The Great Artesian Basin (GAB) covers one fifth of Australia and is the largest groundwater ‘basin’ on the continent. Groundwater from the GAB is a vital resource for pastoral, agricultural and extractive industries, underpinning at least $12.8 billion in economic activity annually, as well as providing town water supplies and supporting environmental and cultural values.

The Australian Government, through the National Water Infrastructure Development Fund – Expansion, commissioned Geoscience Australia to undertake the project ‘Assessing the Status of Groundwater in the Great Artesian Basin’. A key deliverable of this project is a water balance (for 2019) encompassing the main aquifers of the GAB. To facilitate this outcome, a range of tools and techniques to assist in the development of improved hydrogeological conceptualisations of the GAB have been developed and assessed.

This report presents the results of investigations from a pilot study area in the northern Surat Basin, Queensland, with components of the work extending into the wider GAB. The results demonstrate that the application of existing and new geoscientific data and technologies has the potential to further improve our understanding of the GAB hydrogeological system thus supporting the responsible management of basin water resources.

Groundwater recharge potential within the GAB intake beds has been investigated using techniques that consider variations in physical and environmental characteristics. Empirical modelling assessing deep drainage as a recharge proxy suggests that, with isolated exceptions, diffuse recharge potential is generally low across most of the study area. The spatial variability in recharge potential can assist in the interpretation and/or interpolation of estimates derived from other techniques, such as chloride mass balance. The results of machine learning modelling suggest that further work is needed to better constrain uncertainty in input and training datasets, and in the development of robust translations of outputs to hydrogeologically meaningful products.

The chloride mass balance (CMB) method remains the most appropriate tool for estimating long-term mean gross recharge to GAB aquifers in the northern Surat Basin. New upscaling methods provide significant improvements for mapping regional scale groundwater recharge rates and quantifying uncertainties associated with these estimates. Application of multiple techniques to the assessment of groundwater flow and recharge processes is necessary to complement CMB recharge estimates, and reduce associated uncertainty. Analysis of groundwater environmental tracers are recommended for constraining CMB recharge rates.

Integrated geological assessments using airborne electromagnetic data in conjunction with other geophysical and geological data (e.g., reflection seismic, wells) are effective at characterising aquifer architecture to better understand geometry, flow pathways and structural controls relevant to recharge and connectivity at local to regional scales.

Significant effort has gone into updating the regional geological framework at the whole-of-GAB scale, combining legacy and new data with recent knowledge to revise the hydrogeological conceptualisation of the GAB. This assists in constraining interpretations of regional depositional architecture and lithological heterogeneity within hydrogeological units, particularly those properties that influence groundwater storage and flux. Assessment of lateral and vertical heterogeneity of hydraulic properties within and between aquifers and aquitards in the northern Surat Basin has refined our understanding of potential groundwater connectivity and compartmentalisation.

This study provides an improved hydrogeological framework to support revised water balance estimates for the GAB, and insights into potential recharge variability that may impact those input components. Targeted examples from the northern Surat Basin demonstrate the application of the techniques and tools employed, including methods to reduce uncertainty. The outcomes of this work underpin a revised hydrogeological conceptualisation for the GAB, a standardised basis for establishing future investigations, and a framework for more informed water management decision-making.