Southwest Egypt is an arid area with no surface water and limited resources of useable groundwater in the well-known Nubian Sandstone Aquifer System. These groundwater reserves have been heavily exploited since the 1960s, which has led to substantial decline in the potentiometric surface of the aquifer. A calibrated regional numerical model with refined grids on the pumping centers has been used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifers. The results indicate that there is a real danger of either dewatering the shallow aquifer in some areas (e.g., Kharga Oasis), or increasing the water depth to uneconomic lifting depth. They also indicate that, although the planned extraction rates in Dakhla, Farafra, and Bahariya oases are feasible for at least the coming 100years, the present rate for Kharga Oasis and the planned rate for the East Oweinat area have to be reduced substantially.

Dakhla Oasis is located in the Western Desert of Egypt. Groundwater exploited from the Nubian Sandstone aquifer is the only available water resource in this area. This resource has been heavily exploited since 1960, which has led to a substantial decline in the potentiometric surface of the aquifer. A regional numerical groundwater flow model, calibrated under unsteady-state conditions, has been developed and used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifer. To account for local details and to allow a precise analysis of pumping and the resulting drawdown in Dakhla Oasis, a local-scale model was developed by refining the grid cells in the calibrated regional model. The local-scale model gave a detailed picture about the expected drawdown due to the different groundwater management options in the next 100years. The simulated results indicated that the planned increase in groundwater extraction will have a major impact on groundwater flow patterns in the whole area located southwest of Dakhla Oasis.El oasis Dakhla est situado en el gran desierto occidental de Egipto. El agua subterrnea que se extrae del acufero de roca arenosa nubia es la nica fuente de agua disponible en esta rea. Este recurso ha sido explotado en medida considerable desde 1960. Este hecho he causado una disminucin sustancial en la superficie potenciomtrica del acufero. Se ha desarollado un modelo de flujo de agua subterrnea numrico regional calibrado bajo condiciones de estado variable. Este modelo se ha utilizado para investigar el impacto hidrodinmico que diferentes opciones de manejo de aguas subterrneas tienen sobre la potenciometra del acufero. Se desaroll un modelo de escala local mediante el refinamiento de las clulas de malla en el modelo regional calibrado con el objecto de involucrar los detalles locales y de permitir un anlisis preciso del bombeo y disminucin del nivel de aqua resultante en el oasis Dakhla. El modelo de escala local proporcion un imagen detallada de la disminucin de nivel esperada segn las diferentes opciones de manejo de agua subterranea en los prximos 100aos. Los resultados simulados indican que el incremento de extracin planificado en la agua subterrnea tendr un gran impacto en el patrn de flujo de agua subterranea en toda el area ubicada al suroeste del oasis de Dakhla.Loasis de Dakhla est situe dans la partie occidentale du dsert dgypte. La seule source deau disponible dans la rgion provient de lexploitation de laquifre grseux de Nubian. Cette ressource a largement t exploite depuis 1960, rsultant en la diminution significative de la surface pizomtrique de laquifre. Un modle numrique dcoulement rgional de leau souterraine, calibr en rgime transitoire, a t dvelopp et utilis afin dtudier les impacts hydrodynamiques de diffrents scnarios de gestion de laquifre sur la surface pizomtrique. Afin dinclure les particularits locales et de raliser une analyse prcise du pompage et du rabattement qui y est associ dans lOasis de Dakhla, un modle local dcoulement a t dvelopp en raffinant le maillage dans le modle rgional pralablement calibr. Le modle local dcoulement fournit une image dtaille du rabattement prvu pour les cent prochaines annes selon les diffrents scnarios de gestion de laquifre. Les rsultats obtenus par simulation numrique indiquent que laugmentation prvue dans lexploitation de leau souterraine aura un impact majeur sur les patrons dcoulement de leau souterraine dans toute la rgion situe au sud-ouest de loasis de Dakhla.

ABSTRACT: A three-dimensional GIS-based groundwater flow model for the Nubian Sandstone Aquifer in the eastern Sahara was developed and calibrated under steady-state and transient conditions. The model was used to simulate the response of the aquifer to climatic changes that occurred during the last 25,000years. The simulation results indicated that the groundwater in this aquifer was formed by infiltration during the wet periods 20,000 and 5,000years b.p. The recharge of groundwater due to regional groundwater flow from more humid areas in the south was excluded. It also indicates that the Nubian Aquifer System is a fossil aquifer, which had been in an unsteady state condition for the last 3,000years.Fue desarrollado un modelo de flujo de agua subterrnea en tres dimensiones, basado en un SIG, para el Acufero Arenisca Nubian en el Sahara Oriental, el cual fue calibrado para condiciones de estado estacionario y transitorio. El modelo se us para simular la respuesta del acufero a los cambios climticos que ocurrieron durante los ltimos 25000 aos. Los resultados de esta simulacin indicaron que el agua subterrnea en este acufero, se form por infiltracin, durante los perodos hmedos que hubo hace 20000 y 5000 aos, antes del presente. Fue excluida la recarga del acufero debida a un flujo regional de agua subterrnea proveniente de reas con un clima ms hmedo en el sur. El modelo tambin muestra, que el Sistema Acufero Nubian es un acufero fsil, el cual ha permanecido en una condicin de estado no estacionario, durante los ltimos tres mil aos.Pour laquifre grseux Nubien de Sahara -Est on a mis au points un modle tridimensionnel, bas sur GIS. Le modle a t calibr tant pour lcoulement stationnaire que pour lcoulement transitoire. On a simul aprs la rponse de laquifre aux changements climatiques des derniers 25000 ans. Les rsultats des simulations indiquent que la nappe a t recharge par des infiltrations pendant une priode humide qui stend 5000 et 20000 ans, ds temps actuel. On na pas pris en compte la recharge de laquifre par la zone plus humide situe dans sa partie sud. Le modle indique aussi que leau de laquifre Nubien est une eau fossile qui a eu un coulement transitoire pendant les derniers 3000 ans.

ABSTRACT: The Quaternary aquifer of Wadi Ham, UAE has been overexploited during the last two decades to meet the increasing water demands. As a result, the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated. In this paper, a 2D earth resistivity survey was conducted in Wadi Ham in the area between Fujairah and Kalba to delineate the seawater intrusion. Existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data. Results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D resistivity data to identify three zones of water-bearing formation (fresh, brackish, and salt-water zones). Along the four 2D resistivity profiles, the depth to the fresh-brackish interface exceeded 50m at the western part of the area and was in the order of 10m or less in the eastern side near the shoreline. Depth to the brackish-saline water interface reached about 70m in the western side and was in the order of 20m in the eastern side. The thickness of the fresh water zone decreases considerably in the farming areas toward Kalba and thus the degree of seawater intrusion increases.

ABSTRACT: Groundwater pumping from Kalbha and Fujairah coastal aquifer of the United Arab Emirates (UAE) has increased significantly during the last two decades to meet the agriculture water demands. Due to the lack of natural replenishment from rainfall and the excessive pumping, groundwater levels have declined significantly causing an intrusion of seawater in the coastal aquifer of Wadi Ham. As a result, many pumping wells in the coastal zone have been terminated and a number of farms have been abandoned. In this paper, MODFLOW was used to simulate the groundwater flow and assess the seawater intrusion in the coastal aquifer of Wadi Ham. The model was calibrated against a five-year dataset of historical groundwater levels and validated against another eleven-year dataset. The effects of pumping on groundwater levels and seawater intrusion were investigated. Results showed that reducing the pumping from Khalbha well field will help to reduce the seawater intrusion into the southeastern part of the aquifer. Under the current groundwater pumping rates, the seawater will continue to migrate inland.

ABSTRACT: Drilling information, historical water table levels, groundwater salinity records of the existing water wells in Wadi Al Bih area, United Arab Emirates, were stored in a geodatabase and used to characterize the geological and hydrogeological settings of this area. A 2D earth resistivity imaging survey was conducted for the first time in the Northern UAE to determine the potential of the Quaternary aquifer and its groundwater quality in the areas where there are no monitoring wells. The results of the chemical analyses of the collected groundwater samples together with the inversion results of the resistivity data were used to draw a total salinity map and determine the spatial variations in groundwater quality. The inversion results of the 2D earth resistivity imaging data indicated that the Quaternary aquifer in the study area is in a good connection with the underlying carbonate aquifer. It also indicated that the carbonate aquifer is of major regional and vertical extension and it contains the fresh water in this area. The data stored in the developed database were used to produce different types of geopotential maps.

ABSTRACT: Arid coastal regions are more vulnerable to groundwater deterioration problems. Intensive groundwater abstraction from the coastal aquifer of Wadi Ham, United Arab Emirates, caused a severe saltwater intrusion problem. Given the deterioration of groundwater quality, domestic water supply from well fields have been terminated and replaced by desalinated seawater. In addition, many farms in southeast Fujairah city have been abandoned. This paper develops a two-dimensional finite element groundwater flow and solute transport model to simulate the spatial and temporal variations of the salinity distribution in the coastal aquifer of Wadi Ham, taking into account the transition zone between freshwater and seawater bodies. All simulations were conducted in the horizontal view under transient conditions. The available historical records of the water table levels were used to calibrate and validate the developed model. Emphasis was placed on the response of the transition zone to different pumping scenarios in Wadi Ham. The results indicated that the seawater intrusion problem has evolved rapidly during the last two decades. Unlike previous investigations, this study presents the most accurate quantitative and qualitative assessment of available groundwater in the Wadi Ham aquifer under different pumping scenarios

ABSTRACT: Arid coastal regions are more vulnerable to groundwater deterioration problems. Intensive groundwater abstraction from the coastal aquifer of Wadi Ham, United Arab Emirates, caused a severe saltwater intrusion problem. Given the deterioration of groundwater quality, domestic water supply from well fields have been terminated and replaced by desalinated seawater. In addition, many farms in southeast Fujairah city have been abandoned. This paper develops a two-dimensional finite element groundwater flow and solute transport model to simulate the spatial and temporal variations of the salinity distribution in the coastal aquifer of Wadi Ham, taking into account the transition zone between freshwater and seawater bodies. All simulations were conducted in the horizontal view under transient conditions. The available historical records of the water table levels were used to calibrate and validate the developed model. Emphasis was placed on the response of the transition zone to different pumping scenarios in Wadi Ham. The results indicated that the seawater intrusion problem has evolved rapidly during the last two decades. Unlike previous investigations, this study presents the most accurate quantitative and qualitative assessment of available groundwater in the Wadi Ham aquifer under different pumping scenarios

ABSTRACT: A water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the United Arab Emirates. An intensive 2D Earth Resistivity Imaging (ERI) survey was conducted in selected areas to assess the available groundwater resources and delineate the salt-water intrusion. Drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology, degree of saturation, and groundwater salinity and thus to improve the interpretation of ERI data. The results of the chemical analyses of water samples collected from the wells along with the 2D ERI survey profiles were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids. This relationship was used along with the true resistivity sections resulting from the inversion of 2D ERI data to identify and map three zones of water-bearing formation (fresh, brackish, and salt-water zones) in the coastal areas. The results indicated that the depth to the fresh-brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline. Because of the high resistivity contrast between dry and water saturated fractured rocks; this method was very successful in detecting water-filled fractures and cavities in the carbonate aquifer. The application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and/or saturated with saline or brackish water from the surrounding clayey materials.