Using Airborne Electromagnetics (AEM) for Rapid Identification and Assessment of Managed Aquifer Recharge (MAR) Options in the Darling Floodplain, N.S.W., Australia

Abstract

The Broken Hill Managed Aquifer Recharge (BHMAR) project is part of a larger strategic effort aimed at securing the town of Broken Hill's water supply and identifying significant water‐saving measures for the Darling River system. To meet the challenge of rapidly identifying and assessing potential MAR targets and groundwater resources over a large area (>7,500 km2) within a short timeframe (18 months), it was concluded that the only cost‐effective method was airborne electromagnetics (AEM). The SkyTEM time domain system was chosen and 31,834 line km of data was acquired in 9 weeks. The AEM data was validated by a 4,500m drilling program. The study has confirmed the location of several large potential MAR targets in close proximity (<40km) to the existing water supply infrastructure. The AEM survey has also mapped key confining aquitard units. ‘Holes’ in the overlying clay unit appear to provide preferential recharge of the underlying Pliocene aquifers along losing reaches of the Darling River and Talyawalka Creek. The hydrogeological complexity revealed by AEM mapping and validated by drilling provides a diversity of potential MAR options. At this same time, this brings with it a challenge of understanding a range of complex hydrogeological and hydrogeochemical processes. The provision of robust inversions in short timeframes, initially using the iTEM software and subsequently LCI and SCI inversions using the Aarhus Workbench, greatly assisted with targeting drilling and rapid hydrogeochemical assessment of targets. Overall, the BHMAR project is the first application of AEM technology and an integrated hydrogeological systems approach to MAR target detection and assessment. It has demonstrated the potential for large data‐poor areas to be assessed rapidly, with a high degree of confidence. The success of the approach is dependent on the use of a phased approach within a broader risk assessment framework.