As part of Geoscience Australia's Exploring for the Future Program, the Upper Darling–Baaka River Floodplain groundwater project has contributed to an improved understanding of hydrogeological systems of the Darling–Baaka River system in arid to semi-arid northwest New South Wales, a region where a lack of water security impacts communities, the environment, and limits economic opportunities.
One aspect of the project involved analysing groundwater and surface water hydrochemical data to assess aquifer characteristics, inter-aquifer and groundwater-surface water connectivity, as well as groundwater recharge and discharge dynamics. Sixty-eight groundwater and twenty-one surface or rainwater samples were collected. 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 and legacy 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 Darling–Baaka River, and the saline groundwater systems that characterise most of the alluvium throughout the study area.
Integrating this hydrochemical data with other geoscientific data provided new insights into hydrogeological processes relevant to key water management issues, including controls on the distribution of low salinity groundwater.
Presented at the 52nd Congress of International Association of Hydrogeologists (IAH2025)