Origins, flow paths, and mean travel times of water in an Australian alpine catchment

Understanding water origins, flowpaths, and the timescales over which precipitation becomes streamflow are critical for knowledge of the functioning of catchments. Catchments on the Great Dividing Range along the east coast of Australia are important sources of flows into Murray Darling basin for agricultural and drinking water use. This study collected a unique dataset that includes hydrometric measurements and samples of groundwater, surface water and precipitation between 2016 to 2020 to investigate hydrological processes in the Corin catchment, an alpine catchment in south-eastern Australia. Water samples were analysed for major ion chemistry and stable isotopes in water, and eight samples were selected for analysis of tritium activities. Major ion chemistry and stable isotope values were used to assess the relative contributions of water from two contrasting geological areas of the catchment to streamflow. Streamflow exiting the catchment had a consistently different chemical and isotopic signature compared to the groundwater found in the catchment valley. Instead, streamflow consistently resembled water originating from the slopes of the catchment that are underlain by a relatively younger geology. The mean travel times (MTT) of valley groundwater are likely to be in the decades, while baseflows are estimated to have a MTT of around 7 years. This work demonstrates the power of a multi-tracer approach to unravel the hydrological complexities of headwater catchments in south-eastern Australia.