Thermal convection in the Great Artesian Basin, Australia

High groundwater temperatures at shallow levels have been recorded in the G reat Artesian Basin, Australia. In the most part of the Basin geothermal gr adients are above the global average. It is suggested that geothermal gradi ents determine the groundwater flow patterns in the Basin aquifers. Six ext ensive regions where Rayleigh numbers exceed the critical value for the ons et of thermal convection are identified. Further numerical experiments with parameters derived from field observations show that thermal convection ca n actually occur in these regions. The identified convective regions are la rge in size (of the order of 100 km horizontally) and coincide with importa nt groundwater management zones. Within the convective regions the groundwa ter flow is not horizontal but has a significant vertical component. Therma lly-induced vertical flows result in intensive mass transfer within and bet ween aquifer layers. In the groundwater management context, the latter mean s a higher degree of vulnerability of the Basin aquifers. Numerical models with incorporated coupling between heat and mass transfer processes are sho wn to be appropriate for the impact assessment of management strategies in the Basin.