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Assessment of recharge in a structurally complex upland karst limestone aquifer situated in a semi-arid environment is difficult. Resort to surrogate indicators such as measurement of spring outflow and borehole discharge, is a common alternative, and attempts to apply conventional soil moisture deficit analysis may not adequately account for the intermittent spate conditions that arise in such environments. A modelling approach has been made using the West Bank Mountain Aquifer system in the Middle East as a trial. The model uses object oriented software which allows various objects to be switched on and off. Each of the main recharge processes identified in the West Bank is incorporated. The model allows either conventional soil moisture deficit analysis calculations or wetting threshold calculations to be made as appropriate, and accommodates both direct recharge and secondary recharge. Daily time steps enable recharge and runoff routing to be calculated for each node. Model runs have enabled a series of simulations for each of the three aquifer basins in the West Bank and for the whole of the West Bank. These provide recharge estimates comparable to those prepared by earlier workers by conventional means. The model is adaptable and has been successfully used in other environments.

The inter-relations between the sea, coastal river and groundwater were studied in the eastern Mediterranean bar-built estuary of Alexander River (Israel), which is subjected to seawater encroachment. In this river, seawater encroachment occurs in response to coastal waves and down-river discharge events. Accordingly, significant stratification occurs mostly during winter (1–3 times a year) following sandbar breaching, with salinities at the deep layer reaching 35 and 27 ‰, 500 and 3,900 m from the shoreline during the study period, respectively. During the summer, the water in the estuary is partially mixed and the salinity in the deep layer significantly decreases, but never below 6 ‰. Salinization of the aquifer adjacent to the river was studied by electrical resistivity and crosschecked with observations in shallow boreholes. Both methods suggest that aquifer salinization is site-dependent, with the extent of salinization being controlled by the local geology. While in sandy units, salinization extends to at least 80 m from the river channel, salinization is limited to no more than 20 m from the river in silty units. The existence of the low-permeability units adjacent to the river prevented salinization of the regional aquifer. Based on these findings, significant salinization impact on the aquifer in the near future due to the ongoing sea-level rise is not anticipated.

Groundwater recharge is a key factor in water-balance studies, especially in (semi-)arid areas. In this study, multiple methods were used to estimate groundwater recharge in the Ordos Plateau (China), including reference to water-table fluctuation, Darcy’s law and the water budget. The mean annual recharge rates found were: water-table-fluctuation method (46–109 mm/yr); saturated-zone Darcian method (17–54 mm/yr); and water-budget method (21–109 mm/yr). Generally, groundwater-recharge rates are higher in the eastern part of the plateau where the land surface is covered by permeable sand that is favorable for infiltration. Along with results from previous studies using the empirical method, the chloride-mass-balance method, the unsaturated-zone Darcian method and the hydrograph-separation method, groundwater recharge rates were compared. There is no one method that would consistently produce the largest or smallest estimate of annual recharge for all groundwater systems. The largest recharge estimates were usually determined using the unsaturated-zone Darcian method and the smallest estimates were usually determined using the chloride-mass-balance method. Comparison of multiple methods is found to be valuable for determining the range of plausible recharge rates and for highlighting the uncertainty of the estimates.

Newly acquired high-quality data are being used to reinterpret the Surat Basin flow systems of the Great Artesian Basin (GAB) in Australia. This paper revisits and updates previous interpretations of flow in the Hutton Sandstone with detailed analysis of the Dawson River area in the northern Surat Basin. Combining analysis of high-resolution permeability measurements with hydraulic head and hydrochemistry data supports the contention that there is significant flow towards the northeast, counter to the canonical regional flow conceptualisation of the GAB. The analysis in this work better identifies the likely discharge to be in the area that the Dawson River intersects the Hutton Sandstone. Heterogeneity in physical and hydrochemical properties suggests that local flowpaths are more complex than previously thought and, at least in this part of the Hutton aquifer, very little recharge contributes to flow deeper in the basin. These results provide a firm basis on which to refine and develop numerical hydrodynamic models of the basin, at least for the Hutton aquifer.

Changes in groundwater level during earthquakes have been reported worldwide. In this study, field observations of co-seismic groundwater-level changes in wells under different aquifer conditions and sampling intervals due to near-field earthquake events in Taiwan are presented. Sustained changes, usually observed immediately after earthquakes, are found in the confined aquifer. Oscillatory changes due to the dynamic strain triggered by passing earthquake waves can only be recorded by a high-frequency data logger. While co-seismic changes recover rapidly in an unconfined aquifer, they can sustain for months or longer in a confined aquifer. Three monitoring wells with long-term groundwater-level data were examined to understand the association of co-seismic changes with local hydrogeological conditions. The finite element software ABAQUS is used to simulate the pore-pressure changes induced by the displacements due to fault rupture. The calculated co-seismic change in pore pressure is related to the compressibility of the formation. The recovery rate of the change is rapid in the unconfined aquifer due to the hydrostatic condition at the water table, but slow in the confined aquifer due to the less permeable confining layer. Fracturing of the confining layer during earthquakes may enhance the dissipation of pore pressure and induce the discharge of the confined aquifer. The study results indicated that aquifer characteristics play an important role in determining groundwater-level changes during and after earthquakes.

Water flow is an essential aspect in the long-term management of mine tailings. Flow through tailings piles deposited on the surface influence chemical reactions and the migration of pollutants into the environment. This study focuses on one of the tailings piles from the former Le Cellier mining site (Lozère, France) resulting from uranium heap leaching. The site is now decommissioned, and all seepage water is collected and treated before release into the environment, with monitoring on a daily or monthly basis since 1991. From the calculated water balance, it is noted that evapotranspiration corresponds to 45% of the precipitation and affects the hydrological behaviour of the pile in summer and autumn. Auto-correlation analyses suggest that the drain discharges have a low inertia with a memory effect of 2–3 months. The cross-correlations between the rainfall and the drain discharges indicate a quarterly to semiannual pattern, in which the flows react to rainfall and influence the chemical parameters. A hydrodynamic model was developed with the HYDRUS software package, which describes the expected average hydrologic behaviour of the pile according to the monthly observed discharge data (2010–2018). The homogeneous and the stochastic distributions of hydraulic conductivity produced simulations showing that the water distribution in the pile varies seasonally according to the wet and the dry periods. However, the water content (2.9–3.8%) remains low throughout the simulation period, suggesting a possible reactivity of the tailings and that, during rainfall events, leaching and dissolution of residual acid from sulphate-bearing minerals increase.

The Boom clay is considered as a candidate host rock for the Belgian disposal of radioactive waste. Thanks to the recent sinking of a new shaft to extend the Underground Research Laboratory (URL) at the Mol site, new in-situ data have been obtained. They consist in the observation of significant fracturing, evidenced during the excavation of the shaft annexes, and in correlated hydraulic perturbations in the far field (maximum of 0.2 MPa at 60-m radius). These observations cannot be explained from simple poroplastic models that predict a maximum perturbation extent of 25 m under full deconfinement. Thus, models with increasing complexity are built to explain this discrepancy. It is proposed that the low-support pressure imposed by the primary lining, combined with the long time over which this support condition held, has favoured the decompression of the clay massif through time-dependent effects, mainly skeleton viscosity. This resulted in near-field fracturing, leading to an apparent increase of the excavated radius and to a hydraulic perturbation in the far field. This interpretation still needs to be validated/invalidated with future research. The effect on the overall performance of the repository is expected to remain small due to the self-healing nature of the fractures.

Groundwater discharge and non-point source (NPS) loading were evaluated along an urban reach of an eastern-slopes Rocky Mountains river (Bow River, Canada) to understand sources of water-quality impacts and baseflow. The discharge did not increase measurably over a 16-km reach. Groundwater in the river-connected alluvial aquifer was a mixture of river and prairie groundwater, with elevated chloride concentrations (average 379 mg L–1) from road salt. Alluvial groundwater was the major NPS of chloride discharging to the river. Although the mass-flux based estimates of groundwater discharge were small (mean 0.02 m3 s–1 km–1, SD = 0.04 m3 s–1 km–1, n = 30), the associated chloride mass flux over 16 km was significant (equivalent to that discharged from the city’s largest wastewater-treatment-plant effluent). Although local groundwater baseflow was previously thought to contribute significantly to overwinter baseflow in this reach, little contribution was measured in this study. Low baseflow generation is consistent with long-term river discharge data that show almost all of the baseflow generation occurs in the Rocky Mountain reach. Thus, local watershed areas are important for water-quality protection, but climate change in the headwaters is most salient to long-term flow.