EVALUATION OF GROUND WATER POTENTIALITIES OF SOME VULNERABLE AREAS AROUND THE MEDITERRANEAN SEA COST, EGYPT, USING 1-D AND 2-D INVERSION OF DC RESISTIVITY DATA

In arid countries like Egypt, the traditional sources of water are not enough to construct a sustainable development. So, the real sustainable development should depend on the underground water especially in the arid areas, like the western and eastern deserts. As a strategic vulnerable area, the strip of the Mediterranean Sea Cost was our target for this research with emphasis on El-Dabaa and Rosetta areas. As most of coastal areas the groundwater aquifer is highly affected by salt water intrusion from the Mediterranean Sea in dramatic regimes from region to another. This means that fresh groundwater may have variation in distribution all over the area, which makes it hard to estimate water depth and type (fresh, brackish or saline) at any region.

The current research focus on monitoring the under groundwater aquifers and examine the effect of sea water on these aquifers and the validity of the usage of these aquifers using geophysical data. For this purpose, we carried out 1-D and 2-D inversions based on the least squares method with smoothness constraints for a Schlumberger Vertical Electric Sounding (VES) data to identify the types of groundwater aquifer (fresh, brackish or saline), distribution, freshwater depth and thickness and estimating subsurface lithology.

The study area is covered by seventy five 1-D VES stations with current electrode separation (AB/2) ranges from 1.5 m to 250 m or 350 m. During the data processing, some of 1-D VES data has been inverted to 2-D measured at 30 VES stations composing six 2-D profiles covering the study areas. The objectives of this work are to find the dramatic variation of the fresh groundwater and its distribution over the area, and estimate water depth and type (fresh, brackish or saline) at any region of the study area.

The inverted resistivity distribution at relatively shallow depth shows an important low resistivity zone that probably reflects salt water alteration zone (northern parts). Depth to the freshwater bearing layer reaches its maximum at the south and decrease towards the north. From quantitative interpretation, Invasion of salt water started at depth about 10 m, Thickness of freshwater bearing layer ranging from 15 to 25 m, while at depth of about 150 m all the layers are saturated with salt water.