Accurately characterizing the distribution of hydraulic parameters is critical for any site investigation, particularly those dealing with solute or contaminant transport. Despite the fact that many tools are currently available for both characterizing (e.g. soil core analysis, slug and pumping tests, direct push techniques, etc.,) and modeling (e.g. geostatistical interpolators, construction of geological models, etc.,) heterogeneous aquifers, this still remains a challenge. In this thesis, hydraulic tomography (HT), a recently developed tool for characterizing and modeling heterogeneous aquifers is evaluated under both laboratory and field conditions. To date, both steady state hydraulic tomography (SSHT) and transient hydraulic tomography (THT) have been demonstrated at the laboratory scale, however, only SSHT has been rigorously validated through the prediction of independent tests (those not used for estimating the distribution of hydraulic parameters), and comparison to other characterization/modeling techniques. Additionally, laboratory and field validations of HT using comparisons other than the prediction of independent pumping tests (e.g. prediction of solute transport) are lacking. The laboratory studies performed in this thesis address some of these gaps by: i) rigorously validating THT through the prediction of independent pumping tests, and comparison to other characterization techniques; ii) using HT estimated parameter distributions to predict the migration of a conservative tracer in a heterogeneous sandbox aquifer; and, iii) predicting the flow of water to a well in a heterogeneous, unconfined, sandbox aquifer. For all three cases, HT was compared to more traditional characterization/modeling approaches, such as; the calculation of homogeneous effective parameters, kriging of point data, or the creation and calibration of a geological model. For each study the performance of HT was superior to the other characterization methods. These laboratory experiments demonstrated both the ability of HT to map aquifer heterogeneity, and the critical need for accurately understanding heterogeneity in order to make accurate predictions about a system. In this regard, HT is a powerful tool at the laboratory scale where the forcing functions (i.e., boundary conditions, flow rates, etc.,) are accurately known. While several field scale HT studies have been reported in the literature, none attempt to validate 3D THT through the prediction of independent pumping tests, or through comparison to known geology. The application of THT at the field scale presents unique challenges not faced in the laboratory setting. For example, boundary conditions are not accurately known and it is not possible to instrument a field site as densely as a sandbox aquifer. In the field studies conducted as part of this thesis, THT was validated by comparing estimated hydraulic parameter fields to known geology (borehole data) and simulating 9 pumping tests that were performed at the site. The THT analysis was able to capture the salient features of the aquifer (the presence of a double aquifer separated by an aquitard), and was able to reasonably reproduce most of the pumping tests. For comparison purposes, a homogeneous model and three additional heterogeneous models were created: i) permeameter estimates of hydraulic conductivity from soil cores were interpolated via kriging; ii) the transition probability/Markov Chain approach was used to interpret material classifications from borehole logs; and iii) a stratigraphic model was created and calibrated to pumping test data. Of these cases, THT and the calibrated stratigraphic model performed best, with THT performing slightly better. This work indicates that it is possible to interpret multiple pumping tests using hydraulic tomography to estimate the 3D distribution of hydraulic parameters in heterogeneous aquifer systems. Also, since hydraulic tomography does not require the collection and analysis of a large number of point samples, it is likely comparable in cost to other characterization/modeling approaches.

Accurately characterizing the distribution of hydraulic parameters is critical for any site investigation, particularly those dealing with solute or contaminant transport. Despite the fact that many tools are currently available for both characterizing (e.g. soil core analysis, slug and pumping tests, direct push techniques, etc.,) and modeling (e.g. geostatistical interpolators, construction of geological models, etc.,) heterogeneous aquifers, this still remains a challenge. In this thesis, hydraulic tomography (HT), a recently developed tool for characterizing and modeling heterogeneous aquifers is evaluated under both laboratory and field conditions. To date, both steady state hydraulic tomography (SSHT) and transient hydraulic tomography (THT) have been demonstrated at the laboratory scale, however, only SSHT has been rigorously validated through the prediction of independent tests (those not used for estimating the distribution of hydraulic parameters), and comparison to other characterization/modeling techniques. Additionally, laboratory and field validations of HT using comparisons other than the prediction of independent pumping tests (e.g. prediction of solute transport) are lacking. The laboratory studies performed in this thesis address some of these gaps by: i) rigorously validating THT through the prediction of independent pumping tests, and comparison to other characterization techniques; ii) using HT estimated parameter distributions to predict the migration of a conservative tracer in a heterogeneous sandbox aquifer; and, iii) predicting the flow of water to a well in a heterogeneous, unconfined, sandbox aquifer. For all three cases, HT was compared to more traditional characterization/modeling approaches, such as; the calculation of homogeneous effective parameters, kriging of point data, or the creation and calibration of a geological model. For each study the performance of HT was superior to the other characterization methods. These laboratory experiments demonstrated both the ability of HT to map aquifer heterogeneity, and the critical need for accurately understanding heterogeneity in order to make accurate predictions about a system. In this regard, HT is a powerful tool at the laboratory scale where the forcing functions (i.e., boundary conditions, flow rates, etc.,) are accurately known. While several field scale HT studies have been reported in the literature, none attempt to validate 3D THT through the prediction of independent pumping tests, or through comparison to known geology. The application of THT at the field scale presents unique challenges not faced in the laboratory setting. For example, boundary conditions are not accurately known and it is not possible to instrument a field site as densely as a sandbox aquifer. In the field studies conducted as part of this thesis, THT was validated by comparing estimated hydraulic parameter fields to known geology (borehole data) and simulating 9 pumping tests that were performed at the site. The THT analysis was able to capture the salient features of the aquifer (the presence of a double aquifer separated by an aquitard), and was able to reasonably reproduce most of the pumping tests. For comparison purposes, a homogeneous model and three additional heterogeneous models were created: i) permeameter estimates of hydraulic conductivity from soil cores were interpolated via kriging; ii) the transition probability/Markov Chain approach was used to interpret material classifications from borehole logs; and iii) a stratigraphic model was created and calibrated to pumping test data. Of these cases, THT and the calibrated stratigraphic model performed best, with THT performing slightly better. This work indicates that it is possible to interpret multiple pumping tests using hydraulic tomography to estimate the 3D distribution of hydraulic parameters in heterogeneous aquifer systems. Also, since hydraulic tomography does not require the collection and analysis of a large number of point samples, it is likely comparable in cost to other characterization/modeling approaches.

The objective of this study is to demonstrate the ability of riverstage tomography to estimate 2-D spatial distribution of hydraulic diffusivity (D) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 65 wells and stream stage data from 5 gauging stations. In order to accomplish this objective, wavelet analysis is first conducted to investigate the temporal characteristics of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated over seasonal and annual periods while that between precipitation is less significant. Subsequently, spatial cross-correlation between seasonal variations of groundwater level and riverstage data is analyzed. It is found that the correlation contour map reflects the pattern of sediment distribution of the fan. This finding is further substantiated by the cross-correlation analysis using both noisy and noise-free groundwater and riverstage data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of riverstage tomography is then tested with these synthetic data sets to estimate D distribution. Finally, the riverstage tomography is applied to the alluvial fan. The results of the application reveal that the apex and southeast of the alluvial fan are regions with relatively high D and the D values gradually decrease toward the shoreline of the fan. In addition, D at northern alluvial fan is slightly larger than that at southern. These findings are consistent with the geologic evolution of this alluvial fan. (C) 2017 Elsevier B.V. All rights reserved.

Using cross-correlation analysis, we demonstrate that flux measurements at observation locations during hydraulic tomography (HT) surveys carry non-redundant information about heterogeneity that are complementary to head measurements at the same locations. We then hypothesize that a joint interpretation of head and flux data can enhance the resolution of HT estimates. Subsequently, we use numerical experiments to test this hypothesis and investigate the impact of stationary and non-stationary hydraulic conductivity field, and prior information such as correlation lengths, and initial mean models (uniform or distributed means) on HT estimates. We find that flux and head data from HT have already possessed sufficient heterogeneity characteristics of aquifers. While prior information (as uniform mean or layered means, correlation scales) could be useful, its influence on the estimates is limited as more non-redundant data are used in the HT analysis (see Yeh and Liu [2000]). Lastly, some recommendation for conducting HT surveys and analysis are presented.

Hydraulic tomography is a cost -effective technique for characterizing the heterogeneity of hydraulic parameters in the subsurface. During hydraulic tomography surveys, a large number of hydraulic heads (i.e., aquifer responses) are collected from a series of pumping or injection tests in an aquifer. These responses are then used to interpret the spatial distribution of hydraulic parameters of the aquifer using inverse modeling. In this study, we developed an efficient sequential successive linear estimator (SSLE) for interpreting data from transient hydraulic tomography to estimate three-dimensional hydraulic conductivity and specific storage fields of aquifers. We first explored this estimator for transient hydraulic tomography in a hypothetical one-dimensional aquifer. Results show that during a pumping test, transient heads are highly correlated with specific storage at early time but with hydraulic conductivity at late time. Therefore, reliable estimates of both hydraulic conductivity and specific storage must exploit the head data at both early and late times. Our study also shows that the transient heads are highly correlated over time, implying only infrequent head measurements are needed during the estimation. Applying this sampling strategy to a well -posed problem, we show that our SSLE can produce accurate estimates of both hydraulic conductivity and specific storage fields. The benefit of hydraulic tomography for ill -posed problems is then demonstrated. Finally, to affirm the robustness of our SSLE approach, we apply the SSLE approach to transient hydraulic tomography in a hypothetical two- dimensional aquifer with nonstationary hydraulic properties, as well as a hypothetical three-dimensional heterogeneous aquifer.

The objective of this study is to estimate 2-D spatial distribution of hydraulic conductivity (Ks) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 88 wells and stream stage data from 4 gauging stations. In order to accomplish this analysis, wavelet analysis is first carried out to investigate the periodic cycles of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated in terms of seasonal and annual periods. Subsequently, seasonal variations of groundwater level in response to stream stage variation are utilized to estimate the Ks spatial distribution by spatiotemporal cross correlation analysis, cokriging, and river stage tomography. Prior to applications of these methods to the alluvial fan, performances of each approach are evaluated and compared with reference field of a noise free synthetic experiment. It is found that all of the approaches could yield similar general spatial pattern of Ks. Nevertheless, river stage tomography seems to reveal a higher resolution of spatial Ks distribution. When the geologic zones are provided in river stage tomography analysis as prior information, the accuracy of estimated Ks values improves. Finally, results of the applications to data of the alluvial fan reveal that the apex and southeast of the alluvial fan are regions with relative high Ks and the Ks values gradually decrease toward the shoreline of the fan. These two areas are considered as the possible main recharge regions of the aquifer. It is also observed that Ks at northern alluvial fan is slightly larger than that at southern. These findings seem consistent with the geologic evolution of this alluvial fan.

The purpose of this study is to investigate the importance of prior information about hydraulic conductivity (K) by Kriging, using point K data and/or residual covariance, on improvements of K estimates at the North Campus Research Site (NCRS). Among many methods that can characterize the mean or detail distribution of hydraulic conductivity (K), the Cooper-Jacob straight line solution, Kriging using point K data, single-well pumping tests inversion and Hydraulic Tomography (HT) have been compared in this study, using the head data collected from 15 cross-hole pumping tests collected at NCRS, where 9 existing wells were installed with packer system and the pressure responses at different intervals in different wells were monitored with transducers. It is found that the HT method, which fuse all the available pumping test data, yields more accurate and consistent results. However, many studies have indicated that the hydraulic data combined with geologic investigation will improve the HT estimates. Thus, in this study, hard data of K obtained by permeameter (227 data points) are brought in using Kriging and combined with HT to yield better estimate K field. Moreover, the validations of unused tests indicate that the estimated K obtained using collected K information makes more accurate predictions.

Ce manuscrit de thèse présente une nouvelle approche pour caractériser qualitativement et quantitativement la localisation et les propriétés des structures dans un aquifère fracturé et karstique à l’échelle décamétrique. Cette approche est basée sur une tomographie hydraulique menée à partir de réponses à une investigation de pompages et interprétée avec des méthodes d’inversions adaptées à la complexité des systèmes karstiques. L’approche est appliquée sur un site karstique d’étude expérimental en France, une première fois avec des signaux de pompage constants, et une deuxième fois avec des signaux de pompage harmoniques. Dans les deux cas, l’investigation a fourni des réponses de niveaux d’eau de nappe mesurés pendant des pompages alternés à différentes positions. L’interprétation quantitative de ces jeux de réponses consiste à les reproduire par un modèle avec un champ de propriété réaliste adéquat généré par inversion. Les méthodes d’inversions proposées dans ce manuscrit permettent de reconstruire un champ de propriétés hydrauliques réaliste en représentant les structures karstiques soit par un réseau généré par automates cellulaires, soit par un réseau discrétisé. Les résultats d’interprétations obtenus sur le site d’étude expérimental permettent d’imager les structures karstiques sur une carte et de « lire » leur localisation. De plus, les résultats obtenus avec les réponses à des pompages harmoniques tendent à montrer le rôle de la fréquence du signal sur les informations portées par les réponses. En effet, les fréquences plus élevées caractérisent mieux les structures les plus conductrices, alors que les fréquences plus faibles mobilisent des écoulements également dans des structures karstiques moins conductrices. / This thesis manuscript presents a novel approach to characterize qualitatively and quantitatively the structures localization and properties in a fractured and karstic aquifer at a decametric scale. This approach relies on a hydraulic tomography led from responses to a pumping investigation and interpreted with inversion methods adapted to the complexity of karstic systems. The approach is applied on a karstic experimental study site in France, a first time with constant pumping signals, and a second time with harmonic pumping signals. In both applications, the investigation resulted in groundwater level responses measured during alternated pumping tests at different locations. The quantitative interpretation of these sets of responses consists in reproducing these responses through a model with an adequate realistic property field generated by inversion. The inversion methods proposed in this manuscript permit to reconstruct a realistic hydraulic property field by representing the karstic structures either through a network generated by cellular automata, or through a discretized network. The interpretation results obtained on the experimental study site permit to image the karstic structures on a map and to‘read’ their localization. Furthermore, the results obtained with the responses to harmonic pumping tests tend to show the role of the signal frequency on the information carried by the responses. In fact, higher frequencies better characterize the most conductive structures, while lower frequencies mobilize flows also in less conductive karstic structures.

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