Rural water systems (RWS) are commonly used to provide water to households for domestic uses (drinking, cleaning, washing, and sanitation) in developing countries. Water supply practitioners often classify these systems as single-use water systems (SUS) or multiple-use water systems (MUS). Smallholder farming communities in rural western hills of Nepal typically use such systems for both domestic and income-generating productive activities (e.g., agriculture, livestock, dairy, bio-gas, Rakshi), regardless of whether they were designed for single or multiple water uses. Therefore, this research frames both systems as providing multiple-use water services that enhance the productive activity and livelihoods of small- holders. Little is known on the factors that influence the productive activity of households in the western middle hills of Nepal and the impact these activities have on the technical performance of water systems (measured by duration of system breakdowns). This research identifies the extent of water-related productive activities in rural Nepali households supported by single-use water systems (SUS) vs. multiple-use water systems (MUS), and explores the factors that enables households to engage in high-levels of productive activity. The vast majority of households were found to engage in small-scale productive activities no matter what the rural water systems were designed to support, and more than half of them earned an income from water-based activities. Households engaged in high-levels of productive activity farm as a primary occupation, use productive technologies, are motivated to pursue productive activities, have received water-related productive activity training, and have received external support related to productive activities. A multinomial regression was used to predict the factors associated with high levels of productive activities undertaken by small farms. A hierarchical regression model was then used to examine both household- and system-level variables that contribute to the breakdown of rural water systems, focusing on the duration of breakdowns. The predictors of water system breakdowns include social factors (household involvement in decision-making during water system planning and construction and a household's sense of ownership toward the water system), technical factors (the management capacity of the water user committee and activity level of the system operator), economic factors (income earned from water-based productive activities), and geographic factors (the distance from the village to the water source). Finally, a conceptual model was developed to help identify strategies for implementing and scaling-up MUS. Scaling-up strategies for MUS begin with community participation in lo- cal government planning and budgeting. Under a new Constitution that went into effect in January 2017, newly formed local governments are to be provided with the funding and budget authority to determine local service priorities and how these services will be funded, designed, and implemented. The scaling-up of MUS would require local government officials, water system users, and private actors to develop the technical and institutional capacity needed to build and manage MUS, including the many support services needed by small- holder growers to realize its benefits. This research also examines the potential approaches that could enable subsistence farmers to become viable commercial producers. While growers are typically risk-adverse producers, this research identifies the mediating factors that could expand the long-term engagement of these producers in commercial agricultural production. These factors include adequate access to year-round irrigation, the use of improved production technologies and practices, improved access to rural markets, and improved production skills. The findings of this research will also be of value to Governmental, Non-Governmental Organizations (NGOs) and private sector actors who are looking to effectively mobilize their resources and expertise in support of smallholder farming in the hills of Nepal. / Doctor of Philosophy / A vast majority of farmers in the western middle hills of Nepal are smallholders who often use family labor and follow traditional agricultural and water use practices. They have been traditionally using rural water systems to meet their multiple water needs alongside domes- tic uses (drinking, cleaning, washing, and sanitation). There is growing interest for these systems to also be used for small-scale productive activities such as growing vegetables and livestock production. Evidence shows that these activities are an important source of income for farming families. However, little is known on the conditions that are needed to expand these activities and improve livelihoods. This research identifies the conditions under which rural water systems can become productive and technically sound, and outlines the strategies that can be deployed to scale-up productive activities. The research examines a broad range of perspectives (from rural farmers to development experts) on the limited commercialization of rural agriculture in the rural middle hills of Nepal and the potential approaches to promoting agricultural growth and commercialization among small landholders. The substance farmers were found to require both the means and motivation (i.e., extensive support services such as access to markets, input suppliers, irrigation and agricultural technologies, and production training) to become commercial farmers. Second, more than 90% of households were engaged in small-scale water-based production activities and more than half of them earned an income from these activities. The research revealed the conditions that enabled these households to engage in high levels of productive activities. Further, the factors that affect water system breakdowns were investigated. Since farmers are engaged in small-scale production, the interlinkages between productive income and system performance were examined. Finally, the research explores how multiple-use water services have the potential to be scaled-up in the middle hills of Nepal and beyond. Successful scaling-up strategies begin with community participation in local government planning and budgeting. This activity needs to be supported by substantial capacity building among government officials, water system users, and private actors on the factors needed to expand the productive use of water. Broad implementation of multiple-use water systems also requires careful documentation and dissemination of their benefits to key state and non-state actors. The results from this research can be used to identify appropriate households, communities, and water systems for programs focused on expanding water and agricultural productivity. Therefore, this research will have important implications for the Nepali government with regards to what policy, capacity development, and institutional arrangements need to be addressed to implement productive and sustainable rural water systems. This research can also be of special interest to Non-Governmental Organisations (NGOs) and private sector actors looking to effectively mobilize their resources and expertise relating to a smallholder farming in Nepal.

[pt] A simulação numérica é uma ferramenta essencial para a engenharia de reservatórios moderna, em particular no desenvolvimento de campos de óleo marítimos. A maioria das simulações de reservatórios utilizam malhas estruturadas em três dimensões, com tamanho variando de alguns milhares a dezenas de milhões de células. Algumas simulações apresentam um alto custo computacional que pode dificultar os estudos de desenvolvimento de um campo, mesmo com a alta capacidade computacional disponível hoje. Malhas de simulação não-estruturadas são uma alternativa para reduzir o tamanho dos modelos de reservatórios (e, consequentemente, o tempo de execução das simulações), sem sacrificar a qualidade dos resultados. Este trabalho utiliza malhas de Voronoi, também conhecidas como malhas de bissetores perpendiculares, uma vez que suas propriedades permitem simplificar as equações discretizadas do escoamento em comparação com outros tipos de malhas não-estruturadas. Dois passos são críticos para a criação de um modelo não-estruturado de reservatórios a partir de um modelo geológico refinado: geração da malha e transferência de escala das propriedades. A maioria dos métodos propostos para ambas as tarefas utilizam informações de simulações na malha refinada. Embora essa abordagem apresente bons resultados, pode ser muito custosa e precisa ser refeita caso haja alterações significativas nas condições de escoamento. Este trabalho discute técnicas para geração de malha e transferência de escala que não dependam de simulações na escala fina. As técnicas utilizam apenas a distribuição de propriedades de reservatórios e o posicionamento de poços, falhas e outras feições discretas. A abordagem adotada para geração da malha parte de uma disposição regular de pontos que são redistribuídos de acordo com um mapa de espaçamento previamente definido. Dois algoritmos iterativos para redistribuição desses pontos baseados em modelos físicos são propostos. Diversos critérios de espaçamento também são investigados. Dois algoritmos de transferência de escala em malhas não-estruturadas são propostos. Estes métodos se baseiam nas técnicas de Cardwell and Parsons e de renormalização para transferência de escala em malhas estruturadas. Por fim, exemplos representativos são utilizados para demonstrar as potencialidades e eficácia das estratégias propostas. / [en] Numerical simulation represents an essential tool for modern reservoir engineering, especially for the development of offshore oil fields. Most reservoir simulations are performed on three-dimensional structured grids, with a size ranging from a few thousands to tens of millions of cells. Some simulations can have a high computational cost that hinders the field development studies, even using the processing power available nowadays. Unstructured meshes are an effective alternative to reduce the size of reservoir models (and, consequently, the overall simulation time) without sacrificing the quality of the results. In this work, we adopt Voronoi meshes, also known as perpendicular bisector grids, since their properties simplify the discretized flow equations in reservoir simulations when compared to other types of unstructured meshes. Two main steps are critical to creating an unstructured reservoir model from a refined geological model: grid generation and upscaling of the reservoir properties. Most methods employed for both steps rely on information obtained from simulations using fine-scale meshes. Although this approach yields good results, it can be time-consuming and may be optimal only for the specified set of flow conditions. This work discusses the generation of unstructured grids and upscaling techniques that do not require any previous simulations. Instead, they are based only on reservoir property distributions and the location of discrete features such as wells and faults. The proposed grid generation strategy starts from a regular set of points and then redistributes them according to a previously defined spacing map. Two iterative redistribution algorithms based on physical models are presented, and several criteria for spacing maps are also investigated. Two upscaling algorithms for unstructured grids are proposed, based on the Cardwell and Parsons and renormalization techniques for structured meshes. Finally, representative examples are presented to demonstrate the capabilities and effectiveness of the proposed strategies.

Une colonne de séparation d'air réalise un écoulement liquide-gaz à contre courant dans une structure complexe, le garnissage. Au sein de ce garnissage, l'écoulement du liquide est du type film drainé par gravité, alors que l'écoulement du gaz est turbulent. La fonction de ces contacteurs est de développer une surface d'échange interfaciale aussi grande que possible pour favoriser le transfert d'un composé chimique de la phase liquide vers la phase vapeur (et inversement) tout en offrant des pertes de charge raisonnables. Ces dispositifs sont constitués par l'assemblage de plaques métalliques ondulées, avec ou sans perforations, où deux plaques adjacentes sont respectivement inclinées d'un angle et son opposé par rapport à l'axe de la colonne. Ce type de contacteur peut être considéré comme un milieu poreux bi-structuré avec un taux de porosité élevé. Les écoulements peuvent être décrits à deux échelles : une échelle du pore et une échelle macroscopique. A cause de cette double structuration, la modélisation macroscopique des écoulements dans ce type de structure reste un problème difficile. En particulier, les mécanismes macroscopiques qui entraînent l'étalement d'un jet dans les garnissages sont incompris. Par ailleurs, une difficulté de modélisation supplémentaire est due aux effets liés à la turbulence. Au cours de cette thèse, nous avons développé, à partir d'une méthode de changement d'échelle, un modèle complet pour simuler les écoulements et le transfert de matière dans les colonnes équipées de garnissages structurés. Notre étude se focalise sur les trois points suivants. Premièrement, nous avons obtenu, à l'aide d'une prise de moyenne volumique, une loi de Darcy-Forchheimer qui inclue les effets de la turbulence. Ensuite, pour modéliser la dispersion radiale du liquide dans la colonne, nous avons trouvé pratique de séparer la phase liquide en deux films distincts, qui s'écoulent sur chaque plaque ondulée selon des directions préférentielles différentes. Ces phases fictives ne sont pas indépendantes puisque de la matière peut passer de l'une à l'autre au niveau des points de contact entre les feuilles ondulées. Finalement, nous avons proposé un modèle macroscopique pour simuler le transport d'espèces chimiques dans un système diphasique, multiconstituants. Tous les paramètres effectifs qui apparaissent dans ce modèle sont évalués à partir de solutions analytiques ou numériques de l'écoulement à la petite échelle. Les résultats de simulation ont été comparés avec succès à des mesures expérimentales obtenues en laboratoire ou sur pilote industriel. / Structured packings play a large role in chemical engineering processes involving gasliquid separation such as air distillation unit or CO2 absorption columns. Such structures maximize the exchange surface between gas and liquid while pressure drops remain low enough. Generally, the columns are operated in the counter-current flow mode : a liquid gravity film is sheared by the turbulent flow of a gas phase. The packings are made of an assembly of corrugated sheets where two adjacent sheets are respectively inclined by an angle and the opposite of this angle from the vertical axis. We can apprehend such a device as a bi-structured porous medium with high porosity defining two scales of description : a pore-scale and a macro-scale assimilated to the packing scale. Due to this peculiar structured geometry, the flow modeling from a macroscopic point of view, remains a challenging problem that has to be overcome to design enhanced devices. In particular, the macroscopic phenomena that leads to the spreading of a liquid point source at the top of a packing are still unknown, and the classical two-phase flow models in porous media failed to properly catch the liquid distribution within the column. Moreover, turbulence effects lead to additional difficulties. We developed a comprehensive mathematical model based on a multi-scale analysis to simulate gas-liquid flow through the distillation columns. We investigate three main points. First, we derived a Darcy-Forchheimer law that includes turbulence effects using the method of volume averaging. Then, to model the liquid spreading, we found convenient to split the liquid phase into two fictitious phases flowing along each sheet with a preferential direction. Moreover, these phases are not (except perhaps at very low saturation) completely independent since adjacent sheets are in contact and the liquid can flow from one sheet to the other. Finally, we proposed a macro-scale dispersion model to simulate two-phase, multicomponent transport in structured packing. All the effective properties that appear in this model are evaluated from either simulations or analytical solutions of the flow at the pore-scale. Simulation results have been successfully compared to laboratory-scale experiments and industrial-scale measurements.

Ce travail entre dans le cadre de l’étude des interactions eau-roche dans le cas du stockage du CO2 en milieu géologique. Un intérêt particulier est accordé aux hétérogénéités des paramètres associés aux phénomènes géochimiques. Ces hétérogénéités peuvent s’observer à différentes échelles: celle des grains (les minéraux présentent des défauts de cristallinité et des impuretés), et l’échelle centimétrique/pluri-décamétrique. En particulier, les paramètres thermodynamiques (logK) et de cinétique chimique (dans ce travail nous avons considéré le produit de la constante cinétique k par la surface spécifique S soit kS comme "paramètre de cinétique chimique") sont connus à partir des expériences de laboratoire pour des échantillons de quelques centimètres de dimension, alors que l’on s’intéresse aux réactions minéralogiques à l’échelle des réservoirs.Nous avons évalué les caractéristiques géostatistiques de la variabilité spatiale après réaction à travers des simulations de transport réactif dans lesquelles différents paramètres (logK et kS) sont perturbés avec une première variabilité imposée. Une combinaison de deux approches est ainsi abordée : déterministe et géostatistique. Le code du transport-réactif COORES (IFP-EN et Ecole nationale supérieure des mines de Saint-Etienne) a été utilisé pour les simulations déterministes et le système géochimique étudié concerne la dissolution du diopside avec précipitation de minéraux secondaires comme la calcite et la magnésite.Après analyse par la méthode des plans d’expériences, les résultats montrent qu’une corrélation spatiale élevée combinée avec une grande variance de dispersion des minéraux favorise une réactivité importante des minéraux lorsqu’on perturbe le paramètre de cinétique chimique kS. Par ailleurs une vitesse d’injection élevée accélère le processus de dissolution du minéral étudié. La variabilité spatiale du paramètre thermodynamique n’a cependant pas d’effet significatif sur les résultats, le système se comporte comme dans le cas homogène. Du point de vue de l’homogénéisation du paramètre kS, on retrouve l’influence de l’historique de dissolution. / The present work is based on the study of water-rock interactions in the case of CO2 storage in geological media. Particular attention is devoted to heterogeneities at different observation scales geochemical phenomena. These heterogeneities can be observed at different scales: the grain (mineral crystallinity present defects and impurities), and the centimeter scale / multi- decametric (rocks are heterogeneous at different scales). In particular, the thermodynamic parameters logK and chemical kinetics kS (in this work we considered the product of the rate constant k by the specific surface area S is kS as "chemical kinetics parameter") are known from laboratory experiments to a few centimeters in size, while we are interested in mineralogical reactions across tanks.We propose to evaluate the geostatistical characteristics of the local variability after reaction through simulations of reactive transport on a small scale in which various parameters (logK and kS) are perturbed with a first spatial variability imposed. A combination of both approaches is discussed: deterministic and geostatistical for the study of geochemical problems at different scales. The reactive transport code - COORES (IFP - EN and Ecole nationale supérieure des mines de Saint -Etienne) was used for deterministic simulations and the geochemical system studied concerns the dissolution of diopside with precipitation of secondary minerals such as calcite and magnesite.After analysis by the method of design of experiments, the results show that high spatial correlation variance combined with high dispersion of minerals promotes a high reactivity when minerals chemically disturbing is the kinetic parameter kS. In addition, a high velocity injection accelerates the dissolution of the mineral studied. However, the effect of spatial variability of the thermodynamic parameter, did not significantly affect the results, the system behaves as in the homogeneous case. From the standpoint of homogenizing the parameter kS, include the influence of the history of dissolution.

Certaines applications industrielles nécessitent des niveaux d’étanchéité exceptionnels pour permettre la réalisation d’un vide poussé ou pour répondre à des enjeux de sécurité radiologique par exemple. Ces niveaux de haute étanchéité statique sur des assemblages démontables sont obtenus à l’aide de joints entièrement métalliques. La fuite résultante de l’assemblage n’est due qu’à la persistance d’un champ des ouvertures à l’interface entre le joint d’étanchéité et la bride d’assemblage, conséquence d’un contact imparfait entre les deux surfaces rugueuses. Le champ des ouvertures à l’interface de contact est assimilable à une fracture rugueuse hétérogène, de nature multi-échelle, et peut en principe être obtenu par un calcul de déformations mécaniques préalable. Dans ce travail, on s’intéressera plus particulièrement à l’écoulement gazeux raréfié dans le régime glissant au sein de cette fracture. Pour les régimes modérément raréfiés,l’écoulement est modélisé par l’équation de Reynolds faiblement compressible avec correction de glissement de premier ordre aux parois que l’on développe. On effectue ensuite un changement d’échelle par la méthode de la prise de moyenne volumique, permettant d’établir un modèle macroscopique d’écoulement à l’échelle d’un élément représentatif, où le débit massique est relié au gradient de pression via le tenseur de transmissivité. Celui-ci, caractéristique de l’élément représentatif de fracture, est calculé par résolution d’un problème de fermeture et est dépendant de la microstructure ainsi que du libre parcours moyen représentatif sur l’élément. Pour remonter à l’écoulement dans l’ensemble de la fracture, hétérogène à cette échelle, celle-ci est subdiviséeen pavés sur chacun desquels est calculé un tenseur de transmissivité local par la méthode sus-citée. Ensuite, l’écoulement dans ce champ de tenseurs est résolu par une méthode des éléments finis de frontière, donnant la transmissivité apparente glissante du joint dans son ensemble. Cette approche à deux échelles, vue comme outil d’aide à la conception, permet une réduction de la complexité de calcul par rapport à une simulation directe, rendant possible une analyse plus efficace du comportement d’un système d’étanchéité. Pour valider l’utilisation du modèle de glissement d’un point de vue macroscopique et s’affranchir des incertitudes sur le calcul de déformation mécanique, des puces nanofluidiques de type réseau hétérogène de canaux droits sont fabriquées par photolithographie par niveaux de gris. Des essais expérimentaux de mesure de fuite sont réalisés sur ces géométries modèles, représentant des joints idéalisés. Ces essais sont effectués en appliquant une forte différence de pression d’hélium par utilisation d’un spectromètre de masse mesurant la fuite, produisant une condition de vide en sortie de puce.Selon les puces, les régimes de raréfaction atteints vont alors du régime glissant au régime moléculaire. Le débit de fuite mesuré est alors supérieur à celui prédit par le modèle de premier ordre, l’écart restant inférieur à un ordre de grandeur quel que soit le régime / Some industrial applications require exceptional sealing levels to maintain ultra-high vacuumconditions or for radiological safety concerns for example. Such high performance static sealingconditions on mechanical assemblies are reached using entirely metallic gaskets. The resultingleak-rate is only due to the persistence of an aperture field at the seal-flange interface,consequence of a non-ideal contact between the two rough surfaces. This aperture field can beviewed as a rough and heterogeneous fracture, of multi-scale nature, and can be obtained by aprior contact mechanics computation. In this work, we are interested on the rarefied flow of a gasin this fracture, drawing our attention to the slip regime. For such moderately rarefied regime, theflow is described by the slightly compressible Reynolds equation with a first-order slip-flowcorrection at the walls, which we develop. Using the method of volume averaging, an upscalingprocedure is performed to derive the macroscopic flow model at the scale of a representativeelement, and where the mass flow rate is related to the pressure gradient by the transmissivitytensor. This latter is characteristic of the representative fracture element and is obtained by solvingan auxiliary closure problem which depends on the micro-structure as well as the representativemean free path on the element. To compute the flow in the whole fracture, heterogeneous at thisscale, it is subdivided in tiles on which a transmissivity tensor is locally computed by theaforementioned method. Then, the flow problem in this tensor field is solved using a boundaryelement method, leading to the apparent slip-corrected transmissivity of the entire aperture field.This two-scale approach is a conception tool which reduces the overall complexity with respect toa direct numerical simulation, allowing a more efficient analysis of the behavior of a sealingassembly. To validate the use of slip models at the macroscopic level and to eliminate theuncertainties of the contact mechanics computation, nanofluidic chips composed ofheterogeneous network of straight channels are fabricated using a grayscale photolithographytechnique. Experimental measurements of the leak-rate are performed on these idealizedgeometries that mimic a seal assembly. They are realized by applying a strong helium pressuredifference on the chip using a mass spectrometer to measure the leak, which produces a nearvacuum condition at the outlet. Depending of the chip, the rarefaction regime ranges from slip tofree-molecular. The measured leak-rate is greater than predicted by the first order model, thoughbeing of the same order of magnitude whatever the regime

La contamination des ressources en eaux souterraines par une phase organique non miscible à l'eau couramment appelée NAPL (Non Aqueous Phase Liquid) constitue aujourd'hui un défi scientifique majeur compte tenu de la durée de vie d'un tel polluant. Bien que l'activité bactérienne (généralement présente sous forme de biofilm) joue un rôle crucial dans le devenir à long terme de ces effluents, peu d'études existent à l'heure actuelle sur son impact dans des conditions multiphasiques (i.e., à proximité de la source). En effet, dans la zone saturée, sous l'action des forces capillaires, le NAPL se retrouve souvent piégé, en effet, sous forme de «gouttelettes» au niveau des pores. Ce comportement spécifique au polluant modifie la dynamique du système biofilm/milieu poreux saturé et d'importantes questions restent encore ouvertes : accessibilité du polluant, modification de la tension interfaciale, production de biosurfactant, effet de toxicité (inhibition de la croissance bactérienne). Pour tenter de répondre à ces questions, nous avons adopté une approche aussi bien théorique qu'expérimentale. L'approche théorique porte sur le développement d'un modèle macroscopique décrivant le transport multiphasique en milieu poreux pour un système eau/NAPL/biofilm. Elle repose sur la méthode de prise de moyenne volumique, appliqué aux équations décrivant le couplage écoulement/transport à l'échelle du pore, permettant d'effectuer le changement d'échelle et dériver un modèle à deux équations. Le modèle est établit sous les hypothèses d'équilibre de masse local à l'interface fluide/biofilm et les contraintes associées à ces hypothèses ont étés définies. L'influence des caractéristiques microscopiques (arrangement des grains, fraction volumique du biofilm, distribution des blobs de NAPL, mouillabilité) sur les propriétés effectives du milieu (coefficient de dispersion, coefficient d'échange de masse) est discutée au travers des résultats issus des simulations. Ensuite, le modèle macroscopique a été comparé avec succès à la simulation numérique direct à l'échelle du pore pour la géométrie 2D complexe considérée. Quant à l'approche expérimentale, elle consiste à étudier le transport et la biodégradation du toluène en présence des bactéries Pseudomonas Putida F1 à l'aide d'un milieu poreux transparent 2D (micromodèle). Premièrement, nous avons étudié la dissolution du toluène résiduel sans bactéries et des courbes de dissolution du toluène ont été obtenues. Les résultats de dissolution du toluène en condition abiotique ont été comparés avec succès aux résultats du modèle théorique. Ensuite, l'étude expérimentale en micromodèle a porté sur la dissolution du toluène en condition biotique. Les résultats de ces études (courbes de dissolution et évolution de la saturation résiduelle) ont montré un impact significatif de la présence des bactéries sur les processus de dissolution par comparaison au cas abiotique. / Contamination of groundwater resources by an immiscible organic phase commonly called NAPL (Non Aqueous Phase Liquid) represents a major scientific challenge considering the residence time of such a pollutant. Although bacterial activity (usually in the form of biofilm) plays a crucial role in the long term fate of these effluents, very few works are focused on the study of such processes in multiphase conditions (oil/water/biofilm systems). The NAPL often gets trapped, in fact, under the action of capillary forces in the saturated zone in the form of «droplets» within the pores. This specific pollutant behavior changes the dynamics of biofilm /saturated porous medium system where important questions remain open: accessibility of the pollutant, changes in interfacial tension, biosurfactant production, toxicity effect (inhibition of bacterial growth). Modeling the transport of chemical species in the presence of bacteria is an extremely complex issue in terms of scale. We will use an experimental and theoretical approach to address these questions. In this thesis, we developed a macroscopic model describing multiphase transport in porous media for a water/NAPL/biofilm system. A volume averaging method has been applied here to the equations at the pore scale to make the upscaling and derive the model. This two-equation model is established under the assumptions of local mass equilibrium at the fluid/biofilm interface and the constraints associated with these assumptions were defined. The effect of microscopic features (arrangement of grains, volume fraction of the biofilm, distribution of NAPL blobs, wettability) on the effective properties of the media (dispersion coefficient, mass exchange coefficient) is discussed through some results from simulations. Subsequently, the macroscopic model has been successfully compared with the direct numerical simulation at pore scale for a 2D complex geometry. The experimental approach consists of studying transport and biodegradation of toluene in the presence of bacteria Pseudomonas Putida F1 using a flowcell. First, we studied the dissolution of toluene in abiotic conditions and toluene dissolution curves were obtained. The results of toluene dissolution in abiotic conditions were compared with success the results of the theoretical model. Finally, an experimental study in flowcell on the dissolution of toluene under biotic conditions was performed. The results of these studies (dissolution curve and evolution of toluene saturation) showed a significant impact of the presence of bacteria on the dissolution process compared to the abiotic case.

Methane is an important greenhouse gas that is relatively long-lived in the atmosphere, and wetlands are a major natural source of atmospheric methane. Methane emissions from wetlands are variable across both space and time at scales ranging from meters to continents and a comprehensive accounting of wetland methane efflux is critical for quantifying the atmospheric methane balance. Major uncertainties in quantifying methane efflux arise when measuring and modelling its physical and biological determinants, including water table depth, microtopography, soil temperature, the distribution of aerenchymous vegetation, and the distribution of mosses. Further complications arise with the nonlinear interaction between flux and derivers in highly-heterogeneous wetland landscape. A possible solution for quantifying wetland methane efflux at multiple scales in space (‘upscaling’) is repeated observations using remote sensing technology to acquire information about the land surface across time, space, and spectra. These scaling issues must be resolved to progress in our understanding of the role of wetlands in the global atmospheric methane budget from peatlands. In this thesis, data collected from multiple aircraft and satellite-based remote sensing platforms were investigated to characterize the fine scale spatial heterogeneity of a peatland in southwestern Scotland for the purpose of developing techniques for quantifying (‘upscaling’) methane efflux at multiple scales and space. Seasonal variation in pools such as expansion and contraction was simulated with the LiDAR data to investigate the expansion and contraction of the lakes and pools that could give an idea of increase or decrease in methane emissions. Concepts from information theory applied on the different data sets also revealed the relative loss in some features on peatland surface and relative gain on others and find a natural application for reducing bias in multi-scale spatial classification as well as quantifying the length scales (or scales) at which important surface features for methane fluxes are lost. Results from the wavelet analysis demonstrated the preservation of fine scale heterogeneity up to certain length scale and the pattern on peatland surface was preserved. Variogram techniques were also tested to determine sample size, range and orientation in the data set. All the above has implications on estimating methane budget from the peatland landscape and could reduce the bias in the overall flux estimates. All the methods used can also be applied to contrasting sites.

Comprendre l'altération du verre nucléaire dans un réseau de fracture au sein d'un bloc de verre vitrifié est important pour la sûreté du conditionnement des déchets nucléaires (quantification des risques associés au relâchement des radionucléides). L’évaluation de la performance du stockage géologique des déchets nucléaires passe obligatoirement par la modélisation de l’altération aqueuse d’un bloc de verre nucléaire fracturé, l’échelle de temps envisagée (plusieurs milliers d’années) dépassant toute possibilité d’expérience directe. Cette thèse vise donc à combler le fossé entre les simulations d'écoulement et de transport à l'échelle du réservoir et la modélisation à l'échelle micrométrique des processus interfaciaux verre-eau, en apportant l'évaluation quantitative de la dégradation aqueuse du verre à l'échelle d’un bloc.Pour aborder ce problème, les objectifs principaux de cette thèse ont été fixés comme suit : (i) la reproduction des résultats expérimentaux obtenus précédemment (pour quelques fractures modélisées de manière discrète en mode diffusif), (ii) l’analyse de l'impact des géométries de fractures sur la quantité de verre altéré pour quelques fissures modélisées de manière discrète, (iii) l’étude de la possibilité d'adaptation du modèle géochimique à la modélisation dans le cadre de l’approche milieu équivalent, (iv) la mise au point d'une méthodologie de caractérisation, (v) la modélisation géostatistique et géométrique de réseau de fractures à l’échelle d’un conteneur de verre, (vi) le calcul des paramètres équivalents diffusifs, hydrauliques et les paramètres qui contrôlent la cinétique de dissolution de verre, et au final, (vii) la modélisation de transport réactif à l’échelle d’un conteneur.À titre illustratif, la méthodologie de la caractérisation de réseau fracturé proposée, basée sur le traitement des images, a été appliquée aux images bidimensionnelles (2D) de haute résolution de deux blocs de verre. Cette application a permis de mettre en œuvre à la fois les données directes obtenues par mesures des paramètres d’un réseau fracturé de verre vitrifié et les données indirectes explicatives issues des simulations thermomécaniques. L’application a abouti à la création de multiples réalisations de tessellation de réseaux fracturés équivalents qui ont ensuite été utilisées comme représentations physiques pour les calculs de la perméabilité équivalente, de la diffusion équivalente et des paramètres contrôlant la cinétique de dissolution de verre borosilicaté. L'évolution de la quantité de verre altéré obtenue en effectuant la modélisation de transport réactif appliquée à plusieurs réalisations de la tessellation de réseau fracturé équivalent a été comparée aux données expérimentales d’un essai d'altération aqueuse d'un conteneur non radioactif de verre nucléaire. Les résultats montrent que la méthodologie conçue offre une opportunité pour mieux comprendre l'impact de la fracturation sur l'altération aqueuse du verre vitrifié et constitue un outil fiable permettant de prendre en compte différents scénarios d'évolution du stockage. / Understanding the alteration of nuclear glass in a fracture network of a vitrified glass block is important for the safe conditioning of nuclear waste (quantification of the risks associated with radionuclide release). Performance assessment of geological nuclear waste repositories entails modelling of the long-term evolution of the fractured nuclear glass block aqueous alteration, because the considered time scale, of several thousands of years, is beyond the range of any direct experimental perspectives. This dissertation aims then to bridge the gap between the reservoir-scale flow and transport simulations and the micron-scale modeling of the glass-water interfacial processes, by bringing the quantitative evaluation of the glass aqueous degradation at the block scale.To tackle this issue, the main objectives of this thesis were fixed as follows: (i) reproduction of the experimental results previously obtained (for some fractures modeled in a discrete way in the diffusive mode),(ii) analysis of the impact of fractures geometries on the quantity of altered glass at the scale of some fractures modeled in a discrete way, (iii) investigation of the possibilities of the geochemical model adaptation for the equivalent homogenous modeling, (iv) establishment of a methodology for glass block fracture network characterization, (v) geostatistical and geometric modeling, (vi) calculation of the equivalent diffusive, hydraulic and glass dissolution kinetics controlling properties and (vii) upcoming reactive transport modeling at the scale of one canister.As an illustrative example, the proposed image processing-based fracture network characterization methodology was applied to two-dimensional (2D) high-resolution images of two blocks of vitrified glass. This application brought into service both hard data obtained by direct measurement of the fracture network and soft physics-based explanatory data and resulted in the creation of multiple realizations of fracture network equivalent tessellation that were further used as physical representation for the calculation of the equivalent hydraulic, diffusive, and alteration kinetics - controlling properties. The evolution of the quantity of altered glass obtained by conducting reactive transport modeling applied to several realizations of the equivalent fracture network tessellation was compared with the experimental data of the aqueous alteration test of a non-radioactive full-scale nuclear glass canister. The results show that implementation of the devised procedure presents an opportunity for better understanding the impact of fracturing on aqueous alteration of borosilicate glass and provides a reliable tool enabling different scenarios of repository evolution to be accounted for.

Il est prévu une augmentation de l’intensité et de la fréquence des sécheresses dans les années à venir à cause des changements climatiques. Puisque la productivité des peupliers est étroitement liée à la disponibilité en eau, il existe un risque de déclin de la production de bois dans les peupleraies. L’optimisation de la biomasse produite en regard de l’eau consommée (efficience d’utilisation de l’eau, WUE) apparaît alors être une question de recherche prometteuse. Des études précédentes ont montré une diversité clonale de WUE chez les peupliers, pilotée principalement par la conductance stomatique (gs). Cependant, gs et l’assimilation en CO2 ne sont pas toujours connectés, ce qui peut conduire à de fortes variations de WUE au niveau foliaire. De plus, puisque la mesure de l’efficience d’utilisation de l’eau au niveau de la plante entière (TE) est laborieuse à mesurer, les expérimentations sont souvent réalisées en serre. Toutefois, les conditions contrôlées d’une serre conduisent à un environnement très différent des conditions naturelles, et les comparaisons de WUE entre conditions contrôlées et naturelles sont rares dans la littérature. Nous avons évalué la diversité des dynamiques stomatiques au sein de génotypes de peupliers sous conditions témoins et sous sécheresse en serre et en pépinière. Nous avons examiné le lien entre différents facteurs physiologiques, morphologiques et moléculaires et les dynamiques stomatiques, ainsi que leur influence sur TE. De plus, nous avons étudié la relation entre différents estimateurs de WUE et ses composantes entre des conditions contrôlées et naturelles. Le contenu en éléments minéraux et l’expression de gènes candidats ont également été quantifiés à deux moments de la journée pour analyser leur relation avec gs. Nous avons observé une variabilité génotypique significative des dynamiques stomatiques à la fois en réponse à l’irradiance et au VPD, de plus modifiée par la sécheresse et les conditions de croissance. La taille et la densité des stomates ainsi que la transpiration foliaire étaient fortement corrélées aux dynamiques stomatiques en serre, mais très peu en pépinière. Ces résultats soulignent l’importance et la complexité de ces mécanismes à l’échelle de la plante entière. WUE au niveau de la feuille et de la plante entière étaient relativement stables au sein des génotypes et entre conditions de croissance, mais bien moins avec la sécheresse. Enfin, des contenus en éléments et des expressions géniques distinctes ont été observées entre faces de la feuille et enter moments de la journée, en lien avec gs. Ces résultats fournissent de précieuses informations pour mieux comprendre les divers mécanismes foliaires pilotant WUE au niveau de la plante entière. / The number of drought events is expected to increase in intensity and frequency as a result of climate change. Since poplar productivity is closely linked to water availability, there is an increasing risk of decline in wood production from poplar plantations. Optimization of the ratio of biomass production to water used (i.e. water use efficiency, WUE) appears therefore as a relevant target for poplar research. Previous studies have shown the clonal diversity of WUE in poplar is driven mainly by stomatal conductance (gs). However gs and photosynthesis are not always tightly coupled which can result in large variations of WUE at leaf level. Additionally, because transpiration efficiency (TE) is laborious to measure, experiments are often conducted in pots in glasshouses. However in controlled conditions the environment is widely different than in the field and comparisons of WUE in controlled and field conditions are scarce in the literature. We assessed the diversity of stomatal dynamics among poplar genotypes under control or drought conditions grown in a glasshouse and in the field. We investigated the link between physiological, morphological and molecular factors and stomatal dynamics, and their influence on TE. Furthermore, we examined the relation between different estimators of WUE and its components between controlled and field conditions. Element content and candidate gene expression in the guard cells were also quantified at two times during the day to analyze their link to stomatal conductance. We found among the four genotypes studied significant genotypic variability of stomatal dynamics to irradiance and VPD which was altered by drought and growing conditions. Stomatal size and density as well as water use, but not WUE, were correlated to stomatal dynamics, emphasizing the importance and complexity of such mechanisms at the whole plant scale. Good agreements between leaf-level and whole-plant WUE among genotypes and between growing conditions were also found. Finally, distinct guard cell element contents and candidate gene expression, between leaf sides and time of day, linked with stomatal conductance draw attention to the diversity of components contributing to TE. These findings provides valuable information to better understand the diverse, sometimes unsuspected, leaf-level mechanisms driving water use efficiency at the whole plant scale.

<p>One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration.</p><p>A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale.</p><p>An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities. </p><p>Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient.</p><p>A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated.</p><p>Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.</p>