Hydrogeology Journal最新文献

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.

Land subsidence in the city of New Orleans (USA) and its surroundings increases flood risk, and may cause damage to buildings and infrastructure and loss of protective coastal wetlands. To make New Orleans more resilient to future flooding, a new approach for groundwater and subsidence management is needed. As a first step in developing such an approach, high-quality and high-resolution subsurface and groundwater information was collected and synthesized to better understand and quantify shallow land subsidence in New Orleans. Based on the collected field data, it was found that especially the low-lying areas north and south of the Metairie-Gentilly (MG) Ridge are most vulnerable to further subsidence; north of the MG Ridge, subsidence is mainly caused by peat oxidation and south of the MG Ridge mainly by peat compaction. At present, peat has compacted ~31% on average, with a range of 9–62%, leaving significant potential for further subsidence due to peat compaction. Phreatic groundwater levels drop to ~150 cm below surface levels during dry periods and increase to ~50 cm below surface during wet periods, on average. Present phreatic groundwater levels are mostly controlled by leaking subsurface pipes. Shallow groundwater in the northern part of New Orleans is threatened by salinization resulting from a reversal of groundwater flow following past subsidence, which may increase in the future due to sea-level rise and continued subsidence. The hydrogeologic information provided here is needed to effectively design tailor-made measures to limit urban flooding and continued subsidence in the city of New Orleans.

Abstract

With an extent of ~1,860,000 km², the Upper Mega Aquifer System on the Arabian Platform forms one of the largest aquifer systems of the world. It is built up by several bedrock aquifers (sandstone and karstified limestone aquifers), which are imperfectly hydraulically connected to each other. The principal aquifers are the Wasia-Biyadh sandstone aquifer, and the karstified Umm Er Radhuma and Dammam limestone aquifers. The stored groundwater is mainly fossil. Groundwater recharge took place in the geologic past under more humid climatic conditions. Due to the good water quality and high yield, the aquifers are intensively exploited, which has caused depletion of the groundwater resources. The presented qualitative and semi-quantitative description of the hydrogeology and the groundwater budget is the basis for integrated groundwater management of the aquifer system.

Abstract

The radius of influence of a vertical circulation well was studied, taking the difference between the hydraulic head caused by the operation of the vertical circulation well and the initial state of the hydraulic head as the index. Based on the influence of well operation, the aquifer properties and technical parameters of the vertical circulation well on hydraulic head difference, an evaluation method for determining the radius of influence of the well was constructed. The software COMSOL Multiphysics was used to simulate the variation in hydraulic head and the flow field under different working conditions. The results show that increasing the operating time and flow rate, with an increased horizontal permeability, could lead to an increase of the influence radius, while an increase in the vertical permeability could lead to a decrease in the influence radius. Running time, horizontal permeability, vertical permeability, the distance between the lower screen section and the waterproof bottom plate, and the distance between the upper and lower screen sections, all have a great influence on the flow field. Thus, a calculation formula for quantitatively estimating the radius of influence of vertical circulation wells was obtained.

Intense use of groundwater in urban areas requires appropriate monitoring, which in turn necessitates proper data management with employment of increasingly sophisticated statistical methods and mapping tools. An example of such an urban area with intensive use of groundwater is the study area of GeoPot Project, namely Munich (Germany) and its surroundings. The aim of the presented study was to provide a description of the hydrogeochemical characteristics of the aquifers occurring in the Quaternary and Upper Freshwater Molasse (German: Obere Süßwassermolasse – OSM) sediments and to further improve the understanding of interactions between the aquifers. The focus was put on the identification of hydrochemical facies, the chemical signatures of different water types, an understanding of occurring processes, and spatial relationships between the aquifers. In order to deal with hydrogeochemical data generated for this study, as well as with data coming from existing external databanks (e.g. BIS-BY), a methodology of quality assurance was developed. The analytical methods focused on multivariate statistics. To enhance the interpretation of the obtained clusters, a recently developed three-dimensional geological model was used for better understanding and presentation. It was found that in the study area, deeper aquifer systems represent the most distinct hydrogeochemical signature of the Na–HCO₃ water type. In the remaining clusters, a transition from deeper (alkaline) to shallow (alkaline-earth) groundwater can be observed. The results of the study can be utilized for improved, sustainable groundwater management.

Abstract

Groundwater-level monitoring networks provide vital information for hydrogeological studies. Including exploited domestic wells in these monitoring networks can provide a low-cost means of obtaining a broader set of data; however, the use of these sites is limited because the frequent pumping of these wells generates outliers in the recorded time series. Here a slope criterion is applied to identify and remove outliers from groundwater-level time series from exploited domestic wells. Nonetheless, eliminating outliers creates a problem of missing values, which biases the subsequent time series analysis. Thus, 14 imputation methods were used to replace the missing values. The proposed approach is applied to groundwater-level time series from a monitoring network of 20 wells in the Lanaudière region, Québec, Canada. The slope criterion proves very effective in identifying outliers in exploited domestic wells. Missing values generated by outlier removal can reach up to 99% of the recorded data. Among the characteristics of the missing value pattern, the gap size and the position of the gaps along the time series are the most important parameters that affect the performance of the 14 imputation methods. Of the imputation methods tested, linear interpolation and Stineman interpolation, and then Kalman filtering, were the most effective. The present study demonstrates that exploited domestic wells can be used for groundwater monitoring by removing the outliers and imputing the missing values.

The origin and setting of the extensive aquifer systems that underlie Jakarta (the capital city of Indonesia), and the impacts that have resulted from their largely unchecked exploitation, are described. The ready availability of groundwater has been key to the city’s growth and prosperity, but it has come at a cost. Jakarta is now the most rapidly subsiding capital city in the world and subject to frequent flooding. These impacts have become major factors in the decision to relocate to a new capital city, named Nusantara, currently under construction on the island of Borneo.

The high groundwater salinity of crystalline aquifers in semiarid areas is generally attributed to the dissolution and leaching of meteoric salts that have been progressively evapoconcentrated in the different hydrological compartments under dry climate conditions. A numerical model, simulating water and salt balances, was developed from a case study in Northeast Brazil to: (1) test the validity of this hypothesis, through the quantification of all relevant water cycle processes in the studied watershed, and (2) demonstrate how changes in land cover can impact groundwater salinity. Computations showed that the aridity and the high evapo(transpi)ration rates from the unsaturated zone and/or surface water (ponds, reservoirs) cannot lead to the observed aquifer salinization levels, but only to concentrations of a few tens or hundreds of mg L^–1 (Cl^–). The only process that can induce a high groundwater salinity, with chloride concentrations up to several g L^–1, is the transpiration of groundwater by the deep roots of the vegetation, with a rate reaching 100% of the annual recharge. In this case study, the vegetation involved is the native Caatinga forest. Simulations of the long-term dynamics of groundwater salinity indicate that aquifer areas with high salinity are relicts of the Caatinga pre-colonization period during which subterranean endorheic conditions were prevailing. Following the Caatinga deforestation linked to colonial agricultural development, aquifer recharge increased and endorheism ceased. Consequently, these aquifers may have now been experiencing a desalination process for about three centuries. The desalination spatial variability drivers are explained in the paper.

In a changing world, long datasets for groundwater have great value, as they do for all components of environmental monitoring. However, there is a global scarcity of such datasets, with few extending beyond 30 years and even fewer to 50 or 100 years. Hydrogeological investigations and groundwater management activities benefiting from long-term data are listed, the successful use of such datasets illustrated, and the reasons for their scarcity discussed.