A Comparison of Methods for Streamflow Uncertainty Estimation

International audienceStreamflow 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

Recalculation of historical streamflow series. Impact assessment and valorization

Rating curves used to calculate discharge from water level must be extrapolated beyond the range of measured discharges, due to the difficulty of measuring flood discharge. This induces large uncertainties and the flood discharge series can be unreliable. This paper presents a methodology to update and correct historical flood flows, so as to propose homogeneous and less biased data. The benefit of using hydraulic modeling is discussed. This methodology is applied to a large sample of hydrometric stations of the EDF (Electricité De France) network, and the impact on peak flows deviations is analyzed

Integrated representation of hydropower facilities in an operational flood warning system for a mountainous watershed

An integrated flood forecasting system adapted to mountain basins is under construction at the flood forecasting service of the French Northern Alps (SPCAN), whose jurisdiction area covers the whole Isère River basin (12000km2). Most parts of this area are harnessed for hydropower production, thus modifying flows at all the main sections of the stream network. A semi-distributed conceptual modeling approach was chosen for predicting warning levels at daily time step. Before giving results on the strategic warning point of Montmèlian, simulations on two representative sub-basins of about 1000 km2 are detailed. The first sub-basin includes the large Sautet dam, on the Drac River. The second, on the Isère River, includes the large dam of Tignes and is characterized by multiple diversions. The influence of hydroelectric facilities was analyzed for reconstituting natural flows. Then, a two-steps modeling strategy was deployed: firstly, natural reconstituted flows were simulated; next, the effect of hydroelectric works was introduced, considering the operating status of the main reservoirs and of the water intakes, the latter being aggregated together as a unique equivalent device. While keeping a reasonable level of model complexity, the developed tool provides accurate simulations of observed flood events and is planned to be further used in real-time

Réanalyse des chroniques patrimoniales de débit. Évaluation de l'impact et valorisation

L'archivage d'une série de débit en base de données à l'issue d'une phase de validation et de critique est souvent considéré par l'hydromètre comme l'étape finale du processus de production de données. Cependant, lors de la valorisation ultérieure de ces données dans le cadre d'études hydrologiques, de nouveaux éléments de connaissance relatifs à la station hydrométrique (jaugeages haut débit, modélisation hydraulique, etc.) peuvent être disponibles et conduire à se réinterroger sur la nécessité d'actualiser le calcul des débits via la mise à jour des courbes de tarage. De même, une mise en perspective historique des différentes pratiques des producteurs de données met en évidence une hétérogénéité dans le processus d'élaboration des données. La présente communication propose une méthodologie pour réanalyser les chroniques patrimoniales de débit, de manière à proposer des séries homogènes et moins biaisées. Cette méthodologie est ensuite appliquée à un échantillon de 60 stations hydrométriques. Il ressort de cette étude qu'aucune tendance nette n'est mise en évidence sur les écarts en volume et en crue entre les séries réanalysées et les séries historiques, mais des corrections peuvent néanmoins être sensibles dans certains cas. Un cas d'application est enfin détaillé pour mettre en évidence les impacts potentiels de la réanalyse des chroniques de débit sur la détermination des débits extrêmes. En perspectives, une réflexion peut être menée sur le rôle du producteur de données vis-à-vis de l'hydrologue utilisant ces données, sur l'intérêt d'inscrire ces réanalyses de chroniques dans une démarche pérenne et systématique. La question de la valorisation et la traçabilité de telles études est également posée

A novel method to mitigate TSV electromigration for 3D ICs

International audienceThree-dimensional (3D) integration is considered to be a promising technology to tackle the global interconnect scaling problem for tera-scale integrated circuits (ICs). 3D ICs typically employ through-silicon-vias (TSVs) to connect planar circuits vertically. Due to its immature fabrication process, several defects such as void, misalignment and dust contamination, may be introduced. These defects can increase current densities within TSVs significantly and cause severe electromigration (EM) effect, which can degrade the reliability of 3D ICs considerably. In this paper, we propose a novel method to mitigate EM effect of the defective TSV. At first, we analyze various possible TSV defects and demonstrate that they can aggravate electromigration dramatically. Based on the observation that EM effect can be alleviated significantly by balancing the direction of current flow within TSV, we design an on-line self-healing circuit to protect defective TSVs, which can be detected during test procedure, from EM without degrading performance. Experimental results show that our proposed method can achieve tens times improvement on mean time to failure (MTTF) compared to the design without using such method with negligible hardware overheads and power consumption

Mitigate TSV Electromigration for 3D ICs - From the Architecture Perspective

International audienceThree-dimensional (3D) integration is considered to be a promising technology to tackle the global interconnect scaling problem for tera-scale integrated circuits (ICs). 3D ICs typically employ through-silicon-vias (TSVs) to connect planar circuits vertically. Due to its immature fabrication process, sev- eral defects such as void, misalignment and dust contamination, may be introduced. These defects can increase current densities within TSVs significantly and cause severe electromigration (EM) effect, which can degrade the reliability of 3D ICs considerably. In this paper, we propose a novel method to mitigate EM effect of the defective TSV. At first, we analyze various possible TSV defects and demonstrate that they can aggravate electromigration dramatically. Based on the observation that EM effect can be alleviated significantly by balancing the direction of current flow within TSV, we design an on-line self-healing circuit to protect defective TSVs, which can be detected during test procedure, from EM without degrading performance. Experimental results show that our proposed method can achieve tens times improve- ment on mean time to failure (MTTF) compared to the design without using such method with negligible hardware overheads and power consumption

La variabilité en fonction du temps des relations hauteur débit. Sa prise en compte dans l'estimation des incertitudes des données hydrométriques par une méthode tabulée

La démarche engagée depuis plusieurs années par la communauté des hydromètres pour quantifier les incertitudes associées au processus d'élaboration des données de débit mériterait de trouver des applications opérationnelles. La présente étude incite notamment les gestionnaires des stations hydrométriques à mieux valoriser les jaugeages effectués en systématisant la démarche de précision du modèle de courbe de tarage. Les auteurs proposent ensuite une démarche simplifiée de quantification de l'incertitude associée à une valeur de débit prédite par une courbe de tarage à partir du calcul de l'écart type des écarts en pour cent des jaugeages à la courbe de tarage et d'une tabulation en fonction des quantiles de débits observés. Elle s'appuie sur une démarche classique d'identification des sources d'incertitude et de leur propagation. Cette méthode permet de proposer une estimation de l'incertitude observée en moyenne sur les stations françaises pour la médiane des débits observés. On propose la formulation suivante : pour 45 à 55 % des stations françaises, la valeur la plus probable de l'incertitude au seuil de confiance de 95 % pour le quantile 50 % des débits observés en France est inférieure à 22 %

Computing Detection Probability of Delay Defects in Signal Line TSVs

International audienceThree-dimensional stacking technology promises to solve the interconnect bottleneck problem by using Through-Silicon-Vias (TSVs) to vertically connect tiers. However, manufacturing steps may lead to partly broken or incompletely filled TSVs that may degrade the performance and reduce the useful lifetime of a 3D IC. These are latent defects that affect circuit performance and reliability in stacked ICs and can be modeled as small-delay defects (SDDs). Due to combinations of switching activity, supply noise and crosstalk, TSV delays can experience speed-up or slowdown that could let SDDs go undetected by conventional test methods. In this work, we present a metric based on probabilistic delay analysis to detect SDDs induced by resistive opens that occur on signal line TSVs. Our experimental result will show the accurancy of the proposed metric

Tempête Alex du 2 octobre 2020 dans les Alpes-Maritimes : une contribution de la communauté scientifique à l’estimation des débits de pointe des crues

International audienceThe Alex storm caused particularly catastrophic floods in the Roya, Tinée and Vésubie valleys(south-eastern France) on 2 October 2020. This event will certainly serve as a reference for floodrisk management in the future and it is important to document it as far as possible, in order topreserve its memory and enable further studies. Different national services and operators havebeen involved to gather and consolidate datasets describing this event. This article presentsa contribution from the scientific community to the reconstruction of the event’s peakdischarges, conducted within the HyMeX research programme. Field cross section surveysmade it possible to obtain 32 peak discharge estimates, contributing to a detailed descriptionof the flood genesis on the main rivers and their small tributarieLa tempête Alex, qui a touché le 2 octobre 2020 les vallées de la Roya, la Tinée, et la Vésubiedans les Alpes-Maritimes, constitue un événement de référence qu’il est important de docu-menter au mieux pour en conserver la mémoire et permettre son étude ultérieure. Lesdifférents services et opérateurs de l’État se sont largement mobilisés pour acquérir et regrou-per des jeux de données décrivant cet événement. Cet article présente une contribution de lacommunauté scientifique à la reconstitution des débits de pointe des crues, conduite dans lecadre du programme de recherche HyMeX. Des relevés de sections d’écoulement ont permisd’obtenir 32 estimations de débits de pointe, contribuant à la connaissance des crues obser-vées sur les cours d’eau principaux et leurs petits affluents

Hydrométrie et normalisation

Normalization allows to define a common language among the actors in a particular field, to clarify, to harmonize practices and to define the level of quality, safety and less environmental impact of practices.In France, in the field of hydrometry, the normalization work is carried out by the AFNOR / X10C commission. After several years of inactivity, the commission was recently reactivated two years ago, under the impulse of a few motivated actors. The objective of this paper is to highlight the added value of standardization in the hydrometry activity, through a few concrete examples of standards.The organization of standardization at national and international level may seem complex. A presentation of the different standardization structures is therefore proposed, as well as the process of developing a standardLa normalisation permet de définir un langage commun entre les acteurs d'un domaine particulier, de clarifier, d'harmoniser les pratiques et de définir le niveau de qualité, de sécurité, de moindre impact environnemental des pratiques.En France, dans le domaine de l'hydrométrie, les travaux de normalisation sont menés par la commission AFNOR/X10C. Après plusieurs années d'inactivité, la commission a été réactivée il y a deux ans, sous l'impulsion de quelques acteurs motivés. L'objectif de cette communication est de mettre en avant la plus-value de la normalisation dans l'activité d'hydrométrie, à travers quelques exemples concrets de normes.L'organisation de la normalisation au plan national et international peut sembler complexe. Une présentation des différentes structures de normalisation est donc proposée, ainsi que le processus d'élaboration d'une norme