<p> Human interventions in the hydrologic cycle have intensified to the extent that water resources cannot be managed and understood in isolation from anthropogenic influences. New approaches are needed to understand the effects of humans on hydrology, especially in regions of the world with limited hydrologic records. This dissertation focuses on a case study of the Arkavathy watershed adjacent to Bangalore, India, which has been transformed by rapid urbanization, intensification of agriculture, and over-exploitation of water resources over the last 50 years. During this time, the disappearance of streamflow in the watershed was largely overlooked as Bangalore shifted from Arkavathy-sourced water supply to imported water and farmers from surface water to groundwater irrigation. With Bangalore continuing to expand its water footprint and local groundwater resources drying up, moving towards sustainable water resources management in the Arkavathy requires overcoming the general absence of local hydrological records to develop an understanding of the changing hydrology of the watershed. To this end, a multifaceted research approach is developed and applied to the Arkavathy watershed to identify the dominant hydrologic dynamics within the watershed and understand the conditions under which hydrologic change occurred. This research reveals a number of important findings. First, humans are the primary drivers of change in this watershed, as neither precipitation variability nor increases in temperature can explain the observed changes in hydrology. Second, hydrologic change within the watershed is spatially heterogeneous, with drying occurring in the northern part of the watershed and increased surface water availability downstream of Bangalore. Third, streamflow decline in the northern Arkavathy has most likely been caused by extensive groundwater depletion driven by groundwater irrigated agriculture. And finally, management strategies designed to reverse groundwater depletion by constructing check dams within the surface water network are unlikely to succeed on the scales pertinent to watershed management. In addition to understanding water resources within the Arkavathy, this work serves as a foundation for understanding the trajectory of water resources in the region. This research also presents an approach for investigating historical hydrologic change in a poorly monitored watershed, understanding human-water interactions, and supporting long-term predictions for sustainable water management.</p><p>

<p> Years of conflict, political instability, and national emergencies have left behind very little information on water resources in Liberia, West Africa. This research leverages major ion and trace element analysis, <i> Escherichia coli</i> (<i>E. coli</i>) field tests, and high-throughput sequencing of microbial 16S rRNA genes to address these gaps and develop a comprehensive snapshot of groundwater quality in the region surrounding Monrovia, the capital city. A novel protocol to collect and preserve microbial DNA from groundwater under tropical field conditions lacking a constant source of electricity was employed and yielded high quality DNA sequences of bacterial and archaeal phylogenetic marker genes. </p><p> Multivariate compositional data analysis methods were used to investigate geochemical processes impacting groundwater quality throughout the study area. Low conductivity, low pH groundwaters were found to dominate the system with the majority of geochemical variability in the water samples attributed to surficial inputs both natural and anthropogenic. The implicated low buffering capacity of the groundwater system suggests a high risk associated with mining operations in Liberia. From a public health perspective, nitrate contamination, attributed to widespread but localized infiltration of human and or animal waste/fertilizer(s), was identified as the most important chemical water quality issue. Sulfate was found to be indicative of urban water cycling processes. </p><p> Although nitrate, arsenic, and lead concentrations exceeded WHO guidelines in several wells, <i>E. coli</i> was identified in 39% of all groundwaters analyzed, suggesting fecal contamination as the most significant regional water quality risk to human health. Deeper wells had significantly (p &lt; 0.05) lower probability of <i>E. coli</i> contamination, with no <i> E. coli</i> encountered in any well greater than 22 meters deep. Sequencing of 16S rRNA genes revealed highly variable microbial community compositions. Surficial inputs are suggested as the major drivers of microbial diversity and community composition. Groundwaters that tested positive for <i> E. coli</i> in the field were found to have significantly higher estimates of microbial alpha diversity (p &lt; 0.05) than groundwaters that tested negative. Additionally, nitrate, silica, pH, and several other geochemical constituents were found to be strongly correlated with shifts in microbial community structure. </p><p> The identification of a wide diversity of pathogen-associated bacteria to the genus and species level suggests that microbial contamination is more widespread than indicated by the <i>E. coli</i> field test alone. Results highlight the vulnerability of aquifers in Liberia to contamination and call for an increased investment in the water supply infrastructure and enhanced monitoring of chemical and microbial constituents throughout the country. This work will help the government of Liberia establish baseline water-quality conditions and provides an initial set of water resource databases to improve water-quality monitoring capacity.</p><p>

<p>A better understanding of groundwater flow through bedrock fractures is critical to applications involving heat and solute transport. Pumping tests performed to characterize these systems are often ill-suited because the radius of penetration quickly expands beyond the inter-well distance, gaining information beyond the well pair of interest. Periodic hydraulic tests allow the radius of penetration to be controlled by the frequency of oscillation, and testing at multiple frequencies gives parameter estimates for a range of spatial scales. Periodic pumping tests were performed at the Mirror Lake experimental fractured rock hydrology field site in New Hampshire. Results suggest a more complex, 3D network of connectivity than previously indicated by constant rate pumping tests. The relative degree of connectivity, given by diffusivity, corresponds to early-time response seen in the constant rate test. This confirms that the periodic tests investigated at a smaller penetration radius than the steady response from constant pumping.

<p> Percolation rates in Managed Aquifer Recharge (MAR) facilities, such as recharge basins and stream channels, can vary widely through both time and space. Natural variations in sediment hydraulic conductivity can create &ldquo;dead zones&rdquo; in which percolation rates are negligible. Clogging is a constant problem, leading to decays in facility percolation rates. Measuring percolation rate variations is important for management, maintenance, and remediation of surface MAR facilities. </p><p> We have used Fiber Optic Distributed Temperature Sensing (FODTS) to monitor percolation in a long narrow river channel separated from an active river by a levee. The alluvial sediment in the river channel varies widely in texture and water balance is difficult to monitor independently. The off-river channel was monitored by installing a fiber optic cable in the subsurface and measuring the propagation rate of the diurnal temperature oscillations carried downward with infiltrating water. In this way, heat was used as a tracer of percolation rates along the section defined by the 1800 meters of buried cable. We were able to confirm the FODTS measurements of percolation in the Off River Channel and demonstrate its wide applicability. Results from the measurements have been used to understand both the hydraulic behavior of percolation in the facilities and to make management decisions regarding facility operations and the potential need for additional surface sediment remediation.</p><p>

<p> Multi-model analysis (MMA) considers multiple model interpretations of a system. MMA provides a more realistic assessment of uncertainty associated with model predictions because both uncertainty of individual models and uncertainty associated with different model structures are considered. Models are evaluated for the strength of evidence that they represent an unknown system using different Information Criteria (IC) equations. IC equations are designed to assess the likelihood that a model in a set of models represents the true but unknown system. IC equations do not include a component which identifies a deficient model. Therefore, inclusion of deficient models in the set of models leads to poor model-averaged results. Evaluation of models to assess whether available observation data sufficiently support the model structure is an important step in MMA. Measures for evaluating models include: 1) failure to reach proper convergence during non-linear regression; 2) unreasonable parameter estimates; 3) unreasonable confidence intervals on parameters or a coefficient of variation greater than ten for one or more parameters; 4) high correlations between parameters; 5) determinant of the correlation matrix less than 1x10^-12; 6) condition number of the Jacobian matrix greater than 2000; and 7) unreasonable confidence intervals on predictions.</p><p> Experiments presented herein are designed to evaluate how components of AIC, AICc, BIC, and KIC rank models and assign model probabilities, and to demonstrate how removing deficient models improves MMA results. Synthetic models are used to represent true but unknown systems in contrast to experimental models that are created to simulate a simplified version of the unknown system based on observation data taken from the synthetic models. AIC, AICc, BIC, and KIC generally assign high probability to deficient models. AICc generally assigns high probability to deficient models if 1) there are many observation data or 2) there are few observation data and the model fits the data well. KIC generally assigns high probability to deficient models because these models have low Fisher Information. AIC and BIC are influenced by the goodness-of-fit and are more likely to assign high probability to more complex models because these models are generally over-fitted. Removing deficient models results in improved MMA results using AIC, AICc, BIC and KIC.</p><p>

<p> The Niles Cone Basin (NCB) within Alameda County, California, contains portions of the basin under perennial and ephemeral artesian groundwater conditions. This study used 349 wells installed throughout the basin&rsquo;s four-aquifer system to delineate the spatial distribution of the 86 wells that have gone artesian between 1995 and 2015. Artesian wells within all four aquifers occur at elevations below 5.2 meters above sea level (MASL) but predominantly below 3.0 MASL. Even at lower elevations, artesian conditions do not occur in regions of major pumping owing to significant drawdown. Within topographically-low regions, wells may not be artesian where well-heads are located at higher elevations, such as on a levee or other elevated landforms. This can be observed throughout the Newark and Centerville aquifers where artesian wells are located near non-artesian wells during the same monitoring event. Precipitation influences artesian conditions with artesian events correlated with increases in precipitation generally during, but not limited to, the early spring months. The water levels of the shallow Newark Aquifer were found to respond independently from the three deeper aquifers. Those deeper aquifers were observed to be in hydraulic connection with one another, displaying synchronous water level changes with time across the basin.</p><p>

<p> Glacier melt affects the geochemical composition of rivers; however, quantifying the glacier contribution to subarctic watershed-scale runoff has attracted limited attention. To estimate glacier contribution, we conducted a 6-year geochemical hydrograph separation study in a geologically heterogeneous glacierized watershed in Interior Alaska. Water samples were collected daily from Jarvis Creek during late April through September. Source waters were collected synoptically each year from rain, snow, baseflow (winter discharge), and the glacier terminus discharge. All samples were analyzed for stable water isotopes and dissolved ion concentrations. Stream surface water samples have large seasonal and inter-annual geochemical variation, however, source waters show distinct chemical signatures allowing the application of a geochemical hydrograph separation model to quantify relative source contribution to lowland streamflow. Considerable inter-annual differences within source water signatures emphasize the importance in informing the model with source waters sampled for each season. We estimated a seasonal average of 35% (20 to 44%) glacier terminus discharge contribution with a daily range of 2 (May) to 80% (September). If glacier contribution was to cease completely, stream discharge would be reduced by 48% and 22% in low and high rainfall summers, respectively. Combined with the documented shrinkage of glaciers, our findings emphasizes the need for further research on glacial wastage effect on subarctic watersheds.</p><p>

The problem of selecting appropriate mathematical models for use in studying hydrological phenomena has created a situation in which the choice of suitable models by hydrologic practitioners has become exceedingly complex. The extensive comments in the literature indicate that neither the traditional system of technical journals nor the more modern computer -based retrieval schemes have really solved the problem. Further examination shows that similar problems have arisen in many fields, hence a well organized attack on the specific problem of hydrologic model choice can have a more general application. The present problem is identified as a requirement to codify and make accessible to users information in a more directly user oriented format. The problem of model choice arises at several levels, ranging from decision on what fundamental structure to use, to choice of parameters, and on to model calibration and validation. This paper is focused on a scheme to aid in model structure choice. The essential ingredients of model structure choice, and indeed of many choice processes, are extracted and embedded in a generalized set theoretic mathematical notational framework in order to give some insight into the nature of the problem. Within this framework the specialized features of the model choice problem are analyzed, and a specialized model is developed for assisting in model choice and all problems similarly situated. These considerations lead to the development of a finite vector of objective statements with codified responses prepared by a panel of qualified researchers who are willing and able to construct the essential information in a user oriented format. It is required that the panel not only couch their information in objective oriented terms but that they also generate value judgments for the individual components. In this way, those using the system can take advantage of the expert opinions embedded in the model while, at the same time, tailoring the choice to meet their own specific needs and aspirations. This results in what is defined as a mathematical CHOICEMODEL. The implementation of a system for interactive computation of the CHOICEMODEL is described in detail, and the associated computer programs are presented in appendices. A detailed instruction manual is given, and the implementation of the method is illustrated by an easily understood model of the ingredients of the problem of selecting an 8 -track stereo tape deck for home use. The plan is outlined whereby hydrologic choice models can be developed within the CHOICEMODEL system by a selected panel of expert EVALUATORs.

Aquifers hosted in fractured crystalline rocks are generally characterized by low porosity and strongly heterogeneous and anisotropic flow paths, with flow and transport dominated by discrete fracture sets. In general, zones of high hydraulic conductivity correlate with zones of high fracture intensity and fracture connectivity. Fractured rock hydraulic conductivity, however, is not only a function of spatial fracture distributions, but also displays dynamic variability due to changes in fracture aperture with changes in effective stress, such as those due to groundwater pumping and seasonal variations in water level. Some studies suggest hydromechanical coupling plays a minimal role in hydraulic conductivity alteration at shallow depths, whereas other studies attribute hydraulic conductivity alteration directly to hydromechanical coupling, thus raising a fundamental science question: what is the role of hydromechanical coupling in shallow fractured rock aquifers? This study investigates the role of hydromechanical coupling in shallow fractured rock aquifers from 3 perspectives. First, a sensitivity study presents the results of analytical and numerical modeling to determine what key hydromechanical parameters are important in the shallow crust under realistic stress states. Results suggest that hydraulic conductivity alteration is dominated by fracture normal closure, with shear dilation playing a minimal role, and that shallow dipping fractures are likely to have the highest hydraulic conductivity relative to steeply dipping fractures due to compressional deviatoric stress states. These results suggest that depth-dependent hydraulic conductivity trends observed in nature may be due in part to hydromechanical phenomena, and thus fractured rock characterization should include hydromechanical characterization. Study two presents the results of an aquifer-scale fractured rock characterization at Gates Pond, Berlin, MA in which hydromechanical variables are constrained in the field and coupled with structural and hydraulic characterization, including stress-tests, long-term water level monitoring, isotope analysis and earth tide analysis, to provide insight into the mechanical properties of the aquifer. Results of this study reveal an interesting field setting in which the mechanical properties of the aquifer are homogeneous throughout the study area, but the aquifer is compartmentalized by foliation parallel fractures that restrict hydraulic connection between wells that are placed perpendicular to foliation. Gates Pond also displays a hydraulic conductivity trend in which Foliation Parallel Fractures (FPF) have a decreasing transmissivity with increasing depth, and tectonic fractures display a decrease in transmissivity with increasing dip. Such observations suggest a conceptual model in which FPFs dominate flow in the shallow subsurface, with transmissivity decreasing with depth, where Tectonic fracture become the dominate flowing set. These results are consistent with the results of analytical and numerical modeling predictions from Chapter 1. Lastly, the third study presents results of a regional scale correlation of critically stressed fractures and fracture transmissivity in the Nashoba terrane, eastern Massachusetts. Whereas Chapter 1 suggests that fracture transmissivity is strongly modified by fracture normal closure, which is supported by field observations in Chapter 2, many workers suggest that flowing fractures are those that are critically stressed, and are thus strongly modified by shear dilation. This study addresses the role of shear dilation by identifying critically stressed fractures at a regional scale and correlating resolved stresses on transmissive fractures to fracture transmissivity. Fracture characteristics, transmissivity and borehole breakouts are characterized for 17 wells from throughout the Nashoba terrane. Critically stressed fractures are identified using inferred stress states, and correlation of critically stressed fractures to fracture transmissivity is investigated. Results suggest that transmissivity is weakly correlated to the ratio of shear to normal stress, and that ratio is strongly correlated to fracture dip. A conceptual model is proposed in which shallow dipping fractures are more likely to be critically stressed, such as FPFs in the shallow subsurface; however, high transmissivity fractures need not be critically stressed. Thus, it is concluded from observations in this dissertation that fractures in the shallow crust are most sensitive to fracture normal closure, although shear dilation may enhance transmissivity. The complex interaction between normal closure and shear dilation results in shallow dipping fractures being the most transmissive in the shallow subsurface, with tectonic fractures becoming more important with increasing depth. Each of the 3 studies presents a unique contribution to the study of hydromechanical coupling in fractured rock aquifers, with each study supporting the hypothesis that hydromechanical coupling may alter hydraulic conductivity of fractures in the shallow subsurface, contributing to observed depth-dependent hydraulic conductivity trends, variable hydraulic conductivity as a function of fracture dip, and dynamic permeability. Results of these studies show that hydromechanical coupling affects hydraulic conductivity of fractures in the shallow crust, and should therefore be incorporated into fractured rock aquifer characterization in conjunction with standard structural and hydrogeologic characterization.

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