GEOPHYSICAL INVESTIGATIONS FOR DELINEATION OF POTENTIAL GROUNDWATER ZONES IN JIZAN AREA, SOUTHERN RED SEA COAST, SAUDI ARABIA

The decreasing of water quality in the coastal zones of Jizan area, southwest of Saudi Arabia has become a major concern. With the aim of providing valuable information on the hydrogeologic system of the aquifers, Gravity, magnetic and geoelectric resistivity data were used. Analysis and modeling of the gravity and magnetic data showed that the coastal area of Jizan is divided into a series of faulted tilted blocks by structural faults trending is the NW (Red Sea) trend. The geoelectric resistivity results indicate that the interpreted faults play a great role in the seawater intrusion where the seawater invaded the coastal aquifers through the crushed rocks in fault zones related to the Red Sea Rift rifting. In addition, it is observed that the upper surface of the low resistivity saline water-bearing layer rises forming a cone of ascension where the salt water in this layer rises up. This could be referred to the unwise extraction from the coastal aquifers and the extraction of fresh groundwater greater than the recharge always produce a lowering of the freshwater and consequently a salinization process begins in the aquifer as the seawater flows forming the so-called cone of ascension or up-coning of saline water surface. Along some sections, the sea water intrusion is observed as controlled by the lithologic variations and this is referred to the alluvial sediments of the ancient buried stream channels that could represent potential pathways for saltwater intrusion and make a hydraulic connection between the aquifer beds and the sea water.