Electrical methods are the most useful in groundwater investigation and these are described in detail. The use of different terminology between electromagnetic and galvanic methods is explained and several integrated studies of the use of these techniques provided. Factors impacting the bulk electrical conductivity are described and the variation with frequency noted.
The resistivity sounding method is briefly described before a detailed description of the electrical image method given. The application of data collection using multi-cable methods and multi-channel measurements is described for both resistivity and induced potential measurements. Examples of time-lapse resistivity, agricultural applications in 2D and 3D, including time-lapse 3D, are presented.
Forward and inverse modelling of electrical resistivity has much in common with the analysis of groundwater data. The 3D finite difference formulation for forward modelling is described. The inversion of resistivity data is described but methods are not reviewed in detail as extensive software packages are available.
A description of apparent conductivity (resistivity) measurements using electromagnetic methods is compared with measurements made with resistivity (galvanic) techniques with particular emphasis on borehole siting in fractured rock terrains.