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Hyperspectral imagery is a promising tool for bathymetric retrieval because that might be more robust than traditional imagery. However, in fluvial sciences, this approach has only been applied to short reaches for which sparse bathymetric information is available and studies extrapolating such models to longer reaches are lacking. In this paper, we use linear regression and random forest (RF) regression to derive bathymetric estimates from hyperspectral data acquired under two different flow conditions: an unmanned aerial vehicle (UAV) acquisition at 27 m3.s−1 (base flow) and an airplane acquisition at 127 m3.s−1 (mean flow) for reaches of 0.35 km and 20 km, respectively. Using a 2D bathymetric model based on a green LiDAR acquisition, we generate calibration and validation data for the 20 km reach and the two flow conditions. First, we show that the airplane dataset is able to retrieve base flow bathymetry with a similar accuracy to the UAV acquisition (5–10 cm) despite having been acquired at a higher discharge. Then, we show that we can extrapolate bathymetric models calibrated on a smaller reach to the 20 km study reach with a loss in accuracy compared to an RF model calibrated on the study reach (20–30 cm vs. 5–10 cm). By analysing the errors from our models, we show that the accuracy of the extrapolated models dropped due to an underprediction of deep pool areas and changes in the optical properties of the water column and substratum across the study reach, with some spectral bands performing more poorly. The better performance of the random forest calibrated on the study reach led us to suggest using multi-band machine learning models when attempting bathymetric predictions over long river corridors, and highlights the need to cover the range of environmental conditions in the target reach when acquiring field data. [ABSTRACT FROM AUTHOR]

This study investigates stress-deformation behavior in Himalayan tunnels, focusing on how geological features impact stability. The objective is to enhance the understanding of displacement phenomena, particularly in tunnels traversing jointed rocks. A modified support system, to specific rock mass classifications, is employed to address the unique challenges posed by geological discontinuities. Kinematic analysis reveals a 20% probability of wedge failure due to these discontinuities. Numerical analysis using Hoek–Brown parameters identifies significant stress concentrations at the tunnel crown, especially in jointed sections, where increased convergence and displacement (1.2 mm at the crown compared to 0.25 mm at the walls) highlight the susceptibility to deformation. The study indicates the critical need for specialized support in jointed regions to mitigate stability risks. Article highlights: This study contributes understanding of complex interactions between geological features and tunnel stability, regarding stress-deformation phenomena in Himalayan tunnels. The analysis identifies significant stability concerns, including a concerning 20% probability of wedge failure and increasing stress levels at the tunnel crown. It underscores the importance of support systems and proactive risk management strategies to mitigate instability risks, particularly in ultramafic sections characterized by higher stresses. The research highlights the importance of considering dynamic loading conditions, validation with field data, and long-term variations in stress and deformation for a comprehensive understanding of tunnel stability. Future investigations should explore the influence of groundwater flow and seismic information, to examining advanced support systems. [ABSTRACT FROM AUTHOR]

Comprehending and measuring heat transfer (HT) mechanisms in groundwater systems is crucial for tackling diverse issues and maximizing the use of subterranean resources while reducing ecological consequences. Groundwater flow is frequently simulated and predicted using mathematical models, such as Darcy's law, which governs the movement of fluids through porous media. Thus, a theoretical analysis of HT is therefore carried out for a time‐independent 3D power‐law (PL) nanofluid (NF) flow on the stretching rotating porous disc near the stagnation region, subject to convective boundary condition, using the MHD, heat source/sink, and thermal radiation effects. A numerical simulation via the Keller Box method is performed using PDEs as the mathematical model for the suggested problem. Investigations are conducted on how several classes of pertinent characteristics affect temperature, velocity, surface drag forces, and HT rate. It has been observed that the radial velocity of the disc increases with an escalation in the permeability of the porous media whereas the azimuthal velocity, however, tends to decrease. Additionally, the rate at which heat is transferred escalates as the radiation and heat source/sink parameter's strength increases whereas it decays along the Prandtl and Biot numbers. Lastly, the present study's results can be applied to understand the thermal impact on seepage of groundwater, geothermal energy extraction, containment systems for landfills and waste, design of subsurface infrastructure, aquifer thermal energy storage, and impact assessment against climate change. [ABSTRACT FROM AUTHOR]

Miami‐Dade County (MDC) has over 112,000 septic systems, some of which are at risk of compromise due to water table rise associated with sea level rise. MDC is surrounded by protected water bodies, including Biscayne Bay, with environmentally sensitive ecosystems and is underlain by highly transmissive karstic limestone. The main objective of the study is to provide first estimates of the locations and magnitudes of septic return flows to discharge endpoints. This is accomplished by leveraging MDC's county‐scale surface‐groundwater model using pathline analysis to estimate the transport and discharge fate of septic system flows under the complex time history of groundwater flow response to pumping, canal management, storms, and other environmental factors. The model covers an area of 4772 km2 in Southeast Florida. Outputs from the model were used to create a 30‐year (2010 to 2040) simulation of the spatial–temporal pathlines from septic input locations to their termination points, allowing us to map flow paths and the spatial distribution of the septic flow discharge endpoints under the simulated conditions. Most septic return flows were discharged to surface water, primarily canals 52,830 m3/d and Biscayne Bay (5696 m3/d), and well fields (14,066 m3/d). Results allow us to identify "hotspots" to guide water quality sampling efforts and to provide recommendations for septic‐to‐sewer conversion areas that should provide most benefit by reducing nutrient loading to water bodies. [ABSTRACT FROM AUTHOR]

Understanding fate and transport processes for per‐ and poly‐fluoroalkyl substances (PFAS) is critical for managing impacted sites. "PFAS Salting Out" in groundwater, defined herein, is an understudied process where PFAS in fresh groundwater mixes with saline groundwater near marine shorelines, which increases sorption of PFAS to aquifer solids. While sorption reduces PFAS mass discharge to marine surface water, the fraction that sorbs to beach sediments may be mobilized under future salinity changes. The objective of this study was to conceptually explore the potential for PFAS Salting Out in sandy beach environments and to perform a preliminary broad‐scale characterization of sandy shoreline areas in the continental U.S. While no site‐specific PFAS data were collected, our conceptual approach involved developing a multivariate regression model that assessed how tidal amplitude and freshwater submarine groundwater discharge affect the mixing of fresh and saline groundwater in sandy coastal aquifers. We then applied this model to 143 U.S. shoreline areas with sandy beaches (21% of total beaches in the USA), indirectly mapping potential salinity increases in shallow freshwater PFAS plumes as low (<10 ppt), medium (10–20 ppt), or high (>20 ppt) along groundwater flow paths before reaching the ocean. Higher potential salinity increases were observed in West Coast bays and the North Atlantic coastline, due to the combination of moderate to large tides and large fresh groundwater discharge rates, while lower increases occurred along the Gulf of Mexico and the southern Florida Atlantic coast. The salinity increases were used to estimate potential perfluorooctane sulfonic acid (PFOS) sorption in groundwater due to salting out processes. Low‐category shorelines may see a 1‐ to 2.5‐fold increase in sorption of PFOS, medium‐category a 2.0‐ to 6.4‐fold increase, and high‐category a 3.8‐ to 25‐fold increase in PFOS sorption. The analysis presented provides a first critical step in developing a large‐scale approach to classify the PFAS Salting Out potential along shorelines and the limitations of the approach adopted highlights important areas for further research. [ABSTRACT FROM AUTHOR]

Seaver, G.A. and Kuzirian, A.M., 2024. Estuary nitrate sources and trends in Buzzards Bay. Journal of Coastal Research, 40(6), 1055–1067. Charlotte (North Carolina), ISSN 0749-0208. The determination of estuary nitrate sources originating through groundwater was the principal objective of this work. This required long timeline (35-year) measurements over many seasonal cycles. Typically, in this study, nitrate sources were an upgradient from estuaries at a significant distance, usually greater than 300 m (1000 ft), whereas groundwater flow that transported the nitrate near the coast in Buzzards Bay, Massachusetts, traveled only 0.45 m/d (1.5 ft/d). Thus, it takes years before a potential newly discovered nitrate source could be confirmed in the estuary. Investigation of estuary nitrate trends and the significance of obtaining winter nitrate measurements to investigations was more fully developed in this work. This showed that determining the estuarian nitrate trends also required a timeline much longer than the variability of the nitrate influx into the estuary. The large, summer-to-winter high nitrate (but not low nitrate) differences and the system's inherent physiological ecology were central to regulating nitrate in an estuary, despite greatly increased groundwater nitrate input. The winter measurement data explained this phenomenon. Finally, the data measurement program completed in Buzzards Bay proved to be ideal in answering these necessarily long timeline questions. The research suggested a new parameter be used to indicate an excess nitrate state of an estuary. These long-term data also allowed meaningful calculations of estuarine and groundwater nitrate and temperature trends. [ABSTRACT FROM AUTHOR]

The dam of Lampy (Black Mountain, Aude, France) is considered as one of the oldest dams in France. A geophysical survey is performed to better understand the pattern of groundwater flow downstream of this dam in the granitic substratum. Induced polarization is first used to image both electrical conductivity and normalized chargeability. Eight core samples of granite from this site are measured and analysed in the laboratory. Their electrical conductivity and normalized chargeability are expressed as a function of the porosity and cation exchange capacity (CEC). The field data and the petrophysical results are used to image the water content, the CEC and the permeability distribution of the substratum. Then, self-potential is used as a complementary passive geophysical technique, which, in absence of metallic bodies, is directly sensitive to groundwater flow through the so-called streaming potential effect. Indeed, the excess of electrical charges in the vicinity of the solid grains, in the so-called double layer, is dragged by the ground water flow generating in turn an electrical (streaming) current and therefore an electrical field. A map of the resulting self-potential signals is done over the area covered by the induced polarization profiles. This map shows a large positive anomaly with an amplitude of ∼80 mV possibly associated with upwelling groundwater in an area where the soil is water-saturated. A groundwater flow simulation is performed to model this anomaly. This is done in two steps. A preliminary groundwater flow model is built using the permeability and water content distributions obtained from the induced polarization data. Then, this groundwater flow model is updated using the information contained in the self-potential data including the electrical conductivity distribution obtained through resistivity tomography. The algorithm for the inversion of the self-potential data is validated through a 2-D numerical test. This analysis yields a groundwater flow model with the flow being focused through a high permeability zone. This study shows how three geoelectrical methods (self-potential, induced polarization and electrical resistivity) can be efficiently combined to image groundwater flow in the vicinity of a dam. [ABSTRACT FROM AUTHOR]

Groundwater discharges from Silurian bedrock exposures at the Niagara Escarpment have been documented using photography. It is demonstrated that patterns of groundwater discharges are best discernible from ice formation during sub-zero winter conditions. The photographs indicate that discharges at natural exposures tend to follow hydrostratigraphic boundaries, with point seeps indicating channelized preferential flow. At anthropogenic exposures, the groundwater discharges appear more closely related to the actual exposure morphology with vertical fracturing causing vertical flow and bypass of acquitards, as well as aquifers with groundwater discharge occurring at local topographical lows. The associated seeps at anthropogenic exposures may approximate planar preferential horizontal flow horizons if competent beds are encountered. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present study focuses on a site contaminated with halogenated hydrocarbons, utilizing a detailed inventory of contamination data to achieve the precise characterization of groundwater pollution. Employing MOFLOW-2000 software, a groundwater flow model was established for the study area. In conjunction with MT3DMS, a predictive model was constructed to simulate and forecast the spatiotemporal distribution of contaminant migration and attenuation following site remediation. The simulation area was delineated based on geographical features, with the vertical simulation range of strata also determined. To establish a hydrogeological conceptual model for the target remediation site, comprehensive hydrogeological data were collected, encompassing geological structures, hydrological parameters, and rainfall information. Model calibration was based on the six layers of low-permeability aquifer intervals revealed by geological exploration wells MW1–5, as well as the distribution of groundwater-level contours and rainfall data. Based on data from September 2010, an initial three-dimensional model of tetrachloroethylene (PCE) distribution was generated. Subsequently, a solute transport model for PCE was established, incorporating various enhanced reductive dechlorination (ERD) remediation strategies applied at different times and locations. Calibration against actual monitoring data revealed the presence of unmonitored dense non-aqueous phase liquids (DNAPLs) at the site, contributing to the continuous release and elevation of PCE concentrations. By accounting for DNAPL release, the calibrated transport and attenuation model closely matched observed concentration decay patterns, effectively capturing the actual dynamics of contaminant transport and attenuation within the groundwater system. The modeling approach proposed in this study provides important support for contamination remediation and attenuation at the current site, and it is also applicable to simulating and predicting pollution scenarios at similar sites. [ABSTRACT FROM AUTHOR]

Two gravel pit lakes in central Texas were examined over the course of two years with upgradient and downgradient piezometer installations. Groundwater and lake water were sampled bimonthly for nutrients, water levels, and groundwater chemistry, and in addition, rain and lake gauges and mini-piezometers were installed, depth surveys were conducted, and a simple 2D flow model was constructed. The project goal was evaluating and examining flow dynamics and chemical effects as groundwater flows to surface water and back to groundwater with the intent to understand the effects that gravel pit lake systems have on connected shallow groundwater. Both lake systems were shown to be flow-through systems that influence the water quality by decreasing the dissolved nutrients in the groundwater in their vicinity while oxygenating the water and altering the pH. However, the lakes are also prone to high levels of evaporation, meaning that minor improvements to water quality come at the cost of decreasing the quantity of water in storage within the aquifer. Similar groundwater and mine lake systems may show comparable tendencies, providing new information for water managers, regulators, and stake-holders about the potential roles that non-remediated gravel pit lakes may play in local ecosystems and aquifer dynamics. [ABSTRACT FROM AUTHOR]

Lateral groundwater flow (LGF) is an important hydrologic process in controlling water table dynamics. Due to the relatively coarse spatial resolutions of land surface models, the representation of this process is often overlooked or overly simplified. In this study, we developed a hillslope-based lateral groundwater flow model. Specifically, we first developed a hillslope definition model based on an existing watershed delineation model to represent the subgrid spatial variability in topography. Building upon this hillslope definition, we then developed a physical-based lateral groundwater flow using Darcy's equation. This model explicitly considers the relationships between the groundwater table along the hillslope and the river water table levels. We coupled this intra-grid model to the land component (ELM) and river component (MOSART) of the Energy Exascale Earth System Model (E3SM). We tested both the hillslope definition model and the lateral groundwater flow model and performed sensitivity experiments using different configurations. Simulations for a single grid cell at 0.5° × 0.5° within the Amazon basin show that the definition of hillslope is the key to modeling lateral flow processes and the runoff partition between surface and subsurface can be dramatically changed using the hillslope approach. Although our method provides a pathway to improve the lateral flow process, future improvements are needed to better capture the subgrid structure to account for the spatial variability in hillslopes within the simulated grid of land surface models. [ABSTRACT FROM AUTHOR]

Estimating the temporal and spatial patterns of recharge is crucial in Jedeb Watershed, which has shallow aquifers, a proliferation of wells, and limited observations. This paper uses the WetSpass-MODFLOW coupling to evaluate the groundwater recharge in the Jedeb watershed. The ArcGIS tool is used to build grid maps that contain the input data for the WetSpass-M model. These findings are then used to simulate the hydraulic head distribution in the groundwater flow simulation program MODFLOW. WetSpass-M calculated that the long-term spatial and temporal average annual precipitation of 1394 mm is distributed as 99 mm (7.1%) groundwater recharge and 722 mm (51.79%) surface runoff, while 574 mm (41.11%) is lost through evapotranspiration. With such seasonal variations, the groundwater level due to the annual stress period varied from 2164.2 to 2213.1 m. The findings could serve as a benchmark for future research by academics, policymakers, and specialists in regional water resources. [ABSTRACT FROM AUTHOR]

This study enhances the understanding of riverbank filtration and improves management of the Mississippi River valley alluvial (MRVA) aquifer during a managed aquifer recharge (MAR) pilot project at Shellmound, MS. Using high‐resolution electrical resistivity tomography (ERT) and self‐potential (SP) geophysical methods, we characterized the heterogeneous MRVA aquifer and monitored groundwater flow near a pumping well. ERT was used to provide detailed spatial characterization, filling gaps left by airborne electromagnetic (AEM) data and soil boring logs, while SP techniques were used to monitor groundwater flow, predict drawdown trends, and investigate surface‐groundwater interactions. Results showed that SP signals were influenced by groundwater flow, river infiltration, and water mixing due to pumping disturbance of natural geochemical stratification, with significant river interaction observed after 1 h of pumping. The integration of ERT and SP methods revealed lithologic heterogeneity, explaining greater drawdowns on the northern side of the well and increased flow from the riverside. This comprehensive approach offers valuable insights into aquifer management and sustainability. [ABSTRACT FROM AUTHOR]

Using the US Geological Survey groundwater model, we compared spatial distribution, flow exchange, and storage of groundwater between cropland and forestland in the Upper Yazoo River Watershed, Mississippi, from 1900 to 2014. Under normal climate, average groundwater head declined 2.7 m in cropland but only 1 m in forestland over the 115 years. The average groundwater flow from forestland to cropland surpassed the reverse flow by a factor of 238, owing to a higher elevation in forestland and intensive groundwater pumping in cropland. Cropland was a net groundwater sink while forestland was a net groundwater source under all climates. Our findings underscore the discernible impacts of climate changes on groundwater storage and suggest that afforestation in the region would be an alternative for saving groundwater resources and supplying more waters to croplands. This study offers valuable insights into groundwater supply planning not only in Mississippi but also in comparable situations worldwide. [ABSTRACT FROM AUTHOR]

Soil moisture plays a key role in soil nutrient and carbon cycling; plant productivity; and energy, water, and greenhouse gas exchanges between the land and the atmosphere. The knowledge on drivers of spatiotemporal soil moisture dynamics in subarctic landscapes is limited. In this study, we used the Spatial Forest Hydrology (SpaFHy) model, in situ soil moisture data, and Sentinel-1 synthetic aperture radar (SAR)-based soil moisture estimates to explore spatiotemporal controls of soil moisture in a subarctic headwater catchment in northwestern Finland. The role of groundwater dynamics and lateral flow in soil moisture was studied through three groundwater model conceptualizations: (i) omission of groundwater storage and lateral flow, (ii) conceptual TOPMODEL approach based on topographic wetness index, and (iii) explicit 2D lateral groundwater flow. The model simulations were compared against continuous point soil moisture measurements, distributed manual measurements, and novel SAR-based soil moisture estimates available at high spatial and temporal resolutions. Based on model scenarios and model–data comparisons, we assessed when and where the lateral groundwater flow shapes shallow soil moisture and under which conditions soil moisture variability is driven more by local ecohydrology, i.e., the balance of infiltration, drainage, and evapotranspiration. The choice of groundwater flow model was shown to have a strong impact on modeled soil moisture dynamics within the catchment. All model conceptualizations captured the observed soil moisture dynamics in the upland forests, but accounting for the lateral groundwater flow was necessary to reproduce the saturated conditions common in the peatlands and occasionally in lowland forest grid cells. We further highlight the potential of integrating multi-scale observations with land surface and hydrological models. The results have implications for ecohydrological and biogeochemical processes, as well as for modeling hydrology and Earth system feedbacks in subarctic and boreal environments. [ABSTRACT FROM AUTHOR]

The Main Karoo Basin in South Africa is a typical example of an expanding arid region dependent on groundwater resources. Dolerite dikes in the region, analogous to dolerite dikes worldwide, are known to influence subsurface groundwater flow and spatially relate to high-yielding boreholes. Here, the effect of dolerite dikes on groundwater flow is remotely assessed using the Modified Soil Adjusted Vegetation Index derived from high-resolution multi-spectral satellite imagery. From imagery collected during the wet and dry seasons of 2018 and 2021, two aquifer models relating to 505 dikes were identified; (1) barrier-controlled aquifers are induced by ~ 56% of dikes, (2) fractured aquifers are induced by ~ 35% of dikes. Surficial areas overlying aquifers are also shown to sustain vegetation growth through dry seasons. This research demonstrates the efficacy of vegetation indices to rapidly characterise dike-related aquifer models and their seasonal sustainability, critical for effective groundwater exploration and management. [ABSTRACT FROM AUTHOR]

Methods and instrumentation for measuring grout quality in heat pump boreholes, including the measurement of groundwater flow through boreholes outside partly grouted borehole exchanger pipes, have been developed in the Czech Republic. A Semtex charge has also been developed to repair rock massifs, which reliably disconnects borehole exchanger pipes without severely harming the surrounding rock environment or buildings. The resulting hole can then be used for regrouting, thus preventing undesirable vertical water flow through the borehole. [ABSTRACT FROM AUTHOR]

In this paper, optimal growth analysis of spatial disturbances in round submerged jets is performed. Optimal energy growth is studied for various Reynolds numbers Re and frequencies ω. Different velocity profiles proposed by Michalke ["Survey on jet instability theory," Prog. Aerosp. Sci. 21, 159–199 (1984)] are investigated by varying the shear layer momentum thickness δ, while the jet radius R is considered fixed (as characteristic length). In the case of stationary disturbances, there are no amplified eigenmodes, so eventually the energy of such disturbances decays downstream. Such disturbances are characterized by optimal energy growth as a function of streamwise coordinate z. At certain location downstream zmax this value reaches its maximum Gmax and then decays, although not monotonically, unlike the result of the temporary setting [Jimenez-Gonzalez et al., "Modal and non-modal evolution of perturbations for parallel round jets," Phys. Fluids 27, 044105 (2015); Jimenez-Gonzalez and Brancher, "Transient energy growth of optimal streaks in parallel round jets," Phys. Fluids 29, 114101 (2017)]. The well-known scaling G max ∝ Re 2 and z max ∝ Re is confirmed for stationary disturbances. Conversely, for nonstationary disturbances there is a range of frequencies in which an amplified mode is present. In this case, optimal perturbations far downstream consist only of the amplified mode. The main effect of non-modality here is "the energy pumping" of the amplified mode, so the disturbances are characterized by the "energy ratio" G / E m , i.e., the ratio of the energy of an arbitrary perturbation to the energy of the amplified mode. The influence of the shear layer momentum thickness on optimal disturbances is studied; increasing the shear layer momentum thickness of the base flow "smears" the area occupied by the optimal disturbance, although it does not dramatically affect energy gain values, slightly decreasing maximum energy as shear layer momentum thickness increases. Spatial oscillations in the energy of stationary optimal disturbances in jet flows are discovered. The spectrum structure examination shows that the frequency of these oscillations corresponds to the frequencies of the two least damped discrete eigenmodes. [ABSTRACT FROM AUTHOR]

Earthquakes can produce rock damage, poroelastic deformation, and ground shaking that modify fault zone hydrogeologic properties. Coseismic and postseismic hydrologic response to the ruptured fault can serve as constraints on hydrogeologic property changes. Here, we document fluid pressure responses to the 2018 M6.3 Hualien, Taiwan earthquake and model the postseismic fault zone hydrology inferred from very‐near‐fault data. Two groundwater wells located ∼180–250 m from the fault damage zone experienced 10–15 m of groundwater level decline followed by a prolonged (>6 months) recovery. Poroelastic models indicate that strain dilation in the fault's hanging wall can produce water level reductions of several meters. However, the model cannot explain groundwater level change in the footwall nor the delayed postseismic recovery, suggesting fault zone damage played a primary role in both the coseismic and postseismic water level reductions. Fluid flow models incorporating the effects of coseismic fault damage on the temporal evolution of hydrologic fault properties show enhanced hydraulic anisotropy after the earthquake. The best‐fit models show that while both vertical hydraulic conductivity and specific storage likely increased within the fault zone, the horizontal hydraulic conductivity is low, suggesting the fault zone behaves as a hydraulic barrier to cross‐fault flow with modeled diffusivities as low as ∼10−3 m2/s. High‐fidelity hydrologic measurements in the very‐near‐field of fault zones (e.g., within a few hundred meters) may be a useful tool to constrain the spatial and temporal evolution of fault zone properties before, during, and after rupture. Plain Language Summary: Earthquakes damage rock in fault zones. Fractured fault zones allow vertical flow of groundwater. Furthermore, space in the newly created fractures can store more water, which lowers groundwater pressure. Damage in fault zones can also create a barrier to horizontal groundwater flow in aquifers. In this study, we analyzed groundwater response to the 2018 magnitude 6.3 Hualien earthquake in Taiwan. The data were collected close (0.18–2.3 km) to the ruptured fault trace, allowing us to closely observe the groundwater level response to changes in fault zone structure. We found that all the groundwater levels lowered by several meters, with the two sites closest to the fault lowering at least 10 m. Over the next several months, groundwater levels gradually recovered to those before the earthquake. The observations suggest that the fault zone behaves as a barrier for fault‐crossing groundwater flow after the earthquake. Near‐fault hydrologic observations help us understand the pressure state in the fault zone, as well as structure changes after earthquake rupture. Those pressure changes affect tectonic stresses and impact groundwater resources. Key Points: Large coseismic water level declines (>10 m) were observed within ∼250 m of the 2018 M6.3 Hualien, Taiwan earthquakeCalibrated fluid flow models and water level changes support a coseismic pressure drop in the fault zone and decreased cross‐fault flowSpatial heterogeneity in fault zone hydrology may be inferred from the distinct postseismic water level recovery near the fault [ABSTRACT FROM AUTHOR]

Brook Trout (Salvelinus fontinalis) populations have experienced marked declines throughout their native range and are presently threatened due to isolation in small habitat fragments, land use changes, and climate change. The existence of numerous, spatially distinct populations poses substantial challenges for monitoring population status (e.g., abundance, recruitment, or occupancy). Genetic monitoring with estimates of effective number of breeders (Nb) provides a potentially powerful metric to complement existing population monitoring, assessment, and prioritization. We estimated Nb for 71 Brook Trout habitat units in mid‐Atlantic region of the United States and obtained a mean Nb of 73.2 (range 6.90–493). Our modeling approach tested whether Nb estimates were sensitive to differences in habitat size, presence of non‐native salmonids, base flow index, temperature, acidic precipitation, and indices of anthropogenic disturbance. We found significant support for three of our hypotheses including the positive influences of available habitat and base flow index and negative effect of temperature. Our results are consistent with presently observed and predicted future impacts of climate change on populations of this cold‐water fish. Importantly, these findings support the use of Nb in population assessments as an index of relative population status. [ABSTRACT FROM AUTHOR]

Over-exploitation of groundwater in arid and semi-arid regions requires an understanding of dynamics for effective management strategies. This study uses an artificial neural network (ANN) to predict groundwater levels using initial water level, pumping, and hydrological and meteorological input variables. A sensitivity analysis assessed predictors' impact on accurate groundwater level prediction. The accuracy of predictions by the ANN model was examined through different performance evaluation criteria and the result achieved is satisfactory as compared to reasonable statistical indicator values. A comparison of results simulated by the ANN model and numerical groundwater flow model (MODFLOW) was carried out and it was found that the prediction of the ANN model was consistently superior to that of the numerical model. Therefore, data-driven models such as ANN can provide better predictions of groundwater level that will aid in groundwater resource management. [ABSTRACT FROM AUTHOR]

Resolvent analysis is a powerful tool that can reveal the linear amplification mechanisms between the forcing inputs and the response outputs about a base flow. These mechanisms can be revealed in terms of a pair of forcing and response modes and the associated energy gains (amplification magnitude) at a given frequency. The linear relationship that ties the forcing and the response is represented through the resolvent operator (transfer function), which is constructed through spatially discretizing the linearized Navier–Stokes operator. One of the unique strengths of resolvent analysis is its ability to analyze statistically stationary turbulent flows. In light of the increasing interest in using resolvent analysis to study a variety of flows, we offer this guide in hopes of removing the hurdle for students and researchers to initiate the development of a resolvent analysis code and its applications to their problems of interest. To achieve this goal, we discuss various aspects of resolvent analysis and its role in identifying dominant flow structures about the base flow. The discussion in this paper revolves around the compressible Navier–Stokes equations in the most general manner. We cover essential considerations ranging from selecting the base flow and appropriate energy norms to the intricacies of constructing the linear operator and performing eigenvalue and singular value decompositions. Throughout the paper, we offer details and know-how that may not be available to readers in a collective manner elsewhere. Towards the end of this paper, examples are offered to demonstrate the practical applicability of resolvent analysis, aiming to guide readers through its implementation and inspire further extensions. We invite readers to consider resolvent analysis as a companion for their research endeavors. [ABSTRACT FROM AUTHOR]

The Arborea plain in Sardinia (Italy) is classified as a nitrate vulnerable zone (NVZ). In the present study, the individual work steps that are necessary to progress from the existing 3D hydrogeological model to a 3D numerical groundwater model using the interactive finite-element simulation system FEFLOW 7.4 are shown. The results of the transient flow model highlight the influence of the drainage network on the overall groundwater management: the total water volume drained by the ditches accounted for approximately 58% of the annual outflow volume. The numerical transport simulations conducted from 2012 to 2020 using hypothetical field-based nitrate input scenarios globally underestimated the high concentrations that were observed in the NVZ. However, as observed in the field, the computed nitrate concentrations in December 2020 still varied strongly in space, from several mg L−1 to several hundreds of mg L−1. The origin of these remaining local hotspots is not yet known. The modeling of rainfall fluctuations under the influence of climate change revealed a general long-term decline in the groundwater level of several tens of centimeters in the long term and, in conjunction with a zero-nitrate scenario, led to a significant decrease in nitrate pollution. Although hotspots were attenuated, the concentrations at several monitoring wells still exceeded the limit value of 50 mg L−1. [ABSTRACT FROM AUTHOR]

There are many situations where groundwater flow has high flow rates, causing large seepage forces. Examples are flows around highly conductive fractures and tunnels. We present a new analytic element for a tunnel in an elastic medium. We combined the analytic element method for groundwater flow with that for linear elasticity, and include the seepage force as a body force in the linearly elastic model. We represent tunnels and fractures as analytic elements. The solution for the case considered is limited to steady state flow and fluid-to-solid coupling. We present examples of the computed seepage forces around a tunnel and a fracture as well as a comparison with another numerical model. [ABSTRACT FROM AUTHOR]

Natural radiogenic isotopes (primarily 87Sr/86Sr) from hot springs in the Upper Geyser Basin of the Yellowstone Plateau volcanic field and associated rocks were used to evaluate groundwater flow patterns, water‐rock reactions, and the extent of mixing between various groundwater sources. Thermal waters have very low uranium concentrations and 234U/238U activity ratios near 1.0, which limit their utility as tracers in this reducing setting. Thermal waters have higher Sr concentrations (<22 ng/g) and a wide range of 87Sr/86Sr values that vary both temporally at individual discharge sites and between adjacent springs, indicating that conduits tap different subsurface reservoirs to varying degrees. Sr from local rhyolites have 87Sr/86Sr compositions that bound the range of values observed in groundwater throughout the basin. Non‐boiling springs on the west flank of the basin discharge water with low 87Sr/86Sr consistent with flow through young volcanic rocks exposed at the surface. Boiling springs in the central basin have higher 87Sr/86Sr values reflecting interactions with older, more radiogenic volcanic rocks. Variability in upwelling thermal waters requires mixing with a low 87Sr/86Sr component derived from young lava or glacial sediments, or more likely, from deeper sources of hot groundwater circulating through buried Lava Creek Tuff having intermediate 87Sr/86Sr. Isotope data constrain basin‐wide output of thermal water to 110–140 kg·s−1. Results underscore the utility of radiogenic Sr isotopes as valuable tracers of hydrothermal flow patterns and improve the understanding of temperature‐dependent water‐rock reactions in one of the largest continental hydrothermal systems on Earth. Plain Language Summary: Radiogenic isotopes of strontium (87Sr/86Sr) vary widely in rocks and the waters that interact with them. We use 87Sr/86Sr in waters from hot springs in the Upper Geyser Basin of the Yellowstone Plateau volcanic field to help define patterns of groundwater flow through subsurface volcanic rocks. Lava flows and tuffs adjacent to and underlying the basin have different 87Sr/86Sr compositions reflecting different crustal and mantle components incorporated during rhyolite generation. Groundwater interacting with those rocks inherits their 87Sr/86Sr signature, which can then be used to trace subsurface flowpaths. Modern and past hot springs along the basin margin discharge water having low 87Sr/86Sr values that indicate groundwater was restricted to shallow flowpaths through younger volcanic rocks. Hot springs in the central basin have compositions reflecting mixing between groundwater flowing through deeper and older, high‐87Sr/86Sr volcanic rocks and groundwater having lower 87Sr/86Sr values. The low‐87Sr/86Sr component could be derived from shallow sources (young volcanic rocks or glacial sediments) or from more‐deeply buried tuff associated with the most recent collapse of the Yellowstone caldera. The data presented here provide a means of tracing hydrothermal flow patterns in complex volcanic environments and improve the understanding of hydrothermal activity in one of the largest active continental magmatic systems on Earth. Key Points: Water from hot springs in the Upper Geyser Basin has 87Sr/86Sr derived from volcanic rocks flanking and underlying the basinVariable 87Sr/86Sr in water from springs in proximity and over time reflect mixing between groundwater in distinct rock reservoirsReducing conditions along flowpaths yield groundwater with low U concentrations and 234U/238U activities near 1.0 [ABSTRACT FROM AUTHOR]

Various hydrogeological problems like groundwater inflow, water table drawdown, and water pressure redistribution may be encountered in the construction of hydraulic projects. How to accurately predict the occurrence of groundwater inflow and assess the drainage effect during construction are still challenging problems for engineering designers. Taking the Jinzhai pumped storage power station (JPSPS) of China as an example, this paper aims to use different methods to calculate the water inflow rates of an underground powerhouse and evaluate the drainage effect caused by tunnel inflow during construction. The methods consist of the analytical formulas, the site groundwater rating (SGR) method, and the Signorini type variational inequality formulation. The results show that the analytical methods considering stable water table may overestimate the water inflow rates of caverns in drained conditions, whereas the SGR method with available hydro-geological parameters obtains a qualitative hazard assessment in the preliminary phase. The numerical solutions provide more precise and reliable values of groundwater inflow considering complex geological structures and seepage control measures. Moreover, the drainage effects, including a seepage-free surface, pore water pressure redistribution, and hydraulic gradient, have been accurately evaluated using various numerical synthetic cases. Specifically, the faults intersecting on underground caverns and drainage structures significantly change the groundwater flow regime around caverns. This comparative study can not only exactly identify the capabilities of the methods for cavern inflow in drained conditions, but also can comprehensively evaluate the drainage effect during cavern construction. [ABSTRACT FROM AUTHOR]

To ascertain the effects of conventional hydrochemical components on the presence of endogenous fine loess particles (EFLPs) in groundwater over loess regions, Na+, NO3− and Cu2+, as conventional hydrochemical components, were employed in batch tests with EFLPs from a typical loess as aquifer media in Guanzhong Plain, China. The results showed that EFLPs had high zeta potential (ζ) and remained suspended over 40 h, indicating their good dispersity and potential to be suspended in groundwater. ζ was employed to replace electrostatic repulsion in the DLVO equation to determine the critical coagulation concentrations for Cu(NO3)2 and NaF as 0.1 mmol/L and 50 mmol/L for 1.1 µm D50 EFLPs, which were almost consistent with the batch test results and greater than those in the groundwater, respectively, further implying that EFLPs are likely to be suspended in groundwater. The multi-factor tests showed that the key factors including particle size, hydro-chemical component and concentration interacted with each other and their relative magnitudes varied in the test processes, where the effects of concentration strengthened while those of the component weakened. So, hydrogeochemical conditions were beneficial to the suspension of EFLPs and the benefit got strong along the groundwater flow path, which is conducive to the cotransport of EFLPs with pollutants in groundwater over loess regions. [ABSTRACT FROM AUTHOR]

We present a new analytical solution to study the mechanical coupling on tidal‐induced head fluctuations in a coastal aquifer system. The conceptual model consists of two overlying confined units that extend infinitely under the sea. The proposed model assumes that the tidal fluctuations in the overlying aquifer are described by the classical equation derived by van der Kamp. For the underlying aquifer, a closed form analytical expression is derived by solving a boundary value problem that considers the loading effect produced by the overlying unit. The amplitude and phase lag of the underlying aquifer depend on both the specific storage and the thickness of the overlying unit. A parametric study shows that the mechanical coupling effect can be important for both large values of specific storage and thickness of the overlying aquifer. [ABSTRACT FROM AUTHOR]

Inverse problems aim at determining model parameters that produce observed data to subsequently understand, predict or manage hydrological or other environmental systems. While statistical inversion is especially popular, its sampling‐based nature often inhibits its application to computationally costly models, which has compromised the use of the Generalized Likelihood Uncertainty Estimation (GLUE) methodology, for example, for spatially distributed (partial) differential equation based models. In this study we introduce multilevel GLUE (MLGLUE), which alleviates the computational burden of statistical inversion by utilizing a hierarchy of model resolutions. Inspired by multilevel Monte Carlo, most parameter samples are evaluated on lower levels with computationally cheap low‐resolution models and only samples associated with a likelihood above a certain threshold are subsequently passed to higher levels with costly high‐resolution models for evaluation. Inferences are made at the level of the highest‐resolution model but substantial computational savings are achieved by discarding samples with low likelihood already on levels with low resolution and low computational cost. Two example inverse problems, using a rainfall‐runoff model and groundwater flow model, demonstrate the substantially increased computational efficiency of MLGLUE compared to GLUE as well as the similarity of inversion results. Findings are furthermore compared to inversion results from Markov‐chain Monte Carlo (MCMC) and multilevel delayed acceptance MCMC, a corresponding multilevel variant, to compare the effects of the multilevel extension. All examples demonstrate the wide‐range suitability of the approach and include guidelines for practical applications. Key Points: We extend the Generalized Likelihood Uncertainty Estimation methodology to a strategy that considers multiple resolution levels (MLGLUE)We demonstrate the acceleration with MLGLUE for different spatial (groundwater flow model) and temporal (rainfall‐runoff model) resolutionsWe show that inversion results from multilevel and conventional methods align and discuss factors affecting computational efficiency [ABSTRACT FROM AUTHOR]

This study develops two new analytical models for constant rate pumping at a partially penetrating well in a double‐porosity confined aquifer, considering skin and formation zones. One model, referred to as the two‐zone model, incorporates a flow equation to depict the flow in the skin around the well. The other model, named the source‐term model, introduces a novel source term at the outer rim of the skin to reflect the effects of both the skin and wellbore storage. The analytical solutions for both models are derived by the Laplace transform and finite Fourier cosine transform. Additionally, a finite element solution for the source‐term model is presented. Results suggest the source‐term model is suitable to most wells when the width of the skin is less than 1 m and the radius of influence exceeds the outer rim of the skin. Temporal drawdown distribution for a negative skin exhibits a triple‐humped shape with two flat stages, while that for a positive skin shows monotonous increase. The source‐term model enables orthogonal 5 × 5 nodes for finite element approximation to discretize a well and its adjacent skin. The finite element solution aligns with early drawdown data measured at an observation well under the effects observed in two field constant rate pumping tests. In conclusion, this study introduces a novel approach to modeling two‐zone flow, which may find practical utility in field applications. Plain Language Summary: Numerical modeling experts always say finely discretizing space as many nodes achieves accurate simulation of groundwater flow in aquifers. However, it takes unnecessary addition to computational cost with applying a large number of orthogonal nodes to discretize the circular rim of a well and the ring‐shaped skin zone around the well. The radius rw of a well is usually 0.1 m. The inner radius of the skin zone equals rw; the other outer radius rs usually falls in 1 m. Our example demonstrates the number of the orthogonal nodes is about 600 if rw = 0.1 m, rs = 1 m, and the well rim is discretized as four nodes, but the prediction of a conventional model is incorrect. This study introduces a new groundwater flow model. The model allows orthogonal 5 × 5 nodes to discretize a well rim and its surrounding skin zone, which is practical at low computational cost. This new model is applied to two field constant‐rate pumping tests in which a well extracts groundwater with a constant volumetric rate. Results suggest the predicted water level by the new model approaches the measured water level in the tests. The model may serve as a useful alternative for groundwater pumping and simulations. Key Points: Two novel analytical models are proposed for flow due to constant rate pumping at a two‐zone double‐porosity confined aquiferOne model named as two‐zone model is built by applying flow equations to both skin and formation zonesA new source term is introduced in the other model, called as source‐term model, to reflect the effects of the skin and wellbore storage [ABSTRACT FROM AUTHOR]

As the Brahmaputra is a transboundary river, the availability of river flow and hydrometeorological data is less in the public domain for the Brahmaputra river basin. Hence, estimation of water balance is difficult for the basin. However, the basin is one of the major populated basins in India and Bangladesh. With the increase in anthropogenic activities, climate change, etc., a proper hydrological and hydraulic study of the basin is essential. Total drainable water storage (TDWS) is one of the fundamental hydrological quantities of a basin that accounts for the long-term average water stored in a basin. In this study, the TDWS of the Brahmaputra basin is estimated. For an ungauged and giant river such as Brahmaputra, where frequent hydrological surveys are not possible, the estimation of TDWS using satellite-based data is highly beneficial and cost-effective. The estimation of TDWS is based on the assumption that storage and discharge have a linear relationship. First, the historical daily discharge data is used to assess the river basin's base flow parameters (recession constant and base flow index). When passed through Eckhardt's digital filter, these parameters and the monthly discharge data give the base flow time series for the basin. From the linear relationship between base flow and the gravity recovery and climate experiment's (GRACE) total water storage anomaly, TDWS for the Brahmaputra basin is estimated. Here in the study, the TDWS is obtained by considering Pandu, Guwahati, as the outlet point for the river catchment. [ABSTRACT FROM AUTHOR]

This case study documents the morphogenesis of a new karstic landform consisting of a calcareous tufa mound with a gypsum caprock that developed at La Saline Lake, an oxbow of the Athabasca River in northeast Alberta, Canada. The development of this novel tiered carbonate‐sulphate mound architecture resulted from emplacement above the largest known buried salt dissolution collapse‐subsidence karst system, which was superimposed by an overlying buried carbonate karst. Dissolution of halite‐anhydrite beds of the Middle Devonian Prairie Evaporite, 200 m below, resulted in extensive subsidence and brecciation of the overlying Upper Devonian carbonate karst. The development of the calcareous tufa mound resulted from meteoric‐driven groundwater mixed with glacial meltwater directed along the shallowly buried karstic carbonate terrain of Middle‐Upper Devonian limestone, which floors the McMurray Formation, the main reservoir unit of the Lower Cretaceous Athabasca Oil Sands. The flow of the carbonate‐saturated groundwater responsible for the emplacement of the tufa mound at the surface was abruptly redirected along a deeper pathway in response to dissolution collapse‐subsidence adjustments within the buried salt karst of the Prairie Evaporite. The redirected groundwater flow deeper encountered an anhydrite‐dominated segment of the salt dissolution trend within the Prairie Evaporite Formation, 200 m below. The migration up‐section of sulphate‐saturated brine onto the surface of the previously formed tufa mound resulted in the emplacement of a gypsum caprock as a new landform. [ABSTRACT FROM AUTHOR]

Groundwater contaminant transport problems remain challenging with respect to their computing requirements. Thus, it often limits the exploration of conceptual uncertainty, that is mainly related to large scale structural features and due to limited characterization. Here, to facilitate geological conceptual uncertainty exploration, we develop further the use of graph representation for geological models to approximate groundwater flow and transport. We consider a faulted multi-heterogeneous-layer medium to test our approach. The existing rank correlation between shortest path distribution from a contaminant source to the model domain outlet and cumulative mass distribution at the outlet enables to perform scenario selection. The scenario selection approach relies on a metric combining the Jaccard dissimilarity and the Wasserstein distance to compare binary images. Among a set combining eight alternative scenarios, where three faults can either act as a flow barrier or a preferential path, we show that the use of graph-approximations allows to retain or reject scenarios with confidence as well as to estimate the individual probability of a fault to act as a barrier or a path. This methodology framework opens up possibilities to explore more thoroughly conceptual geological uncertainty for processes affected by flow and transport. [ABSTRACT FROM AUTHOR]

The ex-situ treatment of arsenic is widely adopted; however, there are emerging concerns related to system maintenance, material replacement, and waste generation. There is a scope to explore in-situ arsenite [As (III)] remediation in the aquifers. The main objective of this study is to evaluate the performance of in-situ synthesised FeS in immobilising As (III) in the natural groundwater when transported through a three-dimensional (3-D) porous media system. In this study, a 3-D tank of 0.50 m × 0.30 m × 0.30 m (L × W × H) was packed with natural sand to represent the subsurface porous media system. The homogeneous packing and uniform flow were ensured before synthesising FeS in-situ, where a total of 1.5 pore volumes (PVs) of 20 mM sodium sulfide (Na2S) and 20 mM ferrous sulfate (FeSO4) reagent solutions were injected alternatively into the pre-saturated porous media. Finally, 300 ± 15 μg/L of As (III) spiked natural groundwater was passed through the porous media, and the samples were collected through several sampling ports for analysing for total As and Fe. The result suggests that the concentration of As (III) reaches below 11 μg/L within 644 min (4 PVs) of injection of reagents. Furthermore, almost 88.4% of As (III) get immobilised after passing 31 PVs of contaminated water. In brief, almost 406 L of As contaminated groundwater can be treated by injecting 21 L of reagents with a reagent-to-treated water ratio of 1:20. [ABSTRACT FROM AUTHOR]

Hydrological Ecosystem Services (HES) are crucial components of environmental sustainability and provide indispensable benefits. The present study identifies critical hot and cold spots areas of HES in the Aglar watershed of the Indian Himalayan Region using six HES descriptors, namely water yield (WYLD), crop yield factor (CYF), sediment yield (SYLD), base flow (LATQ), surface runoff (SURFQ), and total water retention (TWR). The analysis was conducted using weightage-based approaches under two methods: (1) evaluating six HES descriptors individually and (2) grouping them into broad ecosystem service categories. Furthermore, the study assessed pixel-level uncertainties that arose because of the distinctive methods used in the identification of hot and cold spots. The associated synergies and trade-offs among HES descriptors were examined too. From method 1, 0.26% area of the watershed was classified as cold spots and 3.18% as hot spots, whereas method 2 classified 2.42% area as cold spots and 2.36% as hot spots. Pixel-level uncertainties showed that 0.57 km2 and 6.86 km2 of the watershed were consistently under cold and hot spots, respectively, using method 1, whereas method 2 identified 2.30 km2 and 6.97 km2 as cold spots and hot spots, respectively. The spatial analysis of hot spots showed consistent patterns in certain parts of the watershed, primarily in the south to southwest region, while cold spots were mainly found on the eastern side. Upon analyzing HES descriptors within broad ecosystem service categories, hot spots were mainly in the southern part, and cold spots were scattered throughout the watershed, especially in agricultural and scrubland areas. The significant synergistic relation between LATQ and WYLD, and sediment retention and WYLD and trade-offs between SURFQ and HES descriptors like WYLD, LATQ, sediment retention, and TWR was attributed to varying factors such as land use and topography impacting the water balance components in the watershed. The findings underscore the critical need for targeted conservation efforts to maintain the ecologically sensitive regions at watershed scale. [ABSTRACT FROM AUTHOR]

Streamflow generation and biochemical hotspots are significantly influenced by groundwater contributions distributed along the drainage network. However, identifying the geomorphic landscape features that drive groundwater‐surface water interactions remains challenging. In this study, we investigate the role of knickpoints in controlling these interactions in a mountainous stream in Switzerland. We employ a combination of synoptic sampling of environmental tracers, endmember mixing calculations, and groundwater flow simulations. Our findings reveal substantial groundwater seepage concentrated near the knickpoint of the main river stem. Using parsimonious groundwater flow modeling, we validate the hypothesis that the topographical shape of the knickpoint enhances local groundwater discharge rates. We quantify that approximately 20% of the total catchment streamflow originates from around the knickpoint. These results indicate that knickpoints are significant hotspots for groundwater seepage and physicochemical mixing, providing a clear method for identifying major localized sources of streamflow generation. Plain Language Summary: In ice‐free catchments, groundwater is the main water source maintaining streamflow during extended dry periods. In addition to its importance for water resources, locations where groundwater contributes to surface stream water are important hotspots where interactions between biological and chemical processes occur, that have major implications for aquatic ecosystems. However, those hotspots remain difficult to identify. Specifically, our understanding on the relationships between landscape and groundwater discharge in streams remains limited. In our study of a Swiss Alpine catchment, we sampled a stream for water chemical analysis and used statistical and numerical models to find where groundwater emerges into the stream. We discovered that most groundwater enters the stream around a "knickpoint", a location where the stream profile becomes steeper. According to our calculations, this knickpoint, although of minimal extent, contributed one fifth of the total streamflow in the catchment. Although our results are site‐specific, knickpoints are ubiquitous in mountain areas, thus they might be important when predicting water availability and biogeochemical fluxes at regional scale. Key Points: We highlight the sporadic nature of groundwater seepage hotspots along a river profileKnickpoints influence groundwater flow patterns, creating preferential mixing zones between groundwater and surface watersBiogeochemical hotspots are influenced by knickpoints in mountainous hydrographic network [ABSTRACT FROM AUTHOR]

Carbonate and karst aquifers are of great importance for human water supplies, for supporting aquatic habitats and providing ecosystem services. Optimizing the groundwater withdrawals is therefore essential for obtaining the maximum flow rate for human purposes while minimizing the negative effects on the environment. In particular, when the abstraction of groundwater occurs through wells, the problem of defining the sustainable yield arises. This study analyzes pumping tests conducted in carbonate and karst aquifers in southern Italy to derive indications for defining the sustainable yield of yields. The four examined cases concern the Mesozoic–Cenozoic platform and transition pelagic carbonate rocks characterized by different degree of fracturing and karstification and hosting a carbonate aquifer with variable average groundwater yields. The analysis compared drawdown–time trends and their derivatives for 35 pumping tests with theoretical curves to identify the flow dimension. Parameters useful for examining the well yields were then determined. The results show that the response to the pumping of the investigated aquifers is very variable, both among the different sites and within the same site. Well yields are very different due to aquifer heterogeneity, local hydrostratigraphy and structural setting, and position of the pumping center within the groundwater flow system. To determine the operational pumping rate for a well in this environment, this study emphasizes the importance of analyzing drawdown trends over time to correctly predict the well's long-term response to pumping. Specifically, when pumping induces a steady-state drawdown response, the focus for defining the sustainable abstraction shifts to the basin or aquifer scale. Conversely, when a transient drawdown response to pumping results, the well's capacity to capture groundwater becomes the primary factor for well yield and its sustainability. [ABSTRACT FROM AUTHOR]

Shallow groundwater is an important resource, especially in low- and middle-income countries; however, shallow groundwater is particularly vulnerable to point sources of pollution such as latrines or unlined waste disposal ponds. The objective of this paper is to derive a quantitative criterion for siting an extraction well and an upgradient point source of pollution to ensure that they are hydraulically disconnected, i.e., that no water flows from the point source to the well. To achieve this objective, we modeled the flow of shallow groundwater considering uniform regional flow, a single point source of pollution, and a single extraction well. For any set of flow rates and upgradient point source distance, we sought the minimum "off-center distance" ymin (i.e., the distance in the direction perpendicular to regional flow) that ensures the well and the point source are hydraulically disconnected. For constituencies with access to computing resources and coding expertise, we used a computer-based method for determining ymin that is exact to within the accuracy of a root-finding algorithm; this approach is recommended when computer access is available. For constituencies lacking these resources, we determined a simple, closed-form, approximate solution for ymin that has an average error of less than 3% for the conditions we tested. For a subset of scenarios in which the point source is sufficiently far upgradient of the well (n = 77), the root mean square relative error of the approximate solution is only 0.52%. We found that ymin depends on a length parameter (Qw + Qps)/QR, where Qw is the extraction rate of the well, Qps is the injection rate of the point source, and QR is the regional groundwater flow rate per unit of perpendicular length. Either the exact solution or the closed-form approximation can help to site wells near point sources of pollution, or to site point sources near wells, in a manner that protects the health of the well user. The approximate solution is valuable because many constituencies that rely on shallow wells for water supply and latrines for sanitation also lack access to the computer resources necessary to apply the exact solution. [ABSTRACT FROM AUTHOR]

In this study, an ensemble inflow-prediction system was developed for a hydropower-generation dam in the upper Sai River basin, and the accuracy of ensemble inflow prediction, which is important for efficient dam operation, was investigated. First, the Water and Energy Based Distributed Hydrological Model for Snow (WEB-DHM-S), a hydrological model developed for the Sai River basin, can represent the hydrological process from warm to cold seasons. Next, a system was developed on the Data Integration and Analysis System (DIAS) to predict inflows into the dam by inputting real-time meteorological data and ensemble rainfall forecast data into WEB-DHM-S. The WEB-DHM-S was calibrated and validated over a 3-year period from August 2015 to July 2018, and showed good agreement with observed inflows from base flow to peak flow and snowmelt runoff in each year. The results of inflow forecasting during frontal rainfall in August 2021 by inputting ensemble rainfall forecasts up to 39 h ahead showed that at the Inekoki Dam site, the total inflow (volume) to the peak was predicted with an accuracy of within 20% at 30 h, 24 h, 18 h, 12 h, and 6 h before the peak. These ensemble inflow forecasts can help optimize dam operations. [ABSTRACT FROM AUTHOR]

Land subsidence, marked by a decline in surface elevation, poses a significant threat to urban infrastructure and safety. Accurate subsidence information and a reliable prediction model are crucial for prevention and control. In this study, we used persistent scatterer interferometric synthetic aperture radar (PSInSAR) technology to obtain long-term land subsidence data and analyzed subsidence characteristics in Decheng District. By integrating hydrogeological and groundwater data, we developed a three-dimensional groundwater flow and one-dimensional compaction model through numerical simulation. Furthermore, the subsidence data monitored by PS-InSAR were used to further constrain and validate the model. The evolution trend of land subsidence under different groundwater exploitation scenarios was predicted and analyzed. The results showed that from May 2017 to December 2021, the cumulative maximum subsidence in Decheng District reached -173 mm. The subsidence area is mainly concentrated in the northern area, and its subsidence center is near Qiaoyuan Town. According to the Land Subsidence Prevention and Control Plan of Dezhou City, Shandong Province (2018-2025), we set up different groundwater mining scenarios with the goal that the rate of land subsidence in the key prevention and control area is less than 35 mm/yr in 2025.The Fluidsolid coupled model prediction analysis results indicated that a 30% reduction in groundwater exploitation is reasonable. [ABSTRACT FROM AUTHOR]

Solute transport in unsaturated conditions is important in various applications and natural environments, such as groundwater flow in the vadose zone. Studies of unsaturated solute transport show complex characteristics (e.g. non-Fickian transport) due to larger variations in the pore-scale velocities compared to transport in saturated conditions. However, the physical processes at the pore scale are still not completely understood because direct three-dimensional observations at the pore scale are very limited. In this study, single-phase and two-phase solute transport was directly characterized by performing tracer injection experiments in a sintered glass and Bentheimer sandstone sample. These experiments were imaged by continuous scanning with fast laboratory-based micro-computed tomography. The network-scale flow velocities and transport properties were characterized by using the pore-based transient concentration fields to determine the tracer's arrival time and filling duration in every pore. Important measures for dispersion (the scalar dissipation rate and filling duration) were determined and indicated a wide range in pore-scale velocities and the existence of stagnant and flowing pores for the unsaturated experiments. Furthermore, we performed the first quantification of the mass transfer coefficient between stagnant and flowing pores on three-dimensional experimental data. We also calculated the tortuosity directly from the interstitial velocity and the pore-based velocity. This was found to be 13% higher in unsaturated conditions compared to saturated conditions. Our results indicate that pore-scale structural heterogeneity increases the differences between saturated and unsaturated solute transport. This study thus provides further insight into pore-scale spreading and mixing of dissolved substances in unsaturated porous media. [ABSTRACT FROM AUTHOR]

The Colorado River is a vital water source for the western United States, yet the river is governed by disjointed and outdated policies that have left water management fragmented and water quantities overallocated. Groundwater is an overlooked component of Colorado River Basin (CRB) water supplies, making it vulnerable to overuse from disparities in uncoordinated protective management strategies. In this study, we analyzed state level groundwater policies to reveal the diversity and efficacy of groundwater governance mechanisms. The existing groundwater management plans for each state throughout the basin are fragmented and limited in scope. We found that with policies only covering 22% of the basin, they do not provide adequate protection at the basin scale for the sustainable use of groundwater resources in the face of increasing demands, creating a positive feedback loop that reinforces the scarcity issue. We conclude that a comprehensive management plan that can fully address resource use throughout the CRB is necessary for the sustainable use of groundwater and its contribution to base flow in the Colorado River. We suggest that such a plan could be derived through an interstate compact like the Colorado River Compact that is used for surface water management. [ABSTRACT FROM AUTHOR]

Spring discharge decline induced by increasing groundwater pumping under the background of increasing water demand for agricultural, industrial, and domestic utilizations has been recognized as a significant geo-environmental issue which poses a great threat to springshed eco-environmental safety. In this study, numerical approach was utilized and a series of 3D groundwater flow models based on the MODFLOW module were developed to simulate current-stage and future trends of spring discharges under the impacts of increasing groundwater pumping due to the rapid development of tourism in the BL spring located in Xilin Gol League in east Inner Mongolia (China), for the purpose of understanding the responses of spring discharges to various groundwater pumping scenarios in future. Simulation results indicated that: (1) spring discharge has reduced from 201.4m³/d to 193.7m³/d (reduction ratio of 3.80%) under current-stage pumping scheme; (2) the spring-discharge-affected zone is 2.025 km² under current-stage pumping scheme and groundwater pumping within this zone contributes to spring discharge decline; (3) impact of the pumping well located nearest to the BL spring is the most significant while impact of the pumping well located farthest to the BL spring is negligible; and (4) spring discharge would reduce 25%, 50%, 75%, and 100% if total pumping rate of the seven abstraction wells would increase from 45.8 m³/d (current-stage pumping scheme) to 297.7, 586.2, 888.5, and 1,176 m³/d, respectively. The outcome of this study can provide useful references for advising sustainable groundwater exploitation strategies to meet the requirement of groundwater supply under the premise of spring discharge management and eco-environmental protection. [ABSTRACT FROM AUTHOR]

The planning and management of water in the river basins require the identification of places where the quality of groundwater is being threatened. The risk of launching the accumulated pollutants present in the solid phase of the soil may be caused by both the changes in the pressure gradients in the aquifers and the changes in the hydrogeochemical balances. In the example of the Ner river valley, into which wastewater from the Łódź agglomeration has been discharged, the factors threatening the chemical status of groundwater were determined. This assessment was carried out based on the results of the determination of the hydrodynamic balance disturbances in the Upper Cretaceous formations, model studies of groundwater flow and hydrogeochemical studies conducted on the sorption complex of the Ner alluvium as well as the chemistry of the river water, alluvial water and groundwater. The results showed that the river water is heavily anthropogenically transformed. Model studies have shown that when the Ignacew -intake wells are pumped collectively, the inflow takes place through the Ner valley, where the hydrogeological window between the Quaternary and the Upper Cretaceous aquifers is found. The withdrawal by the Ignacew intakes may result in the reversal of piezometric pressures in the valley, which creates the possibility of the infiltration of polluted surface water into groundwater. Observations indicate the need to take into account the zones where surface water and water from the river alluvium are a real threat to the chemical status of the aquifers. These aspects are important when determining the protection zones and in renewable and disposal resource assessments of the Main Groundwater Reservoirs. [ABSTRACT FROM AUTHOR]

Karstic landscapes, shaped by water dissolving rocks, are unique ecosystems with complex water systems. Karst aquifers, vital for over 25% of the world’s drinking water, offer a sustainable resource but are vulnerable, such as pollution and over-extraction. Therefore, it’s important to understand the potential and capacity of karst springs in areas suffering from water shortages. Hydrogeological and speleological studies are crucial for understanding the unique characteristics of karst springs. Moreover, epiphreatic caves located near the water table at the interface between vadose and phreatic zones in karst landscapes, hold valuable information about past geological events. By identifying their former presence and location in uplifted limestone regions, we can reveal phases of uplift, lowering of the base level, and the rate of vertical karst development. Consequently, epiphreatic caves and associated karst processes are of considerable interest for understanding past geological changes. Here, we present an integrated study of a spring in the epiphreatic Cokragan Cave, which is an important water resource for the Uşak region, using both speleology and hydrogeology. The complex Cokragan Cave system, stretching over 2050 m, reveals multiple past groundwater levels through its geometry, with elevation differences suggesting tectonic influence. Between 2003 and 2007, Cokragan spring discharged an average of 63.5 million m3/yr, while recharge averaged 62.37 million m3/yr. Measured discharge ranged from a maximum of 1.488 m3/s to a minimum of 0.108 m3/yr. In-situ measurements and analysis of 13 samples revealed the groundwater’s physicochemical characteristics, including major ions such as calcium, magnesium, and bicarbonate, and trace elements such as arsenic, boron, iron, manganese, and zinc. [ABSTRACT FROM AUTHOR]

This study investigates the influence of topography on wind turbine flow and power efficiency. Specifically, a standalone wind turbine is positioned at the top of idealized two-dimensional hills, and the effects of hill geometry and turbine position are systematically investigated. Various parameters are studied, including hill slope, distance between the leeward side of the hill and the turbine, turbine hub height, and hill size. Overall, it is observed that the turbine wake is consistently stronger in the hill cases compared to the flat case. This is attributed to two characteristics of hill flows: (1) the negative streamwise velocity gradients on the leeward side of the hills and (2) the reduced turbulence above the hilltops and hill wake regions. In addition, it is observed that the turbine induction factor is consistently increased in the hill cases compared to the flat case, while the turbine power and thrust coefficients are reduced. In practice, this means that turbines on the hills produce less power output than those on flat terrain for an equivalent wind potential, with the potential decrease in power output reaching more than 20 % for certain cases. Altogether, the results offer new insights into the effect of topography on turbine power efficiency. In addition, the study identifies clear relationships between the turbine power coefficient, the induction factor, the overall maximum deficit, and the base flow pressure gradient. These relationships could potentially be used to predict the change in power efficiency based on the wake flow or the base flow. Overall, the results show a clear connection between the turbine power efficiency and the turbine wake development. [ABSTRACT FROM AUTHOR]

Shock–shock interactions (SSIs) are widespread in hypersonic vehicles. The mutual interaction between multiple shock waves can result in severe pressure loads and increase the thermal load. The SSI induced by a double wedge configuration is a classical problem. This paper describes a novel U-electrode surface arc actuator that produces a supermultichannel array surface arc discharge under hypersonic conditions. High-speed schlieren measurements are used to investigate the SSI induced by the hypersonic double wedge and plasma control under Mach 8 flow conditions. The results show that the shock wave array induced by the plasma forms a virtual compression surface. This surface deforms the shock wave induced by the first wedge, and the oblique shock wave in front of the secondary wedge and the SSI region disappear due to the uplift and hot gas mass disturbance from the impact. Because the applied actuation frequency is higher than the characteristic frequency of the base flow field, the high-frequency pulsations of the shock wave are controlled by the plasma actuation. Additionally, the low-frequency instability is suppressed. Thus, the aerodynamic load and low-frequency instability of the double wedge configuration under high-Mach-number conditions are effectively regulated. [ABSTRACT FROM AUTHOR]

The supersonic base flow with an exhaust jet is significantly unsteady, whose characteristics can be influenced by the exhaust jet states. By the exhaust jet, we mean the working fluid produced by the rocket engine and exhausted by the base nozzle in supersonic velocity, which is used to generate thrust. A numerical investigation of the base flow at Mach 1.96 is carried out via the delayed detached eddy simulation. The effects of presence, expanded states, and temperature of the exhaust jet on the unsteady characteristics are analyzed. Compared with the exhaust jet off, the exhaust jet presence causes the base pressure fluctuation intensity to increase in the high-frequency band (SrD > 0.5) and changes the dominant mode from wake oscillation (SrD = 0.12) to the periodically expand-shrink of the exhaust jet diameter (SrD = 0.16). Compared with the underexpanded state, the overexpanded exhaust jet induces the flow separation inside the nozzle, which causes a decrease in the base pressure fluctuation intensity in the high-frequency band (SrD > 1.0), and the separation point movement and exhaust jet oscillation constitute the dominant mode (SrD = 0.13). Compared with the low-temperature jet, the base pressure fluctuation intensity is slightly reduced in the high-frequency band (SrD > 1.0) for the high-temperature jet, and the flapping motion of the jet shear layer becomes the dominant mode (SrD = 1.5). [ABSTRACT FROM AUTHOR]