The validation of RESOLVE AEM data in the Riverland, South Australia, to determine their value in mapping a regionally significant, near surface hydrogeological unit

Abstract

In the Riverland region, the South Australian Salinity Mapping and Management Support Project used the helicopter-borne RESOLVE EM system to map conductive fine textured materials (the Blanchetown Clay) in the unsaturated zone as a basis for groundwater recharge modelling. Ground validation of the AEM data included 14 boreholes, which target various observed conductivity responses that were present in the 106 kHz and 25 kHz apparent conductivity images. Evidence from down-hole induction logs, measurements of water and chloride content and texture from drill core, indicates that conductivity can be used to map near surface clay. However, ambiguity arises due to the presence of shallow conductive saline groundwater, which can be confused with the presence of clay. A ``Clay thickness map', produced from the constrained inversion of the HEM data effectively depicts the spatial distribution and thickness of clay, and eliminates problems of separating areas of clay from areas of conductive groundwater.