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Produced from a 250 dpi scanned image of the original out-of-print 1967 map Available as a product from NT Geological Survey or as a resource from GA Library

Airborne electromagnetic (AEM) methods for near-surface hydrogeological investigations have undergone significant improvements in the past 10-15 years, particularly in the development of calibrated systems designed for high-resolution groundwater and environmental investigations (Sorensen & Auken, 2004; Auken et al., 2006). Important advances have been also been made in the development of rapid computational methods for AEM inversion (e.g. Christensen, 2002; Christensen et al., 2009), enabling conductivity models to be available for integration into real-time, short-term hydrogeological investigations (Lawrie et al., 2012). The processing of AEM data and the presentation of electrical conductivity data as maps and sections is now routine, and particularly effective for regional mapping in shallow-dipping sedimentary environments (Lane, 2002; Lawrie et al., 2009, 2012). In Australia, the application of electromagnetic (EM) methods for hydrogeological investigation is made more complex by the highly salinized nature of many landscapes, which can also be often deeply and variably weathered. In many instances, the electrical conductivity distribution does not equate with formation (and/or hydrogeological) boundaries, but instead to a combination of groundwater salinity and formation composition and texture (Lawrie et al., 2000, 2009). Despite these additional challenges, AEM is the only broadacre technique that can detect and resolve key functional elements of near-surface groundwater systems (Spies & Woodgate, 2005). The complex electrical structure of Australia's near-surface landscapes and the presence of conductive layers and basement in many regolith terrains has necessitated the development of constrained inversion approaches that utilise a priori geological, hydrogeological and hydrogeophysical data (Green & Munday, 2004; Lane et al., 2004; Lawrie et al., 2012). Constrained inversions, combined with rigorous technology selection, and appropriate calibration and validation procedures have enabled the successful mapping of potential groundwater resources and salinity hazards in several floodplain environments (Walker et al., 2004; Lawrie et al., 2009, 2012; Christensen & Lawrie, 2012). Importantly, studies in Australia have also demonstrated that the benefits from new AEM technologies and constrained inversion modeling are maximised when these technologies are employed within multi-disciplinary, systems-based approaches to the analysis of problems (George et al., 2003). Systems-based approaches incorporate an understanding of landscape evolution and scale, utilise modern investigative approaches to the conceptualisation of groundwater systems, and incorporate data on mineralogy, petrophysics, hydrology, ecology, topography, hydrogeochemistry and hydrodynamics. Within this multi-disciplinary research framework, the power and long-term value of AEM-based datasets for groundwater management lies largely in providing stakeholders with a range of customized interpretation products derived from the integration of electrical conductivity data with other hydrogeological, hydrogeophysical and hydrochemical datasets (George et al., 2003; Lawrie et al., 2000, 2009, 2012). The Broken Hill Managed Aquifer Recharge (BHMAR) project, in western N.S.W., Australia, has built significantly on the principles, methodologies, experience and products developed for salinity mapping and management in Australia. This included, a staged approach to technology selection and survey design, and the use of a 4D systems approach to integrate

The Broken Hill Managed Aquifer Recharge (BHMAR) project is part of a larger strategic effort aimed at securing Broken Hill's water supply and identifying significant water-saving measures for the Darling River system. In this study, airborne electromagnetics (AEM) mapping validated by drilling, field and laboratory measurements has identified significant volumes of fresh to acceptable quality groundwater stored beneath the Darling Floodplain. These potential resources were identified in 14 discrete targets within Pliocene aquifers (Calivil Formation and Loxton-Parilla Sands) at depths of 25-120m. The Calivil Formation occurs predominantly within structurally-controlled palaeovalleys. Aquifer quality is best where thick (30-50m), high-yielding zones (test flows > 25 L/s) occur in palaeochannels at the confluence of palaeo-river systems. Here, the hydraulic properties make the Calivil Formation aquifer best suited for groundwater extraction (and/or MAR injection), with excellent recovery efficiencies predicted where ambient salinities are low. The aquifer is sandwiched between variably thick clay aquitards, and is confined to semi-confined. Indicative groundwater volumes have been calculated using groundwater salinity and texture mapping derived for the AEM depth slices, combined with porosity statistics derived from laboratory measurements and borehole nuclear magnetic resonance (NMR) logging. In most of the targets, further investigation is required to quantify natural recharge and discharge processes, identify the negative impacts associated with groundwater pumping (particularly the potential for saline groundwater ingress), delineate the more transmissive parts of the formation, and assess the economics and logistics of borefield and water supply design. Calibrated, transient numerical groundwater flow and solute transport models are also needed to determine appropriate groundwater extraction rates. The multi-disciplinary systems-based methodology used in this project has enabled rapid identification and assessment of largely unknown potential groundwater resources and aquifer storage. These have the potential to provide drought security for regional communities and industries, and to assist with regional development.

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