A numerical method (SIMPLE DIRK Method) for unsteady incompressible viscous flow simulation is presented. The proposed method can be used to achieve arbitrarily high order of accuracy in time-discretization which is otherwise limited to second order in majority of the currently used simulation techniques. A special class of implicit Runge-Kutta methods is used for time discretization in conjunction with finite volume based SIMPLE algorithm. The algorithm was tested by solving for velocity field in a lid-driven square cavity. In the test case calculations, power law scheme was used in spatial discretization and time discretization was performed using a second-order implicit Runge-Kutta method. Time evolution of velocity profile along the cavity centerline was obtained from the proposed method and compared with that obtained from a commercial computational fluid dynamics software program, FLUENT 6.2.16. Also, steady state solution from the present method was compared with the numerical solution of Ghia, Ghia, and Shin and that of Erturk, Corke, and Goökçöl. Good agreement of the solution of the proposed method with the solutions of FLUENT; Ghia, Ghia, and Shin; and Erturk, Corke, and Goökçöl establishes the feasibility of the proposed method.

A numerical method (SIMPLE DIRK Method) for unsteady incompressible viscous flow simulation is presented. The proposed method can be used to achieve arbitrarily high order of accuracy in time-discretization which is otherwise limited to second order in majority of the currently used simulation techniques. A special class of implicit Runge-Kutta methods is used for time discretization in conjunction with finite volume based SIMPLE algorithm. The algorithm was tested by solving for velocity field in a lid-driven square cavity. In the test case calculations, power law scheme was used in spatial discretization and time discretization was performed using a second-order implicit Runge-Kutta method. Time evolution of velocity profile along the cavity centerline was obtained from the proposed method and compared with that obtained from a commercial computational fluid dynamics software program, FLUENT 6.2.16. Also, steady state solution from the present method was compared with the numerical solution of Ghia, Ghia, and Shin and that of Erturk, Corke, and Goökçöl. Good agreement of the solution of the proposed method with the solutions of FLUENT; Ghia, Ghia, and Shin; and Erturk, Corke, and Goökçöl establishes the feasibility of the proposed method.

Le problème du rendement de la distribution des eaux potables a récemment fait l’objet de nombreux travaux de recherche. En effet, les ruptures des canalisations et les fuites sont des phénomènes assez fréquents en milieu urbain. Afin de réduire au maximum les risques de fuite à long terme, près de 60 % des réseaux d’eau potable sont construits ou renouvelés avec des conduites en polyéthylène de troisième génération, PE100. De par ses caractéristiques, c’est un matériau de choix pour les réseaux d’adduction d’eau. Mais la présence d’un défaut superficiel peut générer la rupture de la conduite sous l’effet d’écoulement transitoire. Afin d’étudier ce problème, notre étude est décomposée en deux parties. La première est consacrée à l’étude de l’effet dynamique du comportement viscoélastique du matériau sur l’écoulement transitoire à l’aide d’un modèle mathématique que nous avons développé dans cette thèse. Nous avons démontré que le comportement viscoélastique du PE100 joue un rôle primordial dans l’amortissement du phénomène du coup de bélier et de résonance. En cas de présence de couplage de jonction, l’étude de l’interaction fluide-structure est nécessaire pour définir correctement les fréquences propres d’un système de conduites. Ensuite, dans la seconde partie, nous avons étudié le comportement à la fissuration des conduites en PE100 présentant un défaut. A l’aide d’essais expérimentaux et de modélisations par éléments finis, nous avons démontré que le concept de la mécanique élasto-plastique de rupture, l’intégrale J, peut définir avec une précision acceptable le comportement à la fissuration d’une conduite en PE100. Nous avons cherché à déterminer l’intégrale J à l’aide d’un modèle semi-empirique afin de définir une relation entre la pression d’amorçage de fissure, la taille de défaut (fissure semi-elliptique) et la géométrie de la conduite / The efficiency of potable water distribution systems has been recently the subject of much research. Leakages or a ruptures, occurring in pipes, are quite a frequent phenomenon in urban areas. In order to minimize long-term risks of leakage, about 60% of potable water networks are built or renewed with the third generation of polyethylene pipe, PE100. It is a material with various features, which makes it a widely used material in the water supply networks. However, under transient conditions and with a surficial defect in the pipe, a failure occurs. To investigate this issue, our study is divided into two main parts. The first part is studying the dynamic effect of the viscoelastic material under transient flow conditions using a developed mathematical model. We have demonstrated that the viscoelastic behavior of PE100 plays a primordial role in the damping of water hammer and resonance phenomenon. In case of presence of coupling junction, a study of the fluid structure interaction is mandatory to correctly define the natural frequencies of a piping system. In the second part, we have investigated the crack behavior of PE100 pipes with defects. Using the experimental tests and finite elements results, we have demonstrated that the concept of elastic-plastic fracture mechanics, the J-Integral, define with reasonable accuracy the behavior of cracked PE100-pipe. At the end, we sought to determine the J-Integral with a semi-empirical model in order to define a relationship between the crack initiation pressure, the dimension of semi-elliptical surface cracks and the geometry of the pipe

O objetivo deste estudo é compreender a dinâmica das partículas no estuário do rio Araranguá (SC) em termos de transporte em suspensão, deposição e exportação, em diferentes condições físico-químicas da água, com pH baixo (<4,5) e normal (>=7), e sob condições de regime transiente da descarga fluvial. O estuário do rio Araranguá é classificado como altamente estratificado e dominado pela descarga fluvial. Um aspecto fundamental nos processos que controlam a dinâmica de materiais em suspensão no estuário é a atividade de lavra e beneficiamento do carvão, que gera uma drenagem ácida no rio Mãe Luzia. O seu pH baixo (&#732;3) indica que o processo de floculação é intensificado no interior do estuário. Com o objetivo de melhor entender a hidrodinâmica do estuário, um modelo tridimensional foi implementado para a região. O modelo foi calibrado e validado com dados observados. Simulações com diferentes picos de descarga fluvial (100, 400, 700 e 1000 m3.s-1) e baixa descarga (30 m3.s-1) foram realizadas. Para calcular o transporte do material particulado em suspensão foi desenvolvido um modelo Lagrangeano da trajetória da partícula. O modelo da trajetória utiliza os resultados do modelo hidrodinâmico e a velocidade de decantação das partículas. O estuário respondeu rapidamente às variações da descarga fluvial. A cunha salina foi transportada para fora do estuário durante os picos de 700 e 1000 m3.s-1. A descarga fluvial é o fator dominante no controle da intrusão da salinidade no estuário e, em condições de baixa descarga, o transporte advectivo de sal é dominado pelo termo dispersivo da circulação gravitacional. O tempo de residência médio das partículas no estuário foi menor em condições de pH baixo. A exportação das partículas aumentou com o aumento da descarga fluvial (pico de 1000 m3.s-1), sendo que 27% e 30% foram exportadas para a plataforma interna durante os experimentos com pH baixo e pH normal, respectivamente. A região de deposição das partículas indica que com a diminuição do pH, as partículas passam a depositar mais à jusante no estuário. O evento de descarga de 1000 m3.s-1 não foi capaz de remover a grande maioria das partículas do estuário, mas foi responsável por redistribuir as partículas ao longo do médio estuário, onde se depositaram em condições favoráveis com baixas velocidades e ausência de salinidade. O trabalho demonstra que apesar da alta estratificação do estuário, a acidez de suas águas, seu padrão de circulação, com baixas velocidades e a presença da cunha salina, possuem um papel fundamental no transporte das partículas, resultando em maior potencial de retenção do material em suspensão no estuário do rio Araranguá. / The present study assessed the dynamics of particles of the Araranguá (SC) river estuary in terns of suspended transport, deposition and exportation in different conditions of physical-chemical of water, with low (<4,5) and normal pH (>=7), and transient of river discharge conditions. The Araranguá river estuary is a highly stratified flash-flood dominated. The river basin of the Mãe Luzia river, one of the main tributaries of the Araranguá river, is performed the activity of mining and coal processing, wich generates an acidic drainage. Its low pH indicates that flocculation process is intensified in estuary inner. With the objective of better understanding the estuarine processes, a three-dimensional hydrodynamics model was implemented. The model was calibrated and verified using observational data. Simulations were conducted with freshet peak ranged over 100, 400, 700 and 1000 m3.s-1. Lagrangian particle tracking algorithms was developed to represent the suspended particle transport at estuary. The particle tracking used the montion resulting from hydrodynamics model and the particle settling velocity. The estuary responded quickly the river discharge variations. During the pulse event the velocities at water column were unidirectional down-estuary is shown the barotropic dominates over baroclinic component. During the highest flash flood event (700 and 1000 m3.s-1) the salt water was pushed out of the estuary. The river discharge is a dominating factor affecting the salinity intrusion in the estuarine system and under low discharge conditions the advective salt transport is dominated by dispersive term of gravitational circulation. The mean residence time of the particles was lowest in pH low conditions. The particles export is great as the river discharge is rising (1000 m3.s-1) with 27% and 30% exported to inner shelf during the experiments with low and normal pH, respectively. The particles deposition local indicates that with the pH decrease the particles become to be deposited further downstream. The discharge event of 1000 m3.s-1 was not able to remove all particles out, but was response to redistribute the particles along of the meddle estuary, where settling in favorable conditions at low velocities and absence of salinity. The study shows that although high stratification of estuary, the acidity of water, the pattern of circulation, at low velocities, and the salt wedge presence play a fundamental role in the transport of particle matter resulting in increased the potential retention of suspended matter in the Araranguá river estuary.

Obwohl der Bedeutung von hyporheischen Zonen als Übergangsbereiche zwischen Flüssen und angrenzenden alluvialen Aquiferen eine wachsende Anerkennung zuteilwird, sind dynamische hyporheische Reaktionen auf instationäre hydrologische Bedingungen weiterhin signifikant untererforscht. Um diese Lücke zu schließen, liegt der Fokus dieser Doktorarbeit insbesondere auf den Effekten transienter Abflussverhalten und Temperaturschwankungen in Flüssen auf die raumzeitliche Variabilität von hyporheischen Austauschprozessen. Unter Beachtung dieser Ziele wird ein neues physikalisch basiertes numerisches Modell vorgeschlagen und schließlich angewandt, um systematisch die hyporheischen, durch Sedimentoberflächenstrukturen ausgelösten Reaktionen auf eine Reihe von künstlichen und natürlichen Abflussregimen abzuschätzen. Parameter wie das räumliche Ausmaß der hyporheischen Zone, hyporheische Austauschrate, mittlere Aufenthaltszeit, Temperatur des hyporheischen Flusses sowie das Denitrifikationspotenzial werden definiert, um den Einfluss der Antriebskräfte und Regulatoren auf dynamische hyporheische Reaktionen zu quantifizieren. Die Ergebnisse zeigen, dass mit zunehmendem Abfluss generell das räumliche Ausmaß der hyporheischen Zone vergrößert wird; jedoch bestimmen geomorphologische Bedingungen und Grundwasserflüsse erheblich das Ausdehnen und Zusammenziehen hyporheischer Zonen zusammen mit Strömungen, Wärme- und Stoffaustausch zwischen Fluss und Grundwasser. Temperaturvariabilität, ein wichtiger Faktor, welcher oft in hydrodynamischen Studien vernachlässigt wird, zeigt direkte kontrollierende Effekte beim Bestimmen hyporheischer Austauschraten und mittlerer Aufenthaltszeiten. Weiterhin spielt die Dynamik von Grundwasserständen eine entscheidende Rolle bei hyporheischen Austauschprozessen. Das Optimieren der Terminierung von Grundwasserförderung ist ausschlaggebend für die Regulierung von Wasserqualität, Nährstoffkreisläufen und der Entstehung thermischer hyporheischer Refugien. / Although there is a growing recognition of the importance of hyporheic zones as transitional areas connecting rivers and adjacent alluvial aquifers, the dynamic hyporheic responses to unsteady hydrological conditions are still significantly understudied. To bridge this gap, the present PhD thesis primarily focuses on the effects of transient river discharge and temperature fluctuations on the spatiotemporal variability of hyporheic exchange processes. With these objectives in mind, a novel physically based numerical model is proposed and then applied to systematically evaluate bedform-induced hyporheic responses to a series of synthetic and natural hydrological regimes. Metrics including spatial hyporheic extent, hyporheic exchange rate, mean residence time, temperature of hyporheic flux, and denitrification potential are defined to quantify the impact of drivers and modulators of dynamic hyporheic responses. Results indicate that increasing river discharge generally enlarges the spatial hyporheic extent; however, geomorphological settings and groundwater fluxes substantially modulate the expansion and contraction of hyporheic zones along with flow, heat and solute exchange between river and groundwater. Temperature variability, an important factor which is often neglected in hydrodynamic studies, displays direct controlling effects in determining hyporheic exchange rates and mean residence times. Groundwater table dynamics also play a critical role in hyporheic exchange processes. Optimizing the timing of aquifer pumping is crucial for regulation of water quality, nutrient cycling, and the formation of thermal hyporheic refugia. The findings largely advanced our mechanistic understandings of dynamic hyporheic responses to varying transient flow and temperature conditions, and therefore shed lights on improving river management and restoration strategies.

Dans ce travail, nous étudions le comportement rhéologique de suspensions concentrées de fibres non-browniennes. Dans un premier temps, nous avons élaboré de nouvelles méthodes expérimentales en géométrie torsionnelle plan-plan, pour mesurer la viscosité, les deux différences de contraintes normales, ainsi que les contraintes normales d'origine particulaire. Nous avons été en mesure d'apporter des résultats originaux qui ont été interprétés en termes d’évolution de la microstructure des suspensions de fibres. Les mesures de la viscosité en régimes stationnaire et transitoire ont permis de mettre en évidence l'importance de l'orientation et de l'effet du confinement sur la viscosité. Par ailleurs, nous avons obtenu pour la première fois des mesures indépendantes des deux différences de contraintes normales en géométrie torsionnelle plan-plan. Les mesures de la pression dans le fluide interstitiel nous ont donné accès aux contraintes normales particulaires et apporté une première mise en évidence expérimentale du phénomène de migration des fibres dans les suspensions non-browniennes. Dans un deuxième temps, nous avons établi deux modèles théoriques qui tentent d'expliquer la rhéofluidification des suspensions de fibres concentrées par une compétition entre des forces adhésives entre fibres et les forces hydrodynamiques et qui proposent un scénario de formation et de destruction d'agrégats. Les résultats de ces modèles sont alors confrontés aux mesures expérimentales et rendent bien compte du comportement de la viscosité sur une large gamme de taux de cisaillement. / In this manuscript we investigate, both experimentally and theoretically, the rheological behavior of concentrated non-Brownian fiber suspensions. The experiments consist in developing new methods for measuring the viscosity, the two normal stress differences as well as the particle normal stresses, in torsional plate-plate geometry. We were able to bring original results that have been interpreted by the evolution of the microstructure of the fiber suspensions during the flow. The experiments in stationary and transient regime highlight the importance of fiber orientation and the effect of the confinement on the viscosity measurement. For the first time, the first and the second normal stress differences have been measured separately in a torsional flow. Furthermore, thanks to the measurement of the pore pressure in the suspensions, an estimation of the particle normal stresses has been carried out and, for the first time the phenomenon of fiber migration in non-Brownian suspensions has been evidenced. From a theoretical point of view, we developed two complementary models that tend to explain shear-thinning behavior in concentrated fiber suspensions by a balance between adhesive and hydrodynamic forces and propose a scenario for the formation and the destruction of aggregates. These models are then tested against experimental measurements in a wide range of shear rates.

<p>Moisture can significantly affect flexible pavement performance. As such, it is crucial to remove moisture as quickly as possible from the pavements, mainly to avoid allowing moisture into the pavement subgrade. In the 1990s the Indiana Department of Transportation (INDOT) adopted an asphalt pavement drainage system consisting of an open-graded asphalt drainage layer connected to edge drains and collector pipes to remove moisture from the pavement system.</p> <p>Over the intervening two decades, asphalt pavement materials and designs have dramatically changed in Indiana, and the effectiveness of the pavements drainage system may have changed. Additionally, there are challenges involved in producing and placing open-graded asphalt drainage layers. They can potentially increase costs, and they tend to have lower strength than traditional dense-graded asphalt pavement layers. </p> <p>Given the potential difficulties, the overall objective of this research was to evaluate the effectiveness of the INDOT’s current flexible pavement drainage systems given the changes to pavement cross-sections and materials that have occurred since the open-graded drainage layer was adopted. Additionally, the effectiveness of the filter layer and edge drains were examined.</p><p><br>Laboratory experiments were performed to obtain the hydraulic properties of field-produced asphalt mixture specimens meeting INDOT’s current specifications. The results were used in finite element modeling of moisture flow through pavement sections. Modeling was also performed to investigate the rutting performance of the drainage layers under various traffic loads and subgrade moisture conditions in combination with typical Indiana subgrade soils. The modeling results were used to develop a design tool that can assist the pavement designer in more accurately assessing the need for pavement drainage systems in flexible pavements.<br></p>

The disposal of waste from agricultural activities has been recognised as a source of environmental contamination by endocrine disrupting chemicals (EDCs). The New Zealand dairy industry produces a large volume of dairy farm effluent, which contains EDCs in the form of estrogens. Most of this dairy farm effluent is applied onto the land for disposal. Groundwater and soil contamination by estrogens following waste application on the land have been reported overseas, but our understanding of the processes and factors governing the fate of estrogens in the soil is poor. Therefore the main goal of the present study was to better understand the fate and transport of estrogens, in particular 17β-estradiol (E2) and estrone (E1) in soil. In order to quantify E1 and E2 in drainage water and soil samples, chemical analysis by gas-chromatography mass-spectrometry (GC-MS) was carried out. This included sample extraction, sample clean-up through silica gel and gel permeation chromatography, and sample extract derivatisation prior to analysis. In order to develop a reliable method to extract estrogens from soil, research was conducted to optimise E1 and E2 extraction conditions by adjusting the number of sonication and shaking events, as well as the volume and type of solvent. Among five solvents and solvent mixtures tested, the best recovery on spiked and aged soil was obtained using an isopropanol/water (1:1) mix. A microcosm experiment was carried out to determine the dissipation rates of E2 and E1, at 8°C and at field capacity, in the Templeton soil sampled at two different depths (5-10 cm and 30-35 cm). The dissipation rates decreased with time and half-life values of 0.6-0.8 d for E1 and 0.3-0.4 d for E2 were found for the two depths studied. A field transport experiment was also carried out in winter, over three months, by applying dairy farm effluent spiked with estrogens onto undisturbed Templeton soil lysimeters (50 cm in diameter and 70 cm deep). The hormones were applied in dairy farm effluent at 120 mg m⁻² for E2 and 137 mg m⁻² for E1. The results of the transport experiment showed that in the presence of preferential/macropore flow pathways 0.3-0.7% of E2 and 8-13% of E1 was recovered in the leachate at the bottom of the lysimeters after 3 months, and 1-7% of the recovered E2 and 3-54% of the recovered E1 was leached within 2 days of application. These results suggest that leaching of estrogens via preferential/macropore flow pathways is the greatest concern for groundwater contamination. In the absence of preferential/macropore flow pathways, a significant amount (> 99.94%) of both hormones dissipated in the top 70 cm of soil, due to sorption and rapid biodegradation. Surprisingly, in all cases, estrogen breakthrough occurred before that of an inert tracer (bromide). This could not be explained by the advection-dispersion transport of estrogens, nor by their presence as antecedent concentrations in the soil. It was therefore suggested that colloidal enhanced transport of estrogens was responsible for the earlier breakthrough of estrogens and caused the leaching of a fraction of the applied estrogens to a soil depth of 70 cm. A two-phase model, adapted from a state-space mixing cell model, was built to describe the observed estrogen transport processes under transient flow. The model takes into account 3 transport processes namely, advection-dispersion, preferential/macropore flow and colloidal enhanced transport. This model was able to successfully describe the estrogen transport observed from the lysimeters.

New decline curve models have been developed to overcome the boundary-dominated flow assumption of the basic Arps’ models, which restricts their application in ultra-low permeability reservoirs exhibiting long-duration transient flow regimes. However, these new decline curve analysis (DCA) methods are still based only on production rate data, relying on the assumption of stable flowing pressure. Since this stabilized state is not reached rapidly in most cases, the applicability of these methods and the reliability of their solutions may be compromised. In addition, production performance predictions cannot be disassociated from the existing operation constraints under which production history was developed. On the other hand, DCA is often carried out without a proper identification of flow regimes. The arbitrary application of DCA models regardless of existing flow regimes may produce unrealistic production forecasts, because these models have been designed assuming specific flow regimes. The main purpose of this study was to evaluate the possible benefits provided by including flowing pressures in production decline analysis. As a result, it have been demonstrated that decline curve analysis based on pressure-normalized rates can be used as a reliable production forecasting technique suited to interpret unconventional wells in specific situations such as unstable operating conditions, limited availability of production data (short production history) and high-pressure, rate-restricted wells. In addition, pressure-normalized DCA techniques proved to have the special ability of dissociating the estimation of future production performance from the existing operation constraints under which production history was developed. On the other hand, it was also observed than more consistent and representative flow regime interpretations may be obtained as diagnostic plots are improved by including MBT, pseudovariables (for gas wells) and pressure-normalized rates. This means that misinterpretations may occur if diagnostic plots are not applied correctly. In general, an improved forecasting ability implies greater accuracy in the production performance forecasts and more reliable reserve estimations. The petroleum industry may become more confident in reserves estimates, which are the basis for the design of development plans, investment decisions, and valuation of companies’ assets.

The docotoral thesis titled 'Modeling the effects of Transient Stream Flow on Solute Dynamics in Stream Banks and Intra-meander Zones' investigates flow and solute dynamcis across surface water-groundwater interface under dynamic flow conditons through numerical simulations. The abstract of the thesis is as follows: Waters from various sources meet at the interface between streams and groundwater. Due to their different origins, these waters often have contrasting chemical signatures and therefore mixing of water at the interface may lead to significant changes in both surface and subsurface water quality. The riparian zone adjacent to the stream serves as transition region between groundwater and stream water, where complex water and solute mixing and transport processes occur. Predicting the direction and the magnitude of solute exchanges and the extent of transformations within the riparian zone is challenging due to the varying hydrologic and chemical conditions as well as heterogeneous morphological features which result in complex, three-dimensional flow patterns. The direction of water flow and solute transport in the riparian zone typically varies over time as a result of fluctuating stream water and groundwater levels. Particularly, increasing groundwater levels can mobilize solutes from the unsaturated zone which can be subsequently transported into the stream. Such complex, spatially and temporally varying processes are hard to capture with field observations alone and therefore modeling approaches are required to predict the system behavior as well as to understand the role of individual factors. In this thesis, we investigate the inter-connectivity of streamthe s and adjacent riparia zones in the context of water and solute exchanges both laterally for bank storage and longitudinally for hyporheic flow through meander bends. Using numerical modeling, the transient effect of stream flow events on solute transport and transformation within the initially unsaturated part of stream banks and meander bends have been simulated using a systematic set of hydrological, chemical and morphological scenarios. A two dimensional variably saturated media groundwater modeling set up was used to explore solute dynamics during bank flows. We simulated exchanges between stream and adjacent riparian zone driven by stream stage fluctuations during stream discharge events. To elucidate the effect of magnitude and duration of discharge events, we developed a number of single discharge event scenarios with systematically varying peak heights and event duration. The dominant solute layer was represented by applying high solute concentration in upper unsaturated riparian zone profile. Simulated results show that bank flows generated by high stream flow events can trigger solute mobilization in near stream riparian soils and subsequently export significant amounts of solutes into the stream. The timing and amount of solute export is linked to the shape of the discharge event. Higher peaks and increased duration significantly enhance solute export, however, peak height is found to be the dominant control for overall lateral mass export. The mobilized solutes are transported towards the stream in two stages (1) by return flow of stream water that was stored in the riparian zone during the event and (2) by vertical movement to the groundwater under gravity drainage from the unsaturated parts of the riparian zone, which lasts for significantly longer time (> 400 days) resulting in a theoretically long tailing of bank outflows and solute mass outfluxes. Our bank flow simulations demonstrate that strong stream discharge events are likely to mobilize and export significant quantity of solutes from near stream riparian zones into the stream. Furthermore, the impact of short-term stream discharge variations on solute exchange may sustain for long times after the flow event. Meanders are prominent morphological features of stream systems which exhibit unique hydrodynamics. The water surface elevation difference across the inner bank of a meander induces lateral hyporheic exchange flow through the intrameander region, leading to solute transport and reactions within intra-meander region. We examine the impact of different meander geometries on the intra-meander hyporheic flow field and solute mobilization under both steady-state and transient flow conditions. In order to explore the impact of meander morphology on intrameander flow, a number of theoretical meander shape scenarios, representing various meander evolution stages, ranging from a typical initial to advanced stage (near cut off ) meander were developed. Three dimensional steady-state numerical groundwater flow simulations including the unsaturated zone were performed for the intra-meander region for all meander scenarios. The meandering stream was implemented in the model by adjusting the top layers of the modeling domain to the streambed elevation. Residence times for the intra-meander region were computed by advective particle tracking across the inner bank of meander. Selected steady state cases were extended to transient flow simulations to evaluate the impact of stream discharge events on the temporal behavior of the water exchange and solute transport in the intra-meander region. Transient hydraulic heads obtained from the surface water model were applied as transient head boundary conditions to the streambed cells of the groundwater model. Similar to the bank storage case, a high concentration of solute (carbon source) representing the dominant solute layer in the riparian profile was added in the unsaturated zone to evaluate the effect of stream flow event on mobilization and transport from the unsaturated part of intrameander region. Additionally, potential chemical reactions of aerobic respiration by the entry of oxygen rich surface water into subsurface as well denitrification due to stream and groundwater borne nitrates were also simulated. The results indicate that intra-meander mean residence times ranging from 18 to 61 days are influenced by meander geometry, as well as the size of the intra-meander area. We found that, intra-meander hydraulic gradient is the major control of RTs. In general, larger intra-meander areas lead to longer flow paths and higher mean intra-meander residence times (MRTs), whereas increased meander sinuosity results in shorter MRTs. The vertical extent of hyporheic flow paths generally decreases with increasing sinuosity. Transient modeling of hyporheic flow through meanders reveals that large stream flow events mobilize solutes from the unsaturated portion of intra-meander region leading to consequent transport into the stream via hyporheic flow. Advective solute transport dominates during the flow event; however significant amount of carbon is also consumed by aerobic respiration and denitrification. These reactions continue after the flow events depending upon the availability of carbon source. The thesis demonstrates that bank flows and intra-meander hyporheic exchange flows trigger solute mobilization from the dominant solute source layers in the RZ. Stream flow events driven water table fluctuations in the stream bank and in the intra-meander region transport substantial amount of solutes from the unsaturated RZ into the stream and therefore have significant potential to alter stream water quality.:Declaration Abstract Zusammenfassung 1 General Introduction 1.1 Background and Motivation 1.2 Hydrology and Riparian zones 1.2.1 Transport processes driven by fluctuation in riparian water table depth 1.2.1.1 Upland control 1.2.1.2 Stream control 1.2.2 Biochemical Transformations within the Riparian Zone 1.3 Types and scales of stream-riparian exchange 1.3.1 Hyporheic Exchange 1.3.1.1 Small Scale Vertical HEF 1.3.1.2 Large Scale lateral HEF 1.3.2 Bank Storage 1.4 Methods for estimation of GW-SW exchanges 1.4.1 Field Methods 1.4.1.1 Direct measurement of water flux 1.4.1.2 Tracer based Methods 1.4.2 Modeling Methods 1.4.2.1 Transient storage models 1.4.2.2 Physically based models 1.5 Research gaps and need 1.6 Objectives of the research 1.7 Thesis Outline 2 Flow and Transport Dynamics during Bank Flows 2.1 Introduction 2.2 Methods 2.2.1 Concept and modeling setup 2.2.2 Numerical Model 2.2.3 Stream discharge events 2.2.4 Model results evaluation 2.3 Results and discussion 2.3.1 Response of water and solute exchange to stream discharge events 2.3.1.1 Water exchange time scales 2.3.1.2 Stream water solute concentration 2.3.2 Solute mobilization within the riparian zone 2.3.3 Influence of peak height and event duration on solute mass export towards the stream 2.3.4 Effects of event hydrograph shape on stream water solute concentration 2.3.5 Model limitations and future studies 2.4 Summary and Conclusions Appendix 2 3 Flow and Transport Dynamics within Intra-Meander Zone 3.1 Introduction 3.2 Methods 3.2.1 Meander Shape Scenarios 3.2.2 Surface Water Simulations 3.2.3 3D Groundwater Flow Simulations with Modeling code MIN3P 3.2.3.1 Steady Flow Simulations 3.2.3.2 Stream flow event and Solute Mobilization Set-up 3.2.4 Reactive Transport 3.3 Results and Discussion 3.3.1 Groundwater heads and flow paths in the saturated intrameander zone 3.3.1.1 Groundwater heads 3.3.1.2 Flow paths and isochrones 3.3.1.3 Vertical extent of flow paths 3.3.2 Intra-Meander Residence Time Distribution 3.3.3 Factors affecting intra-meander flow and residence times 3.3.3.1 intra-meander hydraulic gradient 3.3.3.2 Maximum penetration depth 3.3.3.3 Meander sinuosity 3.3.3.4 intra-meander area (A) 3.3.4 Influence of Discharge Event on intra-meander Flow and Solute Transport 3.3.4.1 Spatial distribution of groundwater head and solute concentration 3.3.4.2 Time scales of intra-meander groundwater heads and solute transport 3.3.4.3 Solute export during stream discharge event 3.3.5 Intra-meander reactive transport during stream discharge event 3.3.5.1 Impact of stream discharge on aerobic respiration and denitrification 3.3.5.2 DOC mass removal during stream discharge event 3.4 Summary and Conclusions Appendix 3 4 General Summary and Conclusions 4.1 Summary 4.2 Conclusions 4.2.1 Flow and Transport Dynamics in Near Stream Riparian Zone (Bank Flows) 4.2.2 Flow and Transport Dynamics within Intra-Meander Zone 4.3 Model Limitations and Future Studies Bibliography Acknowledgement