Using regional airborne electromagnetic conductivity data to characterise surface water groundwater interaction in the Cooper Creek floodplain in arid central eastern Australia

Airborne electromagnetic (AEM) data has been acquired at 20 km flight line spacing across much of the Australian continent and electrical conductivity models generated by inverting these data are freely available. Despite the wide line spacing of these data, they are suitable for imaging the shallow subsurface and can greatly assist in understanding groundwater systems. AEM data acquired using a fixed-wing towed system over the Cooper Creek floodplain, an ephemeral, anabranching river system in arid eastern central Australia, were inverted using deterministic and probabilistic methods. We integrate the AEM conductivity data with a range of surface and subsurface data to characterise the hydrogeology of the region and infer groundwater salinity from the shallow alluvial aquifer across an area of more than 14,000 km2. The conductivity data reveal several examples of focused recharge through a river channel forming a freshwater lens within the more regional shallow saline groundwater system. This work demonstrates that regional scale AEM conductivity data can be a valuable tool for understanding groundwater processes at various scales, with implications for water resource management. This work is particularly important in the Australian context, where high quality borehole data is typically sparse, but high quality geophysical and satellite data are often available.