Thermal Convection in the Great Artesian Basin,Australia

High groundwater temperatures at shallow levels have been recorded inthe Great Artesian Basin, Australia. In the most part of the Basingeothermal gradients are above the global average. It is suggestedthat geothermal gradients determine the groundwater flow patterns inthe Basin aquifers. Six extensive regions where Rayleigh numbersexceed the critical value for the onset of thermal convection areidentified. Further numerical experiments with parameters derived fromfield observations show that thermal convection can actually occur inthese regions. The identified convective regions are large in size (ofthe order of 100 km horizontally) and coincide with importantgroundwater management zones. Within the convective regions thegroundwater flow is not horizontal but has a significant verticalcomponent. Thermally-induced vertical flows result in intensive masstransfer within and between aquifer layers. In the groundwatermanagement context, the latter means a higher degree of vulnerabilityof the Basin aquifers. Numerical models with incorporated couplingbetween heat and mass transfer processes are shown to be appropriatefor the impact assessment of management strategies in the Basin.