The Great Artesian Basin (GAB) in Australia underlies semi-arid and arid regions across 1.7 million km2 or one-fifth of Australia. The Basin’s groundwater resources were discovered around 1880 and the development of flowing and pumped artesian waterbores provide water for the sheep and cattle of the grazing industry, homestead and towns, and for oil, gas and mineral mining ventures to exist in and near the Basin. The GAB is a multi-layered confined aquifer system, with aquifers in Jurassic and Cretaceous continental sandstones and intervening confining beds of siltstone and mudstone of the constituent Eromanga, Surat and Carpentaria sedimentary basins. The Basin is up to 3000 m thick and forms a large synclinal structure, uplifted and exposed along its eastern margin and tilted southwest.
Recharge to the exposed aquifers occurs mainly in the eastern margin, an area of relative high rainfall. The western margin in Australia’s arid centre receives minor recharge. Regional groundwater flow is towards the southern, south-western, western and northern margins, and based on isotope hydrology studies, at 1 m/year to 2.5 m/year. Age dating by isotope hydrology studies of the artesian groundwater in the Basin determined ages of up to 1 to 2 million years. Groundwater quality is good, at 500 to 1500 mg/L total dissolved solids, and is predominantly Na-HCO3-Cl type water, with in the southwestern part Na-Cl-SO4 type water. Groundwater temperatures in bores are 300 to 1000 C, and in artesian springs 200 to 450 C. Most flowing artesian springs discharge in the southwest margin and produced carbonate mounds, and contain unique flora and fauna. Spring carbonate deposits have been dated by thermoluminescence and uranium series dating and result in ages between 465 000 ± 43 000 years and 740 000 ± 120 000 years. Lateral groundwater movement in the aquifers dominates, though vertical upwards leakage is considered important. Potentiometric surfaces of the Jurassic and Lower Cretaceous aquifers are still above ground-level throughout most of the Basin, though pressure drawdowns of up to 100 m have been recorded in recent decades in highly developed areas, and consequently some artesian waterbores and springs ceased flowing. Governments supported bore rehabilitation and management programs have led to groundwater pressure recovery in some areas. Computer modelling of the Basin’s hydrodynamics assisted these programs.
Aspects of the hydrogeology, hydrochemistry and isotope hydrology studies of the Great Artesian Basin will be discussed, summarising the recent knowledge on the Basin.