Hydrogeological assessment of springs in the south-central Great Artesian Basin of Australia

Artesian springs support important wetland ecosystems comprising highly specialised, endemic animal and plant species. Understanding the hydrogeological processes that sustain springs is critical to their management and characterisation of the connected groundwater system. This paper focuses on the springs of the Eulo and Bourke supergroups in the south-central part of the Great Artesian Basin in Queensland and New South Wales, Australia. These springs have been heavily impacted by aquifer drawdown, as a result of uncontrolled discharge of artesian water from pastoral bores. This study uses a stratigraphic model of the aquifer and aquitard sediments, a model of the potentiometric surface, existing information on the coverage of basement and surface structures, and a comprehensive field survey of all known springs to identify the association of springs with the edge of the geological basin, basement outcrop, basement highs, surface and deep basement faults, and a thinned aquitard. Many springs in the Eulo Supergroup are associated with basement highs and many springs are associated with deep faults, suggesting that reactivation of these faults may be an important cause of spring discharge. Springs in the Bourke Supergroup previously thought to be outcrop springs (gravity-fed), by virtue of their surface characteristics, are more likely to be artesian springs based on the interpretation of basement geology, surface faults and water chemistry, which align most closely to the Hooray Sandstone, the artesian aquifer underlying the springs.