Developing recharge reduction strategies in the Riverland of South Australia using airborne electromagnetic data ? a case study in tailoring airborne geophysics given a particular target and a desired set of outcomes.

Abstract

The Riverland area, located on the southern bank of the River Murray in South Australia, is a priority area for intervention under the National Action Plan. As part of the South Australian Salinity Mapping and Management Support Project, airborne geophysics was recognised as having potential to provide valuable biophysical data relevent to the management of irrigation development and groundwater recharge reduction in the area. We examine this potential, giving particular regard to the process involved in understanding the target, defining an appropriate geophysical tool and testing whether the desired output could be delivered economically and at an appropriate resolution. The target in the Riverland area is the near surface Blanchetown Clay unit. Forward modelling suggested that a frequency domain helicopter electromagnetic (HEM) system could map spatial variability associated with this unit. A test survey was conducted using the RESOLVE HEM system further demonstrated that potential. CDI?s of these data were compared with shallow drilling, EM31, EM34 and broadband ground TEM data. Results confirmed that near surface conductivity variations mapped by the airborne EM system were associated with the clay and that a product which could be incorporated with hyrogeological models to help predict rechage and influence management decisions in the area could be generated for the whole area.