Delineation of a resistive drainage channel by EM conductivity survey

Abstract

EM conductivity surveys have been carried out over an air-filled drainage conduit, near Alcala de Henares, Spain. The surveys failed to detect a measurable response from the gallery, but successfully delineated a desaturated drainage channel above the conduit. Target diagnosis was assisted by theoretical one-dimensional modelling, which showed that relative response magnitudes can provide a limited basis for source discrimination. The results confirm that conductive features are more likely to be detected than resistive voids. More versatile 2D modelling schemes are required, however, to provide greater interpretative insight and to exploit the full potential of the $\text{EM31}\text{34}$ systems.