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 i a SEA dr an ex Al
Cairo 30 a n ar o 00 tt si a es Siwa Q r SINAI ep 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
Gilf E 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 number of observation wells, was practiced in the 200000.00 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 m3/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 capability to link with GIS system and ARCVIEW gr12 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 MODFLOW, MODPATH, MT3D, MT3DMS, bars42bars12 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).
The base of the aquifer that ranges between - 200 and 1300 m below mean Sea level. The aquifer was simulated as three hydraulically connected zones, because all wells pump from second and third zones, base levels of zone 2 and zone 3 as shown in figures 6 and 7 respectively.
120 Figure 5: Topographic Contour Map
New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork
2.4 Calibration Before the model can perform its tasks in predicting the response of the system to any future activities, it must be calibrated. To use the model in
testing the impact of the proposed operation policy,
the model calibration was achieved using available hydrogeological data. The model was calibrated for steady state flow conditions. The obtained results were with acceptable accuracy, figure 8. During the calibration process, various inputs were adjusted, especially the hydraulic parameters (i.e. hydraulic
conductivity, specific storage or specific yield
distribution), taking into consideration available results of aquifer tests, geological studies and geophysical logs. Figure 9 shows the calibrated groundwater head of the study area.
Figure 6: Base Level Contour Map of Zone2
Figure 8: Results of the Steady State Calibration
Figure 7: Base Level Contour Map of Zone3
121
New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork
T
o
A
350000.00 s y
u
T t
o
A
350000.00 s y
u
t 9.00 Mahariq 100.00 Mahariq Sherka 8.50 90.00 Sherka KHARGA 8.00 300000.00 KHARGA
khla Da Ginah To 80.00 300000.00 7.00 hla Dak ToGinah Bulaq 70.00 Bulaq 6.00 Garmashin 5.00 60.00 Garmashin 250000.00 4.00 50.00 250000.00 3.00
Baris 40.00 2.50 Baris 2.00 30.00 200000.00 1.50 20.00 200000.00 1.00 10.00 0.50
150000.00 0.00
150000.00
500000.00 550000.00
500000.00 550000.00 Figure 9: Calibrated Groundwater Head Map Figure 10: Difference in Drawdown Contour Map of Zone 2 3. Proposed Operation Policy The aim of using the simulation model is to predict the behavior of the aquifer under the influence of proposed future activities and operation policies.
Confident with the calibration process, a rotational
T
o
A
350000.00 s y
u groundwater withdrawal policy was applied on the t calibrated model. The proposed policy was to switch Mahariq 8.50 the withdrawal into a rotational withdrawal. In the Sherka 8.00 applied policy, the pumping wells were divided into KHARGA 300000.00 7.00
hla Dak two groups, each group was`operated alternatingly ToGinah for half a day and the other group was operated the Bulaq 6.00 5.00 second half of the day. The calibrated model was run Garmashin under the effect of switching to rotational 4.00 250000.00 groundwater withdrawal for 3 years to predict the rate 3.00 of change in groundwater drawdowns. The effect of 2.50 Baris rotational withdrawal on mitigating excessive 2.00 drawdowns is measured in terms of achieved 200000.00 1.50 reduction of groundwater drawdowns due to 1.00 switching from continuous to rotational withdrawal. 0.50 The results of applying the proposed 0.00 rotational groundwater withdrawal policy on the 150000.00 pumping wells are shown in figures 10 and 11. They indicated that the reduction in groundwater drawdowns varied between 1 and 9 m for the second 500000.00 550000.00 zone and ranged between 1 and 8.5 m for the third zone. Figure 11: Difference in Drawdown Contour Map of Zone 3
122
New York Science Journal 2013; 6(1) http://www.sciencepub.net/newyork
4. Conclusions and Recommendations Southwestern Desert Egypt) a significant In this study a numerical groundwater model lithostratigraphic unit of the former "Nubian was constructed to evaluate the effect of switching to Series" Mitteilungen der Bayerischen rotational groundwater withdrawal on mitigating Staatssammlung fur Palaontologic und excessive drawdowns. In this regard, a MODFLOW historische Geologie: Vol. 18, pp. 153-166. package Visual MODFLOW 4.2 was utilized to 4. Continental Oil Company (CONOCO) (1987): simulate the proposed rotational withdrawal policy. Geological map of Egypt (scale 1:500,000). The model was calibrated for steady state flow 5. Diab, M. Sh. (1978): A regional conditions and acceptable accuracy was achieved. hydrogeological study of artesian water aquifer The calibrated model was run under the rotational in the Western Desert of Egypt: Symposium on the geology of Middle East, Anqara, Turkia. withdrawal policy for 3 years to predict the rate of 6. El-Hinnawi, M.S (1976): Geology of Abu change in groundwater drawdowns. The obtained Bayan Bolaq stretch, Western Desert: M. Sc. results were analyzed. Consequently, conclusions Thesis, Cairo Unvi., Cairo, 103 p. were deduced. These were: 7. El-Kiki, F.E. and Badawi (1972): "Contribution Rotational withdrawal is a good policy to be to the hydrochemical characteristics of water adapted. bearing horizons in Kharga Oasis" Rend Berber Geol. Soc., The groundwater levels indicated a sustainable 8. Engesgaard, P., and K.L.Kipp, (1992): A recovery throughout the prediction run period. geochemical transport model for redox- controlled movement of mineral fronts in According to the achieved results, it is groundwater flow systems: A case of nitrate recommended to explore the potential of mitigating removal by oxidation of pyrite. Water Resour. excessive drawdowns in the groundwater Res. ,28:2829-2843. development areas through operating pumping wells 9. Ezzat, M. A. (1974): Groundwater Series in the on rotational withdrawal basis. Arab Republic of Egypt Exploitation of groundwater in El-Wadi El-Gedid project area: Corresponding author General Desert Development Authority, Ministry Safaa M. Soliman of Irrigation, Cairo, 149 p. Research Institute for Groundwater, National Water 10. Ghobrial, M.G. (1967): The structural geology Research Center, El Kanter El Khairia, Kalubia, of Kharga Oasis, Egypt Geol. Survey paper no. Egypt. 43, 39 p. [email protected] 11. Hermina, M.H. (1967): Geology of the North- Western approach of Kharga, Egyptian: Geol. References Survey, Cairo, paper No. pp 44-88. 1. Anderson, M.P. and Woessner, W.W. (1992): 12. Himida, I.H. (1968): Aquantitative study of the Applied Groundwater Modeling: Simulation of artesian water exploitation resources in Kharga Flow and Advective Transport. Academic Press and Dakhla Oases, Western Desert of Egypt Inc. San Diego, CA. 381 pp. 13. RIGW, (1999): Hydrogeological Map of Egypt 2. Awad, G. H. and Ghobrial, M. G. (1965): 14. Shata, A. (1961): Remarks on the geological Zonal stratighraphy of Kharga Oasis: Gen. structure of the groundwater reservoir at El- Organ. For Research and Mining. Paper No. 34, Kharga and Dakhla Oases (Western Desert of 77p. Egypt): Bull. Soc. Geograph. Egypte, Vol. 34, 3. Barthel K. W. and Boettcher R (1978): Abu 165 p. Ballas Formation (Tithonian/Berriasian;
123