A numerical time-dependent groundwater model of the Nubian Sandstone Aquifer in Egypt is presented. A complete database of the hydrogeological and drilling information of 850 water wells drilled in the period 1960-2000 was evaluated and used for the model parameter input as well as for its calibration. A steady-state condition is rejected even for the pre-development time as the subsurface inflow across the Egyptian/Sudanese borders is lower than discharge, and the observed hydraulic gradient is residual gradient and not due to steady-state flow. The results of the long-period simulation (10,000 years) indicated that the Nubian Sandstone Aquifer is still under the influence of the past humid period and has been in an unsteady deplenishing process. Therefore, groundwater development plans should be based on this concept. The calibrated model was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the potentiometry of the aquifer. The simulation results indicate that there is a real danger of groundwater depletion, particularly in the shallow aquifer in some areas. In fact, if the planned extraction of 1,200 million m3/year in East Oweinat area is imposed, drawdown after 100 years could be as much as 200 m relative to1960s levels. By this time the cone of depression will extend to Dakhla and Kharga oases.

A numerical time-dependent groundwater model of the Nubian Sandstone Aquifer in Egypt is presented. A complete database of the hydrogeological and drilling information of 850 water wells drilled in the period 1960-2000 was evaluated and used for the model parameter input as well as for its calibration. A steady-state condition is rejected even for the pre-development time as the subsurface inflow across the Egyptian/Sudanese borders is lower than discharge, and the observed hydraulic gradient is residual gradient and not due to steady-state flow. The results of the long-period simulation (10,000 years) indicated that the Nubian Sandstone Aquifer is still under the influence of the past humid period and has been in an unsteady deplenishing process. Therefore, groundwater development plans should be based on this concept. The calibrated model was used to investigate the hydrodynamic impacts of the present and planned groundwater extraction on the potentiometry of the aquifer. The simulation results indicate that there is a real danger of groundwater depletion, particularly in the shallow aquifer in some areas. In fact, if the planned extraction of 1,200 million m3/year in East Oweinat area is imposed, drawdown after 100 years could be as much as 200 m relative to1960s levels. By this time the cone of depression will extend to Dakhla and Kharga oases.

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.