Geogrid reinforced structures have been successfully used for over 25 years. However their design procedures have remained largely focused on ultimate failure mechanisms, originally developed for steel reinforcements. These are widely considered over conservative in determining realistic reinforcement and lateral earth stresses. The poor understanding of deformation performance led many design codes to restrict acceptable soils to selected sand and gravel fills, where deformation is not as concerning. Within UK construction there is a drive to reduce wastage, improve efficiency and reduce associated greenhouse gas emissions. For geogrid reinforced structures this could mean increasing reinforcement spacing and reusing weaker locally sourced soils. Both of these strategies increase deformation, raising concern about the lack of understanding and reliable guidance. As a result they fail to fulfil their efficiency potential. This Engineering Doctorate improved the understanding of horizontal deformation by analysing performance using laboratory testing, laser scanning industry structures and numerical modelling. Full-scale models were used to demonstrate a reduction in deformation by decreasing reinforcement spacing. Their results were combined with primary and secondary case studies to create a diverse database. This was used to validate a finite element model, differentiating between two often used construction methods. Its systematic analysis was extended to consider the deformation consequences of using low shear strength granular fills. The observations offered intend to reduce uncertainty and mitigate excessive deformations, which facilitates the further optimisation of designs.

Les matériaux supraconducteurs présentent des propriétés physiques et géométriques particulières qui exigent des approches de modélisation spatio-temporelle fines, où les méthodes classiques trouvent rapidement leurs limites en termes de convergence, de précision et de temps de calcul. Ce dernier peut être très conséquent, ce qui est incompatible avec les problèmes de dimensionnement et d’optimisation. Dans ce contexte, ce travail a pour objectif de développer des approches de modélisation multiphysique rapides pour le dimensionnement et l’optimisation des systèmes à base de supraconducteurs. Un intérêt particulier est porté pour les méthodes intégrales. Les verrous scientifiques à lever, qui constituent également l’originalité du travail, résident dans l’intégration des lois de comportement E(J) des supraconducteurs dans les schémas numériques de ce type de méthodes. Dans ce travail on développe un modèle numérique afin d’étudier la distribution de la densité de courant et d’estimer les pertes AC dans les supraconducteurs à haute température (HTS). Le modèle développé est basé sur une formulation intégro-différentielle en termes de potentiel vecteur électrique dans les deux domaines fréquentiel et temporel. Une campagne de test est menée afin de valider et de bien cerner les possibilités offertes et les limites de cette approche pour la modélisation des supraconducteurs. / Superconducting materials have particular physical and geometric properties that require spatial-temporal modeling approaches fines, where conventional methods quickly reach their limits in terms of convergence, precision and computational time. The latter can be very consistent, which is incompatible with the design and optimization problems. In this context, this work aims to develop rapid multiphysics modeling approaches for the design and optimization of superconductor-based systems. Particular attention is paid to the integral methods. Scientific obstacles to overcome, which also constitute the originality of the work lies in the integration of behavior laws E (J) of superconducting digital patterns of such methods. A numerical model is developed for a rapid computation of eddy currents in multifilamentary high temperature superconductive (HTS) for the evaluation of AC losses. The developed model is based on an integro-differential formulation in terms of the electric vector potential in the frequency and temporal domains. A test campaign is conducted to validate and clearly identify the possibilities and limitations of this approach for modeling superconductors.

The primary aim of this study was to investigate the sedimentation processes within Buffalo Bay, particularly within and adjacent to the Whitianga tidal inlet, in order to ascertain reasons for the shoaling at both the inlet, and the identified shallow zone around Pandora Rock. Comparison of historic bathymetries suggests the ebb delta and ebb discharge channel of the Whitianga tidal inlet are rapidly accreting and the ebb tidal discharge channel is gradually migrating northeast towards Whakapenui Point. Accretion rates of up to 25 cm y-1 were calculated in the ebb delta and inlet discharge channel area between 1979 and 1995 and aerial photo comparisons suggest the ebb delta area had increased by 400 % between 1990 and 2002. Results of the hydrodynamic and sediment transport modelling suggest the rapid accretion in the ebb delta vicinity is likely to be caused by a combination of catchment estuary inputs, which are deposited on the ebb tide as the ebb flow decelerates over the ebb delta, and inputs that have been moved south along Buffalo Beach by flood currents and an eddy that forms landward of the ebb tidal discharge. Residual tidal velocities further suggest a deposition zone in the ebb delta vicinity resulting from opposing currents and the deceleration of currents. Hydrodynamic modelling results indicate the isolated shallow zone around Pandora rock appears to be caused by a transient eddy in the southern section of Buffalo Bay. The eddy is formed by the ebb tidal discharge from the inlet. Accretion probably occurs in the centre of the eddy which moves north as the ebb tide progresses. Results obtained from a current meter and sediment trap deployed in northern Buffalo Bay suggest suspended sediment transport is minimal in northern Buffalo Bay, only occurring with large wave activity. Results of the hydrodynamic and sediment transport modelling further demonstrate that this area experiences low flow velocities, and has little interaction with the rest of Buffalo Bay. The minimal sediment input to this area, combined with the occasional erosion of the seafloor, primarily by wave activity, is thought to have resulted in long term erosion of northwestern Buffalo Bay between 1938 and 1979. Although the beach and nearshore is eroding, it is likely the addition of sediment would act to stabilise this section of eroding beach. Renourishment material could be provided by the ebb delta, the southern tip of Buffalo Bay or the isolated sandbar northeast of the inlet entrance.

The sustainability of groundwater resources is important for the environment, the economy and communities where surface water is scarce. It is a hidden resource, but additional information can be extracted by combining groundwater measurements and lithological information with groundwater flow equations in groundwater models. The models convert data and knowledge about the groundwater systems into information, such as relative inflow and outflow rates and water-level predictions that can be readily understood by groundwater managers. ¶ The development of models to effectively inform groundwater management policies is, however, a complex task that presents a fundamental scientific challenge. This thesis presents methods and results for water balances calculated using groundwater flow models. Groundwater flow modelling methods and approaches are discussed, and their capabilities and limitations are reviewed. Two groundwater systems are studied for the Great Artesian Basin (GAB) and for the irrigation area near Bowen, Queensland. Three approaches to water balance modelling are applied in comprehensive model-development frameworks that take into account model objectives, data and knowledge availability and sensitivity analysis techniques. The three models show numerical methods of increasing complexity. The Bowen study area is well-suited to the least-complex method because data collection has been a priority there. As a contrast, the GAB is a large, poorly-monitored basin for which more knowledge of the groundwater system can be gained from its simulation by the steady state and transient groundwater flow models. The Bowen impact assessment model calculates dynamic historical water balances. The GAB aquifer models are high-complexity representations of the groundwater system that include predicted responses of the system to changes in hydrological conditions. These are comprehensive and well-documented attempts to model these systems. They provide a platform for scenario investigation and future improvements. ¶ Darcy’s Law was used in a GIS (Geographic Information System) to calculate dynamic water balances for an aquifer near the Queensland town of Bowen. This is the first time this approach has been applied to generate a complete groundwater balance. Over the period 1989-1997 the model estimates average total inflows to be 87 % groundwater recharge by rainfall and irrigation return flow, 12 % river recharge and 1 % inflow across the study area boundary. Outflows are estimated to be 66 % evapotranspiration, 28 % water bore discharge, 4 % discharge to the ocean and 2 % groundwater loss to rivers. Analyses show that evapotranspiration is the most uncertain parameter value. The GIS method was found to be useful for calculating water balances more accurately than analytical methods, because of their simplifying assumptions, and less time consuming than the more complex numerical models developed for the GAB aquifer. ¶ For the GAB, a steady state numerical model was developed and tested and predictive scenarios were run. The purpose of this modelling was both to gain a better understanding of the water balance of the GAB and to provide a tool that could predict water level recoveries under different bore rehabilitation scenarios. The model complexity is greater than in any previous numerical groundwater model of the GAB. In particular, the model uses more data, extends over a larger area and uses a generally finer discretisation than previous models. For the nearest surface artesian aquifer in 1960 the model estimates total inflows to be 60 % groundwater recharge and 40 % diffuse vertical inter-aquifer leakage. The model estimates outflows to be 53 % diffuse vertical leakage, 43 % water bore discharge, 3 % spring discharge and 1 % discharge to the ocean. Analyses show that the model is most sensitive to changes in horizontal hydraulic conductivity and recharge. The model-predicted heads match field measurements with a Scaled RMS error of 0.8 %, which is well within the guideline error of 5 %. The predictive scenarios show net vertical leakage into the aquifer decreasing and net vertical leakage out of the aquifer increasing, as bore flows are reduced. These estimates of inflows and outflows complement other studies of the Basin and add to our understanding of its hydrodynamics. In this way the water balance helps provide a sound basis for the development of GAB groundwater management plans and policies. Through its water level recovery predictions, the model has also been used to support the GAB Sustainability Initiative. ¶ A transient numerical model of the GAB was also developed and tested, and predictive scenarios were run. This model builds on the steady state model, and is more complex, with a calibration period (1965-1999) that is longer than in any previous GAB model. During calibration the model observations were expressed and weighted so that the minimisation of the objective function reflected the relative importance of the model’s potential uses, these being respectively: to simulate the impact of changing bore flows, to more generally inform water management plans and to provide an estimate of the water balance. It was found that the 1960 steady state assumption was not correct. Discluding anthropogenic discharge, the model is most sensitive to recharge and hydraulic conductivity. The model-predicted heads match field measurements with a Scaled RMS error of 2.7 %, which is well within the guideline error of 5 %, but the increased data requirements of the transient model highlighted deficiencies in the data available for the modelling. In particular, the uneven spread of the groundwater measurements over both time and space, the questionable accuracy of measurements from both high temperature and pressure bores, and corroded bores, and the type of discharge measured (for example, maximum yield or flow-as-found), became evident during the calibration of the model. Insights and the value of this work indicates for the first time that at the start of 2005 outflows were estimated to exceed inflows by 266 GL/year, or 62 % of total inflows, and, assuming that inflows through the aquifer’s boundary will not be reduced due to climate change, it will be possible to recover some of the lost groundwater pressure if all stock and domestic bores are rehabilitated and new extractions are limited. In this case the modelling estimates that inflows could exceed outflows by up to 40 % of total outflows.

Le thème général de cette thèse porte sur le comportement des sols et des roches tendres partiellement saturés. Cette condition de saturation partielle entraîne une complexification du comportement et une augmentation des couplages entre les différents phénomènes existants. Nous avons travaillé sur deux applications différentes qui présentent en fait beaucoup de similitudes. Ce travail s'est effectué principalement dans le code aux éléments finis LAGAMINE. Le premier domaine d'étude concerne le stockage de déchets nucléaires de haute activité. Pour ces derniers, le concept de dépôts dans des couches géologiques profondes a été développé afin de protéger les êtres humains et leur environnement des effets néfastes de la radioactivité. L'idée est de construire un système de galeries dans lesquelles seront placés les déchets vitrifiés ; une barrière d'étanchéité ouvragée (généralement des blocs d'argile compactée) remplira le reste de la galerie et assurera un complément à une barrière géologique naturelle. Pour dimensionner ce système complexe, il est nécessaire de bien connaître les caractéristiques hydrogéologiques, thermiques, mécaniques, chimiques et biologiques, ainsi que de comprendre les processus couplés qui ne manqueront pas de s'y développer. C'est la raison pour laquelle se sont créés des URL (Underground Research Laboratories) dans les couches géologiques potentielles, comme le SCK-CEN à Mol. Les modèles numériques viennent en complément des études expérimentales réalisées dans ces laboratoires et aident à la compréhension des mesures effectuées. En effet, le comportement de la barrière d'étanchéité est très complexe, impliquant des phénomènes thermo-hydro-mécaniques prenant place durant l'échauffement (les déchets dégagent toujours une certaine quantité d'énergie) et l'hydratation (par la formation hôte) de la barrière argileuse ouvragée. Dans ce cadre, nous avons développé un modèle d'écoulement multiphasique avec changement de phase ; il permet d'étudier les transferts hydriques et de chaleur se produisant dans la zone proche de la galerie. Les couplages sont nombreux : les variations de température influencent les propriétés des fluides, ces derniers transportent de la chaleur lors de leur déplacement (flux convectifs), ces conditions de saturation partielle (liées à la succion) induisent également des modifications du comportement mécanique de l'argile. Enfin, dans ces milieux très peu perméables, la prise en compte des transferts hydriques en phase vapeur est primordiale. Ces développements ont été réalisés dans le cadre du projet européen CATSIUS CLAY, ce qui nous a permis une comparaison avec d'autres codes de calculs et la validation de notre travail. Le deuxième domaine d'étude est la subsidence des réservoirs pétroliers de mer du Nord. En effet, certains réservoirs se situent dans des couches de craie à plusieurs milliers de mètres sous le niveau de la mer et ils sont exploités à partir d'installations off-shores. La production du pétrole induit une déplétion du réservoir qui s'accompagne d'une compaction ; cette dernière se répercute jusqu'au fond marin et cela met en danger les stations off-shores. La solution actuellement mise en uvre est l'injection d'eau dans le réservoir afin de le repressuriser et de diminuer ainsi la compaction. Malheureusement, cela a provoqué dans ces formations crayeuses un tassement supplémentaire ! Toutefois, celui-ci n'a pas que des aspects négatifs ; la compaction additionnelle permet une récupération secondaire du pétrole, qui n'aurait pu être obtenue autrement sinon. Il est donc très intéressant de pouvoir contrôler le tassement des couches réservoir. Dans le cadre des projets européens PASACHALK, nous avons développé une loi constitutive élastoplastique suivant l'idée que la sensibilité à l'eau d'une craie initialement saturée d'huile est reliée à l'effet de la succion. Cette dernière comprend des effets purement capillaires mais d'autres également (osmotiques par exemple). Nous avons donc construit un modèle multimécanisme avec influence de la succion, en utilisant les outils et concepts développés en mécanique des sols non-saturés (l'argile notamment). On voit dès lors que les modèles de l'argile de scellement et ceux de la craie de réservoir présentent de nombreuses similitudes ! Cette recherche a été facilitée par le fait qu'une craie, similaire à celles des réservoirs de Mer du Nord, affleure dans notre pays ; on l'exploite notamment dans la carrière de Lixhe, en région liégeoise. Cette craie possède les mêmes caractéristiques et propriétés que celles des formations du réservoir. La seule différence réside dans le fait qu'il n'y a jamais eu de pétrole dans ses pores ! L'analyse de l'ensemble des expérimentations réalisées sur ce matériau, nous a permis de mettre en évidence les caractéristiques du comportement de la craie de manière à calibrer notre loi. Enfin, des essais d'injection dans des échantillons nous fournissent un moyen de validation de nos modèles. Ainsi, nous avons réalisé des simulations à l'échelle du réservoir qui ont confirmé que la variation de succion est bien une explication de certaines compactions dans les réservoirs pétroliers.

The behaviour of hydrocarbon fuels in contaminated groundwater systems is studied using a multicomponent reactive transport model. The simulated processes include residual NAPL dissolution, aerobic and anaerobic biodegradation with daughter-product transport, and transport of a reactive carrier with mixed equilibrium/kinetic sorption. The solution algorithm is based on a three-dimensional Galerkin finite element scheme with deformable brick elements and capacity for a free watertable search. Nonlinearities are handled through Picard iteration. Convergence is rapid for most applications and mass balance errors for all phases are minimal. The model is first applied to simulate a pilot scale diesel fuel dissolution experiment in which humic acid is used as a natural organic carrier to enhance dissolution and to promote biodegradation of the aqueous components. The pilot scale experiment is described by Lesage et al. (1995) and Van Stempvoort et al. (2000). The conceptual model includes 8 unique components dissolving from 500 mL of residual diesel fuel within a 3D saturated domain. Oxygen-limiting competitive aerobic biodegradation with a dynamic microbial population is also included. A mixed 2-site equilibrium/kinetic model for describing sorption of the carrier to the aquifer solids was adopted to reproduce the observed breakthrough of the humic acid and organic components. Most model parameters were obtained independently with minimal calibration. Batch sorption data were found to fit well at the pilot scale, however biodegradation and dissolution rates were not well known and had to be fitted. Simulations confirmed the observed 10-fold increase in effective solubility of trimethylnaphthalene, and increases on the order of 2-5 for methyl- and dimethylnaphthalene. The simulated plumes showed almost complete attenuation after 5 years, in excellent agreement with observed data. A sensitivity analysis showed the importance of carrier concentrations, binding coefficients, dissolution and biodegradation rates. Compared to a dissolution scenario assuming no carrier, the humic acid-enhanced dissolution case decreased the remediation time by a factor of about 5. The second application of the model involves simulating the effect of ethanol on the persistence of benzene in gasoline-impacted groundwater systems. The conceptual model includes a 4-component residual gasoline source which is dissolving at the watertable into a 3D aquifer. Comparisons are made between dissolved plumes from a gasoline spill and those from an otherwise equivalent gasohol spill. Simulations have shown that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by at least 150% relative to that from an equivalent ethanol-free gasoline spill. The increase is due to preferred consumption of oxygen by ethanol and a corresponding reduction in the biodegradation rate of benzene while the two plumes overlap. Because of differences in retardation however, the ethanol and benzene plumes gradually separate. The impact therefore becomes limited because oxygen rapidly disperses behind the ethanol plume and benzene degradation eventually resumes. A sensitivity analysis for two common spill scenarios showed that background oxygen concentrations, and benzene retardation had the most significant influence on benzene persistence. A continuous gasohol spill over 10 years was found to increase the benzene travel distance by over 120% and a pure ethanol spill into an existing gasoline plume increased benzene travel distance by 150% after 40 years. The results are highly relevant in light of the forthcoming ban of MTBE in California and its likely replacement by ethanol by the end of 2002.

During the Quaternary period, cyclic glaciations have occurred over a global scale as the result of a climatic variability that affected the Earth's atmospheric, oceanic and glacial systems. Quaternary glaciations and their associated dramatic climatic conditions, such as kilometers-thick ice sheet formation and permafrost migration, are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools to examine groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modelling, such as density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, sea-level change and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (~ -120 kyr to present). The primary objective is to demonstrate the immense impact caused by glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface/subsurface water exchanges (i.e., recharge and discharge fluxes) both in the subglacial and the periglacial environments. The major findings of this study are that subglacial meltwater infiltration into the subsurface dominates when the ice sheet is growing and, conversely, groundwater exfiltrates during ice sheet regression. This conclusion, which seems to be opposite to the classical hydromechanical loading theory, is a consequence of the interaction between the subglacial boundary conditions and the elastic properties of the rocks. Subglacial infiltration rates during ice sheet progression can reach up to three orders of magnitude higher than the infiltration rate into the periglacial environment and the current recharge rate into the Canadian Shield. The impact of the ice sheet on groundwater flow and the brine distribution was dramatic. Hydraulic heads below the ice sheet increase by up to three thousand meters at land surface and up to 1.5 km into the ground. At present time, large over-pressurized zones occur at depth because there has been insufficient time to enable dissipation to their original values. Based on the hydraulic head and solute concentration distribution after the last glacial cycle, it can be shown that the system did not recover to its initial conditions, and that it is still recovering from the last glacial perturbation. The permafrost has the effect of restraining large areas of the subglacial and periglacial environment from surface/subsurface water interaction; the subglacial permafrost appears along with a cold-based ice sheet, which prevents subglacial meltwater production. The occurrence of a shallow trapped pressure zone below the permafrost after the glacial cycle highlights the critical importance of permafrost on the recovery of the flow system after a glacial cycle. As a final contribution, the mean groundwater age across the Canadian landscape at the last interglacial (LIG) and throughout the last glacial cycle was computed. Groundwater age is defined as the time elapsed since the water infiltrated in a recharge zone; the mean groundwater age is the mean age of all the particles of water that would be measured in a sample of water. It was found that at LIG, the mean groundwater ages span a large range of values from zero to 42 Myr. Forty-two Myr old groundwater was calculated at depth where there is little groundwater flow and where a mass of stagnant groundwater exists due to high brine concentrations. During the glacial period, old groundwater below the ice sheet mixes with young subglacial meltwater that infiltrates into the ground and the resulting mean groundwater age is younger. The mixing below the ice sheet occurs at great depth, and locations where the mean groundwater age was older than 1 Myr reaches mean age values between 10 kyr and 100 kyr.

The behaviour of hydrocarbon fuels in contaminated groundwater systems is studied using a multicomponent reactive transport model. The simulated processes include residual NAPL dissolution, aerobic and anaerobic biodegradation with daughter-product transport, and transport of a reactive carrier with mixed equilibrium/kinetic sorption. The solution algorithm is based on a three-dimensional Galerkin finite element scheme with deformable brick elements and capacity for a free watertable search. Nonlinearities are handled through Picard iteration. Convergence is rapid for most applications and mass balance errors for all phases are minimal. The model is first applied to simulate a pilot scale diesel fuel dissolution experiment in which humic acid is used as a natural organic carrier to enhance dissolution and to promote biodegradation of the aqueous components. The pilot scale experiment is described by Lesage et al. (1995) and Van Stempvoort et al. (2000). The conceptual model includes 8 unique components dissolving from 500 mL of residual diesel fuel within a 3D saturated domain. Oxygen-limiting competitive aerobic biodegradation with a dynamic microbial population is also included. A mixed 2-site equilibrium/kinetic model for describing sorption of the carrier to the aquifer solids was adopted to reproduce the observed breakthrough of the humic acid and organic components. Most model parameters were obtained independently with minimal calibration. Batch sorption data were found to fit well at the pilot scale, however biodegradation and dissolution rates were not well known and had to be fitted. Simulations confirmed the observed 10-fold increase in effective solubility of trimethylnaphthalene, and increases on the order of 2-5 for methyl- and dimethylnaphthalene. The simulated plumes showed almost complete attenuation after 5 years, in excellent agreement with observed data. A sensitivity analysis showed the importance of carrier concentrations, binding coefficients, dissolution and biodegradation rates. Compared to a dissolution scenario assuming no carrier, the humic acid-enhanced dissolution case decreased the remediation time by a factor of about 5. The second application of the model involves simulating the effect of ethanol on the persistence of benzene in gasoline-impacted groundwater systems. The conceptual model includes a 4-component residual gasoline source which is dissolving at the watertable into a 3D aquifer. Comparisons are made between dissolved plumes from a gasoline spill and those from an otherwise equivalent gasohol spill. Simulations have shown that under some conditions, a 10% ethanol component in gasoline can extend the travel distance of a benzene plume by at least 150% relative to that from an equivalent ethanol-free gasoline spill. The increase is due to preferred consumption of oxygen by ethanol and a corresponding reduction in the biodegradation rate of benzene while the two plumes overlap. Because of differences in retardation however, the ethanol and benzene plumes gradually separate. The impact therefore becomes limited because oxygen rapidly disperses behind the ethanol plume and benzene degradation eventually resumes. A sensitivity analysis for two common spill scenarios showed that background oxygen concentrations, and benzene retardation had the most significant influence on benzene persistence. A continuous gasohol spill over 10 years was found to increase the benzene travel distance by over 120% and a pure ethanol spill into an existing gasoline plume increased benzene travel distance by 150% after 40 years. The results are highly relevant in light of the forthcoming ban of MTBE in California and its likely replacement by ethanol by the end of 2002.

During the Quaternary period, cyclic glaciations have occurred over a global scale as the result of a climatic variability that affected the Earth's atmospheric, oceanic and glacial systems. Quaternary glaciations and their associated dramatic climatic conditions, such as kilometers-thick ice sheet formation and permafrost migration, are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools to examine groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modelling, such as density-dependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, sea-level change and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (~ -120 kyr to present). The primary objective is to demonstrate the immense impact caused by glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface/subsurface water exchanges (i.e., recharge and discharge fluxes) both in the subglacial and the periglacial environments. The major findings of this study are that subglacial meltwater infiltration into the subsurface dominates when the ice sheet is growing and, conversely, groundwater exfiltrates during ice sheet regression. This conclusion, which seems to be opposite to the classical hydromechanical loading theory, is a consequence of the interaction between the subglacial boundary conditions and the elastic properties of the rocks. Subglacial infiltration rates during ice sheet progression can reach up to three orders of magnitude higher than the infiltration rate into the periglacial environment and the current recharge rate into the Canadian Shield. The impact of the ice sheet on groundwater flow and the brine distribution was dramatic. Hydraulic heads below the ice sheet increase by up to three thousand meters at land surface and up to 1.5 km into the ground. At present time, large over-pressurized zones occur at depth because there has been insufficient time to enable dissipation to their original values. Based on the hydraulic head and solute concentration distribution after the last glacial cycle, it can be shown that the system did not recover to its initial conditions, and that it is still recovering from the last glacial perturbation. The permafrost has the effect of restraining large areas of the subglacial and periglacial environment from surface/subsurface water interaction; the subglacial permafrost appears along with a cold-based ice sheet, which prevents subglacial meltwater production. The occurrence of a shallow trapped pressure zone below the permafrost after the glacial cycle highlights the critical importance of permafrost on the recovery of the flow system after a glacial cycle. As a final contribution, the mean groundwater age across the Canadian landscape at the last interglacial (LIG) and throughout the last glacial cycle was computed. Groundwater age is defined as the time elapsed since the water infiltrated in a recharge zone; the mean groundwater age is the mean age of all the particles of water that would be measured in a sample of water. It was found that at LIG, the mean groundwater ages span a large range of values from zero to 42 Myr. Forty-two Myr old groundwater was calculated at depth where there is little groundwater flow and where a mass of stagnant groundwater exists due to high brine concentrations. During the glacial period, old groundwater below the ice sheet mixes with young subglacial meltwater that infiltrates into the ground and the resulting mean groundwater age is younger. The mixing below the ice sheet occurs at great depth, and locations where the mean groundwater age was older than 1 Myr reaches mean age values between 10 kyr and 100 kyr.

In northern Canada, the glacial isostatic adjustment (GIA) response of the Earth to the former Pleistocene Laurentide and Innuitian ice sheets contributes significantly to the Earth's past and ongoing sea-level change and land deformation. In this dissertation, measurements of Holocene sea-level change and observations of GPS-measured vertical crustal uplift rates are employed as constraints in numerical GIA models that examine the thickness and volume history of the former ice sheets in northern North America. The study is divided into two main sections; the first provides new measurements of Holocene sea-level change collected west of Hudson Bay, while the second presents a GIA modelling analysis for the entire study area of northern Canada. Radiocarbon dating of post-glacial deposits collected in an area just west of central Hudson Bay provides several new constraints on regional Holocene sea-level change. The field collection area is near a former load centre of the Laurentide Ice Sheet (LIS), and the sea-level measurements suggest that following deglaciation, regional sea level fell rapidly from a high-stand of nearly 170 m elevation just after 8000 cal yr BP to 60 m elevation by 5200 cal yr BP. Sea level subsequently fell at a decreased rate (approximately 30 m since 3000 cal yr BP). The fit of GIA model predictions to relative sea-level (RSL) data and present-day GPS-measured vertical land motion rates from throughout the study area constrains the peak thickness of the LIS to be 3.4-3.6 km west of Hudson Bay, and up to 4 km east of Hudson Bay. The ice model thicknesses inferred for these two regions represent, respectively, a 30% decrease and an average 20-25% increase to the load thickness relative to the ICE-5G reconstruction (Peltier 2004), generally consistent with other studies focussing on space geodetic measurements of vertical crustal motion. Around Baffin Island, the fit of GIA model predictions to RSL data indicate peak regional ice thicknesses of 1.2-1.3 km, a modest reduction compared to ICE-5G. A new reconstruction of the Innuitian Ice Sheet (IIS), which covered the Queen Elizabeth Islands at LGM, incorporates the current glacial-geological constraints on its spatial extent and timing history. The new IIS reconstruction provides RSL predictions that are more consistent with regional observations of post-glacial sea-level change than ICE-5G. The results suggest that the peak thickness of the IIS was 1600 m, approximately 400 m thicker than the minimum peak thickness indicated by glacial geology studies, but between 1000-1500 m thinner than the peak thicknesses used in previous regional ice sheet reconstructions. On Baffin Island and in the Queen Elizabeth Islands, however, the modelled elastic crustal response of the Earth to present-day ice mass changes is large. Accounting for this effect improves the agreement between GPS measurements of vertical crustal motion and the GIA model predictions. However, improvements such as the inclusion of spatially non-uniform mass loss and a sensitivity analysis that examines uncertainties of this effect should be incorporated into the modelling of present-day changes to glaciers and ice caps. / Graduate