2/24/2016 Evaluation of the groundwater resources potential of Siwa Oasis using three­dimensional multilayer groundwater flow model, Mersa Matruh Governorate… Original Paper Arabian Journal of Geosciences February 2015, Volume 8, Issue 2, pp 659­675 First online: 28 December 2013 Evaluation of the groundwater resources potential of Siwa Oasis using three­dimensional multilayer groundwater flow model, Mersa Matruh Governorate, Egypt Abdulaziz M. Abdulaziz , Abdalla M. Faid 10.1007/s12517­013­1199­4 Copyright information Abstract Siwa represents the last virgin oasis in the western desert of Egypt. Recently, serious environmental changes pertaining to the invaluable groundwater resources, such soil salinity and expansion in surface lakes have developed due to excessive uncontrolled groundwater discharge associating land development for agriculture. The present work tackles these problems through monitoring the configuration of pressure head in carbonate and Nubian Sandstone aquifers using multilayer groundwater model. Several scenarios for pumping stress are tested, and the results indicated that the optimum pumping should be close to 520,000 m3/day with important disturbances in the pressure head encountered between Bahei El­Din Lake and Zeitoun Lake. This aquifer stress is capable of lowering the pressure head to stop artesian flow and inconsequence saves large water quantities draining daily to the lakes through natural flow and mitigates the waterlogging problems. In addition, minimal changes are observed in the eastern part of the modeled area suggesting additional production wells to tap the aquifer system at this barren area and initiate new development projects. Such results demonstrate the potential of groundwater flow modeling in water resources management to define the optimum pumping scenarios capable to mitigate environmental problems. Keywords 3D Groundwater modeling Groundwater management Arid regions Siwa Oasis Egypt Introduction Over the past century, the total population of Egypt increased from 11 million in 1907 to 73.4 million in 2004, while the area of cultivated land has only increased from 2.25 million to around 3.5 million ha (Abdulaziz et al. 2009). As a consequence, the area of land per capita has fallen from 0.2 to 0.05 ha during the same period (FAO 2005). To accommodate the increasing demands for food, attentions are usually paid to reclaiming the desert, but the success of such agricultural projects is entirely restricted to the availability of sustainable water resources. This is probably the reason behind the development programs of the “New Valley Project” and the “South Egypt Development Project,” great projects of land reclamation around the oases of the Western Desert and south Egypt respectively. While the agricultural land reclamation of the New Valley Project initiated in 1960 is based exclusively on groundwater from the Nubian Sandstone aquifer, the south Egypt development project commenced in 1995 is based on the conjugated use of groundwater from the same aquifer and surface water pumped from Nasser Lake (Ebraheem et al. 2004). Nubian Sandstone is Cambrian to Late Cretaceous and is predominantly continental sediments extending over 2,000,000 km2 underneath the eastern Sahara with confinement condition prevailing to the north of latitude 25° N due to the development of the post­Cretaceous dense limestone, shale, and clay. Groundwater in the Nubian Sandstone aquifer, http://link.springer.com/article/10.1007/s12517­013­1199­4/fulltext.html 1/19 2/24/2016 Evaluation of the groundwater resources potential of Siwa Oasis using three­dimensional multilayer groundwater flow model, Mersa Matruh Governorate… hydrologically unsteady aquifer over the past thousands of years, is known to be fossil water and its abstraction is unrenewable (Hellstrom 1940; Pallas 1980; Heinl and Thorweihe 1993; Ebraheem et al. 2002; Gossel et al. 2004). The calculated in­place groundwater of the Nubian Sandstone aquifer is arguable which generally tends to increase over time: 3,000 km3 (Ambroggi 1966), 20,000 km3 (Gischler 1976), 50,000 km3 (Heinl and Thorweihe 1993), and 28,000 km3 (Ebraheem et al. 2002). But generally only a small portion of these volumes can be suitable for exploitation. Isotopic studies on groundwater supported these implications and asserted the deficit of recent recharge to the Nubian Sandstone aquifer in Egypt. The estimated age of groundwater from the Nubian Sandstone aquifer has broadly varied with the different techniques reporting 10,000–33,000 years (Abdelghafour 1993) and 25,000–40,000 years (Heinl and Brinkmann 1989) using Carbon­14, but much older values (200,000 years–1 Ma; Sturchio et al. 2004) are estimated using Krypton­81 and Chlorine­36 techniques. The recharge to the fractured carbonate aquifer underneath Siwa Oasis is largely disputable between local recharge from the deep Nubian Sandstone aquifer and surface recharge at a faraway catchment area near Gebel Akhdar, Libya (El­Shazly and Abdel­Mogheeth 1991). Accordingly, several pre­development studies are devoted mainly for evaluating the groundwater potential and provide detailed characterization of groundwater quality and quantity in these regions (Ball 1927; Diab 1972; Ezzat et al. 1962; Ezzat 1974, 1976; Hesse et al. 1987; Nour 1996; MPWWR 1998). Large­scale land development usually associates serious ecological and socioeconomic problems, such as waterlogging phenomenon (Masoud and Koike 2004), rapid falling water level and groundwater depletion (Nour 1996; Konikow and Kendy 2005; Venot and Molle 2008), salt water intrusion (Kashef 1983; Ebraheem et al. 1997; Werner and Simmons 2009), and disturbance to the overall groundwater system (Vrba and Pêkný 1991; Abdulaziz 2007; Ahmed et al. 2012). The situation becomes worse if high natural discharge of poor­quality groundwater through natural springs and/or uncontrolled dug wells is involved, which is recognized in Siwa Oasis. Water management is a decisive action with numerous goals that may be partly conflicting to maintain and improve the state of water resources (Pahl­Wostl 2007). The principle objectives of water resources management and plans are to grant the increasing water demands for different uses in a most environmentally effective, socially acceptable, and economically efficient manner (Biswas 2004). Recently, groundwater flow models became the most influential and effective tools that help water resource planners making water plans and depicting management policies through time series with different scenarios using transient simulations. However, managing such transient simulations involves large transient data sets including well pumping data, recharge data, and observation data (Abdulaziz 2007). In addition, Anderson and Woessner (1992) indicated that specifying storage characteristics of the hydrostratigraphic units, influences of the initial conditions and model boundaries, propagation of hydraulic stresses to reach the model boundaries, and discretization in spatial and temporal domains add inherently more complications to transient simulations. Generally, the key factors that influence the model validity involve the selection of boundary conditions that properly simulate the common steady­state calibration and assigning the appropriate time steps with minimal influences on the numerical outputs. Finally, the use of model­ generated head values ensures the initial head data and consistency of input hydrologic parameters (Franke et al. 1987). Siwa represents the smallest oasis located in the Egyptian part of the extensive Libyan Desert and depends exclusively on groundwater resources and drainage water reuse. Recently, farmers started to experience the challenging rising water level in the soil zone together with the groundwater salinity and the escorted waterlogging and soil salinization, especially in the topographically low lands at the proximity of the drainage lakes. To evaluate the adverse environmental impact of such excessive groundwater, the Desert Research Center has initiated a program to periodically monitor the water levels and electric conductivity of groundwater in 60 piezometers tapping the shallow aquifer and soil zone (DRC 1988). A second program sponsored by Research Institute for Groundwater (RIGW) in 2001 carried out extensive hydrogeologic and hydrochemical investigations and surveyed 1,265 piezometers throughout Siwa Oasis to determine wells with excessive discharge and evaluate the variations in chemical composition (Sakr et al. 1999). These studies indicated that more than 50 % of the naturally flowing groundwater through natural springs or wells tapping the confined aquifers is dispensed into salt ponds through the poor drainage system. Through an action plan over the past few years, 80,000 m3/day discharged through 180 critical well was managed and terminated to save approximately 40 % of the disposed groundwater (El­ Hossary 1999). In the present study, the main objective is to develop a multilayer three­dimensional groundwater flow model to Siwa Oasis based on the thorough conceptual understanding of the aquifer system, the established monitoring network, and the available well data. Such a model enables the prediction of future aquifer repercussions to different pumping stresses and the potential of the groundwater system over a relatively long period of time, 50 years. This information is extremely valuable in evaluating the available groundwater resources and demonstrates the significances groundwater modeling applications.