USE OF THE GEOELECTRICAL TECHNIQUE TO DETECT THE SALINE-FRESH WATER INTERFACE IN THE COSATAL AREA BETWEEN SEDI ABD EL-RAHMAN - EL DABAA AREA, NORTHWESTERN COAST OF EGYPT

The area between Sedi Abd El Rahman and El-Dabaa lies at the western Mediterranean coastal zone of Egypt and extends for about 30 km long. The aims of the present study are to explore the groundwater and to know the effect of seawater intrusion on the freshwater aquifer. Thirty-six Vertical Electrical Soundings using Schlumberger array with maximum AB/2 = 500 m and eight 2-D imaging electrical profiles were carried out.
Based on the interpreted results, five geoelectric layers have been detected in the area. Iso-rsistivity, depth to water, depth to brackish/saline water interface and isopach contour maps beside 6 geoelectric cross-sections (four from them are parallel to the Mediterranean shoreline and the other two are normal to the Mediterranean shoreline) have been constructed.
Interpretation of these maps and sections indicated that the Oolitic limestone represents the shallow groundwater aquifer which can be distinguished into two zones, the upper zone is brackish, while the lower one is the saline due to salt-water intrusion. The interface between brackish and saline water was distinguished along the interpreted N-S geoelectric cross sections. The geoelectric succession reveals that, the aquifer is of free type. The saline water intrusion was recoded in both the soundings and the electrical 2-D imaging profiles. The depth to water is presented at depth ranging between 3.5 m and 24 m. Consequently, the best sites for groundwater exploitation has been chosen. The sea water intrusion is restricted to the northern strip of the area.
The depth to water and the thickness of the brackish water increase towards the southern part, also the depth to the brackish/saline water interface increases in the same direction. Drilled wells are more suitable at the southern parts of the studied area because the depth to brackish water and the its thickness increase southwards. The safe yield was calculated for each sounding station