Hydrological Aspects of Electromagnetic Surveys

Interpreting Electromagnetic (EM) surveys - Electromagnetic induction techniques have now largely replaced previousdescriptive, and largely subjective, techniques used for soil salinity surveys. The question then is a matter of how to interpret the EM data. Avery clear linkage exists between Apparent Electrical Conductivity (ECa) and the total soluble salts in the upper soil profile. This, in turn,can be interpreted as reflecting the degree of vertical/ lateral leaching of soluble salts, or of salt accumulation in the profile. Topography,depth to groundwater and groundwater salinity also appear to affect ECa, although they are not suited to rapid survey techniques and donot necessarily have a direct relationship with either the total salt content of the upper soil profile or the ECa values. The interpretation ofisoconductivity maps in terms of the degree of leaching of the soil profile from point to point provides an added hydrological managementperspective to EM soil salinity surveys.