New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork Mitigation of Excessive Drawdowns via Rotational Groundwater Withdrawal (Case study: El Kharga Oases, Egypt) Safaa M. Soliman Research Institute for Groundwater, National Water Research Center, El Kanter El Khairia, Kalubia, Egypt [email protected] Abstract: Groundwater in Egypt plays important roles in the country's water budget. One of these roles is being the sole source of water for the nomads’ communities in the Western Desert. For this role to be sustainable, careful and scientifically based plans for groundwater withdrawal should be developed. This research was initiated with the objective of mitigating the excessive drawdowns by applying rotational groundwater withdrawal. El Kharga Oases was chosen to be studied because it mainly depends on groundwater as the primary source for water and are suffering from continuous increase in groundwater drawdowns due the excessive groundwater withdrawal, so it was necessary to study the aquifer of El Kharga Oases to find a solution to this problem that is accepted from stakeholders. In this study a numerical groundwater model was constructed to evaluate the effect of switching to rotational groundwater withdrawal on mitigating excessive drawdowns. In this regard, a MODFLOW package Visual MODFLOW 4.2 was utilized to simulate the proposed rotational withdrawal policy. The model was calibrated for steady state flow conditions with acceptable accuracy; the calibrated model has been run under the rotational withdrawal policy for 3 years to predict the rate of change in groundwater drawdowns. The results show sustainable recovery of groundwater levels throughout the prediction run period. [Safaa M. Soliman. Mitigation of Excessive Drawdowns via Rotational Groundwater Withdrawal (Case study: El Kharga Oases, Egypt). N Y Sci J 2013; 6(1):118-123]. (ISSN: 1554-0200). http://www.sciencepub.net/newyork. 18 Key word: El Kharga, groundwater, drawdowns, sustainability 1. Introduction Oases belongs to Lower Cretaceous and mainly The Western Desert encompasses a number consist of coarse to medium sands with high of oases that have been mainly inhabited by nomads. permeability (Figure 2). This permeability varied The environment of the oases is characterized by land from one area to another depending on the deposition marks constituting of springs around which nomads conditions and also by intercalations of silts. The could survive on scattered agricultural plots. The Nubian Sandstone thickness reaches a minimum investigated area lies in the central part of the value in the southern part of the study area and is Western Desert as shown in figure 1. El Kharga gradually increasing to the north. The basement rocks extends roughly north-south parallel to the Nile appear at the surface in the south and at a depth up to Valley. It is located 140 km to the east of El-Dakhla 1100 meters in the north. This aquifer system overlies Oasis and 220 km south of Assiut City. It is bounded the Pre-Cambrian basement Complex, thus, ranging by long. 30° 20´ and 30° 40` E and lat. 25° 05` and in age from Cambrian to the Pre-Upper Cenomanian. 25° 30` N (CONOCO, 1987). El Kharga Oases has one of the longest El-Kharga depression has the same climatic continuous records of human use of groundwater in characteristics of the Western Desert. It has an arid the world. Groundwater in El-Kharga Oases is climate; mostly rainless with an annual intensity considered the sole source for water used mainly for rainfall of 2.35 mm. The maximum air temperature irrigation and other purposes. Groundwater in the reaches 40.2 C in June, while the minimum attains Kharga is withdrawn from springs as well as shallow 5.8 C in January, with average evaporation rate of and deep artesian wells. Till the 1959, nearly, all the 413.66 mm/month. wells were originally flowing. However, with the The geology and hydrogeology framework exploitation of groundwater from deep wells for of El Kharga Oases was described in early irrigation, the natural flows declined as more and puplications by Shata (1961), Awad and Ghobrial more closely spaced deep wells were drilled. By the (1965), Ghobrial (1967), Hermina (1967), Himida 1975 many deep wells had ceased to flow. The water (1968), El-Kiki et al (1972), Ezzat (1974), El- demand in the area has been met by pumping from Hinnawi (1976), Barthel et al (1978) and Diab both shallow and deep wells. The general direction of (1978). The Nubian Sandstone aquifer in El Kharga groundwater flow is from all the sides to the centre of 118 New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork El Kharga Oases. Intensive groundwater development same period. The oases are suffering from continuous for irrigation purpose in the Oases started in 1960 increase in groundwater drawdowns due to intensive with an extraction rate of 51 million m3/year, from groundwater withdrawal; so, in this work a numerical naturally flowing 279 shallow wells and springs and groundwater model was constructed to evaluate the 12 deep wells. Extraction was progressively effect of switching to rotational groundwater increased to reach about 101 million m3/year in 1963, withdrawal on mitigating excessive drawdowns. and then decreased to an average rate of 87 million m3/year during the period 1965-1978. Since 1979, groundwater extraction in the oases started to increase again till it reached an annual rate of 118 million m3/year in 1998 (from 192 deep wells and 16 springs), of which 97% is exploited by pumping (Figure 3). 25 00 30 00 35 00 MEDITERRANEAN SEA ria nd xa le A Cairo 30 a n ar o 00 tt si a s Siwa re Q p SINAI e D El- Bahariya E A S W T E E R S N T R El- E E Figure 2: Geological Map of Egypt (modified after RIGW 1999) Farafra Assiut D R N 26 Qena D 00 El- E El- Kharga S Dakhla E S R D E T A T o A 350000.00 s E y Aswan u t S E Gilf Mahariq R Kebir Sherka T Lake Plateau KHARGA Nasser 300000.00 hla Dak To Ginah Study area 0 100 200 22 Km Bulaq 00 Garmashin 250000.00 Fig ure 1: General Location map of the study area Baris Groundwater monitoring of a reasonable 200000.00 number of observation wells, was practiced in the Kharga Oasis compared to other development areas in the Western Desert of Egypt. Monitoring records indicate that during the last 40 years, the water levels 150000.00 have been affected by extraction. Two groundwater depressions are created in the northern part of the oasis around Al Kharga–Malaa extraction zone with a 500000.00 550000.00 maximum drop in water level of 60 m, and in the Well Fields Reclaimed Regions surrounding of Bulaq-Garmashin Zone with a maximum drop in the water level of 35 m during the Figure 3: Detailed Map of the Study Area 119 New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork 2. Numerical Simulation The hydraulic conductivity of the aquifer To study the groundwater situation of the has been measured by pumping test in some study area a numerical model is used to represent the locations, and it varies from 1-3 m/day. region and examine the proposed rotational withdrawal operation policy. The rate of extraction (about 118 million 3 m /year). 400000.00 2.1 Modeling Package 0 0 0 0 0 To simulate the groundwater flow in the 4 study area a three-dimensional groundwater flow 0 0 0 0 package was used. The used package (Visual 6 3 350000.00 Modflow 4.2) is a three-dimensional groundwater mon9 mon10 mon7 mon5mon8 flow and contaminant transport model based on the mon3mon4mon2sh10sh11sh5 sh4mon6mon1 sh6sh3sh9sh7 sh8 0 sh1 0 sh2 kh35 0 0 kh1kh2kh14kh32 finite difference method with rectangular cells. The 2 kh29kh16kh15kh4kh40 3 kh17kh26kh5kh25 kh19kh30kh7kh18kh3kh24kh33kh37kh11kh8 kh38kh20kh27kh36kh9 kh39kh6kh31kh21kh34kh10 kh28kh23kh22kh12gen5kh13 model is capable to handle the saturated and gen10 gen12gen13n6 gen8gen1 300000.00 gen11gen9gen6gen7 gen3gen2gen4 n4n3n2n1bo17bo4bo3 unsaturated flow with homogeneous, heterogeneous, bo10bo13bo20bo18bo12 bo16bo8bo9bo7bo2bo1 0 bo25bo5bo6bo14bo19bo15 0 bo21bo24 0 bo11bo23bo22 0 gr4 isotropic, and anisotropic aquifer system under steady 8 gr8 2 gr2gr7gr5 grm1gr6 state and transient conditions. The model has the gr13 gr11 gr9 gr12 capability to link with GIS system and ARCVIEW 250000.00 gr10gr3 0 bars35bars7 0 bars23 bars22bars8 0 bars11 0 bars6bars5 software. This fully integrated package combines 4 bars3 2 bars26 bars9bars24bars1bars2bars43 bars28bars14bars30bars4 bars31bars36bars10bars29 bars42bars12 MODFLOW, MODPATH, MT3D, MT3DMS, bars33bars37bars25 bars13bars27bars32bars38 bars34bars18bars39 bars40bars16bars15bars19bars44 RT3D, PESST and SEAWAT with the most intuitive bars41bars21bars20 0 0 0 200000.00 0 and powerful graphical interface available. The 0 2 model grid input parameters and results can be visualized in cross-section or plan view at any time 0 0 0 0 during the development of the model or while 6 1 displaying the results (Anderson and Woessner, 150000.00 0 1992; Engesgaard P. and. Kipp K.L.1992). 0 0 0 2 1 480000 510000 540000 570000 600000 630000 650000 2.2 Modeling Grid and Boundaries 500000.00 550000.00 600000.00 650000.00 The model covers an area of about 47600 2 Figure 4: Model Grid and Boundaries km . The aquifer west boundary is considered general head boundary, based on the nearest constant head contour (100-120 m) above mean Sea level, depending on the groundwater levels of study area wells. The other boundaries are no flow boundaries perpendicular on groundwater contour lines. The model grid consists of 4186 cells; relatively small cells were used in the significant areas, the model grid and boundaries are shown in figure 4. 2.3 Model Input The main input data include: The ground surface elevation that ranges between zero and 400 above mean Sea level (Figure 5).