Elucidating the nature of surface water - groundwater interactions beneath a large unregulated river system with the aid of AEM data

The Fitzroy River with its associated alluvial aquifer in northern Western Australia has been considered in planning for Perth?s future water supply and for agricultural development but its potential needs to be informed by detailed understanding of groundwater-surface water interactions occurring along its extent, and in particular must consider and account for the consequences that might arise when extracting groundwater from shallow and deep aquifers linked to this river system. Results from the interpretation of a regional scale longitudinal transect (~274 line kms) of SkyTEM helicopter EM data are presented which elucidate river-bed processes occurring along its extent. The AEM indicate a variable groundwater quality and related aquifer characteristics associated with different parts of the river. A 1D laterally constrained inversion (LCI), was examined against hydrochemical, environmental tracer (including 222Rn and Cl-), and hydrogeological data sampled longitudinally. Combined, they indicate a link between the Fitzroy?s alluvial aquifer system and with underlying Canning Basin sediments. The results demonstrate the value of regional, reconnaissance scale AEM surveys to better define groundwater processes beneath large unregulated river systems.