Geophysical Evaluation for Evidence of Recharging the Pleistocene Aquifer at El-Nubariya Area, West Nile Delta, Egypt

Abstract

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 NaSO 4 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 water aquifers.