Browsing by Author "King, AC"

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    Comparison of groundwater recharge estimation techniques in an alluvial aquifer system with an intermittent/ephemeral stream (Queensland, Australia)
    (Springer Nature Limited, 2017-03-30) King, AC; Raiber, M; Cox, ME; Cendón, DI
    This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred. © 2017 Springer Nature Switzerland AG
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    Identifying flood recharge and inter-aquifer connectivity using multiple isotopes in subtropical Australia
    (Copernicus Publications, 2015-05-19) King, AC; Raiber, M; Cendón, DI; Cox, ME; Hollins, SE
    An understanding of hydrological processes is vital for the sustainable management of groundwater resources, especially in areas where an aquifer interacts with surface water systems or where aquifer interconnectivity occurs. This is particularly important in areas that are subjected to frequent drought/flood cycles, such as the Cressbrook Creek catchment in Southeast Queensland, Australia. In order to understand the hydrological response to flooding and to identify inter-aquifer connectivity, multiple isotopes (δ2H, δ18O, 87Sr/86Sr, 3H and 14C) were used in this study in conjunction with a comprehensive hydrochemical assessment, based on data collected 6 months after severe flooding in 2011. The relatively depleted stable isotope signatures of the flood-generating rainfall (δ2H: −30.2 to −27.8‰, δ18O: −5.34 to −5.13‰ VSMOW) were evident in surface water samples (δ2H: −25.2 to −23.2‰, δ18O: −3.9 to −3.6‰ VSMOW), indicating that these extreme events were a major source of recharge to the dam in the catchment headwaters. Furthermore, stable isotopes confirmed that the flood generated significant recharge to the alluvium in the lower part of the catchment, particularly in areas where interactions between surface waters and groundwater were identified and where diffuse aquifer recharge is normally limited by a thick (approximately 10 m) and relatively impermeable unsaturated zone. However, in the upper parts of the catchment where recharge generally occurs more rapidly due to the dominance of coarse-grained sediments in the unsaturated zone, the stable isotope signature of groundwater resembles the longer-term average rainfall values (δ2H: −12.6, δ18O: −3.4‰ VSMOW), highlighting that recharge was sourced from smaller rainfall events that occurred subsequent to the flooding. Interactions between the bedrock aquifers and the alluvium were identified at several sites in the lower part of the catchment based on 87Sr/86Sr ratios; this was also supported by the hydrochemical assessment, which included the modelling of evaporation trends and saturation indices. The integrated approach used in this study facilitated the identification of hydrological processes over different spatial and temporal scales, and the method can be applied to other complex geological settings with variable climatic conditions.© 2015, Author(s).
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    Use of multi-isotope surveys to identify bedrock-alluvium interactions, Cressbrook Creek Catchment, southeast Queensland
    (International Association of Hydrogeologists, 2013-09-19) King, AC; Raiber, M; Cendón, DI; Cox, ME
    Radiocarbon (14C) is commonly used to study groundwater residence times, but the interpretation of results is often subject to a high degree of uncertainty due to interaction with modern and ‘dead carbon’, especially for relatively young groundwater or groundwater that has interacted with organic material. To address this concern, 87Sr/86Sr ratios, δ2H and δ18O, combined with tritium and radiocarbon are used to identify zones where older bedrock water recharges the alluvial aquifer of the Cressbrook Creek catchment in southeast Queensland. Cressbrook Creek is an intermittent stream that is primarily recharged by groundwater in the upper catchment. The alluvial system overlies variable bedrock with metamorphic rocks, rhyolites and granites in the headwaters, and sedimentary sequences (mostly sandstones) downstream. The catchment has largely been dry during a decade of drought, but has owed continuously since 2010 and experienced severe flooding in January 2011. Groundwater samples collected from alluvial and bedrock aquifers in June 2011 were analysed for a range of environmental tracers. Six alluvial waters were analysed for 14C; of these, four are modern. The other two samples have pMC values of 88.0 and 81.1 (uncorrected ages of 1,045 and 1,680 years; Sites A and B, respectively) whereas tritium analyses indicate an age of less than 100 years for the same samples. This disparity in groundwater ages may have been caused by: 1) seepage of older bedrock groundwater into the alluvium; or 2) carbonate dissolution processes. Therefore, evidence from other tracers, including 87Sr/86Sr, was assessed as an independent constraint to support the conceptual understanding of aquifer interactions. Alluvial groundwater from Site A has an enriched 87Sr/86Sr signature, indicating that it has probably received recharge from the underlying granite aquifer. Groundwater from Site B has a lower 87Sr/86Sr ratio than the other alluvial groundwaters, which indicates this site probably received recharge from the underlying sandstone aquifer.