Hydro-geochemical perspectives on hydrogeological processes in the arid to semi arid Barwon Darling (Baaka) River region, New South Wales, Australia

As part of Geoscience Australia's Exploring for the Future Program, the Upper Darling River Floodplain groundwater project has contributed to an improved understanding of hydrogeological systems of the Barwon–Darling-Baaka River system in northwest New South Wales, a region where a lack of water security impacts communities and the environment, and limits future economic opportunities. Key goals of the project were to assess the quality and extent of groundwater resources within the alluvium of the Barwon–Darling-Baaka River system to provide a greater knowledge base for supporting water management and enhanced drought resilience in the region. Groundwater and surface water hydrochemical and isotopic data were used to inform on aquifer characteristics, inter-aquifer and groundwater-surface water connectivity, and groundwater recharge and discharge in this complex arid to semi-arid alluvial system. Sixty-eight groundwater and twenty-one surface or rainwater samples were collected, and selected sample suites were analysed for field parameters, major and trace ions, stable water isotopes (δ18O, δ2H, δ13CDIC), strontium isotopes (87Sr/86Sr), radiocarbon (14C), sulphur hexafluoride (SF6), chlorofluorocarbons (CFCs), tritium (3H), chlorine isotopes (36Cl/Cl), noble gases (He, 3He/4He, Ne, Ar, Kr, Xe), and radon (222Rn). Statistical clustering analysis of this new data in combination with historical datasets identified three distinct hydrochemical facies: surface water and recently recharged low salinity groundwater, saline alluvial groundwater, and groundwater associated with aquifers of the Mesozoic Great Artesian Basin. Isotope and residence time tracer signatures revealed spatial differences in recharge, groundwater-surface water connectivity, and inter-aquifer connectivity between low salinity groundwater in hydraulic connection with the DarlingBaaka River, and the saline groundwater systems that characterise most of the alluvium throughout the study area. Integrating this hydrochemical data with other geoscientific data and information provides new insights into hydrogeological processes relevant to key water management issues including controls on the distribution of low salinity groundwater, and identification of areas at potential risk from impacts of saline groundwater. Abstract presented at the 30th International Applied Geochemistry Symposium 2024 (IAGS 2024)