الفهرس 
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Abstract
The present study deals with the geological impacts on the water bearing formations in the Wadi El-Natrun area. The study area extends between longitudes 30о 00’00” - 30о 45’ 00” East and latitudes 30о05’ 00” - 30о40’ 00” North. It occupies a portion of the extremely arid belt of Egypt, it characterized by hot long summer and short worm winter with low rainfall and high evaporation intensities.
The area of study is characterized by a low relief and a mild topography with elevations varying from below sea level to about +150. Generally, the investigated area slopes gently towards the northern and eastern directions. Landforms are classified into 3 geomorphic units. These geomorphic units from north to south are: The first is the alluvial plains are classified into young and old alluvial plains. The young alluvial plains represent the main cultivated lands. The old alluvial plains stretch to the west of the young alluvial plain till Wadi El Natrun, on the western side. The second is the structural plains which occupy a wide area to the south and west of the old alluvial plain and the third is the shifting sand consists of drift sands and sand sheets which cover the wide portions of the old alluvial plains and the lowest parts of the large depressions.
The study area is covered by extensive sedimentary exposures ranging in age from Late Cretaceous to Quaternary. In subsurface the sedimentary section has a thickness of about 4000 m resting on the basement rocks.
Folds, faults, unconformities and basaltic intrusions mainly affect the area of study. These types of structural elements are the most important factors controlling the groundwater conditions.
The area of study is mainly affected by two fold systems.
1-The NE-SW folds system (Syrian Arcs); the most conspicuous fold is Abu Roash domal structure.
2-The NW-SE (clysmic) folds system; the most conspicuous folds are Wadi El Farigh and Wadi El Natrun anticlinal structure.
The study area is mainly affected by three normal faults systems. These systems in decreasing order of abundance are as follows:
- NW-SE (Clysmic) system; mostly associated with NW-SE folds. Most of them strike parallel to the folding axes, while others cut the folds diagonally, scarcely crossways. Faults of this class affecting Miocene beds are frequently associated with hydrothermal activity.
- NE-SW (Aqaba) system; represented by normal faults cutting both, Miocene and Pliocene beds. They occasionally dissect NW faults. It can be assumed that this system is either younger than the NW-SE pattern, rejuvenated or nearly equal in age.
-E-W (Tethys) system; located along the southern scarp of Gebel Khashm El Kaoud. NE-SW and E-W trends are assumed younger than those followings a NW direction.
The study area consists of four aquifers system, including two main aquifers system and two a limited aquifers system. The main aquifers are the quaternary aquifer (the extension of the main Delta aquifer) and El-Maghra aquifer (Miocene) aquifer. The aquifers are limited is Pliocene where passes through Wadi Al-Natrun aquifer (Pliocene) and Recent where it are limited only in the Wadi Al Natrun area
Recent aquifer It is limited distribution aquifer; this aquifer is composed from sandy deposits with calcareous intercalation of Aeolian origin, filling the low lands in Wadi El-Natrun depression. The thickness of aquifer ranges between 4 m to 10 m.
The Quaternary aquifer is an extension of the main Delta aquifer covering the middle of the delta and parts of the boundary of its eastern and western basin, which covers the most of the study area and is confined to eastern and northeastern parts of the region. This aquifer fades as we direct towards westwards (Wadi El-Natrun and Wadi al-Fargh).
The Quaternary aquifer is the main water bearing formation occupying northern and northern portions of study area. The Quaternary aquifer is composed mainly of fluviatile graded sand and gravel intercalated (of the Pleistocene age) with thin clay lenses. The saturated thickness of the Quaternary aquifer increases gradually in the northeast direction, it varies from 57m at southwest, (near Cairo-Alex. Desert road) to 334 m at the northeast portion. The shale ratio of the Quaternary water bearing formation show variable values of percentage of shale in aquifer where the percentage increase at west Wadi El- Natrun and decrease at El Sadat city area northeast.
The Pliocene aquifer is confined to the Wadi El-Natrun region (the northwestern part of the study area). The Pliocene sediments are mostly built up of clays underlying the Quaternary aquifer and consists of successive layers of sandstone and limestone of the Pliocene period of the third geological time The thickness of the aquifer ranges from zero (at the low boundary of Wadi El-Natrun) to about 150 meters in the middle while the aquifer limits either clay layers of the same age or sand layers, forming the lower aquifer.
The Pliocene aquifer is hydraulically connected with Miocene through faulting (Abedelbaki, 1983). This situation brought the Pliocene aquifer under the influence of lateral seepage from the Miocene aquifer (Abedelbaki, 1983).
The Miocene aquifer is represented by Moghra Formation of Early Miocene age and covers a wide area in the west and south of the study area. Miocene aquifer has a large geographical distribution in Wadi El Farigh and its extension of El-Bustan area.
It is mainly composed of sand, sandstone and clay intercalations of fluviatile and fluviomarine origin. Miocene aquifer has been deposited on the basaltic sheet at different levels; in the form of horst-like and graben-like structures.
The aquifer thickness varies in different areas where it attains 75m in the eastern area 150 m in wadi El-farigh area, 250 m at wadi El Natrun area and gradually increases in the Qattara Depression (Gomaa 1995).
The main movement of groundwater is from the east to the west and to the North West. There are also some underground aquifers which take the form of radial in all directions, especially in the high water area near Nubaria and Wadi El-Natrun where the contour lines of groundwater levels change from other according to different activities.
• Geoeletrial investigation
A total number of 57 vertical electrical soundings were carried out in the area Wadi El-Natrun, North western desert of Egypt. The interpretation of these VESes was supported by some available private wells in order to define the subsurface geological situation and also to search for the groundwater accumulations in order to allocate develop and manage the groundwater within the national water policy. The survey was done to determine the aquifer geometry and also to define approximate water quality.
Four main geoelectrical units were detected in the study area. The first surface unit has a relatively medium to high resistivity sands and gravels with a mean thickness about 5-8 meters. The second unit has a high resistivity sands and gravels with a mean thickness about 40 meters. The third unit has a different resistivity values range from relatively low value about 14 ohm.m to the NE to relatively high value about 120 ohm.m to the SW. This unit represents the possible El-Moghra sand and gravels aquifers. The maximum thickness of this unit reaches 170m (total depth from the surface reaches 215m). The fourth unit has a low resistivity value representing the clayey base of the aquifer.
The recharge of water aquifer from rosetta branches (fresh water) that clear from the value of salinity and true resistance where the salinity increase from SE direction and decrease in the true resistance and evidence from the hydrochemical analysis from Piper classification.
The relation between the true resistivity values of the aquifer and its T.D.S. the resistivity decrease with increasing the T.D.S. and vice versa. This conclusion is mane clear at this study where the resistivity values were decrease within increasing the T.D.S.to the north western and southwestern parts where Nile delta region and to the North of the wadi El-Natrun depression but they were increased with decreasing the T.D.S. to the North western parts especially at Nile delta region and some parts at wadi El-Natrun depression.
The groundwater of the all aquifers is slightly alkaline to alkaline in reaction. The total water salinity of the recent aquifer varies from 1394 ppm to 2401 ppm increase sharply toward the Western north portion, (RIGW, 1990).
The groundwater salinities of the Quaternary aquifer vary from fresh to brackish water. The hypothetical salts of the Pleistocene ground water are characterized by the dominance of bicarbonate salts (NaHCO3, Mg (HCO3)2and Ca(HCO3)2 Piper interpretation, which reflects Nile fresh water.
The total salinity of the Pliocene aquifer varies from fresh to slightly saline water. Local anomalies in water salinity are detected at northern outlet of Wadi El Natrun, west central part of Wadi El Natrun and west Wadi El Natrun due to the high evaporation rate, the presence of great thickness of clay beds of lagoonal origin with high content of salt, and the low groundwater recharge.
The groundwater of the Pliocene has two water types namely; Wadi El- Natrun aquifer of this type the NaHCO3 and NaCl. The total salinity of the Miocene aquifer varies from fresh to slightly saline water. Local anomalies in water salinity are detected at the area East Cairo-Alex desert road, west El Rayiah El Nasseri and southwest Wadi El Natrun due to the over pumping rates, the presence of shallow clay lenses within the water bearing layers especially west El Rayiah El Nasseri and the low groundwater recharge.
The groundwater of the Miocene aquifer system has two main water types namely; NaHCO3 and (NaCl). The first water type characterizes low salinity contents areas representing the eastern and southern portions, from meteoric water origin.
The second main water type (NaCl), characterizes the relatively high salinity areas at the western portion and some places east and west Desert Road, reflect dominance of marine sediments bearing chloride, sodium, magnesium and calcium elements as well as ultimate phase of groundwater evolution and long term contact time between aquifer matrix and groundwater.