Nubian Aquifer Research Articles

Hydrochemical evaluation of groundwater in the Blue Nile Basin, eastern Sudan, using conventional and multivariate techniques

Hydrochemical evaluation of groundwater systems can be carried out using conventional and multivariate techniques, namely cluster, factor analyses and others such as correspondence analysis. The main objective of this study is to investigate the groundwater quality in the Blue Nile basin of eastern Sudan, and to workout a hydrochemical evaluation for the aquifer system. Conventional methods and multivariate techniques were applied to achieve these goals. Two water-bearing layers exist in the study area: the Nubian Sandstone Formation and the Al-Atshan Formation. The Nubian aquifer is recharged mainly from the Blue Nile and Dinder Rivers through lateral subsurface flow and through direct rainfall in outcrop areas. The Al-Atshan aquifer receives water through underground flow from River Rahad and from rainfall infiltration. The prevailing hydrochemical processes are simple dissolution, mixing, partial ion exchange and ion exchange. Limited reverse ion exchange has been witnessed in the Nubian aquifer. Three factors control the overall mineralization and water quality of the Blue Nile Basin. The first factor includes high values of total dissolved solids, electrical conductivity, sodium, potassium, chloride, bicarbonate, sulphate and magnesium. The second factor includes calcium and pH. The third factor is due to fluoride concentration in the groundwater. The study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater quality evaluation.

Assessment of the long-term hydrologic impacts of Lake Nasser and related irrigation projects in Southwestern Egypt

A two-dimensional groundwater flow model was constructed to investigate the long-term hydrologic impacts of Lake Nasser and the major land reclamation projects that use excess lake water in southwest Egypt. Egypt constructed (1964–1971) the Aswan High Dam, creating the Lake Nasser reservoir (length: 500 km; average width: 12 km) and is constructing the Tushka Canal to channel 5.0×10 9 m 3/yr of Lake Nasser water to reclaim 0.5×10 6 acres of desert lands. The model, constrained by regional-scale groundwater flow and near-lake head data, was successfully calibrated to temporal-observation heads from 1970 to 2000 that reflect variations in lake levels. Predictive analyses for the subsequent 50-yr period were conducted by employing the calibrated model. Simulations of long-term effects, beyond year 2000, of Lake Nasser on recharge and temporal groundwater head (base case scenario) show that recharge from the lake will continue at a much slower rate than during the 30-yr period of 1970–2000 (with approximately 86% reduction in 30-yr recharge). The modest projected pumping and injection activities in the study area are not expected to cause major deviation in the overall head distribution compared to the base case scenario. The investigation of effects of the new irrigation land development on the Nubian aquifer indicated that many of the proposed irrigation areas, especially those with small aquifer thickness, will become fully saturated with introduced water, resulting in potential flooding and salinization.

Uranium isotopic study of artesian and pluvial contributions to the Nubian Aquifer, Western Desert, Egypt

The groundwater systems of the Nubian Aquifer beneath six major oases (Baris, Kharga, Dakhla, Farafra, Bahariya, and Siwa) in the Western Desert of Egypt have been studied to establish their sources and mixing volumes using uranium isotopes. One hundred six groundwater samples from different depths of the Nubian Aquifer have been analyzed for uranium content and 234U/ 238U activity ratio (AR). The aquifer under the Western Desert is known to have more than one source of water. At Bahariya and Farafra Oases, the Nubian artesian water migrating from the south has been augmented by local recharge during pluvial times. At Siwa Oasis in the northwestern desert, a shallower aquifer component migrating from the north or west is also present. At Dakhla, Kharga and Baris Oases in the southwestern desert, the main source is the Nubian artesian water migrating from southeast Uweinat Upland and northwest Sudan. These water masses have distinctive uranium isotopic signatures. The Nubian Aquifer water is characterized by very low U concentrations (<0.05 ppb) and a relatively high 234U/ 238U AR (>1.5). The shallow northwest aquifer water also has a high AR but a much higher U concentration. The locally recharged pluvial waters have high U concentrations (>0.1 ppb) but low ARs, near unity. A diagnostic derivative parameter is excess 234U content. The deep Nubian Aquifer water is characterized by a relatively low excess 234U (<0.02 ppb equivalent), while the shallow Siwa water has a very high excess 234U [(AR−1)(U conc.)]. The Bahariya and Farafara waters are also high in this component, probably because of pluvial water percolation through phosphate rich strata. At all oases, U isotopic mixing diagrams show that the deep aquifer sources predominate; however, the pluvial contributions are significant, ranging from about 5% at remote Baris Oasis to about 26% at the more northerly Farafra Oasis. The observed lowering of potentiometric surfaces in the Western Desert is caused not only by pumping at a rate greater than inflow from the aquifer systems, but also by the withdrawal of pluvial water which in modern times is not being replaced at all.

Chemical and Isotopic Constraints on the Origin of Wadi El‐Tarfa Ground Water, Eastern Desert, Egypt

AbstractWe evaluated the use of the renewable ground water resources of the Eastern Desert to develop sustainable agriculture in Upper Egypt, an alternative that could alleviate some of Egypt's dependence on water from the Nile River. Ground water from shallow aquifers in the Eastern Desert of Egypt, near the intersection of Wadi El‐Tarfa and the Nile River, was analyzed for chemical compositions, stable isotope ratios, and tritium activities. The ground water has a range in total dissolved solids of 300 to 5000 mg/L. Values of δD and δ18O range from ‐10 to +34 %o and ‐2 to +5.2 %o, respectively, and defines a line having a slope of 5.7 that intersects the meteoric water line at about δD = ‐15 %o on a plot of 8D versus δ18O. These findings indicate that the water might have been derived by a combination of evaporation of and salt addition to regional precipitation. Only one sample could have been derived directly by evaporation and transpiration of modern Nile River water. Salinization of the ground water could have occurred through dissolution of marine aerosol dry fallout, carbonate minerals, gypsum, and other trace evaporitic minerals at and near the ground surface. Tritium activities ranged from 0.04 to 12.9 TU (tritium unite), indicating that all but one of the samples were derived at least partly from precipitation that occurred within the last 45 years. These data indicate that Nubian Aquifer paleowater is not a significant component of the shallow aquifers of this portion of the Eastern Desert. The most likely source of this ground water is sporadic flash flood events yielding locally voluminous recharge that accumulates in coarse sediments and fractured rock beneath alluvial channels. The magnitude of this renewable ground water resource and its potential for supporting sustainable agriculture require further investigation.

Precipitation Source Inferred from Stable Isotopic Composition of Pleistocene Groundwater and Carbonate Deposits in the Western Desert of Egypt

An Atlantic source of precipitation can be inferred from stable isotopic data (H and O) for fossil groundwaters and uranium-series-dated carbonate spring deposits from oases in the Western Desert of Egypt. In the context of available stable isotopic data for fossil groundwaters throughout North Africa, the observed isotopic depletions (δD −72 to −81‰; δ18O −10.6 to −11.5‰) of fossil (≥32,000 yr B.P.) groundwaters from the Nubian aquifer are best explained by progressive condensation of water vapor from paleowesterly wet oceanic air masses that traveled across North Africa and operated at least as far back as 450,000 yr before the present. The values of δ18O (17.1 to 25.9‰) for 45,000- to >450,000-yr-old tufas and vein-filling calcite deposits from the Kharga and Farafra Oases are consistent with deposition from groundwaters having oxygen isotopic compositions similar to those of fossil groundwaters sampled recently at these locations.

Application of combined geophysical and hydrogeological techniques to groundwater exploration: a case study of Showak-Wad Elhelew area, Eastern Sudan

Combined geophysical and hydrogeological investigations were carried out to evaluate the groundwater potential in part of Eastern Sudan. From the interpretations, two major basins were identified: Wad Elhelew and Showak basins. The first is a NNE-SSW trending basin with maximum thickness of 2.2 km. The other is a shallower basin with a maximum thickness not exceeding 0.25 km. Within these basins groundwater occurs essentially in two major aquifers: the Nubian aquifer and Neogene-Recent deposits. Quantitative assessment of groundwater volumes in Showak-Wad Elhelew area gives storage capacity for the upper zone of the Nubian aquifer as 4000 million m 3 and 8000 million m 3 for the lower zone. The safe yield is estimated to be 40 million m 3. Showak basin has a storage capacity of 840 million m 3 and a safe yield of 8.4 million m 3. The storage capacity of the Neogene-Recent deposits is estimated at 112 million m 3, one kilometer away from the banks of Setit and Atbara Rivers and a safe yield of 11.2 million m 3.

Paleogeographical development and correlation of Continental Strata (former Nubian Sandstone) in northeast Africa

The main result of geological work of our group in Egypt and Sudan was the subdivision of the so-called Nubian Sandstone in its type-area Nubia and in the surroundings of Nubia. More than 20 formations have been identified, ranging in age from Cambrian to Paleocene and comprising an impressive number of facies variations. The only characteristic these strata have in common is their position near the northern edge of the African craton. This position caused similiarities within the continental facies and it also influenced marine sedimention, which in general took place in shallow to very shallow seas. The former Nubian Sandstone is strata deposited on both sides of shallow transgressions or in shallow, purely continental basins. Variations of facies were mainly influenced by changes of climate. Except for shallow marine carbonates of Early Tertiary age present in a larger area in northwestern Sudan, all sediments formenly called Nubian Sandstone are of clastic nature including thick sequences of paleosols.Based on the stratigraphical and the sedimentological results, an analysis is now possible on the paleogeographical and the structural development of large parts of NE Africa. At the same time, the results are used as a basis for hydrogeological studies (including a hydrogeological model for the whole Nubian Aquifer System) and for interpretations of the potential of sedimentary mineral deposits.The structural development is dominated by two major elements: pre-existing structural trends (Precambrian developments) and their activation in response to major events of global tectonics. Internal orientation of structural units and related distribution of sediments in this cratonal area of NE Africa was mainly controlled by the major structural pattern formed during cratonization before the Cambrian and by reactivation of selected older elements during plate motion. Preference of reactivation changed several times, depending on differences in the plate situation at the different global events.

Hydrochemical and Environmental Isotopes Investigation in South Western Part of Sudan

According to the chemical composition of water, a vertical hydrochemical stratification has been observed, sodium bicarbonate water is predominant in deep Nubian aquifer, while calcium bicarbonates occur in the marginal and shallower zones of this aquifer. In comparison with more arid regions of North Africa no chloride types has been found within it. Stable isotope data clarifies the interaction between the different water bodies. The Nubia water is the most depleted on its stable heavy isotopes content while surface water is very enriched due to evaporation. The results give very important information about the sources of recharge of the groundwater in the area. The groundwater is mainly meteoric water from two sources of recharge first is paleo-water of paleo-climatic and second is recent water of local precipitation. Die chemische Zusammensetzung der Wutser zeigen eine vertikale hydrochemische Stratigraphie, wobei Natriumbicarbonatwasser bei den nubischen tiefen Speichern vorherrschend sind, wahrend d...

Sr isotope study of vein and cave calcites from southern Israel

The strontium isotope compositions of secondary calcites from the Negev, southern Israel, were compared to those of the marine carbonate host rocks, which range in age from Triassic to Eocene, in order to understand fluid source and migration through fracture systems in dominantly carbonate strata. The Sr isotopes of these calcite clusters are divided into two groups: (1) calcites with 87 Sr 86 Sr values greater than those of the host carbonates; and (2) calcites with 87 Sr 86 Sr values close to the values of the host carbonate. 1. (1) These secondary calcites were found on the main tectonic lines of the Negev (faults and fold axes) and are enriched in 87Sr ( 87 Sr 86 Sr = 0.707709-0.709151 ) relative to the marine carbonate country rocks ( 87 Sr 86 Sr = 0.707251–0.70755 , with one exception). These calcites are associated or crossed by thin veins filled by Fe- and Mn-oxides. 2. (2) Secondary calcites with 87 Sr 86 Sr values close to those of the marine carbonate country rocks (0.7073–0.7077) are found in karstic caves and veins, and are located in sites which are not on the major faults and fold axes. These calcites are not crossed by Fe- and Mn-oxides. The isotopic results indicate that the solutions from which the secondary minerals of the first group precipitated were not in isotopic equilibrium with the marine host rocks. The possible source of the precipitating solutions can be either surface rain descending through the fault system or ascending groundwaters from the deep Nubian aquifer (Paleozoic to Early Cretaceous in age). In both cases there would be a limited interaction with the host sandstone rock which usually is depleted in Sr. The similarity of the 87 Sr 86 Sr values to those of the host rocks in the second group suggests that the main source of Sr in these calcite crystals was from the dissolution of the marine carbonate country rocks by rain- and flood waters.

A groundwater model of the Nubian aquifer system

Abstract The origin of the vast amount of water of the Nubian aquifer system in northeast Africa has been under controversial discussion among hydrogeologists. Does the water flow under more or less steady state conditions from intake beds in the humid Tibesti mountains or in the Ennedi mountains in Chad? Or was it recharged locally in the vicinity of the present oases during an earlier more humid climate so that present extraction actually means groundwater mining under unsteady conditions? An answer from a hydrodynamic point of view is presented using a two-dimensional horizontal finite element groundwater model simulating large-scale flow from the Chad to the Qattara depression. It includes a leakage concept for the confined northern part in order to simulate possible recharge in the vicinity of the east Saharian depressions during humid phases. According to steady state simulations, infiltration solely in the southern highlands does not suffice to maintain the presently observed water levels. Large-scale flow from the Chad highlands to the Qattara depression is insignificant. Thus the system was mainly filled by local recharge. A calibration for the 1960–1980 period was carried out on the model in order to adjust geological system parameters in the vicinity of the Egyptian depressions. An 80 years simulation for the future extraction of planned pumping centres in Egypt and Libya leads to the conclusion that there will be little interference between them in the unconfined part but a common drawdown cone in the Egyptian New Valley area. Some water extracted in Egypt will be drawn from Sudan and Libya. The existing projects in Egypt and Libya extract about 0.5 km3 year−1, being the same order of magnitude as the natural groundwater discharge. The combined future projects would extract 5 km3 year−1, which is about ten times the natural outflow. Thus these projects would change the natural groundwater flow system completely. A comprehensive explanation of the aquifer behaviour seems to indicate a groundwater age far beyond the apparent 14C ages. Groundwater mainly flows between regions of (former) recharge and discharge. The presently extracted groundwater of the Egyptian oases was formed to a great extent during several humid phases in the unconfined part of the Nubian Aquifer in south-west Egypt. This part of the aquifer has been in a depleting process for several thousand years.

Paleohydrology of the Nubian Aquifer northeast of the Blue Nile, near Khartoum, Sudan

Environmental isotopes and ionic water chemistry have been used to study the aspects of recharge to the Nubian aquifer near the confluence of the Blue and White Niles. The results indicated that recharge to the phreatic Nubian aquifer occurs mainly through bed transmission losses of the Blue Nile during flood times and is limited to a zone 13 km east of the river. The groundwater in this zone and the Blue Nile water are relatively enriched in the stable heavy isotopes and are both characterized by a sodium bicarbonate watertype low in sulphate and chloride. Beyond this zone the groundwater is much depleted in heavy isotopes and contains more than 2000 ppm of total dissolved solids, and is dominated by a calcium-sodium bicarbonate water type rich in chloride. Away from the Blue Nile values of heavy isotopes in the Nubian aquifer are quite different from those of modern rainfall of the region and correlate fairly well with values of a colder climatic zone. Hence it is postulataed that the regional gradient of the Nubian aquifer is a decaying fossil gradient of a pluvial period in the Pleistocene.

Computer simulation of ultrasonic testing

Electromagnetic Investigation of the Sub-Surface (EISS) is a Ground Penetrating Radar (GPR) operating at very low frequencies in the HF range (2–4 MHz) that was designed to investigate the composition and structure of the Martian subsurface to depths of ~1 km. EISS can operate in both a monostatic and bistatic configuration, the latter being made possible by the simultaneous operation of two separate instrument platforms. The first, a fixed lander, utilizes one surface-deployed dipole antenna made of two 35 m-long resistively-loaded monopoles to transmit radar pulses into the subsurface. Echoes from subsurface reflectors are then received by either similar electrical receiving antennas (on the lander) or by a much smaller magnetic sensor that can be mounted either on the lander or on a mobile platform, such as a rover.In this paper, we report on the successful test of EISS bistatic mode of operation during a field campaign in the West Egyptian desert. From the analysis of the measured propagation delays, the dielectric constant and the depth of several reflecting subsurface interfaces were retrieved. Up to 226 coherent additions (or stacking) were performed resulting in the detection of buried interfaces and in particular of the Nubian Aquifer at a depth >200 m. The results obtained with the small magnetic sensor were consistent with those obtained with the electrical antennas, suggesting that such an experiment can meet the constraints of a space mission.

Aspects of Egyptian Hydrogeology

ABSTRACT The hydrometeorology of Egypt is examined and the groundwater situation analyzed with reference to the use of environmental isotopes and the information they can provide as to pluvial and post-pluvial inputs to the Nubian aquifer system. Recharge to and discharge from this vast reservoir of partly fossil water indicate its dynamic state. The water table has declined appreciably in historic times. Lack of data makes extreme caution advisable in drawing general conclusions.

Groundwater development, Kharga Oases, Western Desert of Egypt: A long-term environmental concern

The groundwater reserves in Kharga Oases have been studied for the long-term socioeconomic development in the area. The Nubian Sandstone, which consists of a thick sequence of coarse clastic sediments of sandstone, sandy clay interbedded with shale, and clay beds, forms a complex aquifer system. The Nubian Aquifer has been providing water to artesian wells and springs in the Kharga Oases for several thousand years.