A study in eastern Taiwan evaluated the importance of montane water contribution (MC) to adjacent valley-plain groundwater (VPG) in a tectonic suture zone. The evaluation used a ternary natural-tracer-based end-member mixing analysis (EMMA). With this purpose, VPG and three end-member water samples of plain precipitation (PP), mountain-front recharge (MFR), and mountain-block recharge (MBR) were collected and analyzed for stable isotopic compositions (δ²H and δ¹⁸O) and chemical concentrations (electrical conductivity (EC) and Cl⁻). After evaluation, Cl⁻ is deemed unsuitable for EMMA in this study, and the contribution fractions of respective end members derived by the δ¹⁸O–EC pair are similar to those derived by the δ²H–EC pair. EMMA results indicate that the MC, including MFR and MBR, contributes at least 70% (679 × 10⁶ m³ water volume) of the VPG, significantly greater than the approximately 30% of PP contribution, and greater than the 20–50% in equivalent humid regions worldwide. The large MC is attributable to highly fractured strata and the steep topography of studied catchments caused by active tectonism. Furthermore, the contribution fractions derived by EMMA reflect the unique hydrogeological conditions in the respective study sub-regions. A region with a large MBR fraction is indicative of active lateral groundwater flow as a result of highly fractured strata in montane catchments. On the other hand, a region characterized by a large MFR fraction may possess high-permeability stream beds or high stream gradients. Those hydrogeological implications are helpful for water resource management and protection authorities of the studied regions.

For the quantitative evaluation of the impact of mining on a groundwater system, it is necessary to constrain the hydrogeological and mechanical properties. However, the in situ estimation of the mechanical properties of rock such as compressibility and porosity, is often difficult. Additionally, determining the hydraulic properties such as hydraulic conductivity, of rock by conventional methods is often expensive. The response of the groundwater level to external loading such as Earth tides and barometric pressure, couples the hydrogeological and mechanical processes of rocks, thus providing a way to infer these properties in the field. This study compared aquifer parameters inferred from tidal and barometric responses with those inferred from conventional hydraulic tests and rock mechanics tests in three groundwater monitoring wells at a site in China. The results show that the hydraulic conductivity inferred from a tidal response is similar to that of a pumping test. The compressibility values calculated for the three wells are all higher than those determined by experiment, and the porosity values calculated are all lower than those determined by experiment, but the differences between the calculated and experimentally measured values are lower than one order of magnitude. Considering the costs and convenience of the water-level response method, this method is a good choice for obtaining the properties of an aquifer, especially those in areas of tectonic activity and those affected by anthropogenic perturbations.

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.

Although water is scarce in most deserts of the world, the middle-latitude desert of Hunshandake, China, has abundant water resources, mainly groundwater. In this study, isotopic and hydrochemical compositions were investigated to understand the recharge of groundwater in this desert. The groundwaters are fresh and depleted in δ²H and δ¹⁸O, compared with modern precipitation, but have high values of tritium (5–25 TU), indicating that these groundwaters are likely less than 70 years old but not of meteoric origin. Clear differences were observed between the north and south parts of the desert. Groundwater in the northern part is characterized by lower landform elevation, lower ion concentrations, higher tritium contents, higher deuterium excess, and more depleted values of δ²H and δ¹⁸O than that in the southern part. This indicates a discrepancy between the topographic hydraulic gradient and the isotopic and hydrochemical gradients of groundwater in the desert. It also implies different water sources between the two areas. Combined analysis was further performed on natural waters from the Dali Basin and surrounding mountains. It indicated that groundwater in the north is mainly sourced from the Daxin’Anling Mountains, by leaking of the Xilamulan River water through a thick faulted aquifer. Groundwater in the south has two sources, the Yinshan Mountains and Daxing’Anlin Mountains. Therefore, modern focused recharge is more significant for groundwater recharge in the desert than the mechanisms of diffuse recharge. A conceptual model of groundwater recharge is proposed: the MTVG (mountain water – tectonic fault hydrology – unconfined vadose zone – groundwater) mechanism.

Shenzhen is the major financial and high-tech center in southern China. The megacity has grown rapidly in the last 40 years with the population increasing from about 30,000 in 1979 to 20 million in 2016. The study area (2,015 km²) is about 42% urban and 58% undeveloped land. The rapid development of the megacity has resulted in severe degradation of the groundwater and surface-water resources and has created a nearly insatiable demand for water, with an average consumption of 2000 × 10⁶ m³/year. Groundwater is an important component of the baseflow of the many streams in the area and is used for potable water supply and irrigation in some of the rural parts of the municipality. This study develops a conceptual model and quantitative framework for assessing the groundwater resources of Shenzhen. The groundwater system consists of shallow aquifers of alluvium and weathered bedrock overlying low permeability igneous and sedimentary rocks. The complex geologic setting was conceptualized as a block structure with blocks bounded by high-angle faults. The water budget in Shenzhen was quantified. The estimated average groundwater discharge is about 12% of annual precipitation. The study provides a starting point to investigate how a megacity such as Shenzhen should manage and protect its groundwater as a strategic resource and environmental asset. It is also a basic management tool for analyzing and contributing to urban drainage concepts such as the “sponge city”.

A preliminary conceptual model of groundwater flow was developed for the Serra Geral fractured basalt aquifer in order to assess the recharge to the underlying sandstone Guarani Aquifer System, one of the main aquifer systems in Brazil, which supplies water to millions of people. Detailed geological investigations included macroscopic description of the basalt flow units and the underlying sandstone. Petrographic and chemical analyzes were conducted on rock samples from outcrops and from five drilled boreholes. Detailed fracture surveys were accomplished at outcrops to characterize fracture sets and their potential to transmit water in the current tectonic context. Four basalt flows were identified in the Ribeirao Preto area and were named B1, B2, B3 and B4 (from oldest to youngest). The cooling process in flow B3 led to the generation of large sub-horizontal fractures at the contacts B2/B3 and B3-C/B3-E, which are the most transmissive structures. Groundwater flow in the basalt appears to be of the stratabound type because fractures, in general, do not propagate through the basalt vesicular layers, which behave as a regional hydraulic barrier for the vertical groundwater flow. However, it is proposed that the localized, continuous and closely spaced subvertical tectonic fractures, the only features that have the potential to crosscut the vesicular layers and the intertrappe sediments, can vertically connect the sub-horizontal transmissive fractures. Weathering and water seepage, observed in rock exposures, indicate that subvertical NE-trending fractures would be the most transmissive in the Ribeirao Preto area.

The Kasserine Aquifer System (KAS) is a transboundary aquifer, located in an arid region in central Tunisia and extending into northeastern Algeria. The system consists of four compartments: Oum Ali-Thelepte, Feriana-Skhirat, and the Plateau and the Plaine of Kasserine. The challenge of this study was to evaluate the influence of regional faults on groundwater flow in the different compartments of the KAS and to estimate the regional impact of current and future groundwater use. A three-dimensional saturated regional groundwater flow model for the steady state and transient conditions (1980–2015) was created and calibrated. This work was achieved using numerical flow modelling, coupled with geological modelling, using FEFLOW and GeoModeller software. The significance of regional faults as potential barriers or conduits to groundwater flow in the different aquifer compartments was evaluated by considering the different recharge rates. Two connectivity hypotheses were proposed at each major fault, and the general hydraulic relationship of units that are juxtaposed by each fault were considered. This study contributes rigorous estimates for the diffuse and concentrated recharge in the arid study region, and evaluates the groundwater behavior that shows a gradual decline in the water table over time, using a regional model. Different predicted outcomes for the KAS based on variable potential groundwater extraction scenarios for the period 2015–2050 have been developed. The results of numerical simulation provide useful information regarding the behavior of the KAS aquifers, and contribute significant knowledge to guide sustainable practice for present and future groundwater management.