JOINT INVERSION OF TRANSIENT ELECTROMAGNETIC AND DC-RESISTIVITY SOUNDING DATA FOR IMAGING PERCHED WATER OCCURRENCES AT THE BEDOUIN VILLAGE 'FUKA', NORTHWESTERN MEDITERRANEAN COAST OF EGYPT

The Bedouin village 'Fuka' represents a narrow strip along the Alexandria–Marsa Matrouh coastal highway, approximately 225 km from Alexandria and 65 km from Marsa Matrouh. It is roughly centered at latitude 31o 04' 30" N and longitude 27o 55' 45" E, and has an area of some 25 km2. It is among the most attractive development areas in Matrouh Governorate. This attraction is derived from the strategic shallow perched water resources available in the village and relatively low population density, as well as the available natural potentials for near-future tourism. The hydrogeological setting in Fuka basin is highly controlled by the relationship between its regional geomorphology, subsurface geological structures and semi-arid/arid Mediterranean climatic conditions. A total of 32 co-located vertical central in-loop transient electromagnetic (CINL–TEM) and Schlumberger DC–resistivity (DCR) soundings along 7 surveying traverses were conducted. Main objectives were to image and differentiate the shallow perched water-bearing layers from the whole intermediate/deep groundwater occurrences. Following up data viewing and preliminary transformations data were extensively and consistently interpreted, both individually or jointly, in terms of one-dimensional (1D) inverted electrical resistivity smoothed-models along the surveying traverses. Apart from the close resemblance between the encountered CINL–TEM and DCR geoelectric units, when inverting both data sets individually, they are still clearly showing an unsatisfied correlation. Linear equivalence analysis showed that both the individually-inverted CINL–TEM highly-resistive and DCR highly-conductive layers appeared somewhat too thick, and seemed to be relatively overdetermined. A significant resolution improvement for both the shallow and deep resistivity structures has been achieved when inverting both data sets jointly. The layer bounding errors for both the jointly-inverted CINL–TEM highly-resistive and DCR highly-conductive layers were impressively decreased. Finally, the present field survey highlighted the applicability, efficiency and reliability of utilizing both the CINL–TEM and DCR sounding methods, than any individual use, for better imaging and differentiating the strategic shallow perched water-bearing layers from the whole intermediate/deep groundwater occurrences along the Northwestern Mediterranean coastal plain of Egypt.