ASSESSMENT OF FRACTURE SYSTEMS AND THEIR CONTRIBUTION IN THE GROUNDWATER OCCURRENCES IN CARBONATE ROCKS USING GEOELECTRIC TECHNIQUES IN El-HASSANA AREA, NORTH SINAI, EGYPT (CASE STUDY)

Groundwater in El Hassana area represents the main source of water supply which in used for all
purposes. The increasing demand on water and the limitation of its resources in this arid region increases the need to
explore new groundwater resources. Random drilling of new wells in the Upper Cretaceous carbonate rocks show that,
some of these wells were productive and some others were dry. This phenomenon exhibits that the groundwater
occurrence depends mainly on the presence of a fracture zone which needs special geophysical techniques. Electric
Resistivity Tomography including both 2-D and 3-D techniques were used effectively for delineating the fracture
systems in shallow carbonate rocks. Azimuthal collinear Wenner array was conducted at a selected site based on the
obtained results from both 2-D and 3-D surveys. Graphical interpretation of the Wenner array data indicated that the
measured apparent resistivity changed with the orientation of the array for all a-spacing and the dominant fracture
strike is found to be oriented at N 22.5 degrees. The calculated effective vertical anisotropy is found to be varied with
depth due to slight variations in fracture strike and/or variations in fracture density. Results from the collinear Wenner
array data are supported by azimuthal square array which the graphical interpretation coincides with that obtained
from Wenner array.