While several lines of evidence strongly hint at the biological importance of impact-induced hydrothermal systems during the impact cataclysm at ~3.9 Ga, these systems are not well understood. There is unambiguous evidence of hydrothermal activity at many terrestrial craters, but the available samples represent a very limited number of crater diameters and locations within the crater. Therefore, computer models are crucial for learning how impact-induced hydrothermal systems work, how long they last, and whether they provide suitable environments for thermophilic microorganisms. This dissertation presents detailed simulations of hydrothermal activity at the terrestrial craters Chicxulub and Sudbury, as well as at range of crater sizes on early Mars. A well-established computer code HYDROTHERM was used. The models for terrestrial craters were constrained by seismic, magnetic, and gravity surveys, as well as petrological, mineralogical, and chemical analyses of samples (by others).Sudbury crater is ~180 km in diameter, and 1.85 Ga. Simulation results indicate that a hydrothermal system at Sudbury crater remained active for several hundred thousand to several million years, depending on assumed permeability, and produced habitable volumes of up to ~20,000 km^3.Chicxulub crater is also ~180-km in diameter, but only 65 Ma. The lifetime of the hydrothermal system ranges from 1.5 Ma to 2.3 Ma depending on assumed permeability. The temperatures and fluxes observed in the model are consistent with alteration patterns observed by others in borehole samples.Another set of simulations modeled post-impact cooling of hypothetical craters with diameters of 30, 100, and 180 km in an early Martian environment. System lifetimes, averaged for all permeability cases examined, were 67,000 years for the 30-km crater, 290,000 years for the 100-km crater, and 380,000 for the 180-km crater. Also, an ap-proximation of the thermal evolution of a Hellas-sized basin (~2000 km) suggests poten-tial for hydrothermal activity for ~10 Myr after the impact. The habitable volume reached a maximum of ~6,000 km^3 in the 180-km crater model.Possible morphological and mineralogical signs of hydrothermal activity in Martian craters were observed, both in this work and by others. These observations, while by no means definitive, are generally consistent with model predictions.

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2005. / Includes bibliographical references (p. 61-64).

The objective of this study was to use an applied tracer to study lateral ground water flow paths in the top ~0.5 m of clay settling areas (CSA) in order to gain better understanding of hydrologic connectivity of CSAs to the surrounding hydrologic systems. The study site was located on the non-operational Mosaic Fort Mead Mine property in Fort Meade, Polk County, Florida. This lateral tracer test study is a follow up from a vertical tracer test study performed at the same site location in 2007. The CSA is generally composed of a well developed, clay rich, subangular-blocky surface layer ~0-1.0m, which exhibits abundant desiccation cracks plus other macropores underlain by a massive, saturated, clay-rich sublayer from ~1.0-2.5 m. A bromide tracer was applied into an injected trench. All 60L of the applied tracer flowed out of the down gradient face of the trench quickly, over an eleven minute period. The Bromide tracer was rapidly transported laterally and was detected as far as 16 m from the starting point just 24 hours after application, as well as in the inundated north pond adjacent to the study area. Bromide concentration distribution was not uniform over the study area during any time period, with an initial disorganized bromide pulse followed by secondary pulse concentrated on the north side of the sampling area. This spatial-temporal distribution of bromide indicates preferential flow through desiccation cracks or other macropores. Bromide concentrations in the north pond increased over time while pond stage fluctuated due to this shallow lateral macropore dominated flow in and out. Although it is most likely true that flow paths from the CSA to the adjacent hydrologic landscape during the wet season is dominated by rapid shallow lateral flow through macropores, specific flow paths, macropore length, diameter and distribution and fluxes still remain unquantified. Therefore, how the hydrology of CSAs affects the adjacent hydrologic landscape still remain unquantified.

A mathematical model is developed for quantification of aquifer deformation due to ground-water withdrawal and, with some modifications, is potentially applicable to petroleum reservoirs. A porous medium saturated with water is conceptually treated in the model as a nonlinearly viscous fluid continuum. The model employs a new three-dimensional extension, made in this thesis, of Helm's poroviscosity as a constitutive law governing the stress-strain relation of material deformation and Gersevanov's generalization of Darcy's law for fluid flow in porous media. Relative to the classical linear poroelasticity, the proposed model provides a more realistic tool, yet with greater simplicity, in modeling and prediction of aquifer movement. Based on laboratory consolidation tests conducted on clastic sedimentary materials, three phases of skeletal compaction are recognized. They are referred to as "instantaneous compression", "primary consolidation" and "secondary compression" according to Terzaghi and Biot's theory of poroelasticity. Among the three modes of consolidation, material behavior during the secondary compression phase has a nonlinear stress-strain relationship and is strongly time-dependent, exhibiting a phenomenon often known as "creep". In poroelasticity, the primary and secondary compressions have been conceptually considered as two separate physical processes that require two sets of material parameters to be evaluated. In contrast, the proposed poroviscosity model is a unified theory of time-dependent skeletal compression that realistically describes the physical phenomena of sediment compression as one single transient process. As a general model, two sets of governing equations are formulated for Cartesian and cylindrical coordinates, respectively, and allow for mechanical anisotropy and the assumption of principal hydraulic directions. Further simplifications of the governing equations are formulated by assuming mechanical isotropy, irrotational deformation and mechanical axisymmetry, which are more suitable for field applications. Incremental forms of the governing equations are also provided. / Ph. D.

<p>Saturated hydraulic conductivity (<em>K</em>_<em>s</em>) is among the most important soil properties that influence the partitioning of rainfall into surface and subsurface waters and is needed for understanding and modeling hydrologic processes at the field-scale. Field-scale variability of <em>K</em>_<em>s</em> is often represented as a lognormal random field, and its parameters are assessed either by making local- or point-scale measurements using instruments such as permeameters and infiltrometers or by calibrating probabilistic models with field-scale infiltration experiments under natural/artificial rainfall conditions. This research quantifies the uncertainty in the <em>K</em>_<em>s</em> random field when using observations from the above techniques and provides recommendations as to what constitutes a good experiment to assess the field-scale variability of <em>K</em>_<em>s</em>. Infiltration experiments with instruments sampling larger areas (or volumes) are typically expected to be more representative of field conditions than those sampling smaller ones; hence, the uncertainty arising from the field-scale natural rainfall-runoff experiments was evaluated first. A field-averaged infiltration model and Monte Carlo simulations were employed in a Bayesian framework to obtain the possible <em>K</em>_<em>s</em> random fields that would describe experimental observations over a field for a rainfall event. Results suggested the existence of numerous parameter combinations that could satisfy the experimental observations over a single rainfall event, and high variability of these combinations among different events, thereby providing insights regarding the identifiable space of <em>K</em>_<em>s</em> distributions from individual rainfall experiments. The non-unique parameter combinations from multiple rainfall events were subsequently consolidated using an information-theoretic measure, which provided a realistic estimate of our ability to quantify the spatial variability of <em>K</em>_<em>s</em> in natural fields using rainfall-runoff experiments. </p> <p>  </p> <p>With the resolving ability from rainfall-runoff experiments constrained due to experimental limitations, the <em>K</em>_<em>s</em> estimates from in-situ point infiltration devices could provide additional information in conjunction with the rainfall-runoff experiments. With this hypothesis, the role of three in-situ point infiltration devices --- the double-ring infiltrometer, CSIRO version of tension permeameter, and Guelph constant-head permeameter --- was then evaluated in characterizing the field-scale variability of <em>K</em>_<em>s</em>. Results suggested that <em>K</em>_<em>s</em> estimates from none of the instruments could individually represent the field conditions due to the presence of measurement and structural errors besides any sampling biases; hence any naive efforts at assimilating their data (e.g., data pooling, instrument-specific transforms, etc.) and augmenting with field-scale rainfall-runoff observations as informative prior distributions would not be fruitful. In the absence of benchmarks establishing the true <em>K</em>_<em>s</em> field, it is also impossible to quantify these errors; therefore, a posterior coarsening method was used to alleviate their impact when estimating the field-scale variability of <em>K</em>_<em>s</em>. </p> <p>  </p> <p>Finally, the impact of censored moments on the maximum likelihood (ML) estimates of the <em>K</em>_<em>s</em> distribution parameters was studied. Results highlighted the rainfall event's ability to only be able to resolve a fraction of the <em>K</em>_<em>s</em> field, and that the time and duration of peak rainfall intensity play a role in resolving the <em>K</em>_<em>s</em> field, besides the peak rainfall intensity. The reliability of the ML estimates is a function of the fraction of the <em>K</em>_<em>s</em> field resolved by the rainfall event, until a limit when the estimates start to overfit the calibration data. Rainfall-runoff experiments for which the ML estimates resolve 30--80 % of the <em>K</em>_<em>s</em> distribution are likely to be good calibration events. </p>

Mathematical models are used in engineering and the sciences to estimate properties of systems of interest, increasing our understanding of the surrounding world and driving technological innovation. Unfortunately, as the systems of interest grow in complexity, so to do the models necessary to accurately describe them. Analytic solutions for problems with such models are provably intractable, motivating the use of approximate yet still accurate estimation techniques. Particle filtering methods have emerged as a popular tool in the presence of such models, spreading from its origins in signal processing to a diverse set of fields throughout engineering and the sciences including medical research, economics, robotics, and geophysics. In groundwater hydrology, a key component of aquifer assessment is the determination of the properties which permit water resource managers to estimate aquifer drawdown and safe yield. Presented is a particle filtering approach to estimate aquifer properties from transient data sets, leveraging recently published analytically-derived models for confined aquifers. The approach is examined experimentally through validation against three common aquifer testing problems: determination of (i) transmissivity and storage coefficient from non-leaky confined aquifer performance tests, (ii) transmissivity, storage coefficient, and vertical hydraulic conductivity of a confining unit from leaky confined aquifer performance tests, and (iii) transmissivity and storage coefficient from non-leaky confined aquifer performance tests with noisy data and boundary effects. The first two problems are well-addressed and the presented approach compares favorably to the results obtained from other published methods. The third problem, which the presented method can tackle more naturally than previously-published methods, underscores the flexibility of particle filtering and, in turn, the promise such methods offer for a myriad of other geoscience problems

Dans un champ captant, comme celui qui alimente l'agglomération lyonnaise, le fonctionnement de chaque « objet » (bassins d'infiltration, puits, rivières, nappe, zone non saturée) et leurs interactions sont complexes et mal connus. Dans un premier temps, une série d'essais d'infiltration à différentes échelles dans un bassin artificiel de réalimentation a permis de mieux appréhender le fonctionnement de cet ouvrage et de chiffrer les paramètres hydrodynamiques de la zone non saturée. Les résultats des interprétations par méthodes numériques fondées sur l'équation de Richards ont montré que les flux infiltrés dans les bassins dépendent principalement de la conductivité hydraulique à saturation d'une couche située directement sous le sable calibré couvrant le fond du bassin, identifiée comme étant moins perméable que la nappe. Cette couche conditionne l'existence d'une zone non saturée. La réalisation d'essais de pompage dans l'aquifère sur les forages d'exploitation et sur un dispositif spécialement mis en place durant ce travail a permis de déterminer les paramètres hydrodynamiques de la nappe. Une analyse des observations et une modélisation conceptuelle en 2D, puis en 3D ont permis d'identifier les mécanismes prépondérants (stratifications, apports et prélèvements) et de simuler correctement à la fois les flux infiltrés dans un des bassins d'infiltration et la remontée de la nappe. A l'échelle d'un bassin, les flux infiltrés sont variables dans le temps, ils dépendent de l'état de colmatage de la surface d'infiltration mais également de la température de l'eau infiltrée et de l'état hydrique initial du sol sous le bassin. Les analyses de sensibilité réalisées avec les modèles mis en place indiquent que la conductivité hydraulique à saturation de l'aquifère, mais également la proximité des conditions aux limites imposées dans la nappe (les rivières et les puits de pompage) influencent de manière prépondérante la remontée de la nappe. Une modélisation 3D d'un autre secteur du champ captant comprenant deux bassins d'infiltration, deux bras de rivière ainsi que des puits de pompage a été réalisée. La condition à la limite imposée sur les rivières est du troisième type en accord avec l'observation d'un sous-écoulement en nappe. Les échanges nappe/rivières sont calés sur des observations à partir d'une chronique de propagation d'une onde de crue dans la nappe. Des piézomètres en flûte de pan, spécifiquement implantés à proximité d'un bassin, ont permis d'observer des différences de charge hydraulique fortes à différents niveaux de l'aquifère lorsque le bassin d'infiltration est en eau. La modélisation 3D est conforme à ces observations. Elle a confirmé l'importance du rôle d'une hétérogénéité de type argilo-sableuse (de conductivité hydraulique à saturation inférieure aux autres lithologies présentes dans l'aquifère) dans les écoulements (direction et flux). Le modèle développé représente correctement les flux infiltrés via les bassins ainsi que les fluctuations de la piézométrie de la nappe. Il permet de vérifier l'inversion des écoulements par rapport aux infiltrations de la rivière, d'identifier les puits alimentés par les bassins d'infiltration et également de mettre en évidence les flux de nappe passant sous la rivière. / In a well field of the Lyon metropolitan area, designed for drinking water supply, behaviour of each object (infiltration basins, wells, rivers, aquifer, and unsaturated zone) and their interactions are complex and not well-known. As a first step, infiltration tests at different spatial scales in one artificial basin were performed to better understand the basin operation and to estimate the hydrodynamic parameters of the unsaturated zone. Results of interpretation, using numerical methods based on Richards equation, reveal that infiltrated basin fluxes mainly depend on saturated hydraulic conductivity of a layer located just below the calibrated sand layer that cover the basin bottom. Indeed this layer has been estimated to be less permeable than the aquifer, which allows the existence of the unsaturated zone below. Pumping tests in the groundwater have been performed using production wells and a well specially implemented during this thesis work in order to estimate aquifer hydrodynamic parameters. Observations analysis and a conceptual modelling, in 2D and then in 3D, lead to a better understanding of the controlling mechanisms (stratification, input and output) and to simulate both basin infiltration rates and water table rise. Considering the whole basin scale, input fluxes are transient, related to the clogging statement of the infiltration area but also to the temperature of inflow water and the initial statement of the soil just below the basin. Sensibility analyses using the models highlight that the amount of the water table rise is mainly influenced by the aquifer saturated hydraulic conductivity and also by the location of imposed boundaries in the aquifer (rivers and pumping wells). The model properly accounts basin inflow fluxes and water table fluctuations. The model is able to verify if flows are reversed in relation to river exchanges, if wells are fed by infiltration basins and it highlights aquifer flows below the river. A 3D modelling has been realised in another area of the well field, comprising two infiltration basins, two river arms and pumping wells. In agreement with underflow in the aquifer, rivers are imposed in the model as third kind boundary conditions. Aquifer and river exchanges are calibrated with observed data of one aquifer flood-wave propagation. Significant differences of hydraulic heads have been observed at different depths of the aquifer using panpipes piezometers, specifically implemented, close to one infiltration basin. Theses differences are closely related to basin operation. These observations are properly calculated by the 3D model. Using the model, the effect of one sandy-clay heterogeneous layer (whose saturated hydraulic conductivity is lower than the ones of other aquifer lithologies) on aquifer flows (direction and flux) is notable. The model properly accounts basin inflow fluxes and water table fluctuations. The model is able to verify if flows are reversed in relation to river exchanges, if wells are fed by infiltration basins and it highlights aquifer flow below the river.

<p>  </p> <p>The management of water resources in East Africa is inherently challenged by rainfall variability and the uneven spatial distribution of freshwater resources. In addition to these issues, meteorological and water data collection has been inconsistent over the past decades, and unclearly defined purposes or end goals for collected data have left many datasets ineffectively curated. In light of the data intensiveness of current modelling and planning methods, data scarcity and inaccessibility have become substantial impediments to informed decision-making. Among the outputs of this research are 1) a revised technique for evaluating bias correction performance on reanalysis data for use in regions where precipitation data is temporally discontinuous which can potentially be applied to other types of climate data as well, 2) a new methodology for quantifying qualitative information contained in legislation and official documents and websites for the assessment of relationships between documented meteorological and water data policies and resulting outcomes in terms of data availability and accessibility, and 3) a fresh look at data needs and the value data holds with respect to water resources decision-making and management in the region.</p>