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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-327
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
21 Jun 2017
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
A multi-tracer approach to constraining artesian groundwater discharge into an alluvial aquifer
Charlotte P. Iverach1,2, Dioni I. Cendón1,2, Karina T. Meredith2, Klaus M. Wilcken2, Stuart I. Hankin2, Martin S. Andersen3, and Bryce F. J. Kelly1 1Connected Waters Initiative Research Centre, School of Biological, Earth and Environmental Sciences, UNSW Sydney, NSW, 2052, Australia
2Australian Nuclear Science and Technology Organisation, New Illawarra Rd, Lucas Heights, NSW, 2234, Australia
3Connected Waters Initiative Research Centre, School of Civil and Environmental Engineering, UNSW Sydney, NSW, 2052, Australia
Abstract. Understanding pathways of recharge to alluvial aquifers is important for maintaining sustainable access to groundwater resources. Water balance modelling is often used to proportion recharge components and guide sustainable groundwater allocations. However, it is not common practice to use hydrochemical evidence to inform and constrain these models. Here we compare geochemical versus water balance model estimates of artesian discharge into an alluvial aquifer, and demonstrate why multi-tracer geochemical analyses should be used as a critical component of water budget assessments. We selected a site in Australia where the Great Artesian Basin (GAB), the largest artesian basin in the world, discharges into the Lower Namoi Alluvium (LNA), an extensively modelled aquifer, to convey the utility of our approach. Water stable isotopes (ẟ18O and ẟ2H) and the concentrations of Na+ and HCO3 suggest a continuum of mixing in the alluvial aquifer between the GAB (artesian component) and surface recharge, whilst isotopic tracers (3H, 14C and 36Cl) indicate that the alluvial groundwater is a mixture of groundwaters with residence times of < 70 a using 3H and ~ 900 ka using 36Cl methods. In addition, Cl concentrations provide a means to calculate a percentage estimate of the artesian contribution to the alluvial groundwater. In some locations, an artesian contribution of up to 70 % is evident from the geochemical analyses, contrasting historical water balance modelling estimates of 22 %. Our results show that hydrochemical investigations need to be undertaken as part of developing the conceptual framework of a catchment water balance model, as they can improve our understanding of recharge pathways and better constrain artesian discharge to an alluvial aquifer.

Citation: Iverach, C. P., Cendón, D. I., Meredith, K. T., Wilcken, K. M., Hankin, S. I., Andersen, M. S., and Kelly, B. F. J.: A multi-tracer approach to constraining artesian groundwater discharge into an alluvial aquifer, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-327, in review, 2017.
Charlotte P. Iverach et al.
Charlotte P. Iverach et al.
Charlotte P. Iverach et al.

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Short summary
This study uses a multi-tracer geochemical approach to determine the extent of artesian groundwater discharge into an economically important alluvial aquifer. We compare estimates for artesian discharge into the alluvial aquifer derived from water balance modelling and geochemical data to show that there is considerable divergence in the results. The implications of this work involve highlighting that geochemical data should be used as a critical component of water budget assessments.
This study uses a multi-tracer geochemical approach to determine the extent of artesian...
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