ELECTRICAL RESISTIVITY METHODS
PRINCIPLE: Ohm’s law. In an electrical circuit, the current (I) is proportional to the potential difference or the electromotive force, (V), and the resistance R. That is, I = V/R or R = V/I. The materials are classified as Good Conductors and bad conductors or insulators. Good conductors allow the electric current to pass through them e.g., metals, water, etc., and bad conductors or Insulators do not allow electric current to pass through them e.g., rocks, wood, etc.
Application of Resistivity methods.
- Location of Dugwell, Borewell, Tubewell sites.
- Movement of GW flow
- Granular zone in sedimentary areas
- Water quality
- Sea water intrusion studies
- Deep aquifers
- Artificial recharge studies
Electrical sounding: Vertical variation in resistivity with depth is measured. The curve is called as VES curve. xx - hard rock (un-saturated formation)
fractured rock (saturated formation)
Basically, it is an electromagnetic method. It works with a freq of 15-30 kHz of em waves transmitted from a distant navigation transmitter. The em waves are induced into ground, in the presence of conductor or saturated body, secondary em waves are generated.