Browsing by Author "Atkinson, AP"

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    A multi-tracer approach to quantifying groundwater inflows to an upland river; assessing the influence of variable groundwater chemistry
    (John Wiley & Sons, Inc., 2013-11-27) Atkinson, AP; Cartwright, I; Gilfedder, BS; Hofmann, H; Unland, NP; Cendón, DI; Chisari, R
    Understanding the behaviour and variability of environmental tracers is important for their use in estimating groundwater discharge to rivers. This study utilizes a multi-tracer approach to quantify groundwater discharge into a 27 km upland reach of the Gellibrand River in southwest Victoria, Australia. Ten sampling campaigns were conducted between March 2011 and June 2012, and the distribution of 222Rn activities, Cl and 3H concentrations imply the river receives substantial groundwater inflows. Mass balances based on 222Rn, Cl and 3H yield estimates of groundwater inflows that agree to within ± 12%, with cumulative inflows in individual campaigns ranging from 24 346 to 88 467 m3/day along the studied river section. Groundwater discharge accounts for between 10 and 50% of river flow dependent on the time of year, with a high proportion (>40 %) of groundwater sustaining summer flows. Groundwater inflow is largely governed by regional groundwater flowpaths; between 50 and 90% of total groundwater inflows occur along a narrow 5–10 km section where the river intersects the Eastern View Formation, a major regional aquifer. Groundwater 222Rn activities over the 16 month period were spatially heterogeneous across the catchment, ranging between 2000 Bq/m3 and 16 175 Bq/m3. Although groundwater 222Rn activities display temporal variation, spatial variation in groundwater 222Rn is a key control on 222Rn mass balances in river catchments where groundwater and river 222Rn activities are within an order of magnitude of each other. Calculated groundwater discharges vary from 8.4 to 15 m3/m/day when groundwater 222Rn activities are varied by ± 1 σ. © 2013 John Wiley & Sons, Ltd.
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    Sources and transit times of water in headwater temperate rainforest streams
    (Copernicus Publications, 2019-04-07) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, U
    Headwater catchments are important sources of water for many river systems. Unlike lower reaches of rivers that are frequently connected to alluvial aquifers, headwater catchments are commonly developed on indurated rocks that lack extensive groundwater systems. The observation, however, that many headwater streams are perennial implies that streamflow is sustained by water contained in fractures, soils, and/or the regolith. Understanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning and predicting the response of catchments to changing climate or land use. This study determines water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream indicates that water from soil pipes is the major contributor to streamflow. By contrast, riparian zone groundwater and water from elsewhere within the soils contributes little to streamflow. The streams are gaining and the lack of riparian zone groundwater inputs may be due to the presence of low hydraulic-conductivity organic-rich streambed sediments or compartmentalisation of shallow groundwater by clays in the weathered rocks. Similarly, pockets of isolated water within the soils that are not connected to the soil pipes also exist. The stream water has tritium (3H) activities of 1.80 to 2.06 TU, with slightly higher activities recorded during the higher winter flows. The water from the soil pipes has 3H activities of 1.80 to 2.25 TU, the riparian zone groundwater has 3H activities of 1.35 to 2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. The 3H activities of all these catchment waters are significantly lower than those of modern rainfall (2.6 to 3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These mean transit times are consistent with the waters being resident in the catchment for sufficient time for weathering reactions and evapotranspiration to occur. While the discharge from the soil pipes increases following periods of high rainfall, this water is stored for several years within the catchment before discharge (probably within the weathered regolith). Thus, the increase in discharge is not the simple transmission of recent rainfall through the macropores but mobilisation of younger stores of water as the catchment wets up. The long mean transit times of the stream water imply that it is derived from a relatively large store (>108 m3) and is buffered against year-on-year variations in rainfall. However, longer-term variations in rainfall or land use will likely impact streamflow. © Author(s) 2018. CC Attribution 4.0 license.
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    Understanding the sources and transit times of water sustaining streamflow in upland catchments
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, U
    Headwater catchments are important sources of water in many rivers. While headwater catchments are commonly developed on indurated rocks without extensive groundwater systems, the observation that many headwater streams are perennial implies that they are sustained by water in fractures, soils, or the regolith. Understanding the sources and transit times of water in headwater streams is important for understanding catchment functioning and predicting the impacts of changing climate or land use. This study uses major ion geochemistry and tritium (3H) to determine water sources and transit times in first-order streams in the Otway Ranges, southeast Australia. Comparison of the geochemistry of soil water, water from soil pipes (macropores), and riparian groundwater indicates that macropore flow is the major contributor to streamflow. The streams are gaining and the lack of riparian zone groundwater inputs may be due to the presence of low hydraulic-conductivity organic-rich streambed sediments or compartmentalisation of shallow groundwater by clays in the weathered rocks. Similarly, much of the soil water exists in isolated pockets of isolated water that are not connected to the soil pipes. The stream water has tritium (3H) activities of 1.80 to 2.06 TU. These are significantly lower than the 3H activities of modern rainfall (2.6 to 3.0 TU), even during the higher winter flows. The water from the soil pipes has 3H activities of 1.80 to 2.25 TU, the riparian zone groundwater has 3H activities of 1.35 to 2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. Mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. Relatively long mean transit times are consistent with the major ion geochemistry that implies that waters are resident for sufficient time for weathering reactions and evapotranspiration to have occurred. While the discharge from the soil pipes increases following periods of high rainfall, the long mean transit times implies that this water is stored for several years within the regolith before discharge, with storage volumes estimated as >108 m3. Thus the increase in streamflow is not the simple transmission of recent rainfall through the macropores but mobilisation of existing catchment stores. The streams will be buffered against year-on-year variations in rainfall but are vulnerable to longer-term variations in rainfall or land use. Management of these catchments needs to consider the impacts on the macropores and the delayed responses caused by the large storage volumes. © The Authors
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    Using 14C and 3H to understand groundwater flow and recharge in an aquifer window
    (Copernicus Publications, 2014-12-09) Atkinson, AP; Cartwright, I; Gilfedder, BS; Cendón, DI; Unland, NP; Hofmann, H
    Knowledge of groundwater residence times and recharge locations is vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge from rainfall and recharge from the Gellibrand River. To determine recharge patterns and groundwater flow paths, environmental isotopes (3H, 14C, δ13C, δ18O, δ2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. The water table fluctuates by 0.9 to 3.7 m annually, implying recharge rates of 90 and 372 mm yr−1. However, residence times of shallow (11 to 29 m) groundwater determined by 14C are between 100 and 10 000 years, 3H activities are negligible in most of the groundwater, and groundwater electrical conductivity remains constant over the period of study. Deeper groundwater with older 14C ages has lower δ18O values than younger, shallower groundwater, which is consistent with it being derived from greater altitudes. The combined geochemistry data indicate that local recharge from precipitation within the valley occurs through the aquifer window, however much of the groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High. The Gellibrand Valley is a regional discharge zone with upward head gradients that limits local recharge to the upper 10 m of the aquifer. Additionally, the groundwater head gradients adjacent to the Gellibrand River are generally upwards, implying that it does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High. © Author(s) 2014.
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    Using geochemistry to understand water sources and transit times in headwater streams of a temperate rainforest
    (Elsevier B. V., 2018-12) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, U
    Understanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning. This study determines the water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream suggests that water from soil pipes is the major contributor to streamflow. The tritium (3H) activities of the stream water are between 1.80 and 2.06 TU, the water from the soil pipes has 3H activities between 1.80 and 2.25 TU, the riparian zone groundwater has 3H activities of 1.35–2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. These 3H activities are significantly lower than those of local modern rainfall (2.6–3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These estimates are consistent with the major ion and stable isotope data, which imply that mean transit times were sufficiently long to allow weathering of minerals and/or organic matter and evapotranspiration to occur. The long mean transit times imply that water flows in this upper catchment are buffered against year-on-year variations in rainfall, but may change due to longer-term variations in rainfall or landuse. © 2018 Elsevier Ltd.