SP – Spontaneous Potential

Spontaneous electrical potentials occur in nature where e.g. electrolytes with different concentrations are in galvanic contact with each other or where there is a capillary flow of groundwater due to a hydraulic head. Naturally occurring potentials are composed of a DC component due to electrochemical processes and a time-varying component that is due to variations in the earth’s magnetic field, temperature variations and variable groundwater flow. SP measures the electric potential between two stations. Non-polarized electrodes are used to avoid interference on the recorded signal. One of the electrodes is usually stationary and is used as a reference as the other electrodes is moved around the survey area.
The electric potential due to capillary liquid flow through the ground is called streaming potential. Streaming potential arises from groundwater flows, where water acts as an electrolyte that dissolves and carries mainly positive ions dissolved from minerals in the ground. The water flows from negative to more positive potential values. A change in streaming potential can be due to changes in porosity, saturation or permeability. Positive anomalies are usually seen at groundwater outflow areas whereas negative anomalies can be seen in infiltration areas. Streaming potential measurements can also be used to study the seepage through earth dams and other embankments.

Reference projects:

– A system for automatic monitoring of the core in an embankment dam has been developed and tested on the Eastern Suorva dam in the Luleå river