USE OF VERTICAL ELECTRICAL SOUNDING IN DETERMINING SOME AQUIFER CHARACTERISTICS

This paper is based on a research study within a part of the Nile Valley Aquifer, Egypt.

As a source of uncontaminated water, groundwater is becoming more important for many needs, especially for agriculture and drinking purposes. Therefore, methods used for locating suitable groundwater aquifers and their hydrogeological conditions should be more efficient.

Recently, geophysical methods - particularly the electrical resistivity methods - are playing a satisfactory role in groundwater investigations. Although the resistivity tool will never replace the test drilling for the groundwater investigations, it does sometimes reduce the amount of test drilling through the good selection of test hole sites. This will minimize the information/cost ratio and avoid the excessive drilling use for measuring the hydraulic parameters of any aquifer.

Therefore, in the current study, the gained field data - in the form of a number of Schlumberger Vertical Electrical Soundings (VES’s) within the study area (namely, the part of the Nile Valley Aquifer) - have been interpreted in terms of layer resistivities and thicknesses. The resistivities of different layer materials were interpreted to obtain the final model parameters of the aquifer existing within the study area.

From the above-mentioned parameters, some of the geoelectric indices were estimated. The interpretation revealed the existence of three main geoelectric layers, including the aquifer horizon. Since the current study is mainly devoted to the estimation of the aquifer’s hydraulic parameters, so the aquifer horizon is generally represented by a single representative resistivity value below each VES location. Also, the lithological constituents of any aquifer can be represented by its formation factor, which controls/affects the intergranular surface conductance.

Using such calculated formation factors together with some other existing borehole data, it has been found that some aquifer characteristics (hydraulic parameters) can be estimated from resistivity interpretation. That is to get an idea about the most favorite locations for well drilling needed for the different demands in this specific area. Also, this study took into consideration the variation in the groundwater quality throughout the study area, in terms of salinity variations.