Fil: Lanzaro, María Verónica. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas; Argentina. | En las últimas décadas, el crecimiento urbano ha provocado un impacto significativo en el ambiente. En ocasiones, la ausencia o aplicación inadecuada de planes de ordenamiento urbano ha generado patrones irracionales de uso del suelo caracterizados por una alta concentración en las áreas centrales, en contraposición con una ocupación desordenada en las periferias urbanas con ausencia de regulación normativa. Ambas situaciones acrecientan la degradación ambiental. El aprovechamiento del espacio subterráneo se ha convertido en una alternativa para ciudades con problemas de crecimiento y densidad poblacional, aunque generalmente, no se comprende la compleja interacción entre el uso del suelo y el comportamiento del sistema hídrico subterráneo ni se aborda considerando aspectos normativos. La ciudad de Santa Fe no está exenta de estas situaciones. El objetivo de esta tesis es evaluar la relación entre las construcciones subterráneas existentes y las características del sistema acuífero que subyace a la ciudad de Santa Fe, Argentina, a fin de formular lineamientos técnicos y normativos que optimicen los proyectos de obras subterráneas. Para ello se analizaron las variaciones espaciales y temporales de niveles freáticos para un período de 10 años, la calidad química del agua subterránea, y los diversos usos actuales del suelo con aprovechamiento subterráneo. Los resultados obtenidos contribuirán a la seguridad, funcionalidad y racionalidad económica de futuras obras subterráneas y a la generación de una conciencia de gestión integral que asuma la relación compleja entre el uso del suelo urbano y el medio hidrogeológico en la toma de decisiones y planificación de la ciudad. | In recent decades, urban growth has caused a significant impact on the environment. Occasionally, the absence or improper application of urban planning plans has generated irrational land use patterns characterized by highly concentration in central areas, as opposed to a disorderly occupation in urban peripheries with the absence of urban regulation. Both situations increase environmental degradation. The use of underground space has become an alternative for cities with problems of growth and population density, although the complex interaction between land use and the behavior of the groundwater system is not generally understood, nor is it addressed considering regulatory aspects. The city of Santa Fe is not exempt from these situations. The objective of this thesis work is to evaluate the relationship between existing underground constructions and the characteristics of the aquifer system that underlies the city of Santa Fe, Argentina, in order to formulate technical and normative guidelines to optimize underground works projects. To this end, the spatial and temporal variations in groundwater levels for a period of 10 years, the chemical quality of the groundwater, and the various current land uses with underground use were analyzed. The results obtained will contribute to the safety, functionality and economic rationality of the projects of future underground works and to the generation of an integral management awareness that assumes the complex relationship between urban land use and the hydrogeological environment in decision-making and city planning.

This study improves knowledge on the hydrogeology of Ischia Island, an active volcano of southern Italy. Combining previous published and unpublished data with newly collected data, and through the results of simplified numerical models, the existing conceptual hydrogeological model of the volcanic island has been reviewed and the present impact of intensive withdrawals on the island’s groundwater resources has been examined. Two areas with different hydrogeological characteristics have been recognized: (1) the resurgent block of Mt. Epomeo, where an independent and uplifted basal groundwater circulation exists; (2) the external areas of Mt. Epomeo, where a continuous basal aquifer and local discontinuous perched aquifers have been distinguished. The marginal faults of the resurgent block of Mt. Epomeo represent the preferential pathways of ascending deep fluids. In natural conditions, the island’s aquifers are recharged by rainfall and by deep fluids from beneath, discharging towards the sea and the springs. Since the start of activity at the spa facilities, involving intensive pumping from wells, a further and significant recharge of the aquifers has come from seawater and from increased upwelling of the deep fluids. Although this does not compromise the sustainability of the groundwater withdrawals in quantitative terms, the pumping rates determine the quality of the water captured by the wells. The great variability in temperature and chemical composition of groundwater of the island is also influenced by local hydrogeological parameters and characteristics of the wells from which the water samples were taken, as well as the phenomena of interaction among different end-members.

Effective management of groundwater resources requires an understanding of the complexity of groundwater systems by the experts, and a certain level of understanding and trust in management by the community. Groundwater data sharing and visualisation systems are being used across the world to provide an insight into groundwater systems. The 3D Water Atlas of the Surat Basin, Queensland, Australia, provides a way of visualising and analysing hydrogeochemical information in a way that is accessible to a wide audience. It combines data on the location, construction, water chemistry and water levels of groundwater bores within the framework of a geological model and other spatial datasets. It is freely available on a single Web-based interactive three-dimensional (3D) platform. Visualisation tools such as line graphs of groundwater bore water levels, pie charts and animations of major ions, can be used to advance understanding of groundwater resources. For example, a general regional decline, but with local variability in Hutton Sandstone groundwater levels in the Surat Basin can be seen by using the 3D Water Atlas. The combination of groundwater data with filtering, analysis and visualisation tools in the 3D Water Atlas helps to communicate complex hydrogeological concepts. It can also assist with the management of groundwater resources by improving confidence in decision-making, as necessary information can be viewed together, in context. Although the 3D Water Atlas was produced for the Surat Basin, its design means that 3D Water Atlases for different regions can be produced easily.

Permafrost in Arctic watersheds limits soil biological activity to a thin, seasonally thawed active layer that contributes water to streams. In many hillslopes, relatively wet drainage features called water tracks have distinct freeze-thaw patterns that affect groundwater flow and storage, and thus the export of heat and solutes to Arctic streams. This study uses groundwater flow and energy transport models to examine potential controls on the timing and duration of freeze–thaw conditions and the magnitude of temperature fluctuations within water tracks and their adjacent hillslopes. The simulated length of the active-layer thaw season varies by 1 month over the range of snow-cover and mean annual air-temperature scenarios simulated. The timing and duration of freezing is particularly sensitive to depth and duration of snow cover. Thus, the deeper snowpack covers that can accumulate in water tracks contribute to their more persistent thaw conditions and their ability to conduct groundwater downslope. A three-dimensional simulation shows that during the summer thaw season, the water track captures groundwater laterally from half way across the hillslope. The models presented here elucidate key mechanisms driving small-scale variation in the active-layer thermal regime of tundra hillslopes, which may be responsible for changes in drainage-network geometry and Arctic biogeochemical fluxes under a warming climate.

Submarine groundwater discharge (SGD) is widely acknowledged as a key driver of environmental change in tropical island coral reefs. Previous work has addressed SGD and groundwater-reef interactions at isolated submarine springs; however, there are still many outstanding questions about the mechanisms and distribution of groundwater discharge to reefs. To understand how groundwater migrates to reefs, a series of offshore ²²²Rn (radon) and submarine electrical resistivity (ER) surveys were performed on the tropical volcanic island of Mo’orea, French Polynesia. These surveys suggest that fresher water underlies the fringing reef, apparently confined by a <1-m-thick low-permeability layer referred to as a reef flat plate. Reef flat plates have been documented elsewhere in tropical reefs as thin, laterally continuous limestone units that form through the super-saturation of calcium carbonate in the overlying marine waters. In other tropical reefs, the reef flat plate is underlain by a highly permeable karstic limestone formation, but the submarine reef geology on Mo’orea is still uncertain. Numerical modeling of two-dimensional reef transects and SGD quantifications, based on water budget and radon/salinity mass balance, support the confining nature of the reef flat plates and indicate important implications for SGD impacts to tropical reefs. Except where incised by streams or local springs, reef flat plates may route SGD to lagoons or to the reef crest 100s of meters offshore. Because groundwater can transport pollutants, nutrients, and low pH waters, the reef flat plate may play an important role in the spatial patterns of reef ecology and coastal acidification.

Stable isotopic composition (δ²H, δ¹⁸O) of river water, groundwater, and paddy water in the Mun River catchment, northeast Thailand, were determined to investigate the hydrological processes and the impacts of natural and anthropogenic activities on the water cycle. Quantities of δ²H (−93.9 to −25.4‰) and δ¹⁸O (−12.24 to −2.22‰) in river water in the wet season follow the trend: upper reaches > middle reaches ≈ lower reaches. Trends for δ²H (−52.3 to −22.0‰) and δ¹⁸O (−6.37 to −1.36‰) in the dry season are: upper reaches ≈ middle reaches > lower reaches. In the dry season, groundwater (δ²H: −57.5 to −34.6‰, δ¹⁸O: −8.24 to −4.40‰) shows a lighter isotopic composition, and paddy water (δ²H: −18.2‰, δ¹⁸O: −0.72‰) shows the highest isotopic composition. Spatial variation of δ¹⁸O and deuterium excess suggests that groundwater exchanges with surface water frequently. Rainfall and river water recharge groundwater in the wet season, and groundwater flows back to the river in the dry season, especially in the middle reaches. This process is most likely related to impoundment of the rivers by large dams. On the other hand, the lowest values of stable isotopes of river water are coincident with the extreme flooding that was produced by Tropical Storm Sonca in July 2017. This study contributes to a better understanding of hydrological processes in the Mun River catchment and provides a perspective on the application of stable isotopes to other large tropical monsoon catchments around the world.

For the quantitative evaluation of the impact of mining on a groundwater system, it is necessary to constrain the hydrogeological and mechanical properties. However, the in situ estimation of the mechanical properties of rock such as compressibility and porosity, is often difficult. Additionally, determining the hydraulic properties such as hydraulic conductivity, of rock by conventional methods is often expensive. The response of the groundwater level to external loading such as Earth tides and barometric pressure, couples the hydrogeological and mechanical processes of rocks, thus providing a way to infer these properties in the field. This study compared aquifer parameters inferred from tidal and barometric responses with those inferred from conventional hydraulic tests and rock mechanics tests in three groundwater monitoring wells at a site in China. The results show that the hydraulic conductivity inferred from a tidal response is similar to that of a pumping test. The compressibility values calculated for the three wells are all higher than those determined by experiment, and the porosity values calculated are all lower than those determined by experiment, but the differences between the calculated and experimentally measured values are lower than one order of magnitude. Considering the costs and convenience of the water-level response method, this method is a good choice for obtaining the properties of an aquifer, especially those in areas of tectonic activity and those affected by anthropogenic perturbations.

Groundwater flow and the geochemical evolution of a freshwater lens in an aquifer on a Pacific atoll were investigated by hydrogeochemical surveys. Sulfur hexafluoride measurements showed that deeper groundwater and groundwater at the periphery of the lens are older, consistent with a downward and outward groundwater flow scheme. This is the typical flow scheme on Pacific atolls where a Holocene–Pleistocene unconformity restricts the shape of the freshwater lens. Enrichment of Mg/Ca in the groundwater is another indicator of a longer residence time, because contact between the groundwater and the carbonate sediments composing the aquifer leads to the release of Mg from high-Mg calcite and the precipitation of Ca as low-Mg calcite. Groundwater quality was also affected by anthropogenic nitrogen loading and aboveground organic matter, which were altered by denitrification and sulfate reduction in the aquifer, especially in the older groundwater. The chemical composition of the groundwater in the center of the island, where saline water is up-coning, implies that freshwater recharge dilutes the older saline water, which as time passes will eventually be replaced by newly recharged freshwater.

‘Blue water’ is the portion of freshwater flowing through rivers and the subsurface (groundwater) that is available for human consumption. ‘Green water’ is the portion stored in the unsaturated soil and vegetation canopy that is available only indirectly. Security of blue and green water resources is assessed over the Dorudzan Dam watershed in southern Iran. Precipitation and temperature data from 22 models of the Coupled Model Intercomparison Project Phase 5 are transiently downscaled at five climatic stations under three Representative Concentration Pathway (RCP) scenarios. The Soil and Water Assessment Tool (SWAT) is used to simulate and quantify blue and green water components over the region at the present time and under climate-change conditions. Climate-change study indicates that precipitation decreases (13–17%) and temperature increases (1.7–3. 3 °C) under the three RCPs, leading to substantial dam-inflow reduction. Evapotranspiration will increase while soil-water content will decrease, further intensifying green-water scarcity and vulnerability. Water use from the Kor River is sustainable at present, but future climate change will raise some ecological hotspots. Groundwater exploitation is currently unsustainable in all aquifers of the study area and climate change will further decrease the available groundwater, leading to intensification of the water crisis. Assessment of inter-annual security under climate change indicates that maximum scarcities of green water and surface blue water occur during spring and summer, and subsurface blue water (groundwater) maxima occur throughout the year. Thus, climate change threatens the future security of water resources in this arid watershed, requiring different management strategies for sustainability.

Salt loads in the Colorado River Basin are a primary water quality concern. Natural groundwater brine discharge to the Dolores River where it passes through the collapsed salt anticline of the Paradox Valley in western Colorado (USA) is a significant source of salt to the Colorado River. An airborne electromagnetic survey of Paradox Valley has provided insights into the three-dimensional distribution of brine in the surficial aquifer. A combination of stochastic and deterministic resistivity inversions was used to interpret the top of the freshwater–brine interface and to qualitatively describe the vertical salinity gradients across the interface. Low-resistivity regions indicative of brine occur near the land surface where brine discharges to the Dolores River and increase in depth several kilometers up-gradient along the axis of the valley. The most conductive parts of the brine plume are found in the areas below and adjacent to the river, suggesting that the brine becomes shallower and more concentrated as it reaches its natural discharge location. A significant freshwater lens overlying the brine west of the Dolores River is spatially correlated to the intermittent West Paradox Creek and agricultural irrigation. Below this lens, the transition from freshwater to brine appears to occur abruptly over a few meters and correlates to available well information. However, away from these regions and particularly with distance from the river, the freshwater–brine interface appears to be more diffuse.