 2 subjects (70 vs. 42%, P < 0.01); the prevalence of coronary artery disease was particularly higher in group 1 (46 vs. 21%, P < 0.02). The prevalence of impaired renal function, evidenced by decreased creatinine clearance, was higher in group 1 (32 vs. 10%, P < 0.005). Other clinical and biological characteristics of both groups were comparable, although group 1 had lower levels of folic acid than group 2 (5.2 +/- 2.9 vs. 7.0 +/- 3.4 ng/ml, P < 0.01). No differences were found for microalbuminuria (33 vs. 31%), retinopathy (45 vs. 42%), or neuropathy (70 vs. 59%) between groups 1 and 2, respectively The degree of insulin resistance was similar in groups 1 and 2 (46 +/- 21 and 42 +/- 20% of HOMA-insulin sensitivity) as was the assessment of beta-cell function (63 +/- 28 and 65 +/- 46%, respectively). No differences in tHcy levels were found between subjects receiving metformin and those not receiving metformin. In contrast, the plasma tHcy level was higher in diabetic patients treated with fibrates (P = 0.0016). CONCLUSIONS: Elevated plasma tHcy levels in type 2 diabetes is associated with a higher prevalence of macroangiopathy and nephropathy when assessed from creatinine clearance indexes and is not associated with different degrees of insulin resistance

Micro- and macrovascular complications and hyperhomocysteinaemia in type 1 diabetic patients.

OBJECTIVE: To determine the range of plasma homocysteine values in a cohort of type 1 diabetic subjects and to analyse the relationship between homocysteine levels and chronic degenerative complications. MATERIAL AND METHODS: 71 type 1 diabetic inpatients admitted for poor glycaemic control and/or treatment of complications, especially macroangiopathic, were included in this study. Chronic diabetic complications, smoking prevalence, as well as current use of drugs were recorded, alongside fasting plasma homocysteine. RESULTS: Age and diabetes duration were 51 (34-63) and 23 (13-32) years respectively (median [percentile 25-75]). HbA(1)c was 9.3% (8.2-10.5). Homocysteine was 9.2 (7.1-13.6) micromol/l, and 17% of patients had elevated homocysteinaemia on the basis of a laboratory cutoff value of 15 micromol/l. Folic acid and vitamin B(12) levels were within the normal range. Univariate statistical analysis showed a significant positive association between homocysteine and age (P<0.001), diabetes duration (P<0.001), systolic blood pressure (P<0.001), plasma creatinine (P<0.001), cholesterol/HDL-C (P=0.021) as well as with retinopathy (P=0.016) and all complications (P<0.001), and a negative correlation with folic acid (P=0.004) and creatinine clearance (P<0.001). Using a multiple regression analysis taking into account major variables, we confirmed an independent association of homocysteine with age (P=0.003), creatinine (P<0.001) and folic acid (P=0.014), but not with vascular complications. CONCLUSIONS: Increased homocysteine is present in 17% of a limited group of poorly controlled type 1 diabetic patients, and is associated with age, creatinine and folic acid levels. In this type 1 population, there was no independent correlation of homocysteine with vascular complications, in particular macroangiopathy