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Tendances conjointes des évolutions thermiques et hydrologiques des rivières : implications pour une gestion durable des écosystèmes et de la ressource en eau dans les bassins versants
No full textInternational audienceClimate change has dramatically increased river temperatures and altered the spatiotemporal dynamics of flows, posing challenges for ecosystem functioning and water resources for anthropogenic uses. This communication proposes an overview of the results from several coupled hydrology-thermal-fish community modeling projects, analyses of observations in the Loire basin and outline future directions. Firstly, sensitivity of streams and rivers to atmospheric warming will be discussed according to thermal and hydrological regimes, their size, the cumulative impacts of reservoirs and shading. In a second step, the evolutions of the co-occurrences of high temperature and low flow will be presented over 57 years (1963-2019) and during the 21st century based on climate scenarios. These associations evolved heterogeneously across the basin, becoming more frequent in the southern basin in both winter and summer. Results on three emblematic migratory fish species will be presented in connection with the counts at fish monitoring stations located on the Loire River, Allier, Vienne and Creuse streams, and highlighting the differentiated role of hydro-climatic conditions. Thirdly, the communication will provide the main scientific obstacles, in particular on the prediction of spatio-temporal heterogeneities in the river temperature and the role of groundwater exchanges. The analysis of thermal infrared images on the Arroux and the Bourbince streams during a heatwave event (41°C) and severe low water in July 2019, will introduce the notions of thermal refuge of cooler water and the need to better locate and characterize them. The increase in the frequency of low flow and high temperature episodes could compromise water availability for human activities, such as drinking water production, irrigation and cooling of nuclear power plants. These results highlight the urgency of adopting more holistic local adaptation strategies (water uses, biogeochemistry, connectivities) to be able to meet the ecological and water resource availability challenges related to climate change.Le changement climatique a fortement augmenté la température des rivières et a modifié la dynamique spatio-temporelle des débits, ce qui pose des défis pour le fonctionnement des écosystèmes et les ressources en eau pour des usages anthropiques. Cette communication se propose de faire le point sur les enseignements tirés de plusieurs travaux de modélisations couplées hydrologie-thermie-communautés piscicoles et d’analyses des observations dans le bassin de la Loire. Dans un premier temps la sensibilité différente des cours d’eau au réchauffement atmosphérique, sera discutée en fonction des régimes thermiques et hydrologiques, de la taille des cours d’eau, des impacts cumulés des retenues, de la végétalisation des berges. Dans un second temps, les évolutions des co-occurrences de température élevée et de faible débit, seront présentées sur les 57 années de suivis (1963-2019) et de scénarios pour la fin du XXIème siècle. Ces associations ont évolué de manière hétérogène à travers le bassin, devenant plus fréquentes dans le sud du bassin en hiver et en été. Des résultats sur 3 espèces de poissons migrateurs emblématiques seront présentés en lien avec les comptages réalisés sur la Loire, l’Allier, la Vienne et la Creuse, et soulignant le rôle différencié des évolutions hydro-climatiques. Dans un troisième temps, la communication donnera les principaux verrous scientifiques, notamment sur la prédiction des hétérogénéités spatio-temporelles de la température des cours d’eau et le rôle des apports d’eau souterraines. L’analyse des images infrarouge thermique sur l’Arroux et la Bourbince lors d’un évènement caniculaire (41°C) et d’étiage sévère de juillet 2019, permettra d’introduire les notions de refuge thermique d’eau plus fraiche et la nécessité de mieux les localiser et les caractériser. L’augmentation de la fréquence de ces épisodes de bas débit et de températures élevés pourrait compromettre la disponibilité en eau pour les activités humaines, telles que la production d’eau potable, l’irrigation et le refroidissement des centrales nucléaires. Ces résultats soulignent l'urgence d'adopter des stratégies d’adaptation locales, plus holistiques (usages, biogéochimie, connectivités) pour pouvoir relever les défis écologiques et de disponibilité des ressources en eau liés au climat
Two Erosion Tests to Quantify Resistance to Erosion During Overflow: The Jet Erosion Test and the Overflow Test
No full textInternational audienceThis report presents three experimental devices for quantifying the resistance to external erosion of a dam or dike embankment during overflow. The first is the Jet Erosion Test initially developed at the Agricultural Research Service (ARS, USA), and currently used by GeophyConsult (France) and INRAE (France). The second experimental apparatus concerns an overflow device on embankment at the CNR-SESAME hydraulic laboratory (France). The third concerns an overflow field device developed by INRAE (France). This set of devices has been used in France for operational needs (e.g. design and hazard studies) and for research (e.g. development of new techniques such as the use of treated soils).Ce rapport présente trois dispositifs expérimentaux permettant de quantifier la résistance à l'érosion externe du talus d'un barrage ou d'une digue lors d'une surverse. Le premier est le Jet Erosion Test initialement développé à l'Agricultural Research Service (ARS, USA), et actuellement utilisé par GeophyConsult (France) et l'INRAE (France). Le second dispositif expérimental concerne un dispositif de surverse sur remblai au laboratoire hydraulique CNR-SESAME (France). Le troisième concerne un dispositif de terrain de surverse développé par l'INRAE (France). Cet ensemble de dispositifs est utilisé en France pour des besoins opérationnels (par exemple, conception et études de danger) et pour la recherche (par exemple, développement de nouvelles techniques telles que l'utilisation de sols traités)
Diagnostic fonctionnel des sols industriels : de la sélection d'un minimum d'indicateurs à leurs applications <i>in situ</i>
No full textInternational audienceLes activités industrielles peuvent induire une dégradation des sols sur de grandes surfaces (imperméabilisation, compactage, etc.). A la cessation des activités, les propriétaires fonciers souhaitant réhabiliter leur site en vue de nouvelles utilisations des sols et dans le cadre de l'objectif "zéro artificialisation nette" sont amenés à estimer l'état fonctionnel des sols. Il est donc nécessaire de développer une approche solide et facile à utiliser pour ces propriétaires afin d'évaluer les fonctions des sols et leur potentiel pour des utilisations futures. Un ensemble minimal d'indicateurs, définis comme des mesures qualitatives ou quantitatives de l'état et/ou des fonctions des sols, a été établi sur la base des propriétés chimiques, physiques et biologiques du sol. La sélection de ces indicateurs s'est faite sur la base de leur contribution à 6 fonctions du sol (e.g. la production de biomasse végétale). Douze zones, considérées comme homogènes en termes de végétation et de type de sol mais avec des usages passés différents (dépôt de cendres, fondations de bâtiments, etc.), ont été sélectionnées sur des sites de centrales thermiques en cours de fermeture. Sur ces zones, au total, 12 profils de sol et 164 échantillons de sol ont été analysés via différents paramètres biologiques, chimiques et physiques. Les premières analyses ont révélé qu'un sol remanié dans le cadre d'une activité industrielle donnée n'aboutira pas à la formation d'un même Technosol et souligne l'intérêt d'intégrer des paramètres biologiques dans les outils de diagnostic fonctionnel des sols.</div
SPH modelling of water flow inside a porous medium using a Riemann based formulation
No full textInternational audienceSimulating granular flows has been a major concern for thepast decades, with various environmental applications such asavalanches, landslides and scour near fluvial, coastal and off-shore constructions. These phenomena involve a porous matrixundergoing large deformations and characterized by a complexbehaviour. Thanks to its ability to handle large deformationsof the medium, SPH appears as a particularly advantageousmethod to deal with these problems. Various SPH schemesalready exist to model the granular medium behaviour, suchas the ones developed by Feng et al. [1], Bui and Nguyen [2](elastoplastic approach) or Gha¨ıtanellis [3] (elasto-viscoplasticapproach). However, to the authors’ knowledge, none of thesepapers show in their results what the water flow looks like insidethe porous structure while it deforms. Consequently, the presentwork aims at presenting a model to simulate the deformationof a granular medium as well as its infiltration by water. Theporous structure is unsaturated and is considered as a continuousmedium. Infiltrated water flows according to Darcy’s or Darcy-Forchheimer’s laws. Two different sets of particles are used forthis purpose, one for the water phase and an other one forthe porous structure, as done by Shimizu et al [4]. Riemann-based schemes have never been used yet for such purpose,though it proved to give accurate results for both fluid [6]and solid mechanics [7]. As a consequence, a new approachis proposed here by applying Riemann-based formulations onboth fluid and solid media. For the moment, the proposedmodel is not yet finished developing and only simulations withundeformable porous matrix are available for the writing of thisabstract. Results with moving, deformable porous matrix will bepresented during the conference
Uncertainty quantification and metamodeling of multi-fidelity CFD computation of a heated fuel assembly
No full textThis study proposes to quantify the uncertainty in a CPU-time costlyComputational Fluid Dynamics (CFD) model used to evaluate local temperaturefield in the situation of blocked fuel assembly in a PWR transfertube. Several uncertain parameters are identified and a first uncertaintypropagation study is conducted on a low-fidelity (poorly refined) mesh forCPU cost issues. Then, using the concept of “support points”, an algorithmis employed to reduce the size of the initial design of experiments.A high-fidelity model (finer mesh, more CPU-time expensive) is then runon this small-size design of experiments. A metamodel was finally builton those high-fidelity results to propagate uncertainties and finely analyzethe results. The successful results that are obtained show that metamodelinghas the potential to overcome the issue of costly CPU-time CFDmodels in the near future. Despite good quantitative results, the mainpurpose of the present study remains the novel methodology that was setup for uncertainty propagation in CFD
La "fabrique" du consentement. Tensions et moralisation autour de la gestion de la donnée
No full textInternational audienceSi la mise en place d’un consentement libre et éclairé des individus dansle processus de collecte, de traitement et de valorisation des DCP a ainsiété pensée comme un élargissement des garanties de protection de la vieprivée la manière dont la déclinaison concrète de ces nouvelles règles s’estopérée n’a pas tardé à faire surgir de vives critiques dénonçant une « farcedu consentement » (Nissembaum, 2019). Au-delà des débats conceptuels, cechapitre se penche sur la manière dont les acteurs dans le secteur de l’énergiequi rencontrent des contestations spécifiques en matière de protection dela vie privée autour de la numérisation des infrastructures et des donnéesont décliné les règles de droits dans des dispositifs techniques ou sociaux.Interrogeant les modalités de « fabrique du consentement », le chapitre saisità la fois les tensions autour de la déclinaison concrète des règles, maisaussi comment cette déclinaison a posé les bases d’une nouvelle approche« morale » des données, incomplète, disputée et inaboutie, mais incontestable
Toward Brague river flood modelling 2: efforts to optimize HPC resources for a TELEMAC-2D code based on shallow water equations
No full textInternational audienceThe Brague river (France) often encounters flash floods, resulting in consequent damages. The cities of Biot and Antibes were particularly affected in October 2015. This flood event was previously studied using both hydrological and hydraulic approaches, such as 2D hydraulic modelling tools (Basilisk, HEC-RAS and TELEMAC-2D) and the FEV approach. Here, we propose to restart from a previous existing numerical model built with TELEMAC-2D, which simulates the flood event of 2015 in the Brague floodplain. This work aims to assess an HPC performance of TELEMAC-2D for this specific case study based on speed-up, efficiency or energy cost, with the goal of estimating optimal configurations for running simulation efficiently. The results show that TELEMAC-2D is strongly scalable. The optimal configuration of cluster nodes and CPUs for a simulation depends on the metric considered, available resources, and the calculation to be performed. Particular attention is paid to energy consumption, which remains poorly studied -at least in the field of hydraulic modelling used on HPC -but is of the utmost importance in the current climatic context. The energy consumption to reach a same solution varies significantly between configurations, up to a difference of 80 %
Hoeffding decomposition of functions of random dependent variables
No full textInternational audienceHoeffding's functional decomposition is the cornerstone of many post-hoc interpretability methods. It entails decomposing arbitrary functions of mutually independent random variables as a sum of interactions. Many generalizations to dependent covariables have been proposed throughout the years, which rely on finding a set of suitable projectors. This paper characterizes such projectors under hierarchical orthogonality constraints and mild assumptions on the variable's probabilistic structure. Our approach is deeply rooted in Hilbert space theory, giving intuitive insights on defining, identifying, and separating interactions from the effects due to the variables' dependence structure. This new decomposition is then leveraged to define a new functional analysis of variance. Toy cases of functions of bivariate Bernoulli and Gaussian random variables are studied
Flow patterns in shallow rectangular reservoirs with open channel inlet or pipe flow inlet at various depths: An experimental study
No full textInternational audienceThis study experimentally assesses the influence of varying the inlet boundary condition on the flow patterns in rectangular shallow reservoirs. Two types of inlet boundary conditions were compared: a free surface inlet channel, and a pressurized circular inlet jet positioned at three different elevations over the flow depth (centroid of the inlet jet situated at 25%, 50%, or 75% of the flow depth). The outlet boundary condition was a free surface channel in all cases. Twenty-two experiments were done with two distinct reservoir lengths (length-to-width ratios of 1.1 and 2.0) and three hydraulic boundary conditions (Froude numbers of 0.14, 0.16, and 0.21). Velocity fields were measured with Large-Scale Particle Image Velocimetry (LSPIV) at the surface, and with an Acoustic Doppler Velocity Profiler(ADVP) at several cross sections. The flow patterns are greatly influenced by the inlet boundary condition and the reservoir geometry, but to a lesser extent by the hydraulic boundary condition. For an inlet circular jet located near the reservoir bottom, an unstable flow type, changing over time in a chaotic manner, was observed regardless of the reservoir length and of the inlet flow rate. The same type of unstable flow pattern was observed for a relatively long reservoir and the lowest tested flow rate, irrespective of the vertical positioning of the inlet jet. In all other tested configurations, a steady reattached jet was found in the reservoir equipped with a pressurized inlet jet. In addition to providing new knowledge on flow patterns in shallow reservoirs with an inlet jet, the experimental data presented here will prove valuable for evaluating flow computational models
Multi-year movements of potamodromous cyprinid species within a highly anthropized river assessed using RFID-equipped fishways
No full textInternational audienceMovements of potamodromous fish are poorly understood, especially in large rivers, because studies often focus on fishway evaluation and diadromous species. Here, we assessed the movements of 808 fish of five potamodromous species (Barbel, Barbus barbus; Common bream, Abramis brama; Nase, Chondrostoma nasus; Asp, Leuciscus aspius and chub Squalius cephalus) over 14 years in a highly anthropized river system, the Rhine River, where hydropower plants were progressively equipped with fishways including RFID antennas. The objectives of the study were 1) to characterize long-term and large-scale individual movement patterns of five potamodromous fish species 2) to assess inter-and intra-specific variations based on quantitative movement metrics and 3) to create a typology of individuals based on their movements. Results showed that, despite high intra-specific variability, the inter-specific differences were strong enough to highlight long-term and large-scale speciesspecific behaviors. Breams exhibited movements that occurred essentially during spawning migration period and at the reach scale. In contrast, barbels were more active, with more movements outside their spawning migration period, showed more large-scale and downstream movements, and used navigation locks more often than other species. For this species, the maximum distance between the two furthest recorded positions at the basin scale was exceptionally high (max = 155 km). We conclude that potamodromous species undoubtedly perform largescale movements, which are characterized by both species-specific and common features. Therefore, efforts need to be made to better consider their ecological needs and swimming capabilities when planning and designing effective fishways for the diverse range of species that move within river systems