Vertical Electrical Sounding (1D VES)

This method mainly depends on measuring the specific resistance of subsurface geological formations due to the flow of an electric current through the ground. Electrical resistivity method is characterized by its ease to use, its flexibility and is immediately adapted to varied problems. The electrical resistivity of rocks depends on rock porosity, permeability, water content and salinity of the bearing water. Increasing in porosity of rocks causing decrease in the resistivity, also increase in the salinity of saturated fluids causing decrease in the resistivity. However, the presence of clays and conductive minerals, obviously reduce the resistivity. Also, the increase of temperature is another factor that leads to reduction of resistivity.

In all electrical resistivity surveying techniques, a known electrical current is passed through the ground between two (or more) electrodes. The potential (voltage) of the electrical field resulting from the application of the current is measured between two (or more) additional electrodes at various locations. Since the current is known, and the potential can be measured, an apparent resistivity can be calculated. The separation between the current electrodes depends on the type of surveying being performed and the required investigation depth. The greater the distance between electrodes, the deeper the investigation required.

Electrical resistivity, also referred to as galvanic electrical methods, is occasionally useful for determining shallow and deep geologic and hydrogeologic conditions. By measuring the electrical resistance to a direct current applied at the surface, this geophysical method can be used to locate fracture zones, faults and other preferred groundwater/contaminant pathways; locate clay lenses, sand channels and locate perched water zones, depth to groundwater, water aquifer…etc. A variety of electrode configurations or arrays (e.g. Wenner, Schlumberger, dipole-dipole) can be used depending on the application and the resolution desired.