Hydrogeology Journal最新文献

The effect of subsurface structures in blocking groundwater seepage has a long-term influence on groundwater level (GWL). A finite difference method (FDM) model considering the actual distribution of subsurface structures in an urban area of Shanghai (China) was established to predict GWL in the phreatic aquifer (Aq0) and the first confined aquifer (AqI). The equivalent hydraulic conductivity (K_eq) of model elements containing subsurface structures, calculated by the effective medium theory, was applied to the model. The predicted GWL fitted the monitored value in Aq0 well. Additional subsurface structures were added to the model to analyze the influence of the distribution type and the proportion (%) of the volume of subsurface structures that occupy the aquifer (V_u). Four scenarios with different distribution types (concentrated, subconcentrated, subscattered, and scattered) and ten scenarios with V_u varying from 5 to 50%, were analyzed. In all scenarios, the regional average GWL in AqI increased compared to the actual conditions because of the decrease in K_eq and the blockage effect on groundwater flow. The influence of scattered distribution on the regional GWL distribution was the smallest, and the subscattered distribution resulted in the most nonuniform GWL redistribution. The blockage effect of the subsurface structures gradually increased with increasing V_u. The increasing rate of ΔL_av (difference in regional average GWL between the predicted and actual scenarios) becomes considerable when V_u is ~29%. Hence, the projected increase in volume of subsurface structures in AqI under the assumed subscattered distribution is suggested to be <29%.

The key factors determining the operational cost and carbon footprint of public water supplies derived from groundwater are identified. Both remain low compared to alternative sources while groundwater levels remain stable and water quality potable, but can increase markedly if derived from overexploited and/or polluted aquifers. Thus, ‘potable source protection zones’ are strongly advocated, and examples from England (UK) and Spain are illustrated. The concept of minimising the carbon footprint of groundwater use for potable water supply is novel, and deserves greater attention.

Saline pans are environments with ephemeral to persistent evaporite crusts, surface and groundwater brine, little to no vegetation, and low topographic gradients. These characteristics make them sensitive to diverse hydrological processes. This research provides guidance on assessing and interpreting fluctuations in saline pan groundwater levels. Observations from the center of the Bonneville Salt Flats, Utah, USA, focused on meteorological and groundwater level fluctuations and were used to quantify evaporation and identify natural environmental controls on saline pan groundwater level variation. Primary water fluxes consist of precipitation and evaporation. Eddy-covariance evaporation measurements, spanning over 1.5 years and capturing diverse surface conditions, were collected. An artificial neural network, trained on meteorological measurements and eddy-covariance-measured evaporation, estimated evaporation over a 6-year period. The saline pan has two states: (1) dry, when water availability rather than evaporative potential limits evaporation, and (2) wet, when evaporative potential limits evaporation. In dry conditions, characterized by evaporation rates of ~0.1 mm/day, groundwater levels with daily average depths ≥5 cm below the surface, demonstrated daily variations >6 cm during summer and seasonal fluctuations >50 cm in response to temperature changes. Groundwater levels did not respond to temperature changes when there was surface water. Groundwater levels rose to the surface under wet conditions. Over multiple years, the system is in balance, with evaporation equaling precipitation.

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.