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With ever increasing demands on water resources, Egypt is facing increasing water needs, demanded by a rapidly growing population, by higher standards of living and by an agricultural policys. West Nile Delta represents a new agricultural area where the reclaimed lands are irrigated with groundwater in addition to surface water. The evaluation of groundwater aquifers in West Nile Delta area requires information about the extension, depth and distribution and source of recharging these aquifers. In this work, an integrated study using geoelectric, geomagnetic, hydrogeologic and hydrochemistry investigations has been applied to evaluate groundwater aquifers and to delineate subsurface structures predominant in the basement rocks at El-Nubariya area, West Nile Delta, Egypt. Thirty-five Vertical Electrical Soundings (VES) have been applied to identify the subsurface geoelctric layers predominant in the study area. As well as a detailed land magnetic survey has been carried out along the study area using two automatic proton precession magnetometers with an accuracy of 1 nT. These surveys allowed us to establish the subsurface structures and their relation with the detected aquifers. The geoelectric results are illustrated along seven geoelectric profiles and correlated with the lithologic and hydrogeologic data of drilled wells. The third geoelectric layer represents the water saturated zone (aquifer) with thickness varies from 14 m to 58 m, increasing to east and southeast directions. The hydrchemisty anlysis shows that the salinity of the water aquifer ranges from 600 ppm in the southeast to 3900 ppm in the south. The major dominant dissolved salt is Nacl. In the east and southeast, the water type becomes more NaSO4 which refers to dissolution of gypsum in addition to fertilizers. The magnetic data have been analyzed using horizontal gradient and 3D magnetic modeling along the locations of geolectric profiles. The results indicate that the fault structures are trending in E-W, NW-SE and NE-SW directions. These faults confirm the results obtained from the well geolectric interpretation. These fault structures act as recharging paths from lower brackish to upper fresh A. Khalil et al. 325 water aquifers.

In the last few years, ALOS/PALSAR (L-band) (HH, HV, VH, and VV) images have been widely used due to their ability to penetrate the surface in certain conditions, such as low moisture or dry friable sandy soil. Images from the ALOS-1 sensor were used to delineate subsurface structures, and optical images such as Landsat-7 ETM + data were used to discriminate between scatterings from the Earth’s surface and subsurface materials. Thus, the Farafra Desert is an optimal geological environment for L-band microwave penetration, as its geology is characterized by friable sand sheets covering limestone (Tarawan Formation). Speckle noise is found in radar images for many reasons, such as when an object strongly reflected between itself and the spacecraft causes noise. Refined LEE filter (RLF) is applied for speckle noise reduction; moreover, full polarimetric ALOS/PALSAR images (PLR) are transformed into circular polarization by changing both angles into orientation angle ψ = 0° and elliptical angle χ = 45°. The validation of ALOS/PALSAR outputs was carried out using ground penetrating radar (GPR) measurements. Three GPR long profiles using a 200 MHz antenna were scanned along with areas that were annotated according to ALOS/PALSAR results (high backscattering coefficient). The GPR system operated by a low-frequency antenna with a frequency of 200 MHz was capable of detecting the annotated geological structures beneath the sand sheets. Furthermore, statistical comparison of L-band SAR and GPR data illustrated a correlation that can reveal identical regions to delineate subsurface structures. These results prove that the integration of synthetic aperture radar SAR (L-band) and on-site low-frequency radar systems can be vital to detect soil structures down to several meters, ultimately innovating Earth observation systems for geological and hydrogeological mapping in arid regions.

The role of the fracture system is important for enhancing the recharge or discharge of fluids in the subsurface reservoir. The Lake Nasser is consider one of the largest artificial lakes all over the world and contains huge bulk of storage water. In this study, the influence of fracture zones on subsurface fluid flow in groundwater reservoirs is investigated using geophysical techniques including seismicity, geoelectric and gravity data. These data have been utilized for exploring structural structure in south west Lake Nasser, and subsurface discontinuities (joints or faults) notwithstanding its related fracture systems. Seismicity investigation gave us the comprehension of the dynamic geological structure sets and proposing the main recharging paths for the Nubian aquifer from Lake Nasser surface water. Processing and modelling of aerogravity data show that the greater thickness of sedimentary cover (700 m) is located eastward and northward while basement outcrops occur at Umm Shaghir and Al Asr areas. Sixty-nine vertical electrical soundings (VES's) were used to delineate the subsurface geoelectric layers along eight profiles that help to realize the subsurface geological structure behind the hydrogeological conditions of the studied area.

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