Geophysical Investigations

Geophysical investigations are mainly made on the surface by using simple portable instruments. Following are the different methods of geophysical investigations by which groundwater studies can be made.

• Electrical resistivity method (used in more than 80% of cases)
• Seismic refraction method (used in the remaining cases)

Electrical resistivity method

This method is mostly adopted because of its successful implementation and accurate details, the electrical resistivity method helps in,

1. Determining the aquifer zone.
2. Knowing fresh water and saltwater contacts in shore regions.

Depending on the necessity, the electrical resistivity method is divided into 3 types,

1. Profiling
2. Sounding
3. The fieldwork of the electrical resistivity method is done, according to the “Winner method” Or “Schlumberger method”. With the help of the curve matching method” Or “Inverse slope method”, the interpretation of the electrical resistivity method is accomplished. The subsurface resistivity is affected by the rock type, porosity, moisture content, and salinity of moisture. This is the principle, involved in resistivity investigation. Hence, resistivity studies show information about all the preceding factors and radial sounding also shows the direction of the flow of groundwater.

Seismic refraction method

The principle on which the seismic investigations depend, is the velocity of shock waves which rely on the fracturing of the medium. The shock waves in the compact formations have a greater velocity when compared to their fractured equivalents. Seismic investigations are helpful in recognizing subsurface fault zones, shear zones etc., which are the possible places for the occurrence of groundwater. The seismic study shows whether fractured zones exist in an area or not but it does not show the occurrence of groundwater in them or not.

In hard rock areas, both the methods (electrical resistivity method and seismic refraction method) are helpful in calculating the thickness of soil and fractured zones. These methods also help in finding dolerite dukes, buried river valleys etc., which have a significant beating on the moment of ground water.

Geological, Geophysical, and Hydrological investigations are used to estimate the physical characteristics of the subsurface by measuring, analyzing, and interpreting seismic, electromagnetic, gravitational, and magnetic fields estimated at the ground surface.

Following are the different methods that are used for groundwater exploration.

1. Geological Investigations
2. Geophysical Investigations
3. Hydrological Investigations