Hydraulic head and groundwater age data are effective in building understanding of groundwater systems. Yet their joint role in detecting and characterising low-permeability geological structures, i.e. hydrogeologic barriers such as faults and dykes, has not been widely studied. Here, numerical flow and transport models, using MODFLOW-NWT and MT3D-USGS, were developed with different hydrogeologic barrier configurations in a hypothetical aquifer. Computed hydraulic head and groundwater age distributions were compared to those without a barrier. The conjoint use of these datasets helps in detecting vertically-oriented barriers. Two forms of recharge were compared: (1) applied across the entire aquifer surface (uniform), and (2) applied to the upstream part of the aquifer (upgradient). The hydraulic head distribution is significantly impacted by a barrier that penetrates the aquifer’s full vertical thickness. This barrier also perturbs the groundwater age distribution when upgradient recharge prevails; however, with uniform recharge, groundwater age is not successful in detecting the barrier. When a barrier is buried, such as by younger sediment, hydraulic head data also do not clearly identify the barrier. Groundwater age data could, on the other hand, prove to be useful if sampled at depth-specific intervals. These results are important for the detection and characterisation of hydrogeologic barriers, which may play a significant role in the compartmentalisation of groundwater flow, spring dynamics, and drawdown and recovery associated with groundwater extraction.

Submarine groundwater discharge (SGD) as a major source of alkalinity has rarely been studied in Jiaozhou Bay, China. The presented study used radon (²²²Rn) and radium isotopes to investigate SGD and its influence on alkalinity and nutrient inputs into the bay. Time-series observations of ²²²Rn were used to quantify groundwater dynamics over tidal time scales and the results showed that the SGD rates at point-scale were 0–67.2 (mean: 17.8) cm/day and 0–43.6 (mean: 12.3) cm/day in wet and dry seasons, respectively. Using radium mass balance models, the SGD in the whole bay was estimated to be (1.29–2.60) × 10⁷ m³/day in wet season and (5.81–6.83) × 10⁶ m³/day in dry season. Thus, both sets of results indicated higher SGD fluxes in wet season than in dry season. Such a seasonal variation pattern suggests a rapid response to local precipitation. The alkalinity fluxes associated with SGD were generally greater than those from the local rivers. Among the nutrient sources, SGD contributed about 63, 24 and 37% of total dissolved inorganic nitrogen, reactive phosphorus and silicate inputs, respectively. These results demonstrated that groundwater seepage is a major factor driving alkalinity and nutrients (especially dissolved inorganic nitrogen) into Jiaozhou Bay. SGD may have an important influence on the budgets of elements (C, N, P) and ecological environments in coastal waters.

Research into the unsaturated zone and groundwater recharge can greatly improve understanding of hydrological processes and assist in sustainable groundwater management. Groundwater recharge of the Ljubljana Field aquifer, a coarse-gravel porous aquifer in Slovenia, was estimated with reference to soil characteristics, outflow data from a weighing lysimeter, and water-table fluctuation. The specific yield of the upper unsaturated zone determined from soil characteristics was 0.141 for the top soil layer (0–0.35 m), between 0.042 and 0.066 for the layer below the top soil (0.35–1.3 m), and between 0.239 and 0.219 for the underlying upper coarse layer. During long dry periods, especially in combination with times of high plant-water requirements, only substantial precipitation events directly contribute to considerable groundwater recharge, as ‘substantial precipitation’ is defined as those rainfall events that fill storage and exceed retention capacity of the upper soil layer. Lysimeter measurements show that 50% of the precipitation is lost by evapotranspiration and the other 50% contributes to groundwater recharge. Most infiltrated water was stored for a short time in the unsaturated zone and did not result in a significant discharge from the lysimeter. Average specific yield, calculated using the water-table fluctuation method, was 0.144. The nature of the gravely unsaturated zone is that once the retention buffer of the soil is exceeded, the water front travels through relatively quickly, which can be seen as an advantage for recharge or a disadvantage for prevention of groundwater pollution.

The Lez aquifer in southern France comprises low-porosity karstified limestones and provides drinking water for ~400,000 inhabitants. Population growth and climate change have increased the stress on the water resources. In order to provide long-term protection and to optimize the water supply, the hydrogeology of the Lez aquifer must be better characterized. This study focused particularly on the St-Clément major fault zone (12 km long with a 500-m normal throw) which was structurally characterized using accurate geological mapping of the area, outcrops analysis and geophysics tools. The research highlights and explains the close relationship between the fault and the karstic occurrences. Moreover, tracer tests and piezometric head variations in boreholes have shown (1) strong interconnection between the observed karstic formations and (2) the major role of St-Clément fault on mass and pressure transfers in the aquifer. At the reservoir scale, the other major faults of the Lez aquifer, such as Corconne-Matelles or Gourg Noir faults, have shown some common morphologic and dynamic characteristics, and suggest a similar hydrogeological functioning. This study then extends this model to a larger scale. It proposes that, in aquifers of low-porosity carbonates, fault zones control the development of the main karstic network which, in turn, controls the main groundwater flows. Thus, faults should be reconsidered in order to improve the vulnerability studies and the quality of karstic aquifer modelling. Therefore, this report can contribute to protecting the groundwater resource, improving yields and optimizing groundwater supply exploitation in this type of aquifer.

The western Great Artesian Basin (GAB) is an important water source for pastoral and town water supplies, as well as for springs containing endemic flora and fauna, within arid Australia. This study focuses on the hydrochemical variations of groundwater and spring discharge in order to determine the major geochemical processes responsible for water quality and evolution across the western GAB. Regional hydrochemical trends within groundwater generally support the modern groundwater potentiometric surface and interpreted flow paths, highlighting that these approximately represent the long-term flow paths. Additionally, the regional chemical variations along the flow paths in the western GAB are complex, with their composition being a function of several controlling processes, including location of recharge, evapo-concentration, mixing and various water–rock interactions. These processes cause groundwater east of Lake Eyre to be predominantly of Na-HCO₃ type, whereas groundwater originating from the western margin is of Na-Cl-(-SO₄) type. The GAB springs appear to be discharging water predominantly from the main GAB aquifer, the J Aquifer; however, a component of the discharging water from several springs is from a source other than the J Aquifer. Current understanding of the hydrochemical variations of groundwater and spring discharge of the western GAB can help provide constraints on groundwater flow, as well as provide an understanding of the geochemical and hydrological processes responsible for water quality evolution.

Vertical leakage (discharge to upper aquifers) is an important but poorly constrained component of water balance in the Great Artesian Basin (GAB), Australia. It ranges from negligible discharge where the GAB is overlain by aquitards, to high discharge where artesian water feeds the shallow unconfined aquifer (thereby raising the water table) causing elevated surface soil moisture and extensive surface salinisation. Adequately representing the temporal and spatial variability of vertical leakage is difficult due to the large scale over which the discharge occurs. An innovative method is presented that integrates a supervised classification of high-discharge zones using time-series Landsat data with landform mapping information to improve classification results. ‘Wetness persistence’ and ‘salt persistence’ classes, determined from the time series data, are related to groundwater discharge processes through a discharge framework that allows scaling up of field-based discharge estimates. The results show that using multi-image classification integrated with landform data will significantly reduce uncertainty by reducing false positives. No significant temporal trends were found in a time series assessment, with results featuring high variability, most likely due to image normalisation issues. The lack of a clear temporal signal suggests that an assumption of steady-state discharge is valid for estimating annual fluxes of vertical leakage. Supervised classification and landform outputs provide updated knowledge on GAB vertical leakage rates by providing useful lower and upper bounds of discharge rates respectively. Additionally, groundwater-dependent ecosystem classification, covering the full extent of the basin margins, is a new source of information resulting from the work.

The misunderstanding of hydrogeological processes together with the oversimplification of aquifer conceptual models result in numerous inaccuracies in the management of groundwater resources. In Central Chile (32–36°S), hydrogeological studies have exclusively focused to alluvial aquifers in valleys (~15% of total area) and mountain-front zones remain considered as no-flux boundary conditions. By a topological approach and an analysis of fractures, the hydrogeological potential of the Western Andean Front along the N–S-oriented Pocuro Fault Zone (PFZ) in the Aconcagua Basin were determined. Perennial springs (23) show evidence of groundwater flows into the fractured Principal Cordillera. Topology allows for quantification of the density of connected fractures within the fault zone and its relationship with groundwater circulation. The study results highlight two areas where the density of fractures and connected nodes (Nc) is high (>2.4 km/km², 2.5 Nc/km²). Both areas are topologically related to the main springs of the PFZ: Termas de Jahuel (discharge ~14.0 m³/h at 22 °C) and Termas El Corazón (discharge ~7.2 m³/h at 20 °C). Outcrop-scale mapping reveals that groundwater outflows from NW–SE fractures, which is consistent with the preferential orientation of the fracture network (N30–60 W) within the PFZ. The results indicate that oblique basement faults are discrete high-permeability structures conducting groundwater across the Western Andean Front from the Principal Cordillera up to adjacent alluvial aquifers (focused recharge). Therefore, the simplistic hydrogeological view of the Western Andean Front (i.e. impervious limit) is partially erroneous.

The original version of this article unfortunately contained a misprint. Eq. 8 was written incorrectly.

Permafrost thaw is a complex process resulting from interactions between the atmosphere, soil, water and vegetation. Although advective heat transport by groundwater at depth likely plays a significant role in permafrost dynamics at many sites, there is lack of direct measurements of groundwater flow patterns and fluxes in such cold-region environments. Here, the finite volume point dilution method (FVPDM) is used to measure in-situ groundwater fluxes in two sandy aquifers in the discontinuous permafrost zone, within a small watershed near Umiujaq, Nunavik (Quebec), Canada. The FVPDM theory is first reviewed, then results from four FVPDM tests are presented: one test in a shallow supra-permafrost aquifer, and three in a deeper subpermafrost aquifer. Apparent Darcy fluxes derived from the FVPDM tests varied from 0.5 × 10⁻⁵ to 1.0 × 10⁻⁵ m/s, implying that advective heat transport from groundwater flow could be contributing to rapid permafrost thaw at this site. In providing estimates of the Darcy fluxes at the local scale of the well screens, the approach offers more accurate and direct measurements over indirect estimates using Darcy’s law. The tests show that this method can be successfully used in remote areas and with limited resources. Recommendations for optimizing the test protocol are proposed.