الفهرس 
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Abstract
Wadi El-Nakheil, is located in the Eastern desert of Egypt and lies between Latitudes 26° 5̀ and 26° 12̀ N and Longitudes 34° 5’ and 34° 9̀ E. (about 12 km west of Quseir area). It represents one of the most promising areas for land reclamation and future projects depending on groundwater for land irrigation and human use.
Scope of the Present Study:
The present study was conducted to investigate the groundwater potentiality at Wadi El Nakhil area. To achieve this goal integrated high resolution airborne magnetic survey and inland seismic refraction measurements were utilized. The objectives of the present study were; (1) to estimate the basement depth, and consequently the thickness of the sedimentary cover which may provide some insights into the ground water potentiality at the site using airborne magnetic survey; (2) mapping the subsurface distributions of geoseismic layers and hence determine the lithology and geometry of shallow and deep water bearing formations using seismic refraction measurements; (3) determine the subsurface structure/lineaments that may play a role in groundwater flow direction and catchment.
Geological and Hydrogeological Background:
The main lithological units in the study area are:
1- Pre Cambrian crystalline basement,(metavolcanic,metesediment and granotiod intrusion).
2- Upper Cretaceous to Eocene called pre-rift sediments (Nubia,
Quseir, Duwi, Dakhla, Tarawan, Esna and Thebes formations) which were deposited unconformably over the Precambrian basement.
3- Late Oligocene-Miocene to Recent syn-rift sediment (Nakheil and Ranga Formations).
4- Late Miocene carbonates and reefs and Pliocene to Recent syn-rift clastics overlie the evaporites in the coastal outcrops.
The main structural tectonic trend analysis of lineament systems of the study area is N-S (East-African) trend; NW-SE (Gulf of Suez-Red Sea) trend; E-W (Syrian arc system) and NE-SW (Aqaba) trend.
The groundwater exploration of the study area is still very limited and only 4 active wells drilled at the site, in addition to one natural spring near the road in the front of Wadi El Nakhil. In Wadi El-Nakhil, the Oligocene sandstone (El Nakhil Formation) is detected as the shallower water bearing formation with a depth to groundwater ranges between 3.5 and 18m. However, the Nubian sandstone represent the deeper water bearing formation and located directly above the basement rocks.
Materials and Methods:
The present study was conducted using the following geological and geophysical data:
1- The aeromagnetic map of the studied area (scale 1:50.000) prepared by Aero-Services Company, 1984 from a project called MPGAP (Minerals, Petroleum and Groundwater Assessment Program).
2- The geological map after Khalil and McClay, 2002, which was used to detect the different rock units.
3- The available software as Surfer 10.0 (2011), Geosoft Oasis Montaje v.8.4 (2014), Excle (2010) and Rose diagram.
4- GODOGRAF program.
5- SeisImager 2D program.
6- The available published geological and geophysical studies of the area.
A- Aeromagnetic Method:
The first step in the interpretation of the aeromagnetic data is to convert the contoured magnetic map-sheet into digital data sets. The digitization is applied to the aeromagnetic map which have the scale (1:50,000).
1- Preparation of the reduced to pole (RTP) magnetic map. This map was prepared by using the Geosoft Oasis Montaje v.8.3.(2014) and the IGRF parameters; magnetic inclination (32.8) and magnetic declination (1.9).
2- The qualitative interpretation of the aeromagnetic data involves the description and interpretation of the obtained filtered magnetic maps.
3- The quantitative interpretation of the aeromagnetic data involves the determination of the basement depth (consequently the thickness of the sedimentary cover) using different techniques as well as the structural trent analysis.
B- Seismic Refraction Method:
In the seismic refraction method, two profiles with variable lengths were measured at nearly the same locations of the 2D magnetic modeling profiles. The first profile (AA`) is oriented NNE-SSW with total length 3680 m and divided into two spreads. Spread 1 to the NE has a length of 1610 m with 168 geophones while spread 2 to the SW has a length of 2070 m with 216 geophones. The second profile (BB`) is oriented NE-SW and has a length of 1840 m with 192 geophones. Along each line, the geophone spacing was 10m and two shots (forward and reverse) were recorded as well as in-line shots every 230 m.
The seismic refraction data were interpreted automatically using a 2D refraction tomographic inversion algorithm (GODOGRAF) to obtain subsurface models of the geoseismic layers and their velocities and thicknesses. The results were constrained by the geologic information and the interpretation of the magnetic method.
Important Findings:
A- Aeromagnetic Method:
1- The northern, northeastern, eastern and southern parts of the map is characterized by the presence of high amplitude magnetic anomalies (greater than 42350 nT) with elongated and semicircular shapes that may due to shallow bodies of high magnetic susceptibility features
2- The depth to the basement using different methods ranges from 9m in the shallow regions and 1500m in deep seated regions.
3- The obtained structural tectonic trend analysis of lineament systems of the study area is N-S (East-African) trend; NW-SE (Gulf of Suez-Red Sea) trend; E-W (Syrian arc system) and NE-SW (Aqaba) trend.
B- Seismic Refraction Method:
The interpretation results of the seismic refraction data showed that the study area is characterized by six geoseismic layers with different velocities and depths as follow:
1- The uppermost geoseismic layer has velocity ranging from 200 to 1000m/s with an average thickness of 5m and represents the Wadi deposits.
2- The second geoseismic layer has a velocity ranging between 1000 and 2000m/s and a thickness varies from 5 to 25m. This geoseismic layer may represent Ranga Formation.
3- The third geoseismic layer has velocity range (2400-3000m/s) and may represent the water saturated layer (El-Nakhil sandstone) with a thickness varies from 15 to 250 m. (the upper aquifer).
4- The forth geoseismic layer is characterized by a velocity ranging from 3000 to 3500m/s and thickness varies from 25 to 420 m. This geoseismic layer may represent Thebes Formation.
5- The fifth geoseismic layer has a velocity ranges from 3500 to 5000 m/s and may represent the deep Nubia sandstone aquifer with thickness ranging from 100 to 600m.
6- The lowermost geoseismic layer (the sixth layer) is characterized by high velocity (more than 5000m/s) may represent the basement complex with unlimited thickness.
7- Four fault zones are clear distributed along AA profile while only one fault zone is appeared in the central part of the BB profile besides; a normal fault is noted in the NNE side of the BB profile.
C- Correlation between Aeromagnetic and Seismic Refraction Results:
The correlation between the results from seismic profiles and magnetic profiles revealed the following:
1- Agreement is found between the results of the obtained thickness and depths from both methods.
2- The thick sedimentary cover is located in WSW and central parts of the Wadi.
3- The NW–SE, NE–SW, E–W, and N–S are the main important structural trends.
4- Two water bearing layers (Aquifers) are detected in the study area:
a. The shallow aquifer which may represent Oligocene aquifer is located at different depths ranging from 15m on both eastern and western sides and increases to 75 meters towards the center. The thickness of this aquifer varies between (10-20 m) in both sides increases to 80-120 in the central parts of the study area.
b. The deepest aquifer which may represent the Nubia sandstone aquifer is detected at 100 -150m depth in the sided areas while it was detected at 300-420 m depth in the central parts of the study area. The thickness of this aquifer is reaching more than 600m.