Browsing by Author "Gray, SS"

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    Identifying groundwater-surface water interactions and groundwater geochemistry in the Upper Murrumbidgee Catchment using surface water surveys
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Gray, SS; Moore, CL; Opdyke, BN; Hughes, CE
    Evidence suggests that potable groundwater occurs within the fractured crystalline rock of the Upper Murrumbidgee catchment, with anecdotal reports that bore yields and fracture networks could form aquifers capable of sustaining regional population growth and agricultural development. However, little knowledge relating to groundwater flow or recharge and discharge mechanisms exists. Hydrogeochemical methods are particularly useful in studying groundwater in complex geological environments. Unfortunately, limited information regarding groundwater geochemistry exists in this catchment. Surface water surveys provide an opportunity to quickly obtain preliminary information regarding groundwater-surface water interactions and likely groundwater geochemistry. Four surface water surveys were conducted at up to 285 sites during wet and dry conditions from September 2017 to April 2019. Physicochemical parameters were collected at each site where water was present, along with samples for stable isotopes (δ18O and δ2H) and dissolved ion analysis. Surface water geochemistry is influenced by interactions between altitude, rainfall, and outcropping geology. Stream electrical conductivity (EC) is positively correlated with altitude and negatively correlated with rainfall in all sub-catchments except the Yass River catchment. Outcrop geology also influenced stream EC, with the EC lowest over Paleozoic granite and granodiorites; moderate over Paleozoic felsic volcanic, Cenozoic mafic volcanic, and Cenozoic alluviums; and highest over Ordovician metasediments. Dissolved ion chemistry is similarly influenced by outcrop geology, and is reflected in preliminary groundwater surveys. The cations Na+ and K+ dominate Paleozoic granite and granodiorite waters while Ca2+ and Mg2+ dominate Cenozoic mafic volcanic waters. Bicarbonate (as HCO3-) is the dominant anion, with elevated HCO3-/Cl- associated with Cenozoic mafic volcanics. This suggests that mineral weathering dominates hydrogeochemical processes. Spatial distributions of stream water δ18O and δ2H highlight potential baseflow areas. Results suggest that potable water is highly probable within Paleozoic granite and granodiorites, with water Na+-K+-HCO3- dominated. Potable water is possible within Paleozoic felsic volcanic, Cenozoic mafic volcanic, and Cenozoic alluviums, with water potentially more suitable for agricultural use due to the higher Ca2+, Mg2+, and HCO3- content. Ordovician metasediment water is more suitable for agricultural use. Surface water survey data will be used in this study to optimise groundwater survey design and develop improved conceptual models to describe groundwater flow and recharge and discharge mechanisms in fractured rock environments in the Upper Murrumbidgee catchment. This will increase our understanding on how water resources may be utilised to support regional population growth and agricultural development, providing future water security for the region. © The Authors
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    Spatial and temporal stable isotope variability within Alpine Streams of the Snowy Mountains
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Parige, R; Gray, SS; Hughes, CE; Opdyke, BN; Moore, CL
    As an alpine region, the Snowy Mountains are identified as susceptible to the impacts of climate change. This is projected to influence annual variability in rainfall and snowfall amounts which will change availability of runoff water. The Snowy Mountains Hydro-electric Scheme has also altered natural flows in the area since the 1970s, changing behaviours of water resources in the Murrumbidgee and Snowy River catchments. Understanding processes that affect and have affected these surface waters can therefore improve the scientific basis for future water resource management decisions of the region. Historical physiochemical data of streams in the Snowy Mountains region has been monitored by NSW government and Snowy Hydro over the past half century. However, little stable water isotope data in alpine streams and rivers currently exists. As stable water isotopes (δ2H and δ18O) are excellent tracers of water through the hydrologic cycle, their use can better current understanding of the regions surface waters. Rapid stream surveys in 2019 have collected stable isotope and physiochemical data of streams within the Snowy Mountains, as well as Murray and Murrumbidgee systems downstream. Analyses of both these and archived samples from 2004-2017 were undertaken for this project. The data was then used with precipitation isotope data from parallel ANSTO studies, and historical records on regional streams for interpretation. Results showed that stable isotopes in streams varied spatially amongst sites with elevation, temperature difference, and location in the reservoir network, with distinct variance over smaller distances with steeper elevation. Temporal affects were seen with the appearance of seasonal snowmelt contributions into streams and climate. Physiochemical data saw trends similar to historical reports, with significant climate and geographic influence. This data will specifically contribute to further research into groundwater sustainability, isotope forensics and agricultural water use led by ANSTO and ANU for future betterment of the catchment. © The Authors