Hydrogeology Journal最新文献

Fracture conduits serve as the primary channels for groundwater runoff in karst areas, controlling the water level and distribution of flow in the groundwater system. To determine the parameters of fracture-conduit karst systems and to analyze the distribution characteristics of the pressure field and flow field, a pipe network calculation method is presented that discretizes the fracture medium and conduit medium into pipes and nodes. The connection rules for nodes and pipes are established, and different water conductivity coefficients are assigned to discrete pipes. Based on the principles of conservation of mass and energy, nonhomogeneous linear control equations are constructed to represent the discrete pipe network (PN). By solving the equations, groundwater parameters can be calculated for the PN. Meanwhile, a laboratory model test was conducted to validate the PN, and the numerical calculation results aligned well with the laboratory test results. In addition, a simple case is compared and verified, and the calculation results are compared with those obtained using the multiphysics software, COMSOL. The results indicate that the PN method can achieve more accurate calculation results with fewer elements. The method calculates the distribution characteristics of the flow field within the water-conducting medium and elucidates the influence of the properties of the medium on the distribution characteristics of the flow field. The research results provide guidance for the distribution of groundwater flow fields in karst areas and are expected to be applied to calculating groundwater pressures and flows in large-scale fracture-conduit systems.

Sea-level rise (SLR) causes groundwater salinisation and water-table rise. The impacts these processes can have on water security, agricultural production and infrastructure are becoming widely recognised. However, some misconceptions relating to SLR impacts on groundwater have been observed among students, which may interfere with further learning and the application of science principles to everyday life. These misconceptions include the following: (1) water-table rise will equal SLR; (2) inland movement of the interface causes the rise in the water table under SLR; (3) seawater intrusion (SI) caused by SLR is small compared to SI caused by pumping. These misconceptions are explored with the aid of simple analytic solutions and a Jupyter Notebook. It is shown that: (1) water-table rise is only equal to SLR above the interface under flux-controlled inland boundary conditions; (2) water-table rise under SLR is not caused by SI, but rather is caused by the change in levels at the coastal boundary; (3) SI caused by SLR is a considerable risk, especially under the head-controlled conditions, which will become more common when land is drained to counter the effects of groundwater shoaling.

Hydrochemical and geophysical methods were used to assess saline paleo-water mass transfer induced by piston flow in the alluvial aquifer of the Oltrepò Pavese plain (northern Italy). The surface aquifer shows salinity contamination from a Tertiary substrate of marine origin, due to mixing of the shallower fresh groundwater with the Po Plain’s deep brines. The study also used continuous monitoring of groundwater electrical conductivity, temperature and piezometric levels. Well logging and geophysical imaging, conducted at different times, revealed that the contamination varies over time, and that the water salinity and the depth of the transition zone (between the surface freshwaters and the deep saline waters) are subject to modifications. This is due to a pressure transfer—and, subsequently, mass transfer−from the groundwater circuits of the nearby Apennine mountains. It suggests that a hydraulic connection exists between the fractured Apennine water circuits and the deeper Mio-Pliocene and Tertiary saline-water circuits found below the plain’s alluvial aquifer. Coinciding with significant recharge episodes that affect Apennine water circuits (prolonged rainfall and snow melt at mid-high altitudes), there is a pressure transfer transmitted along the water circuits in which saline water resides, providing an impulse to rise along the discontinuities and reach the alluvial aquifer. The conceptual model is supported by evidence that wells constructed in correspondence to hydraulically active tectonic discontinuities are affected by the arrival of saline waters with variable delays, while wells sited in sectors not affected by tectonic discontinuities are diluted by ‘fresh’ waters connected to alluvial aquifer recharge.

The geochemical and isotopic composition of deep groundwater in sedimentary aquitards reveals a complex paleo-hydrological system affected by intensive tectonic activity. Water samples collected from deep research boreholes in the Golan Heights (Middle East) exhibit a unique combination of high salinity (>2,000 mg/L Cl) with low Na/Cl (<0.7) and Mg/Ca (<0.3) equivalent ratios, calcium chloride water type [Ca > (HCO₃ + SO₄)], relatively low δ¹⁸O_VSMOW and δ²H_VSMOW values (–7 and –42‰, respectively), and enriched ⁸⁷Sr/⁸⁶Sr ratios compared to the host rocks. The salinity source is related to ancient lagoonary hypersaline brines (10–5 Ma) that existed along the Dead Sea Rift (DSR). These brines intruded into the rocks surrounding the DSR and, based on the current study, also extended away from the rift. Following their subsurface intrusion, the brines have been gradually diluted by ¹⁸O- and ²H-depleted freshwater recharged at high elevations, nowadays leaving only traces of the brines that originally intruded. It is also shown that variable hydraulic conductivities in different formations control the dilution rates and subsequently the preservation of the entrapped brines. A paleo-hydrological reconstruction is provided to demonstrate intrusion and backflow dynamics and also the relationship to freshwater dilution, which was triggered by a tectonically active basin of the nearby continental DSR. Brines that initially migrated from the rift have since been gradually flushed back to the rift through the current natural outlets. As the system discharges, it mixes and converges with a separate hydrogeological system, while still preserving some of the geochemical signals of the ancient brines.

Bioclogging in porous media is common and affects many engineering projects. The temperature of recharge water could significantly affect the process of bioclogging, thus impacting the hydraulic conductivity of porous media. In this study, a series of laboratory percolation experiments was conducted to understand the effects of recharge water temperature. The results of these experiments showed that bioclogging evolved in phases, and the gradual reduction (attenuation) of hydraulic conductivity caused by bioclogging could be described by an inverse logistic model. Analysis of microbial growth suggested that the bioclogging phases were strongly correlated with microbial growth stages. Both the clogging rate and degree of clogging through the seepage column decreased with distance from the inlet. Within the range of 10–25 ℃, the degree of clogging decreased with the increasing recharge water temperature; however, the degree of clogging increased with recharge water temperature within the range of 25–35 ℃. The relative hydraulic conductivity values decreased by 86.9% at a recharge water temperature of 10 ℃, 76.0% at 15 ℃, 65.1% at 20 ℃, 44.9% at 25 ℃, 82.5% at 30 ℃ and 98.7% at 35 ℃. Investigation by scanning electron microscopy found that the microorganism micromorphology differed at different recharge water temperatures, which made a significant difference in terms of clogging degree. A comprehensive model that describes hydraulic conductivity attenuation with varying recharge water temperature has been developed.

The behavior of iron (Fe) in clayey aquitards has a significant effect on the groundwater environment. However, the release processes and impact of Fe within clayey sediments during compaction remain unknown. Two groups of simulation experiments were carried out to demonstrate the migration and transformation mechanisms of Fe during clayey sediment compaction. Experiment A, which simulated a natural deposition condition, revealed that pressurization changed the reaction environment from oxidative to reductive by isolating oxygen. Oxidation of ferrous ions was followed by reduction dissolution of poorly crystalline Fe (III) and crystalline Fe (III) oxides. Under the microbial utilization of organic matter, the main transformation process of sediment Fe was the dissimilatory reduction of poorly crystalline Fe (III) oxides. The total Fe concentration in pore water was 0.09–11.61 mg/L, with ferrous ions predominating among the Fe species. The lower moisture content ((text{<})~36%) in the later stage of compaction inhibited the dissimilatory reduction of Fe (III), and the formation of Fe (II) minerals resulted in a decrease in Fe concentration. Experiment B, which simulated an artificial compaction state, revealed that the sediment Fe was primarily released by physical dissolution because of changes in pore structure and solubility. The concentration of total Fe in pore water was 0.02–1.96 mg/L, with a significant increase in response to a rapid increase in pressure. According to the estimates in the Chen Lake wetland (eastern China), the contribution of clay pore water release accounted for 19.9–31.9% of the average Fe concentration in groundwater during natural deposition.

Published laboratory and field estimates of vertical hydraulic conductivity (K_v) and the anisotropy ratio (K_h/K_v, where K_h is horizontal hydraulic conductivity) have been compared with equivalent groundwater model values, mainly for sedimentary strata. The results show that model K_v values tend to be higher and K_h/K_v values tend to be lower than field estimates for vertical length scales ≥10 m, particularly for coarse-grained unlithified sediments. This difference is attributed to the widespread use of the assumption of K_h/K_v = 1 and particularly K_h/K_v = 10 in groundwater models, regardless of the length scale or strata type represented. The origin of the K_h/K_v = 10 assumption is obscure and not founded on rigorous data analysis. K_h/K_v, and by inference K_v, is frequently an unimportant parameter in model construction and calibration. On balance, this model artefact is attributed to the common reliance on summary head calibration statistics that hide the inadequacies of the MODFLOW paradigm (K_xx = K_yy = K_h, K_zz = K_v) when used for large-scale hydrostratigraphic units with uniform parameterization, fixed K_h/K_v, and 1 ≤ K_h/K_v ≤ 10. However, thin, high-permeability aquifer models or well-defined aquifer/aquitard models are examples where such simplifying assumptions for K_h/K_v are workable, given groundwater quantity objectives. More realistic model values of K_v and K_h/K_v at length scales greater than field estimates could be obtained by independent calibration of K_v and K_h, use of larger-scale field estimates of K_v and multi-level piezometer/observation wells, and calibration to vertical head gradients separate from summary head calibration statistics.

The equivalent porous medium (EPM) method is an efficient approximate processing method for calculating groundwater yield taking into account the equivalent permeability coefficient of a fractured geological medium. The EPM method finds wide application in addressing various hydrogeological problems ranging from local to regional scales; however, the adequacy of the EPM model for evaluating water head and velocity distributions has not been comprehensively assessed. This study quantitatively investigated the influence of fracture and matrix permeability on the EPM model’s suitability, defined by a 15% threshold for hydraulic-head prediction error, via numerical simulations. A fractured porous media system (fracture-matrix system) was considered as the prototype, and the EPM model simulation results were compared with those obtained using the discrete fracture-matrix (DFM) model. Results indicate a decrease in EPM suitability with larger fracture apertures. With a constant fracture aperture, the suitability of the EPM model increases as the matrix permeability increases. The size of the fracture aperture significantly affects the suitability of the EPM model, and it determines the point at which its suitability begins to increase and eventually stabilize. The fitted curve depicting the influence of matrix permeability on the suitability of the EPM model conforms to the Boltzmann formula, and the fracture aperture is linearly related to the parameter x₀ in the formula. The derived empirical formula enables quantitative assessment of the impact of fracture and matrix permeabilities on the suitability of the EPM model in fractured porous media.

Preventing water inrush disasters in mines is crucial for ensuring safe coal production; therefore, it is necessary to adopt a simple and effective method to determine the source and composition of mine water for effective water control in coal mines. The major ions content of groundwater in mining areas is easy to monitor, but the selection of appropriate parameters and calculation methods is key to being able to accurately discriminate between the water sources. In this study, the major ions content of 18 water samples was analyzed by cluster analysis, and a set of mean reference values was constructed for these ions in the mine-impacted groundwater of the saturated aquifers. The coefficient of variation was used to screen the parameters suitable for calculating the composition of mine water, and an innovative concept of characteristic ions, hereby defined as “emblematic” ions, was put forward. These were identified in this study as K⁺ + Na⁺, Ca²⁺, Mg²⁺ and HCO₃^–. The quantitative calculation model of the mine water source is established by using the fuzzy comprehensive evaluation method with the emblematic ions as the evaluation factor. Finally, the accuracy of the mathematical model is verified by comparing the calculated data with the actual observation data.

Developing conceptual models is a critical step in hydrogeological studies that should utilise multiple lines of evidence and data types to minimise conceptual uncertainty, particularly in data-sparse systems. This study used new and existing major ion and isotope (O, H, Sr, C) data sets to refine a previous hydraulic-head-based conceptual model of the Galilee Basin (Australia). The analyses provide evidence for the locations of recharge and discharge areas and determine hydrochemical processes along flow paths to improve understanding of potential source waters to the Doongmabulla Springs Complex (DSC) and to infer mixing within, or exchange between aquifer units. There was good agreement between previously inferred recharge and discharge areas defined using hydraulic head data and interpretations from hydrochemical evolution along groundwater flow pathways, at least where data were available. Major ion and isotope data suggest that the DSC likely receives water from both a relatively shallow, local flow path and a deeper regional flow path. This observation is relevant to previous concerns about threats to the DSC, as mine-induced drawdown may impact the relative contributions to spring discharge from different recharge sources and aquifers. Silicate weathering in the deeper Clematis Formation and Dunda Beds, and evapotranspiration in the overlying Moolayember Formation have strong control on the total dissolved solids content. These findings suggest that the Clematis Formation and Dunda Beds are hydrochemically distinct from the Moolayember Formation, with limited exchange between these aquifers, which has important implications for model conceptualisation and ongoing monitoring of mining activities in the Galilee Basin.