Water storage assessment is an important component of feasibility studies for prospective mining areas. As required by national mineral resources and environmental Acts, this may include assessment of both exploitable and sustainable storage; the former relates to the amount of groundwater stored within the exploitable aquifer depth and the latter is defined as the groundwater that can be sustainably extracted without producing unacceptable environmental and economic problems. A simplified method is proposed to assess the groundwater storage in a typical mine area, Tugela in South Africa. In the area, five aquifers (Natal Group, Coastal plain deposits, Basement aquifer, Ecca Group and Dwyka Group) have better harvest potential compared with others on the basis of borehole yield. The study area was divided into four subareas (A, B, C and F) based on proposed mining boundaries. Both exploitable and sustainable groundwater storage were estimated. The estimated exploitable groundwater storage for subareas A, B, C and F are 20.66, 5.78, 43.12, 36.90 Mm³, respectively, on the basis of current median exploitation depths of each aquifer or geological formation. The calculated sustainable groundwater storage for subareas A, B, C and F are 3.31, 0.89, 6.67 and 6.01 Mm³, respectively, with a total of 16.88 Mm³. Groundwater recharge of the subareas was also estimated for subareas A, B, C and F as 31.92, 11.44, 43.38 and 29.78 Mm³/annum, respectively, with a total of 116.53 Mm³/annum. The assessment method can be applied to other areas with similar hydrogeological settings with the available datasets.

Irrigation in low-lying coastal plains may enhance the formation of fresh groundwater lenses, which counteract salinization of groundwater and soil. This study presents seasonal dynamics of such a freshwater lens and discusses its influence on the salinity distribution of the unconfined aquifer in the coastal plain of Ravenna, Italy, combining field observations with numerical modeling (SEAWAT). The lens originates from an irrigation ditch used as a water reservoir for spray irrigation. The geometry of the freshwater lens shows seasonal differences because of freshwater infiltration during the irrigation season and upconing of deeper saltwater for the remainder of the year. The extent of the freshwater lens is controlled by the presence of nearby drainage ditches. Irrigation also results in a temperature anomaly in the aquifer because of the infiltration of warm water during the irrigation season. The surficial zone in the vicinity of the irrigation ditch is increased considerably in thickness. Finally, different irrigation alternatives and the influence of sea-level rise are simulated. This shows that it is necessary to integrate irrigation planning into the water management strategy of the coastal zone to have maximum benefits for freshening of the aquifer and to make optimal use of the existing infrastructure.

Sharp-interface (or interface) flow models with Dupuit-Forchheimer approximation are widely used to assess, to first order, an aquifer’s vulnerability to seawater intrusion (SWI) and to evaluate sustainable management options for coastal groundwater resources at the screening level. Recognising that interface flow models overestimate SWI, corrections have been proposed to account for the neglected mixing and also for the outflow through a finite gap. These corrections, however, were introduced in the context of specific studies and may not be generally applicable as proposed. The interface model is revisited, placing its corrections in the context of variable-density flow (VDF) theory, by expressing them in terms of the dimensionless parameters governing VDF in schematised (aspect ratio = thickness/length) homogeneous confined coastal aquifers: the coupling parameter (α), a Péclet number (Pe), and the dispersivities ratio (rα). Interfaces are compared to the 50%-salinity lines of VDF numerical solutions and regression equations are developed for estimating the outflow gap and for correcting the length of the interface (terminating with a blunted edge); the dispersion correction, which modifies the interface curvature, is restated with a variable exponent. The corrections for dispersion and for the interface length appear to be the most effective; an outflow gap is important only at small α values (strong advection relative to vertical flow due to density differences). These concepts are applied successfully to calculate the interface position in the lowermost confined sub-unit of the Coastal Plain aquifer of Israel, as an estimate of SWI.

Apparent groundwater ages along two flow paths in the upper Patapsco aquifer of the Maryland Atlantic Coastal Plain, USA, were estimated using 14C, 36Cl and 4He data. Most of the ages range from modern to about 500 ka, with one sample at 117 km downgradient from the recharge area dated by radiogenic 4He accumulation at more than one Ma. Last glacial maximum (LGM) water was located about 20 km downgradient on the northern flow path, where the radiocarbon age was 21.5 ka, paleorecharge temperatures were 0.5–1.5 °C (a maximum cooling of about 12 °C relative to the modern mean annual temperature of 13 °C), and Cl–, Cl/Br, and stable isotopes of water were minimum. Low recharge temperatures (typically 5–7 °C) indicate that recharge occurred predominantly during glacial periods when coastal heads were lowest due to low sea-level stand. Flow velocities averaged about 1.0 m a–1 in upgradient parts of the upper Patapsco aquifer and decreased from 0.13 to 0.04 m a–1 at 40 and 80 km further downgradient, respectively. This study demonstrates that most water in the upper Patapsco aquifer is non-renewable on human timescales under natural gradients, thus highlighting the importance of effective water-supply management to prolong the resource.

Temperature distribution and heat transport are studied in a coastal aquifer at De Panne in the western Belgian coastal plain. Field observations include temperature profiles of groundwater in the dunes and temperature measurements at the water table in a profile on the shore. Freshwater–saltwater distribution is known from previous studies. These are used to constrain a density-dependent model simulating the freshwater–saltwater distribution and heat transport using the SEAWAT code. The yearly fluctuation of the groundwater temperature in the phreatic aquifer under the dunes, shore and sea, and the influence of a tidal inlet in the dunes are simulated. The observations show that seawater temperature variations determine the temperature variations on the shore whereas atmospheric temperature changes determine this in the dunes. Yearly temperature fluctuations imposed at the water table propagate mainly vertically in the aquifer with only limited lateral influence. Heat transport is mainly convection dominated. Thickness of the surficial zone is determined by the amplitude of the groundwater temperature at the water table and the groundwater flow. Establishment of a tidal inlet in the dunes results in asymmetric temperature profiles under and in the vicinity of it.

Understanding groundwater-pumpage sources is essential for assessing impacts on water resources and sustainability. The objective of this study was to quantify pumping impacts and sources in dipping, unconfined/confined aquifers in the Gulf Coast (USA) using the Texas Carrizo-Wilcox aquifer. Potentiometric-surface and streamflow data and groundwater modeling were used to evaluate sources and impacts of pumpage. Estimated groundwater storage is much greater in the confined aquifer (2,200 km3) than in the unconfined aquifer (170 km3); however, feasibility of abstraction depends on pumpage impacts on the flow system. Simulated pre-development recharge (0.96 km3/yr) discharged through evapotranspiration (ET, ∼37%), baseflow to streams (∼57%), and to the confined aquifer (∼6%). Transient simulations (1980–1999) show that pumpage changed three out of ten streams from gaining to losing in the semiarid south and reversed regional vertical flow gradients in ∼40% of the entire aquifer area. Simulations of predictive pumpage to 2050 indicate continued storage depletion (41% from storage, 32% from local discharge, and 25% from regional discharge capture). It takes ∼100 yrs to recover 40% of storage after pumpage ceases in the south. This study underscores the importance of considering capture mechanism and long-term system response in developing water-management strategies.

Salinization in coastal aquifers is usually related to both seawater intrusion and water–rock interaction. The results of chemical and isotopic methods were combined to identify the origin and processes of groundwater salinization in Daguansha area of Beihai, southern China. The concentrations of the major ions that dominate in seawater (Cl⁻, Na⁺, Ca²⁺, Mg²⁺ and SO ₄²–), as well as the isotopic content and ratios (²H, ¹⁸O, ⁸⁷Sr/⁸⁶Sr and ¹³C), suggest that the salinization occurring in the aquifer of the coastal plain is related to seawater and that the prevailing hydrochemical processes are evaporation, mixing, dissolution and ion exchange. For the unconfined aquifer, groundwater salinization has occurred in an area that is significantly influenced by land-based sea farming. The integrated impacts of seawater intrusion from the Beibuwan Gulf and infiltration of seawater from the culture ponds are identified in the shallowest confined aquifer (I) in the middle of the area (site BBW2). Leakage from this polluted confined aquifer causes the salinization of groundwater in the underlying confined aquifer (II). At the coastal monitoring site (BBW3), confined aquifer I and lower confined aquifer II are heavily contaminated by seawater intrusion. The weak connectivity between the upper aquifers, and the seaward movement of freshwater, prevents saltwater from encroaching the deepest confined aquifer (III). A conceptual model is presented. Above all, understanding of the origin and processes of groundwater salinization will provide essential information for the planning and sustainable management of groundwater resources in this region.

The quantification of vertical groundwater fluxes across semi-confining layers is fundamental to evaluate groundwater recharge and discharge rates to and from aquifer systems. Methods to estimate vertical groundwater fluxes from temperature–depth profiles have been available since the 1960s. While some methodologies assume steady-state conditions, changes in land-surface temperatures as well as hydrogeological conditions can lead to transient heat flow conditions. Indeed, many studies have indicated that transient temperatures in deeper confined aquifers are widespread. A study is presented that uses transient-temperature–depth curves obtained from groundwater observation wells in the Chianan coastal plain in southern Taiwan. In this area, sedimentary aquifer systems consist of a stack of alternating sand and mud layers, over several hundred meters in thickness. Groundwater has been abstracted from these aquifers for decades, resulting in large hydraulic gradients between the shallow and deeper aquifers. Hence, vertical groundwater flow is likely enhanced across finer-grained, semi-confining units. A set of temperature–depth profiles is available from this area. Constrained by these profiles, numerical models of one-dimensional transient heat transfer were used to infer vertical fluxes of 3.3 × 10⁻⁸ to 3.9 × 10⁻⁸ m/s using thermal data from 2013 to 2016. An analytical solution was also employed that assumes steady-state conditions. Calculated fluxes using the latter approach were lower, at approximately 1.1 × 10⁻⁸ to 1.6 × 10⁻⁸ m/s. The study suggests that vertical fluxes derived from using Bredehoeft and Papadopulos’s analytical solutions result in underestimates of actual vertical seepage rates across aquitards.