Hydrogeology Journal最新文献

Groundwater at depths exceeding 500 m can be an important source of freshwater. However, the characteristics of deep groundwater in many regions of the world, including Indonesia’s sedimentary basins, remain vaguely defined. This study investigates the pressure regimes, hydraulic head distributions, salinity, and hydrochemical facies of deep groundwater using available evidence from oil and gas exploration wells in the Lower Kutai Basin of Indonesia. Pressure measurements and wireline log data reveal three pressure regimes within the basin: hydrostatic, overpressure, and underpressure. The top of the overpressure varies, from close to the surface onshore to depths of ~4.5 and ~3.8 km in the Mahakam Delta and offshore, respectively. Computed hydraulic heads at the top of the overpressure range from ~191 m above sea level onshore to ~71 m below sea level offshore, and are indicative of regional groundwater flow. The observed salinity of deep groundwater within the basin indicates predominantly brackish or saline conditions. Fresh (total dissolved solids < 1 g/L) groundwater to a depth of ~2 km is found at a small minority of wells onshore and in the delta; no fresh groundwater is found offshore. Four hydrochemical facies are observed: Na⁺/Cl^–, Ca²⁺/Cl^–, Na⁺/HCO₃^–, and Na⁺–Ca²⁺/HCO₃^–. This study indicates that deep fresh groundwater in the Lower Kutai Basin is of localized occurrence. Recharge from meteoric water may replenish deep fresh groundwater within the hydrostatic zone and sustain water supplies, whether brackish or fresh. Water produced from clay diagenesis is also cited as a possible process of freshening deep groundwater.

In Chad, hard-rock aquifers are the main source of drinking water for the population located on basement areas. In these basement aquifers, and in particular those of the Guéra region, water drilling failure rates remain high despite research on one- and two-dimensional electrical resistivity techniques and lineaments as a means to improve access to the resource, mainly because these techniques are only used on an observational and structural basis to locate fractures. This study combines electrical resistivity tomography (ERT) with geology, hydrogeology and geomorphology, in order to characterise the structure and geometry of the aquifer system, assess borehole productivity and determine the factors controlling it. After validating the large dataset and its representativeness, 315 high- and low-yield wells, of which 41 have complete geophysical datasets, were selected. This large dataset allows a multi-parameter approach to (1) better characterise each facies according to its electrical resistivity and (2) clearly identify the main formations constituting the local conceptual hydrogeological model. The most suitable areas for productive boreholes are characterised by the presence of an overburden of <20 m depth, well-developed weathered and fractured horizons of granites and biotite granites (preferably) containing little or no clay, and a nearby drainage network. The most substantial flow rates are found in the first 30 m of the fissured horizon, below the base of the alterites. The experience gained from the present study will guide future analysis of ERT sections in order to reduce the probability of drilling dry wells.

The growing water demand and decreasing groundwater recharge have made groundwater management one of the most severe challenges in most countries of the world, and Iran is no exception. This study aims to examine the optimal groundwater exploitation in three cropping years (2020–2021, 2021–2022, and 2022–2023) in a study of the Silakhor plain, Iran, by use of game theory. Game theory problems involve multidecision-making to address conflicting objectives. Thus, farmers and environmentalists were considered as game theory ‘players’ and their strategies were examined. Two groups of groundwater exploitation scenarios were considered based on both groundwater recharge and the current exploitation. Optimal groundwater exploitation was determined. The results of determining exploitation scenarios based on the current exploitation show that the optimal groundwater exploitation in the Silakhor plain is 103.9, 101, and 99 million m³ in the next 3 years, respectively; these values decrease by 6.7, 7, and 7.4%, respectively, by determining exploitation scenarios based on groundwater recharge. The second major finding is that the farmers’ net benefit will increase by 18% by applying the optimal cropping pattern. Taken together, the results show that the design of the game structure is very important and the basis of the players’ strategies must be determined before using conflict resolution methods.

Preferential flow is usually characterized by rapid and concentrated fluid flow in fractured geological media, and preferential flow paths (PFP) dominate the fluid flux and velocity. Therefore, the identification of PFP is significant for quantitatively characterizing fluid flow in fractured media, especially in discrete fracture networks (DFN). The traditional methods of identifying PFP need to solve groundwater flow models; however, such models are limited by complex groundwater-related problems, the need for detailed hydrogeological survey data, and a high computational workload. In this study, a graph-theory-based flow resistance method is proposed for identifying the PFP in DFN. The method uses the flow resistance of fracture trace lines to identify the corresponding minimum resistance path. The flow resistance is defined as the weighted factor between the adjacent nodes in the fracture network based on the formula of the modified cubic law, and then the Dijkstra algorithm is used to determine the minimum resistance path. The flow resistance method is verified through case analysis by numerical simulation with COMSOL Multiphysics. The results show that the fluid tends to flow along the path with less flow resistance, and the minimum resistance path is essentially consistent with the preferential flow path. The method only needs to extract flow resistance values from the geometric parameters of the fractures, and then quickly analyze the fracture-network pathways to identify the preferential flow path. The method provides an effective and efficient way of identifying the preferential flow path without resorting to complex groundwater flow models to find the solution.

Land deformation is a severe environmental problem that is often caused by groundwater overexploitation. Traditional approaches, such as those based on ground leveling, are used as standard for monitoring land deformation, but they cannot collect enough information for land-deformation mapping. In this study, the time-series Persistent Scatterer Interferometry Synthetic Aperture Radar (PS-InSAR) was used as an improved method to identify land deformation in Cangzhou after the initiation of China’s South-to-North Water Diversion Project (SNWDP). Machine learning (ML) models, including random forest and k-nearest neighbor, were used to determine the relationship between groundwater pressure and land deformation. The results showed that from 2018 to 2022, the deformation rate was up to –115 mm/year in Nanpi and Dongguang and varied between –57 and –26 mm/year in Qingxian and Cangxian. Land deformation after the SNWDP implementation was less than before. The ML models’ results show that the accuracy of the random forest and k-nearest neighbor methods were 85 and 77%, respectively. Evaluation of the groundwater-level trend measured in six wells showed that after the SNWDP implementation, the groundwater pressure started to recover in Cangzhou, but a decline has been observed recently, particularly in 2022. The mean decrease in impurity (MDI) values demonstrates that aquifers IV and III contribute the most to land deformation in Cangzhou, with the highest MDI values of 33 and 26%, respectively. The study provides new insights into the evolution of regional land deformation, and the methods employed in this research can be adopted in other regions with similar conditions.

The Great Ruaha River Catchment (GRC) in Tanzania is facing severe water scarcity due to the growing number of water users in the catchment. The surface-water resources are under stress, leading to increasing dependence on groundwater for water supply. This study aimed to identify and map groundwater potential areas in the GRC using a geographic information system (GIS), remote sensing techniques, and analytic hierarchy process multi-criteria decision analysis (AHP MCDA) tools. The thematic maps representing lithology, lineaments density, precipitation, soil, slope, drainage density, geomorphology, and land use were used to create a groundwater potential zones (GWPZ) map by weighted linear combination (WCL). The results showed that 70% (~60,044 km²) of the catchment area is in zones with moderate groundwater potential, 21.9% (~18,720 km²) in high groundwater potential zones, and 7.87% (~6,726 km²) in low groundwater potential zones. These results highlight the catchment’s overall groundwater potential and identify areas with scarce resources that should be prioritized for protective measures. Watershed managers and policymakers can use this information to make informed decisions on groundwater use and protection, and determine suitable areas for new wells that may have greater yield.

Abstract

The Nubian Sandstone Aquifer System (NSAS) is one of the world’s largest fossil groundwater resources. In northern Chad, notably in the areas of the Tibesti and Ennedi mountains, precipitation occurs seasonally with rates up to 150 mm year^–1. This precipitation could lead to diffuse recharge, as well as concentrated recharge along the episodically flooded wadis. Although it is clear that infiltration occurs under flooded areas, it is unknown if and to what extent the infiltration can recharge groundwater. This study combines remote sensing data on precipitation, evapotranspiration, and the temporal and spatial dynamics of the flooded areas with chemical and stable isotopic data from groundwater and surface water sampled between 2013 and 2016. The combination of these data shows that (1) the only area where diffuse recharge occurs is in the southern area of the Ennedi mountains, where concentrated recharge through the wadis occurs concurrently during the month of August, and (2) southeast of the Tibesti and north of the Ennedi mountains, only concentrated recharge occurs. The length of the flooded areas and thus the spatial extent of concentrated recharge varies significantly from year to year and can last up to 3 months. The study has shown that modern recharge does occur in northern Chad, but to a very limited extent, both in space and time. This means that achieving sustainable management of this renewable resource can only be considered through rigorous quantitative assessments. Furthermore, these findings have important implications for future studies on the regional dynamics of the NSAS.

The distribution of saline water in the upper aquifer and freshwater in the lower aquifer is a characteristic of groundwater resources in the North China Plain (NCP). The phenomenon of groundwater depression cones in confined aquifers, primarily caused by excessive groundwater extraction, has been extensively documented. In line with Darcy’s law, it is noteworthy that the migration of shallow groundwater into confined aquifers can occur due to a substantial difference in hydraulic head between the unconfined and confined aquifer systems. However, based on the monitoring data, the quality of deep groundwater generally remains good. This paper attempts to explain this phenomenon from the perspective of non-Darcian flow in aquitards. A finite difference method is used to solve low-velocity non-Darcian flow to a well in the NCP. The mathematical model considers the threshold pressure gradient to describe non-Darcian flow in the aquitard and assumes Darcian and horizontal flows for both shallow and confined aquifers. The comparison with traditional Darcian flow indicates that the leaky area decreases rapidly when considering the threshold pressure gradient. The leaky area is negatively correlated with the aquitard thickness and the transmissivity of the confined aquifer, and positively correlated with the pumping rate. The non-Darcian vertical flow velocity is significantly lower than that obtained from Darcian theory. The vertical velocity difference between Darcian and non-Darcian flows is significant under the situation of a small aquitard thickness, large pumping rate, low transmissivity and large leakage coefficient when the threshold pressure gradient is large.

The aflaj system in Oman is an ancient irrigation network that delivers water supply to the local population, using gravity transport from the aflaj’s water sources. Ensuring the sustainability of these water sources is crucial, and a thorough understanding of recharge and hydrodynamic relationships among different aflaj is necessary for future planning and development. Major chemical and isotope compositions, including ²H, ¹⁸O, and Sr, are used in this study to identify the sources of water in different aflaj systems and explore connectivity among the various hydrologic systems. The investigation covers a 38,325-km² area in northern Oman, focusing on springs (ainy aflaj), groundwater collection channels (daoodi aflaj), and surface-water collectors (ghaili aflaj). The primary aquifers in the region include Hajar Super Group (HSG), Ophiolite, Tertiary, Alluvium, and Hawasina. The chemistry of aflaj waters is mainly controlled by evaporation and weathering processes. The ²H vs ¹⁸O data display a slope of 5.04, indicating the influence of evaporation. Analyzing the ²H vs ¹⁸O data reveals two groups of springs: one group is recharged from the HSG and Hawasina aquifers, while the other is recharged from HSG and Ophiolite. Daoodi aflaj, on the other hand, are primarily recharged from HSG and Ophiolite, with some contribution from Hawasina. The Mg/Ca ratio exhibits a connection between waters from Hawasina and both HSG and Ophiolite, indicating their hydraulic connectivity. This study suggests that all aflaj receive water contributions from at least two aquifer units, with HSG being the primary source of recharge before connecting with other aquifers.