oa Use of the Skytem Airborne Electromagnetics (AEM) System and Item Fast Approximate Inversion Software to Provide Robust and Rapid Data for Groundwater and Salinity Management, Ord River Irrigation Area, Western Australia

The Ord Valley Airborne Electromagnetics (AEM) Interpretation Project was established to underpin salinity and groundwater management in the Ord River Irrigation Area (ORIA), in NW Australia. While covering the existing irrigation areas, it is also the first time in Australia that AEM data have been acquired to inform potential irrigation expansion. A total of 5,936 line km of AEM data were acquired using the SKYTEM time domain system. Conductivity signatures for key components of the hydrogeological system are non-unique. Interpretation therefore required the use of borehole and landscape analysis constraints. the study has provided greater spatial detail on critical elements of the hydrostratigraphy in the alluvial aquifer. This includes palaeochannel delineation, sand, gravel and clay distribution, the mapping of salt stores and groundwater quality, and the generation of salinity hazard maps. the project has demonstrated the potential for ‘calibrated’ AEM systems and Fast Approximate Inversion software to shorten AEM project timelines significantly. for example: - AEM data inverted using the fast approximate Inversion (iTEM) were obtained within 24 hrs of data acquisition. the early availability of high quality estimates of ground conductivity facilitated the early design of a drilling program, the extension of the survey whilst it was in progress, and the initiation of data Interpretation immediately. - the Initial multi-layer iTEM Inversions had high correlation coefficients (>0.8) when comparing FID points to adjacent borehole induction logs, and the Inversions have proven to be very robust. <br>Overall, this project has demonstrated the benefits of a phased or staged approach to assessing the methods and technologies used as part of a ‘hydrogeological systems’ approach when developing the framework for salinity and groundwater management. the AEM-based products are being used to assist with planning future irrigation infrastructure and strategies, the development of salinity mitigation and groundwater management strategies, and to protect environmental assets.