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The karst aquifer located in the Environmental Protection Area of Lagoa Santa, Minas Gerais, Brazil, exhibits the characteristic morphological features of an evolved karst environment, including large caves, sinkholes, and copious springs. Understanding the hydrogeological characteristics of karst aquifers is crucial for effective management of public resources and prevention of contamination, as these aquifers are highly vulnerable, making it essential to identify and mitigate potential risks. Given the ongoing economic and population growth in this region, the assessment of the hydrogeological parameters that control the dynamics of local flow becomes relevant for the proper evaluation of hydrogeological models and the management of water resources. Four classical pumping test analysis methods were compared to quantify the flow and storativity of the aquifer: Theis (1935), Neuman (1972), Moench (1984), and Agarwal (1980). In addition, indirect estimation methods based on the identification of capture zones and the analysis of recession curves of water courses were employed, since these approaches are cheaper and easier to apply in areas with low information. The statistical analysis of the results suggests that classical solutions can be applied to the karst aquifer to estimate hydrogeological parameters, apart from the Storage Coefficient obtained using the Neuman method. In general, the indirect estimation methods tend to produce values that are consistent with those obtained through direct methods, albeit with some reservations. The transmissivity values obtained from the pumping tests were approximately 3.0 x 10-4 m²/s, while the storage coefficient is estimated to be around 3.7 x 10-3. The indirect estimation methods yield transmissivity values of about 1.8 x 10-4 m²/s using the capture zone method, and storage coefficient values of 4.0 x 10-3 and 3.9 x 10-2 using recession curve analysis. [ABSTRACT FROM AUTHOR]

In this work we analyse the effects of climate change on the recharge and the groundwater flow of the Urucuia Aquifer System in western Bahia State, Brazil (UAS‐BA) in the period 2041–2060. We assessed possible changes and impacts on groundwater recharge with four climate models from the sixth phase of the Coupled Model Intercomparison Project Phase 6 (CMIP6): ACCESS‐ESM1‐5, CanESM5, EC‐Earth3 and MIROC6, under scenarios SSP1‐2.6 and SSP5‐8.5 (Shared Socioeconomic Pathways—SSP). Visual Balan 2.0 aquifer recharge assessment code, and the MODFLOW hydrogeological model were used to analyse the impact of future climate changes on the recharge. The projections of relative change in precipitation, under the SSP1‐2.6 scenario, show a precipitation reduction between 5% and 20%, using ACCESS‐ESM1‐5, CanESM5 and EC‐Earth3 models. Using SSP5‐8.5 scenario, these models behave differently, while the CanESM5 and EC‐Earth3 models indicate an even greater decrease in precipitation, with values up to 35%, the ACCESS‐ESM1‐5 projects an increase in precipitation of up to 25%. Using MIROC6, though, an increase of up to 10% in precipitation in the UAS‐BA is expected, under both scenarios. Regarding temperature, all the models agree with a warming in the future varying from 2 to 3°C. Recharge projections calculated using the Visual Balan 2.0 indicated in general a reduction between 8% and 43%. Using the MODFLOW model, the results show a reduction of recharge to the aquifer varying from 3% to 45% using CanESM5, EC‐Earth3 and MIROC6. The ACCESS‐ESM1‐5 has a 26% reduction (5% increase) under SSP1‐2.6 (SSP5‐8.5). Furthermore, projections indicate a downward trend in the water table in the northern portion of UAS‐BA, reaching a maximum drop of up to 12 m with the CanESM5, under SSP5‐8.5 scenario. [ABSTRACT FROM AUTHOR]

• Hydrogeological model using Equivalent Porous Media and Conduit Network approaches. • Discrete features tool application to represent karst conduits with turbulent flow. • Using tracer test results to calibrate the flow rate of karst springs. The current study consisted of the development of a hydrogeological numerical model in the Lagoa Santa Karst Environmental Protection region, in order to represent the conduit-flow karst springs in the most well-studied karst system in Brazil. Once carbonate aquifers are characterized by a complex 3D pattern with a combination of a double porosity of matrix and conduits, two different modelling approaches were used: Equivalent Porous Medium (EPM), based on Darcy's law, to represent laminar flow in the fractured massif and Conduit Network (CN), using Manning-Stricker Law and the discrete feature tool, to represent the karst conduits with turbulent flow. Modeling was calibrated in a steady-state and simulations of groundwater flow and an evaluation of water exchanges between the karstic aquifer and the other hydrogeological units, were conducted. The model was developed based on data available for many studies carried out in the area, including tracer-derived route data. The calibration results for spring discharges, water levels and mass balance were satisfactory and aligned with modeling good practices. In turn, the hydraulic conductivities and recharge rates obtained by back-analysis were in agreement with literature references. The regional groundwater flow was well represented and indicated how external water entrances can be relevant to explain the higher discharge rates observed in some karstic springs. In addition, the representation of conduits allowed for the simulation of tracer pathways, enabling the inference of potential flow rates to the karstic springs from the particle simulations. [ABSTRACT FROM AUTHOR]

This study refines the hydrogeological conceptual model of an area with three interconnected aquifers, namely the Crystalline Aquifer System (CAS - igneous and metamorphic rocks), which is in contact with the Tubarão Aquifer System (TAS - sedimentary rocks) and the Diabase Aquifer System (DAS – diabase rocks). The detailed investigation involved geophysical logging and hydraulic and hydrodynamic characterization with straddle packers in a local tubular well, in which groundwater presents high uranium concentrations. Hydrogeochemical and isotope (δ2H, δ18O, 3H, δ13C, 14C) analysis in this well and in other three neighboring wells, with lower U concentrations, showed that ancient and modern waters (3H from <0.8 to 1.12 TU, 14C from 69.43 to 78.72 pMC) mix within the aquifer. During groundwater pumping, vertical fractures in the diabase aquifer possibly induce water mixing and recharge of the deeper levels of the aquifers from shallow layers. The high [U] are related to ancient waters from a confined aquifer hosted in CAS that reaches the wells through hydraulically active fractures located deeper than 159 m depth. Groundwater apparent ages do not increase systematically with depth, revealing a complex circulation model for CAS. The results obtained from the other wells, which are all located on drainage lineaments, reveal that one extracts modern water from DAS and TAS, another one extracts modern and ancient water from DAS and CAS, and the third extracts only ancient water from CAS, confirming the complexity of the local hydrogeology. Regarding regional groundwater management, the study revealed the need to characterize the sources of groundwater in each well, in order to protect modern waters from anthropogenic contamination and to protect ancient groundwater from overexploitation, as CAS hosts groundwaters recharged thousands of years ago or more. • Deep wells in fractured and sedimentary interconnected aquifers. • Discrete interval sampling from distinct fracture systems. • Hydrogeological complexity confirmed by groundwater's composition and apparent age. • Water mixing in the fractured aquifer and hydrogeological conceptual model. • Implications on groundwater management in crystalline aquifers. [ABSTRACT FROM AUTHOR]

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In the last decades, accidents involving dams and other hydraulic structures have become more frequent, increasing social pressure on the existing dams safety conditions. This fact demands commitment of professionals and companies with new plant project safety approaches. The failure of a hydroelectric concrete structure can be caused by several factors, however the main causes of failure are related to exceptional floods and foundation-related problems, which are the focus of this paper. In order to understand the influence of the rock mass characteristics, especially the contact plan with the concrete structure, this work considers the variability of geotechnical parameters, drainage efficiency, specific gravities and seismic acceleration to determine the probability of failure of these structures. To achieve this objective, the work makes use of a case study, the spillway of Baixo Iguaçu HPP, on Paraná/Brazil during its design and construction phase, determining the probability of failure by sliding. The study reproduces the foundation condition throughout a FEM hydrogeological model and determines the acting uplift through seepage analysis. The probability of failure was determined by Monte Carlo method using the probability distribution of each variable, performing 5,000,000 evaluations for each simulation. Simulations were performed for flow range varying from the ecological flow (200 m3/s) to exceptional floods with 10,000 years of recurrence time (56,362 m3/s) and its respective water levels. The most critical condition found was the extended operation at the minimum (ecological) flow, while for a normal operation, at the flow of 2598 m3/s, the order of the probability of failure is one in a million. The paper show how using hydrogeological model can lead to more realistic values of uplift pressures than using simplified methods recommended in the international guidelines, and consequently lead to a more realistic probability of failure. [ABSTRACT FROM AUTHOR]

Land cover of river basins has undergone multiple modifications and conversions as a result of various pressures on ecosystems. This study calibrates and validates the Soil and Water Assessment Tool (SWAT) model for determining the hydrological response to land-cover changes in the Lower-Middle São Francisco River sub-basin (LMSFR), Brazil. The SWAT model was calibrated with 1993–1994 data from hydrological station at Juazeiro, while data from the 1995–2004 period were used for validation. We analyzed three scenarios of land cover which were compared to current landscape (pasture land): scenario I (pasture land is replaced by natural vegetation), scenario II (pasture land is replaced by maize crop cultivation), and scenario III (pasture land is replaced by bare soil). Calibration of the SWAT model in the LMSFR produced good results, as all evaluation indices reached satisfactory values in both calibration and validation periods for Juazeiro and validation period at Floresta. However, the calibrated model, when applied to Abreus, did not accurately simulate monthly stream flow (where r 2 = 0.51 and NE = 0.26). Scenario III had the greatest impact and influence on the sediment yield, which corresponded to an increase of 93.7% in comparison to the current land cover. This study identified regions where reforestation should be urgently carried out in the north part and extreme south of the sub-basin due to the overall level of land degradation. [ABSTRACT FROM AUTHOR]

Saline intrusion is a problem that mostly affects coastal aquifers around the world, either owing to anthropic and/or natural factors. The Barreiras Aquifer, which is located on Brazil's northeastern coast and of an unconfined hydraulic nature, is subject to this due to a water demand increase. This aquifer is located in an area structurally controlled by neotectonic activity. Increased complexity occurs in the form of variations in saturated thickness, hydraulic conductivity and exploited flow rates. This study aimed to construct a numerical model of dependent density flow for the Barreiras Aquifer using the SEAWAT software (USGS) and simulate saline intrusion over 20 years of pumping wells that currently exploit approximately 750 m³/h. The results can contribute to local hydrogeological management and assist managers. Simulation results with variation of recharge between dry and rainy periods and reduction of well exploitation flow rates were also obtained. The two main local faults, Boa Cica and Tabatinga, striking NW-SE and NE-SW, respectively, were simulated in a calibrated transient hydrogeological model as zones of high hydraulic conductivity (conduits) as well as in the inverse form (barriers) and offered a better fit considering the faults as zones of relatively higher hydraulic conductivities and preferred pathways for saltwater intrusion progression. A two-dimensional resistivity cross-section was used to constrain the electrical property of the NW striking fault, whether in the form of a resistive anomaly or conductive anomaly. The interpretation of the 2D geoelectric model is consistent with the conductive geoelectric anomaly associated to the Boa Cica Fault, where its transtensional nature favors wider saline contamination. • Boa Cica (NW) and Tabatinga (NE) Faults affecting the Barreiras Aquifer. • Faults as zones of increase hydraulic conductivity. • Preferred paths. • Saline intrusion. • Contamination. [ABSTRACT FROM AUTHOR]

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[Display omitted] • Ferricretes are karstic-fissural covers that overlie the Cauê aquifer. • Mean basic infiltration rates are higher in structured ferricretes. • Karstification is influenced by foliation in structured ferricretes. • Karstification systems are subparallel to the slopes in the detrital ferricretes. • The recharge of the Cauê aquifer is conditioned by the ferricretes water dynamics. In the Iron Quadrangle (IQ), southeastern Brazil, ferricretes usually overlie the banded iron formations (BIFs) of the Cauê Formation, rocks that not only host the most important iron ore deposits of this region but are also its major groundwater source. Little is known about the water dynamics in ferricretes and therefore how they influence the recharge of the subjacent aquifer (Cauê aquifer). The objective of this research was to identify ferricrete typologies and investigate their water dynamics in the Capão Xavier region, northwest of IQ. Field work consisted of macroscopic description of ferricretes, infiltration tests and multitemporal electrical resistivity surveys. Two ferricrete typologies were distinguished: structured ferricretes, which are older and occur on top of plateaus, and detrital ferricretes of colluvial-alluvial origin, which were deposited downslope and in topographic lows. The structured ferricretes preserve the medium- to high-angle foliation inherited from the underlying BIFs, whereas the detrital ferricretes constitute thick packs subparallel to the topographic surface and are intercalated with argillaceous layers in areas of karstic depressions. The structured ferricretes are more porous (20.8% to 24.4%) than the detrital ferricretes (14.4% to 17.6%), hence they have higher mean basic infiltration rates (8.3x10-6 m/s) than detrital ferricretes (2.8x10-6 m/s). Despite these low mean basic infiltration rates, infiltration advances thanks to the karstic-fissural porosity (fractures and joints widened by karstification), and superficial cavities that are connected to caves in the interface between the ferricrete and the subjacent, less resistant, transition horizon. Karstification is controlled by the subvertical foliation in the structured ferricretes and subparallel layering in the detrital ferricretes. Some factors that favor infiltration and deep percolation of water are superficial rugosity in structured ferricretes, and karstic depressions in both typologies. The recharge of the Cauê aquifer is diachronic, firstly taking place via the karstic-fissural system and later via the ferricrete matrix. [ABSTRACT FROM AUTHOR]

Geochemical and environmental isotope techniques are successfully applied to understand the origin and evolution of groundwater in aquifers, with the aim of producing consistent conceptual models. In the present study, δ18O, δ2H, and δ13C stable isotope ratios and 14C and 3H levels were used for this purpose. One of the most important aquifer systems in South America, the Amazon Aquifer System (AAS), remains almost entirely unstudied in this aspect. The combination of hydrochemical and isotopic tracers was applied in a pioneer study to foster the understanding of the driving hydrogeological processes in the southwestern portion of the AAS, in the Acre Sedimentary Basin (ASB), northwestern Brazil. The study area comprises three aquifers: from top to bottom of the system, the Quaternary Aquifer, the Içá–Solimões Aquifer (Paleogene/Neogene), and the Tikuna Aquifer (Cretaceous). The aquifers have distinct hydrochemical characteristics, acidic pH and Na–HCO 3 waters in the Quaternary Aquifer, pH ~8 and Ca–HCO 3 and Na–HCO 3 waters in the Içá–Solimões Aquifer, and neutral pH and Ca–HCO 3 waters in the lower Tikuna Aquifer system. Ion exchange processes predominate in all three aquifers, but carbonate dissolution also occurs in some parts of the Içá–Solimões Aquifer. The Içá–Solimões Aquifer shows a geochemical evolution along the regional flow from southwest to northeast. δ18O and δ2H measurements of the groundwater align with the global meteoric water line, without a significant evaporative effect or dispersion. Groundwater from the Içá–Solimões and Tikuna Aquifers is more depleted than the weighted rainfall average (δ2H = −27.9‰ and δ18O = −5.35‰, respectively). The deuterium excess of the local rainfall is approximately +14‰. Residence times, estimated by 14C, range between 13 and 18 ka in the Içá–Solimões Aquifer and reach approximately 6 ka in the Tikuna Aquifer. In addition, tritium concentrations lower than 0.6 TU pointed to the absence of recent waters in the studied aquifers. Local structural and stratigraphic features in the Serra do Divisor area, where asymmetric folding and faulting occur, affect the functioning and features of these aquifer systems, originating from the erosive exposure of deeper and older layers to recent recharge. Thus, geologically older and subjacent aquifer units (Tikuna Aquifer) hold more recently circulating waters than the younger and shallower ones (Içá–Solimões Aquifer). • Acre basin comprises a three-layered sequence aquifer system. • There are two dominant hydrochemical facies: Ca–HCO 3 and Na–HCO 3 types. • Chemical weathering of silicates and ion exchange effects account for water signature. • Older waters flow in geologically younger units due to structural conditioning. • Current study provided new insights on Acre sedimentary basin aquifers. [ABSTRACT FROM AUTHOR]