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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Hydrol. Earth Syst. Sci., 18, 4951-4964, 2014
https://doi.org/10.5194/hess-18-4951-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
09 Dec 2014
Using 14C and 3H to understand groundwater flow and recharge in an aquifer window
A. P. Atkinson1,2, I. Cartwright1,2, B. S. Gilfedder3, D. I. Cendón4,5, N. P. Unland1,2, and H. Hofmann6 1School of Earth, Atmosphere & Environment, Monash University, Clayton, VIC, 3800, Australia
2National Centre for Groundwater Research and Training, Flinders University, Adelaide, SA 5001, Australia
3Department of Hydrology, University of Bayreuth, Bayreuth, Germany
4Australian Nuclear Science and Technology Organisation, Menai, NSW 2232, Australia
5School of Biological Earth and Environmental Sciences, The University of New South Wales, Sydney, NSW 2052, Australia
6School of Earth Sciences, The University of Queensland, Brisbane, QLD 4072, Australia
Abstract. 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.

Citation: Atkinson, A. P., Cartwright, I., Gilfedder, B. S., Cendón, D. I., Unland, N. P., and Hofmann, H.: Using 14C and 3H to understand groundwater flow and recharge in an aquifer window, Hydrol. Earth Syst. Sci., 18, 4951-4964, https://doi.org/10.5194/hess-18-4951-2014, 2014.
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Short summary
This research article uses of radiogenic isotopes, stable isotopes and groundwater geochemistry to study groundwater age and recharge processes in the Gellibrand Valley, a relatively unstudied catchment and potential groundwater resource. The valley is found to contain both "old", regionally recharged groundwater (300-10,000 years) in the near-river environment, and modern groundwater (0-100 years old) further back on the floodplain. There is no recharge of the groundwater by high river flows.
This research article uses of radiogenic isotopes, stable isotopes and groundwater geochemistry...
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