A controlled artificial recharge and drainage (CARD) system was used to increase freshwater lenses below creek ridges to increase freshwater supply. Creek ridges are typical geomorphological features that lie up to 2 m higher than the surroundings in the reclaimed tidal flat landscape of the southwestern Netherlands. The 5–30-m thick freshwater lenses below the creek ridges are a vital source for irrigation, as the groundwater and surface waters are predominantly saline. However, freshwater supply from these lenses is commonly not sufficient to meet the irrigation demand, which leads to crop damage. The CARD system was tested in the field and the development of the freshwater lens was monitored during the period May 2013 to May 2014. Numerical models, which were used to investigate a long-term effect of the CARD system, predicted that below the center of the creek ridge, the 13–15-m thick freshwater lens increased 6–8 m within 10 years. The total volumetric increase of the freshwater lens was about 190,000 m³ after 10 years, which was about 40 % of the total recharge (natural and artificial recharge). From this increased freshwater lens, up to three times more water can be extracted using horizontal wells, compared to the initial size of the freshwater lens. A higher water table in the CARD system leads to a thicker freshwater lens but a lower storage efficiency. A lower water table has the opposite effect.

A wide range of lithologic units and tectonic disturbances by cross-cutting faults and folds has resulted in the quite complex hydrogeological setting of the sedimentary outlier and its surroundings at Mekelle, northern Ethiopia. The environmental isotopes of oxygen and hydrogen and patterns of dissolved ion concentrations in the groundwater, coupled with understanding of the three-dimensional geological framework, are used to conceptualize the groundwater flow model and recharge–discharge mechanisms in the area. In agreement with the piezometric-surface map, recharge areas are determined to be the highlands (northwest, north, east and south of the study area), characterized by relatively more depleted isotopic compositions, higher d-excess, and lower concentrations of dissolved ions in the groundwater samples; the narrow major river valleys of Giba, Illala, Chelekot and Faucea Mariam are discharge areas. The groundwater divide between the Tekeze and the Denakil basins coincides with the surface-water divide line of these two basins. In most cases, groundwater feeds the semi-perennial streams and rivers in the area. However, isotopic signatures in some wells indicate that there are localities where river flow and seepage from micro-dams locally feed the adjacent aquifers. The lithostratigraphic, geomorphologic, isotopic and hydrochemical settings observed in this study indicate that three groundwater flow systems (shallow/local, intermediate and deep/semi-regional) can exist here. Tritium data indicate that the groundwater in the study area has generally short residence time and is dependent on modern precipitation.

A geographic information system (GIS)-based water-budget framework has been developed to study the climate-change impact on regional groundwater recharge, and it was applied to the Southern Hills aquifer system of southwestern Mississippi and southeastern Louisiana, USA. The framework links historical climate variables and future emission scenarios of climate models to a hydrologic model, HELP3, to quantify spatiotemporal potential recharge variations from 1950 to 2099. The framework includes parallel programming to divide a large amount of HELP3 simulations among multiple cores of a supercomputer, to expedite computation. The results show that a wide range of projected potential recharge for the Southern Hills aquifer system resulted from the divergent projections of precipitation, temperature and solar radiation using three scenarios (B1, A2 and A1FI) of the National Center for Atmospheric Research’s Parallel Climate Model 1 (PCM) and the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Lab’s (GFDL) model. The PCM model projects recharge change ranging from −33.7 to +19.1 % for the 21st century. The GFDL model projects less recharge than the PCM, with recharge change ranging from −58.1 to +7.1 %. Potential recharge is likely to increase in 2010–2039, but likely to decrease in 2070–2099. Projected recharge is more sensitive to the changes in the projected precipitation than the projected solar radiation and temperature. Uncertainty analysis confirms that the uncertainty in projected precipitation yields more changes in the potential recharge than in the projected temperature for the study area.

Groundwater models are useful in improving knowledge of groundwater flow processes, both for testing existing hypotheses of how specific systems behave and predicting the response to various environmental stresses. The recent advent of highly detailed three-dimensional (3D) geological-framework models provides the most accurate representation of the subsurface. This type of modelling has been used to develop conceptual understanding of groundwater in the complex Quaternary deposits of Glasgow, Scotland (UK). Delineating the 3D geometry of the lithostratigraphical units has allowed the most detailed conceptualisation of the likely groundwater flow regime yet attempted for these superficial deposits. Recharge and groundwater flow models have been developed in order to test this conceptual understanding. Results indicate that the direction of groundwater flow is predominantly convergent through the permeable, relatively thick Quaternary deposits of the Clyde valley towards the River Clyde, which runs through Glasgow, with some indication of down-valley flow. A separate nearby system with thick and potentially permeable Quaternary deposits, the Proto-Kelvin Valley, may also be a significant conveyor of groundwater towards the River Clyde, although the absence of local data makes any conclusions conjectural. To improve the robustness of the current model there is a need for an overall increase in good quality groundwater-level data, particularly outside central Glasgow. A prototype groundwater-monitoring network for part of Glasgow is an encouraging development in this regard. This would allow the development of a time-variant groundwater model which could be used to study future modelling scenarios.

Contributions of groundwater to the soil-water balance play an important role in areas with shallow water tables. The characteristics of daytime and nighttime water flux using non-weighing lysimeters were studied from June to September 2012 and 2013 in the extremely arid Xinjiang Uyghur Autonomous Region in northwestern China. The study consisted of nine treatments: three surface conditions, bare soil and cotton plants, each with water tables at depths of 1.0, 1.5, and 2.0 m; and plastic mulch with a water table at 1.5 m but with three percentages of open areas (POAs) in the plastic. The groundwater supply coefficient (SC) and the groundwater contribution (GC) generally varied with surface conditions. Both SC and GC decreased in the bare-soil and cotton treatments with increasing depth of the groundwater. Both SC and GC increased in the plastic-mulch treatment with increasing POA. Average nighttime GCs in the bare-soil treatments in July and August (the midsummer months) were 50.8–60.8 and 53.2–65.3 %, respectively, of the total daily contributions. Average nighttime GCs in the cotton treatments in July and August were 51.4–60.2 and 51.5–58.1 %, respectively, of the total daily contributions. The average GCs in June and September, however, were lower at night than during the daytime. Soil temperature may thus play a more important role than air temperature in the upflow of groundwater.

Well vulnerability assessment is essential for groundwater source protection. A quantitative approach to assess well vulnerability in a well capture zone is presented, based on forward solute transport modeling. This method was applied to three groundwater source areas (Jiuzhan, Hadawan and Songyuanhada) in Jilin City, northeast China. The ratio of the maximum contaminant concentration at the well to the released concentration at the contamination source (cₘₐₓ/c₀) was determined as the well vulnerability indicator. The results indicated that well vulnerability was higher close to the pumping well. The well vulnerability in each groundwater source area was low. Compared with the other two source areas, the cone of depression at Jiuzhan resulted in higher spatial variability of cₘₐₓ/c₀and lower minimum cₘₐₓ/c₀by three orders of magnitude. Furthermore, a sensitivity analysis indicated that the denitrification rate in the aquifer was the most sensitive with respect to well vulnerability. A process to derive a NO₃−N concentration at the pumping well is presented, based on determining the maximum nitrate loading limit to satisfy China’s drinking-water quality standards. Finally, the advantages, disadvantages and prospects for improving the precision of this well vulnerability assessment approach are discussed.

Groundwater recharge is an important metric for sustainable water management, particularly in semi-arid regions. Hard-rock aquifers underlie two-thirds of India and appropriate techniques for estimating groundwater recharge are needed, but the accuracy of such values is highly uncertain. The chloride mass balance (CMB) method was employed to estimate annual groundwater recharge rates in a monsoon-dependent area of Jaisamand Lake basin in Rajasthan, which contains the Gangeshwar watershed. A monitoring program was established within the watershed during summer 2009, with local participation for the collection of rainfall and groundwater samples. Groundwater recharge was estimated spatially over a 3-year period with pre-monsoon and post-monsoon datasets. Recharge rates estimated using the CMB method were then compared to those estimated using the water-table fluctuation (WTF) method. Specific yield was 0.63 % and assumed to be homogenous across the watershed. The average recharge rate derived from the WTF method (31 mm/year) was higher than that derived from the CMB method (24.3 mm/year). CMB recharge rates were also applied to obtain a water balance for the watershed. CMB recharge rates were used to estimate annual groundwater replenishment and were compared with estimates of groundwater withdrawal using Landsat imagery. Over the 2009–2011 study period, groundwater demand was about seven times greater than the estimated groundwater renewal of 5.6 million cubic meters. This analysis highlights the challenges associated with estimating groundwater recharge in fractured hard-rock aquifers, and how renewable groundwater-resource estimates can be used as a metric to promote sustainable water use.

Groundwater time-series modeling has emerged as an efficient approach for simulating the impacts of multiple drivers of groundwater-head variation such as rainfall, evaporation and groundwater pumping. However, a bottom-up approach has generally been adopted whereby the input drivers have been assumed without statistical evidence for their inclusion. In this study, a parsimonious time-series model was adopted which accounts for various drivers and is able to simulate the overall groundwater-head variation. It can also separate the effects of pumping and climate drivers on multi-annual time series of groundwater-level variation. The time-series model consists of a soil-moisture layer to account for non-linearity between rainfall and recharge, as well as different pumping response functions to account for pumping from a single well, lake-induced recharge and the effects of multiple pumping bores. The method was applied to a groundwater-pumping region in south-eastern Australia. The results showed that the model is able to separate the effects of pumping from the effects of climate on groundwater-head variation. However, improved estimation of those influences requires a flexible model structure that can account for spatially varying physical processes within the study region such as the relative influence of single or multiple pumping bores and induced recharge from surface-water bodies.

Recharge through injection wells is a well-established technique to remediate and protect coastal aquifers from saltwater intrusion. In this study, it is shown that hydrothermal doublet installations can also be used to protect coastal aquifers while producing heat or cold for air conditioning. Such a method could be extremely valuable for situations where there is both a need for freshwater and energy production in coastal regions. The efficiency of the proposed approach is tested using Strack’s analytical solution on a wide range of scenarios where the number of injection and pumping wells vary as well as the distance between these wells and the coast. The efficiency is evaluated through four control parameters: the relative freshwater volume, the maximum penetration distance of the saltwater toe, the thermal breakthrough time, and the percentage of injected water recycled. The analysis of these parameters computed for 343 scenarios confirms the efficiency of the method. Those results are extremely encouraging even if they still need to be confirmed through field experiments.

Estimation of groundwater recharge is of critical importance for effective management of freshwater resources. Three common and distinct approaches for calculating recharge rely on techniques of baseflow separation, well hydrograph analysis, and numerical modeling. In this study, these three methods are assessed for a watershed in southwestern Quebec, Canada. A physically based surface–subsurface model provides estimates of spatially distributed recharge; two baseflow separation filters estimate recharge from measured streamflow; and a well hydrograph master recession curve technique calculates recharge from water-table elevation records. The recharge results obtained are in good agreement over the entire catchment, producing an annual aquifer recharge of 10–30 % of rainfall. The annual average estimated across all methods is 200 mm/year. High variability is obtained for the monthly and seasonal recharge patterns (e.g. respectively, 0–30 mm for September and 0–95 mm for the summer), in particular between the baseflow filters and the well hydrograph technique and between the hydrograph technique and the simulated estimates at the observation wells. Recharge occurs predominantly in the spring months for the different approaches, except for the master recession curve method for which the highest recharge estimates are obtained during the summer. The recharge distribution obtained with the model shows that the main recharge area of the aquifer is the Covey Hill region. The use of a fully integrated physically based model enables the construction of an arbitrary number of well hydrographs to enhance the representativity of the master recession curve technique.