Nubian Aquifer Research Articles

Monte Carlo simulation and PMF model for assessing human health risks associated with heavy metals in groundwater: a case study of the Nubian aquifer, Siwa depression, Egypt

Monte Carlo simulation and PMF model for assessing human health risks associated with heavy metals in groundwater: a case study of the Nubian aquifer, Siwa depression, Egypt

Characterization of recharge sources of the Miocene Fluvial Moghra aquifer in the North Western Desert of Egypt

Study regionThe Miocene Fluvial Moghra Aquifer in the North Western Desert of Egypt Study focusThe study integrates stable isotope analyses with aeromagnetic and hydrogeological datasets to accomplish the following: (1) define the primary source(s) of recharge to the Moghra aquifer, (2) assess aquifer connectivity with the Nile River aquifer, and (3) investigate the vertical connectivity of the Moghra aquifer with the underlying Nubian Aquifer System (NAS) through subvertical faults. New hydrological insights for the regionThe findings reveal (1) significant heterogeneity in groundwater isotopic compositions (Group A: δ18O: 1.1–13.8 ‰; δD: 4.6–73.5 ‰, B: δ18O:−0.99 to 0.85; δD: −7.58 to 4.38 ‰; and C: δ18O:−1.1 to −3.4; δD: − 6.3 to −18.2 ‰) indicative of variability in recharge sources. (2) Groundwater compositions west (up to 30 km) of the Nile River (Group A) resemble enriched modern Nile waters following the Aswan High Dam (AHD) construction that give way further west to relatively depleted groundwater (Group B) resembling historical pre-AHD Nile water compositions. (3) Further west from Group B depleted Group C samples occur along intersections of multiple fault systems (NW and NE-oriented faults) interpreted as mixtures of rising highly-depleted paleo Nubian Aquifer System (NAS) waters and pre-AHD Nile waters. (4) The advocated structural control is reported in similar settings in Egypt, suggesting that intersections of multiple fault systems provide regional connections between deep and shallow aquifers in northeast Africa, recharge overlying shallow aquifers, and should be considered in groundwater management scenarios.

Nubian aquifer linkage to the High Aswan Dam Reservoir: Initial assessments of processes and challenges

Egypt, relying heavily on the Nile as its primary water resource, is facing a rising water budget deficit due to increasing consumption, hydroclimatic changes, and upstream river damming. To address the above, innovative management of High Aswan Dam Reservoir (HADR), the third largest artificial reservoir on Earth, and its exchange with the surrounding groundwater system is suggested to develop new agricultural areas. However, the interconnectivity mechanism between the HADR and the fossil Nubian aquifer, the largest transboundary aquifer in Africa, remains speculative due to the lack of in-situ investigations. To address this deficiency, we perform a geophysical survey using aeromagnetic, time-domain electromagnetic, and vertical electrical resistivity sounding in a 330 km2 pilot area to the northwest of the HADR that is hypothesized to have a dense fracture system that could act as a conduit between these two large water bodies. Our survey results show the presence of normal faults cross the reservoir to the tangential basement and the sedimentary cover that are water-saturated and act as recharges to the Nubian fossil aquifer. These in-situ investigations confirm previous orbital gravity observations by GRACE-FO hypothesizing the interconnectivity between the reservoir and the Nubian aquifer, which was subject to debate. We suggest that such connecting areas between these two water bodies can be optimal sites for future agricultural development using improved management of surface water-groundwater exchanges for irrigation. Finally, our findings highlight upcoming challenges for this linkage if the level of HADR reaches below ∼160 m above mean sea level (amsl) due to upstream dam operation during the Nile’s extended drought periods. Under these conditions, the Nubian aquifer could discharge back into the HADR at the investigated site, changing the water budget of the aquifer and compromising the planned agriculture developments in the adjacent areas, which account for ∼ 10 % of the total arable land in Egypt.

Hydraulic and Hydrogeochemical Characterization of Carbonate Aquifers in Arid Regions: A Case from the Western Desert, Egypt

Using geochemical and pumping test data from 80 groundwater wells, the chemical, hydrologic, and hydraulic properties of the fractured Eocene carbonate aquifer located west of the Al-Minya district, the Western Desert, Egypt, have been characterized and determined to guarantee sustainable management of groundwater resources under large-scale desert reclamation projects. The hydrochemical data show that groundwater from the fractured Eocene carbonate aquifer has a high concentration of Na+ and Cl− and varies in salinity from 2176 to 2912 mg/L (brackish water). Water–rock interaction and ion exchange processes are the most dominant processes controlling groundwater composition. The carbonate aquifer exists under confined to semi-confined conditions, and the depth to groundwater increases eastward. From the potentiometric head data, deep-seated faults are the suggested pathways for gas-rich water ascending from the deep Nubian aquifer system into the overlying shallow carbonate aquifer. This mechanism enhances the dissolution and karstification of carbonate rocks, especially in the vicinity of faulted sites, and is supported by the significant loss of mud circulation during well drilling operations. The average estimated hydraulic parameters, based on the analysis of step-drawdown, long-duration pumping and recovery tests, indicate that the Eocene carbonate aquifer has a wide range of transmissivity (T) that is between 336.39 and 389,309.28 m2/d (average: 18,405.21 m2/d), hydraulic conductivity (K) between 1.31 and 1420.84 m/d (average: 70.29 m/d), and specific capacity (Sc) between 44.4 and 17,376.24 m2/d (average: 45.24 m2/d). On the other hand, the performance characteristics of drilled wells show that well efficiency ranges between 0.47 and 97.08%, and well losses range between 2.92 and 99.53%. In addition to variations in carbonate aquifer thickness and clay/shale content, the existence of strong karstification features, i.e., fissures, fractures or caverns, and solution cavities, in the Eocene carbonate aquifer are responsible for variability in the K and T values. The observed high well losses might be related to turbulent flow within and adjacent to the wells drilled in conductive fracture zones. The current approach can be further used to enhance local aquifer models and improve strategies for identifying the most productive zones in similar aquifer systems.

Unveiling the Dynamics and Sustainability of the Nubian Aquifer System in El-Marashda, Egypt Through Geophysical, and Hydrogeochemical Investigations

AbstractThis research investigates the geophysical, hydrogeochemical, and geological characteristics of the Nubian Aquifer System in the El-Marashda area, located beneath the Eastern Sahara Desert in northeastern Africa. The primary objective is identifying the aquifer geometry, assessing groundwater quality, and evaluating environmental pollution levels. A Magnetotelluric survey was employed to examine the subsurface geological composition and electrical resistivity characteristics of the aquifer system. The study revealed a freshwater-saturated Nubian Sandstone layer at depths between 986 and 1009 m with resistivity values of 101 to 182 Ohm.m, indicating a substantial and potentially sustainable groundwater resource. Overlying limestone and Marly Limestone layers influence the aquifer’s permeability and storage capacity. The chemical analysis of water from three wells showed suitability for drinking and irrigation, with no sodium and magnesium levels hazards. The Heavy Metal Pollution Index (HPI) and Heavy Metal Evaluation Index (HEI) indicated low to medium contamination, posing potential environmental health risks. Human health risk assessments using USEPA methodology found acceptable non-carcinogenic risks, with Hazard Quotients (HQs) for heavy metals below 1 and a negligible Hazard Index (HI). The comprehensive investigation underscores the potential for sustainable groundwater utilization in El-Marashda. It highlights the aquifer’s suitability for irrigation, with low contamination levels and minimal health risks. These findings provide a foundation for informed and sustainable water resource management, environmental protection, and resilient infrastructure development in the region. The methodologies and results align with global standards, demonstrating their applicability in globally diverse geological contexts. This research contributes valuable baseline data for future studies and monitoring efforts, whether at local or global sites, emphasizing the importance of continued investigation to ensure sustainable groundwater management.

Hydrologic source identification using stable isotope ratios of bottled drinking water in Egypt

A convenient way to understand hydrologic source identification is to make use of a suitable tracer. Isotopes of oxygen and hydrogen provide that opportunity since the isotope ratios of the primary source, precipitation, can be modified by post precipitation processes. This approach has been tested by carrying out a comprehensive isotope ratios investigation of domestic and imported bottled water sourced and distributed across Egypt. Our collection of bottled water includes 33 samples distributed under 27 distinct brands. We compare the isotope ratios of the bottled water with the isotope ratios of the reported natural water source of this water. The bottled water isotope ratios preserve information about the water sources from which they were derived. The measured oxygen and hydrogen ratios of the studied bottled water samples range from −11.51‰ to 2.94‰, with an average value of −1.89‰ for δ18O and from −81.69‰ to 23.94‰, with an average value of −9.54‰ for δ2H. The observed variability of isotope ratios in the bottled water falls within the span of the natural groundwater resources in Egypt, such as shallow and deep groundwater aquifers as well as claimed non-Egyptian sources. In general, the bottled water samples in the data set can be divided into four distinct groups based on their isotope ratios. One group represents imported bottled water brands, and three groups include domestic brands. The first group represents the imported bottled water brands. Their measured isotopic compositions are similar to those of their claimed sources. The second group has the lowest δ18O and δ2H values and likely originated from the Nubian aquifer. The third and fourth groups appear to have been sourced from the Nile Valley and Delta aquifer. The third group isotopic content and d-excess values indicate a higher degree of mixing with evaporated return flow water. The results provided in this study indicate the diverse hydrogeology of the local bottled water brands. This promises extending the approach to several sites globally.

Investigation of petrophysical and hydrogeological parameters of the transboundary Nubian Aquifer system using geophysical methods

The recent research aims to investigate the petrophysical and hydrogeological parameters of the Nubian aquifer system (NAS) in Northern Khartoum State, Sudan, using integrated geophysical methods, including surface electrical resistivity and geophysical well-logging. The Nubian aquifer is a transboundary regional aquifer that covers vast areas in Sudan, Egypt, Libya and Chad. The well-logs, including self-potential (SP), natural gamma ray (GR), and long normal resistivity (RS), are integrated with Vertical Electrical Sounding (VES) measurements to delineate the hydrostratigraphical units. As a result, two aquifers are detected. An upper aquifer comprises coarse sand with an average thickness of 50 m and a lower aquifer of sandstone with more than 200 m thickness. For a thorough evaluation of the aquifers, in the first stage, the petrophysical and hydrogeological parameters, including formation factor, total and effective porosity, shale volume, hydraulic conductivity, and transmissivity, are measured solely from geophysical well-logs. In the second step, the results of geophysical well logs are combined with VES and pumping test data to detect the spatial variation of the measured parameters over the study area. As a result, the hydraulic conductivity of the Nubian aquifers ranged from 1.9 to 7.8 m/day, while the transmissivity varied between 120 and 733 m2/day. These results indicated that the potentiality of the Nubian formation is high; however, in some regions, due to the sediment heterogeneity, the aquifers have intermediate to high potential. According to the obtained results, it can be concluded that the Nubian Aquifer in Khartoum state is ideal for groundwater development. This research discovered that geophysical approaches can be used to characterize moderately heterogeneous groundwater systems by comparing the Nubian aquifer with similar aquifer systems that have similar hydrogeological settings. This study emphasized the application of universal principles in extrapolating hydraulic parameters in hydrogeophysical surveys. This approach aims to reduce the costs and efforts associated with traditional hydrogeological approaches.

Steady-state simulation of groundwater flow in Khartoum state, Sudan

AbstractThe multi-aquifer system of the Nubian aquifer in central Sudan hydrogeological system was simulated using a three-dimensional steady-state model. The goal of the study is to detect the effect of pumping on the groundwater flow and thus, the aquifer productivity. The conceptual model of the study area was built based on the available geological and hydrogeological data guided by geophysical survey. Processing MODFLOW numerical code was used to calculate the hydraulic head and water balance under the existing boundary conditions. The model accurately simulated the hydraulic head with a determination coefficient of 0.88. The calibrated model indicated that the change in storage is 0.56 m3/day indicating the study area constitutes highly productive zone and is recommended for groundwater developments.

Hydro-chemometrics of the Nubian Aquifer in Sudan: an integration of groundwater quality index, multivariate statistics, and human health risk assessment

This research employed the groundwater quality index (GWQI), multivariate statistical methods, and human health risk assessment model to investigate the suitability of groundwater for domestic uses in northern Khartoum state, Sudan. The groundwater samples were analyzed for eleven physiochemical parameters, including pH, EC, TDS, TH, Cl−, SO42−, NO3−, Ca2+, Mg2+, Na+, HCO3− and the primary investigation indicated the deviation of these parameters from World Health Organization (WHO) standards. The hydrochemical analysis revealed different groundwater facies with the dominance of Ca–Mg–HCO3 water type. Consequently, the groundwater samples were classified, based on GWQI, into three categories as 76.4% of the samples fall in the excellent water class, 17.6% are projected in the good water class, and 5.9% of groundwater samples are considered unsuitable for human consumption. The multivariate statistical methods were applied, including Pearson’s correlation analysis, principal component analyses (PCA), and hierarchical cluster analysis (HCA). Three principal components (PCs) explaining 86.07% of total variances are extracted. These PCs indicated that rock-water interactions and agricultural practices influence groundwater quality in the study area. Additionally, HCA is used to categorize groundwater samples based on the concentration of the physiochemical parameters. Consequently, three types of groundwater were identified as low, medium, and highly mineralized. In the final stage, the non-carcinogenic human health risk was assessed based on the concentration of NO3− using the United States Environmental Protection Agency (USEPA) models. The obtained hazard quotient for children indicated that 64.7% of groundwater samples are beyond the permissible limit (1 <), and the use of these samples may result in health consequences. Therefore, remedial measures are suggested for the sustainable use of groundwater.

Predictionof Protective Capacity of the Nubian Aquifer Using Electrical Resistivity Method in Bahri City, Sudan

Predictionof Protective Capacity of the Nubian Aquifer Using Electrical Resistivity Method in Bahri City, Sudan

Satellite-based estimates of groundwater storage depletion over Egypt

An arid climate accompanied by a freshwater shortage plagued Egypt. It has resorted to groundwater reserves to meet the increasing water demands. Fossil aquifers were lately adopted as the sole water source to provide the irrigation water requirements of the ongoing reclamation activities in barren areas. Yet, the scarcity of measurements regarding the changes in the aquifers’ storage poses a great challenge to such sustainable resource management. In this context, the Gravity Recovery and Climate Experiment (GRACE) mission enables a novel consistent approach to deriving aquifers’ storage changes. In this study, the GRACE monthly solutions during the period 2003–2021 were utilized to estimate alterations in terrestrial water storage (TWS) throughout Egypt. Changes in groundwater storage (GWS) were inferred by subtracting soil water content, derived from the GLDAS-NOAH hydrological model, from the retrieved TWS. The secular trends in TWS and GWS were obtained using the linear least square method, while the non-parametric technique (Mann–Kendall’s tau) was applied to check the trend significance. The derived changes in GWS showed that all aquifers are undergoing a significant loss rate in their storage. The average depletion rate over the Sinai Peninsula was estimated at 0.64 ± 0.03 cm/year, while the depletion rate over the Nile delta aquifer was 0.32 ± 0.03 cm/year. During the investigated period (2003–2021), the extracted groundwater quantity from the Nubian aquifer in the Western Desert is estimated at nearly 7.25 km3. The storage loss from the Moghra aquifer has significantly increased from 32 Mm3/year (2003–2009) to 262 Mm3/year (2015–2021). This reflects the aquifer exposure for extensive water pumping to irrigate newly cultivated lands. The derived findings on the aquifers’ storage losses provide a vital source of information for the decision-makers to be employed for short- and long-term groundwater management.

Assessment of the Nubian aquifer characteristics by combining geoelectrical and pumping test methods in the Omdurman area, Sudan

The recent research is carried out to model the characteristics and productivity of the groundwater aquifer in the Omdurman area, Sudan, by combining electrical resistivity and pumping test methods. Omdurman is the most populous city known as the traditional capital of Sudan. Vertical electrical sounding (VES) survey using Schlumberger array is carried out along four profiles to delineate the potential groundwater zones. Application of 1D geophysical inversion revealed five geoelectric layers, including recent deposits, clay, silicified and ferruginous sandstone, and sandstone. Additionally, based on the outcome of VES inversion, Dar Zarrouk parameters, including transverse resistance and longitudinal conductance, were calculated to model the aquifer characteristics. The transverse resistance ranged from 5587 to 309,853 Ωm2, while the longitudinal conductance varied between 0.14 and 2.5 Ω−1. The hydraulic conductivity and transmissivity are further measured using the VES data, ranging from 1.4 to 5.2 m/d and 435 to 1564 m2/day, respectively. The step-drawdown pumping tests were performed to evaluate the aquifer characteristics and thus validate the result of the geoelectrical method. The transmissivity obtained from the step test varied between 583 and 1226 m2/day, showing an acceptable agreement with those of geoelectrical data. Based on the measured parameters, the aquifer is classified as highly productive and ideal for groundwater development. The step drawdown test was further used to assess the performance of groundwater wells. The results indicated that faulty well design and inappropriate pumping rates influence some wells in the study area, resulting in high drawdown and low well efficiency. Overall, the objectives of the study were successfully achieved; nonetheless, detailed hydrogeological and geophysical investigations are recommended for comprehensive evaluation of the groundwater aquifer.

Isotopic, Geophysical, and Hydrogeochemical Investigations of Groundwater in West Middle Upper Egypt.

The groundwater of the west Assiut and El-Minia districts was evaluated in this paper using geoelectrical, hydrogeochemical, and stable isotope (oxygen-18 and deuterium) studies. In the studied localities, 42 vertical electrical soundings (VES) were taken to evaluate groundwater potential, and the analysis, as well as collection, of 74 samples of Eocene groundwater was carried out. In accordance with the vertical electrical soundings' interpretation, there are four geoelectrical formations and two major water-bearing units that act as aquifers (Pleistocene and Eocene). To determine irrigation suitability, the sodium absorption ratio (SAR), electrical conductivity (EC), residual sodium carbonate (RSC), sodium percentage (Na %), magnesium hazard (MH), Kelley's ratio (KR), and permeability index (PI) were evaluated as irrigation quality parameters. The EC, Na %, and the diagram of the US salinity laboratory indicated that most of the collected samples of groundwater were suitable for irrigation, whereas the RSC and PI pointed out that all of the collected water samples were safe for irrigation. The oxygen and hydrogen isotope values in groundwater samples showed that the Eocene aquifer was recharged by both surface water and the Nubian aquifer.

Mantle-derived fluids in the continental-scale Nubian aquifer

The Nubian aquifer of northeastern Africa is one of the largest confined fossil-water aquifer systems in the world. It is central for ongoing water needs and future development goals of Egypt, Libya, Sudan and Chad. Groundwater extraction and consumptive use over the past 40 years have led to a continuous decline of water level and to the reduction and/or cessation of natural flow in artesian wells and springs. This study introduces new noble gas and stable isotope geochemical data from deep groundwater supply wells of the main oases of the Western Desert of Egypt (Bahariya, Farafra, Dahkla, and Kharga) and places these data in the context of a regional compilation of published hydrological and hydrochemical data. Helium isotopes, stable isotope compositions for water (δ2H; δ18O) and dissolved inorganic carbon (δ13C), salt compositions, and [CO2] suggest deeply derived fluid inputs. Highly variable groundwater temperatures (20–56 °C) also suggest the presence of geothermal inputs that mix with aquifer water. Nubian water displays high PCO2 (up to three orders of magnitude higher than atmosphere) and hydrochemical analysis using δ13C suggests up to ~30% of the CO2 is derived from deep geologic sources. Helium isotope (3He/4He) ratios of samples obtained from the Nubian aquifer range from crustal values of 0.02RA (where RA reflects the 3He/4He in air or 1.384 × 10−6) to values of up to 0.36RA (2.5% mantle helium) in Dahkla Oasis of Egypt and up to 1.4RA (17% mantle helium) in Libya. Correlations among excess heat, increases in [CO2], δ13C, and 3He/4He indicate that small volumes of deeply sourced fluids carrying mantle-derived volatiles are leaking into the Nubian aquifer. Geothermal water apparently ascend along faults and shear zone conduits and mix with regional groundwater. The origin of these volatiles may be partial melts in low velocity upper mantle beneath the aquifer and young magmatism surrounding the Nubian aquifer. Fluid-rock interactions along flowpaths can explain variable associations and correlations among the tracers. Variability of composition and temperature suggest complex fluid mixing within the Nubian aquifer, the existence of fault-bounded hydrologic sub-basins, and a connection between tectonics and water quality. Better understanding of the sources and admixtures of deep geothermal fluid inputs is needed for informed water management.

Isotopic composition of groundwater resources in arid environments

The availability and quality of limited groundwater resources in Egypt are negatively affected by both natural and anthropogenic forces. It is crucial to understand the recharge sources and mechanisms of country-scale aquifers in order to develop sustainable management scenarios for Egypt's groundwater resources. In this study, we compiled all historical hydrogen (δ2H) and oxygen (δ18O) stable isotopic compositions of 1618 ground- and surface-water samples collected for seven major aquifer and reservoir systems in Egypt. These data were then hosted in a public-domain web map application (https://bit.ly/3n9MtrM) that enables users to access, navigate, display, and analyze the isotopic composition of any water sample in Egypt. The developed application and customized web tools were then used to provide improved understanding of the country-wide water resources’ isotopic composition and to investigate the recharge sources and mechanisms of, and provide sustainable management scenarios for, the seven major Egyptian aquifer systems. Results indicate that (1) the alluvial and coastal aquifers are recharged from modern rainfall, floodwaters, and upward leakage from deep aquifers; (2) the Nile Valley and Delta, Moghra, and carbonate aquifers are receiving recharge from the Nile River, modern rainfall, irrigation canals and drains, and upward leakage from deep aquifers; (3) the Nubian aquifer receives modern recharge in areas of higher rainfall or close to surface water reservoirs; and (4) the fractured basement aquifers are recharged from modern rainfall and floodwaters. The developed cost-effective web application will guide locations and techniques for future field data collection; reduce time, efforts, and resources required for field activities; enable improved understanding the country-wide stable isotopic compositions of water resources; enhance understanding of nationwide recharge mechanisms; and enable the scientific community to address country-scale science questions in a unique way.

Integration of hydrochemical and isotopic characteristics for identifying groundwater recharge sources of the Eocene carbonate aquifer, Western Desert, Egypt

The Western Desert is considered as one of the most promising areas for groundwater resource and development in Egypt. The Eocene carbonate aquifer is one of the most exploited aquifers for development in the Egyptian Western Desert, especially in the area west of El-Minia in central Egypt. The present study aims to assess the hydrochemistry of the Eocene carbonate aquifer and the possible recharge sources to this aquifer in the western desert west of El-Minia district. Fifteen groundwater samples from the Eocene carbonate aquifer were analyzed for major ions, heavy metals, oxygen-18, and deuterium to assess the hydrochemistry and isotopic compositions in this area. TDS concentrations ranged from 510 to 1408 mg/l. However, the cluster analysis of the Eocene groundwater samples in the present work, reveals two main groups (A and B) with different chemical and isotopic characteristics. The chemical composition of the studied samples showed that the main chemical facies are Na–Cl, Na–Ca–HCO3, and Na–Cl–HCO3. Silicate weathering control the majority of groundwater samples of the Eocene aquifer, while carbonate dissolution governing the deep groundwater of Eocene carbonate aquifer. Isotope ratios of oxygen (18O) and hydrogen (2H) were used to identify the recharge sources, which showed relatively depleted 18O and 2H isotopic ratios and relative mixing of groundwater from the Eocene Limestone with paleowaters from the deep Nubian aquifer and water from the Nile River. However, the mixing ratio depends mainly on the distance from the Nile River, depth to groundwater, and local geologic structures also contribute to the mixing pattern. The present study indicates the need for a detailed structural study to detect the locations and properties of fractures as it plays a vital role in feeding the Eocene aquifer from the underlying aquifer. Integration of hydrogeochemical data and isotopic compositions provide a better understanding of the geochemical processes that control the groundwater hydrochemistry of the Eocene carbonate aquifer west of El-Minia, Egypt and in areas with similar conditions.

Groundwater mounding: A diagnostic feature for mapping aquifer connectivity in hyper-arid deserts

Shallow aquifer mapping and large-scale characterization of groundwater dynamics in the Saharan-Arabian Desert is largely impeded by the limited hydrological datasets from sparse and unevenly distributed well logs. Today, as these aquifers are depleting at alarming rates in response to climatic and anthropogenic stresses, accurate knowledge of their dynamical characteristics is not only essential for understanding the water deficit in these increasingly populated areas but also to understand the regional and global environmental impacts of such changes. Herein, we suggest that groundwater mounding can be used for assessing aquifer connectivity in hyper-arid deserts. Using the shallow Post Nubian Aquifer System (PNAS) in Egypt as a test site, we integrate remote sensing, isotopic, hydrochemical and geoelectrical methods to characterize the Saharan groundwater mounds, examine the structural control on groundwater dynamics and discuss the potential of future satellite missions to characterize aquifer connectivity. The results suggest that groundwater mounding in the PNAS is attributed to artesian discharge of the deep Nubian Aquifer System (NAS) along the intersection of WNW and E-W major faults. This is evident by the dominant isotopic signature (δ18O: −9.93‰; δ2H: −79.05) of the deep NAS in the shallow PNAS with a percentage of up to 85% in the faulted zone. The 2D-Electrical Restively Imaging (ERI) delineate multiple small-scale mounds, atop of faults, that can attain 37 m height above average water table creating a relatively steep hydraulic gradient and deviating the groundwater flow direction. Future orbital radar sounding missions can benefit from characterizing the geometry of these mounds to define the measurement requirements of such hydrological features. The large-scale time-coherent subsurface mapping of the Saharan-Arabian aquifers can provide unique insights to examine the aquifer connectivity and the response of aquifers to climatic and anthropogenic stresses in desert areas that otherwise cannot be addressed using existing sporadic well-logs.

Integration of geophysical methods for groundwater exploration: A case study of El Sheikh Marzouq area, Farafra Oasis, Egypt

Newly, the Egyptian government initiated huge national projects for the reclamation and sustainable development of 1.5 million acres. Farafra Oasis is recognized as the focus of the first phase of this project where groundwater is the wellspring of the water for irrigation and drinking. Hence, exploration and assessment of groundwater aquifers are very essential in such area. A reconnaissance geophysical survey was conducted in the centre of Farafra oasis using Vertical Electric Sounding (VES), Transient electromagnetic (TEM), Audio-Magnetotelluric (AMT), Control-source Magnetotelluric (CSAMT), and Very Low Frequency (VLF) techniques for the investigation of shallow and deep groundwater reservoirs. In addition, geologic and stratigraphic information from the nearest well was utilized to confirm the geophysical outcomes. Integrated geophysical measurements succeeded to delineate the three zones A, B and C of the Nubian aquifer system in the investigated area. Also, several fault elements were delineated which control the influx and aggregating of the groundwater in both units; shallow and deeper one. Deeper aquifer (zone C) shows generally higher resistivity values, which consider the major aquifer of Nubian sandstone in the Western Desert of Egypt. Geochemical examinations of the groundwater sample show that the water is remarkable for all agriculture purposes (TDS = 95).

Fault zone hydrogeology in arid environments: The origin of cold springs in the Wadi Araba Basin, Egypt

AbstractThe role of faults in controlling groundwater flow in the Sahara and most of the hyper‐arid deserts is poorly understood due to scarcity of hydrological data. The Wadi Araba Basin (WAB), in the Eastern Sahara, is highly affected by folds and faults associated with Senonian tectonics and Paleogene rifting. Using the WAB as a test site, satellite imagery, aeromagnetic maps, field observations, isotopic and geochemical data were examined to unravel the structural control on groundwater flow dynamics in the Sahara. Analysis of satellite imagery indicated that springs occur along structurally controlled scarps. Isotopic data suggested that cold springs in the WAB showed a striking similarity with the Sinai Nubian aquifer system (NAS) water and the thermal springs along the Gulf of Suez (e.g., δ18O = −8.01‰ to −5.24‰ and δD = −53.09‰ to −31.12‰) demonstrating similar recharge sources. The findings advocated that cold springs in the WAB represent a natural discharge from a previously undefined aquifer in the Eastern Desert of Egypt rather than infiltrated precipitation over the plateaus surrounding the WAB or through hydrologic windows from deep crystalline basement flow. A complex role of the geological structures was inferred including: (1) channelling of the groundwater flow along low‐angle faults, (2) compartmentalization of the groundwater flow upslope from high‐angle faults, and (3) reduction of the depth to the main aquifer in a breached anticline setting, which resulted in cold spring discharge temperatures (13–22°C). Our findings emphasize on the complex role of faults and folds in controlling groundwater flow, which should be taken into consideration in future examination of aquifer response to climate variability in the Sahara and similar deserts worldwide.

Application of the multi potential geophysical techniques for groundwater evaluation in a part of Central Sinai Peninsula_ Egypt

This study highlights the groundwater evaluation of the Nubian sandstone aquifers regarding assessing the main structural elements, trends, and depth to the basement rocks that control the groundwater aquifers in Egypt's central Sinai area. Gravity and magnetic data were analyzed using different techniques, such as wavenumber filtering, least-squares separation techniques, and tilt derivatives. Euler deconvolution with different structural indexes (SI), power spectrum analyses, 3-D crustal modeling. The deep-seated structures affecting the study area, and the basement depth, which range between 1170 and 4590 m., have been utilized. The main structural trends affecting the study area were delineated to control the groundwater aquifer's regional geometry. Moreover, it was found that the NorthWest-SouthEast trend direction – Suez Gulf trend – was caused by primary shear, and the NorthEast-SouthWest trend direction – Aqaba Gulf trend – was caused by the secondary shear. The direction of each trend's lateral movement was to the right and the left, respectively. Meanwhile, the geoelectrical resistivity measurements were also utilized to determine the ground water-bearing formations using eighteen deep vertical electrical soundings (VES) stations. The results revealed the depth to the uppermost part of the Nubian sandstone aquifer ranging between 598 and 1106 m; the combination of the depth to the uppermost part of the Nubian aquifer, the depth of the basement relief map revealed that the aquifer thickness varies from 430 to 3750 m, and the resistivity values ranging between 22 and 214 Ω.m.