Browsing by Author "Cox, ME"
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- ItemAssessment of interaction between alluvial, volcanic and GAB aquifers using 3D visualisation and environmental tracers, Lockyer Valley, southeast Queensland, Australia(Australian Geosciences Council, 2012-08-05) Raiber, M; Cox, ME; Cendón, DI; Hartland, AA detailed 3D lithological model framework was developed using GOCAD software to understand interactions between alluvial, volcanic and GAB aquifers and the spatial and temporal distribution of groundwater recharge to the alluvium of the Lockyer Valley. Groundwater chemistry, isotope data (H20-δ2H and δ18O , 87Sr/86Sr, 3H and 14C) and groundwater level time-series data from approximately 550 observation wells were integrated into the catchment-wide 3D model to assess the recharge processes involved. This approach enabled the identification of zones where recharge to the alluvium primarily occurs from stream water during episodic flood events. Importantly, the study also demonstrates that in some sections of the alluvium recharge is also from storm rainfall and seepage discharge from the underlying GAB aquifers. These other sources of recharge are indicated by (a) the absence of a response of groundwater levels to flooding in some areas, (b) old radiocarbon ages, and (c) distinct bedrock water chemistry and δ2H and δ18O signatures in alluvial groundwater at these locations. Integration of isotopes, water chemistry and time-series displays of groundwater levels before and after the 2010/2011 flood into the 3D model suggest that the spatial variations in the alluvial groundwater response are mostly controlled by valley morphology and lithological (i.e. permeability) variations within the alluvium. Examination of the groundwater level variations in the 3D model also enabled quantification of the volumetric change of groundwater stored in the unconfined alluvial aquifer prior to and post-flood events.
- ItemComparison 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, DIThis 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
- ItemGroundwater chemistry baseline of the Walloon coal measures in the Clarence-Moreton and Surat basins, Queensland, Australia(International Association of Hydrogeologists, 2013-09-19) Raiber, M; Cox, ME; Cendón, DI; Feitz, AJThe Walloon Coal Measures (WCM) are a major target for coal seam gas exploration in the Surat and Clarence-Moreton basins in Queensland and New South Wales, Australia. It is now widely acknowledged that an improved understanding of the groundwater baseline is essential. Fundamental is determining the geological framework and an unbiased examination of the natural range, or baseline, of groundwater chemistry of the coal seams and adjacent aquifers. In order to determine the processes that control the spatial variability and evolution of groundwater chemistry, the chemistry baseline data of the WCM for the Surat and Clarence-Moreton basins are placed within the framework of a 3D geological model. In the assessment of the water chemistry baseline, four groundwater chemistry groups were identified from the hierarchical cluster analysis (HCA) which was applied to historical groundwater chemistry records from the Department of Natural Resources and Mines (DNRM) groundwater database. Each of these distinct groups contains groundwaters of a similar composition, which result from a number of different processes (e.g. groundwater recharge or interaction with other aquifers). However, groundwater of only one group has the typical composition of CSG waters, as documented by very high HCO3, and simultaneously low SO4, Ca and Mg concentrations, whereas the chemical composition of groundwater assigned to the other groups suggests that these follow a different evolutionary pathway. Following this initial screening, a total of ~60 samples was collected from the different groundwater chemistry groups for analysis of water chemistry (major, trace, rare earth elements and dissolved gases) and isotopic fingerprinting (d2H, d2H-CH4, d13C-DIC, d13C-CH4, d18O, 87Sr/86Sr,14CDIC and 36Cl/Cl). The analyses were combined with results from a similar groundwater chemistry study undertaken in the Surat Basin during 2009-2011 that aimed to establish a groundwater chemistry baseline for geological storage of CO2. The analyses of dissolved gases shows that there is a strong variability of dissolved CH4 concentration within groundwaters of the WCM, ranging from values below the reporting limit to ~50 mg/L. Likewise, isotope signatures and groundwater residence times within these coal-bearing sequence are highly variable spatially, reflecting the range of processes involved in groundwater evolution as well as the variable composition of these sedimentary rocks.
- ItemHydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivity(Elsevier, 2015-10-01) Duvert, C; Raiber, M; Owen, DDR; Cendón, DI; Batiot-Guilhe, C; Cox, MEIn areas of potential coal seam gas (CSG) development, understanding interactions between coal-bearing strata and adjacent aquifers and streams is of highest importance, particularly where CSG formations occur at shallow depth. This study tests a combination of hydrochemical and isotopic tracers to investigate the transient nature of hydrochemical processes, inter-aquifer mixing and recharge in a catchment where the coal-bearing aquifer is in direct contact with the alluvial aquifer and surface drainage network. A strong connection was observed between the main stream and underlying alluvium, marked by a similar evolution from fresh Ca–Mg–HCO3 waters in the headwaters towards brackish Ca–Na–Cl composition near the outlet of the catchment, driven by evaporation and transpiration. In the coal-bearing aquifer, by contrast, considerable site-to-site variations were observed, although waters generally had a Na–HCO3–Cl facies and high residual alkalinity values. Increased salinity was controlled by several coexisting processes, including transpiration by plants, mineral weathering and possibly degradation of coal organic matter. Longer residence times and relatively enriched carbon isotopic signatures of the downstream alluvial waters were suggestive of potential interactions with the shallow coal-bearing aquifer. The examination of temporal variations in deuterium excess enabled detection of rapid recharge of the coal-bearing aquifer through highly fractured igneous rocks, particularly at the catchment margins. Most waters collected from the coal-bearing aquifer also showed an enhanced influence of weathering during the wet season, which was likely triggered by the water–rock interaction with fresh recharge waters. An increase in both residual alkalinity and carbon isotopic ratios at two locations indicated inter-aquifer mixing between alluvium and bedrock during the wet season. The results of this study emphasise the need for conducting baseline hydrochemical surveys prior to CSG development in order to describe the transient nature of recharge and inter-aquifer mixing processes. © 2015, Elsevier Ltd.
- ItemIdentifying 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, SEAn 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).
- ItemIsoscapes: a 3D visualisation approach to study aquifer connectivity during drought and flood, Lockyer Valley, southeast Queensland, Australia,(International Association of Hydrogeologists, 2013-09-16) Raiber, M; Cox, ME; Cendón, DI; Hartland, A; James, AA 3D geological model of the Lockyer Valley, southeast Queensland, was developed using GOCAD software as a framework to study interactions between alluvial, basaltic and sedimentary bedrock aquifers of the Clarence-Moreton Basin and the spatial and temporal variability of recharge to the alluvium. The isotopic data (δ2h and δ18O, 87Sr/86Sr, 3H and 14C), water chemistry and time-series of groundwater levels before and after the 2010/2011 flood, were integrated within the 3D hydrogeological framework using Groundwater Visualisation System (GVS). Groundwater “isoscapes" (i.e. isotopic landscapes) were developed by spatial interpolation of isotopic results from more than 180 bores to enable the identification of different sources of water that contribute to recharge. The isotopic parameters are displayed as colour-contoured surfaces of the different aquifers and as coloured cylinders of variable thickness marking the position and thickness of the screened interval. Interpretation of isotopic values and their spatial relationships show that recharge to the alluvium primarily occurs from streams following episodic flood events. However, importantly, the study also demonstrates that in some sections of the alluvial plain, recharge to the alluvium is derived from both diffuse rainfall recharge and seepage discharge from the underlying Great Artesian Basin (GAB) aquifers. Bedrock seepage recharge dominates in some parts of the alluvial aquifer during droughts, enhanced by continuous pumping of the alluvial aquifer during the drought, as indicated by overall longer groundwater residence times, and high groundwater salinities. In addition, the hydrochemical signature of recharge from the bedrock is characterised by an isotopic depletion of δ2H and δ18O, and more radiogenic 87Sr/86Sr ratios in alluvial groundwater. The spatial variability of the responses is mostly controlled by catchment morphology and lithological (i.e. permeability) variations within the alluvium. Assessment of the unconfined groundwater levels in the 3D geological model enabled quantification of the volumetric change of groundwater stored in the alluvial aquifer system before and after flood events.
- ItemSeasonal and spatial variations in rare elements to identify inter-aquifer linkages and recharge processes in an Australian catchment(Elsevier B. V., 2015-03-09) Duvert, C; Cendón, DI; Raiber, M; Seidel, JL; Cox, MEWith the aim of elucidating the seasonal behaviour of rare earth elements (REEs), surface and groundwaters were collected under dry and wet conditions in different hydrological units of the Teviot Brook catchment (Southeast Queensland, Australia). Sampled waters showed a large degree of variability in both REE abundance and normalised patterns. Overall REE abundance ranged over nearly three orders of magnitude, and was consistently lower in the sedimentary bedrock aquifer (18ppt<∑REE<477ppt) than in the other hydrological systems studied. Abundance was greater in springs draining rhyolitic rocks (∑REE=300 and 2054ppt) than in springs draining basalt ranges (∑REE=25 and 83ppt), yet was highly variable in the shallow alluvial groundwater (16ppt<∑REE<5294ppt) and, to a lesser extent, in streamwater (85ppt<∑REE<2198ppt). Generally, waters that interacted with different rock types had different REE patterns. In order to obtain an unbiased characterisation of REE patterns, the ratios between light and middle REEs (R(M/L)) and the ratios between middle and heavy REEs (R(H/M)) were calculated for each sample. The sedimentary bedrock aquifer waters had highly evolved patterns depleted in light REEs and enriched in middle and heavy REEs (0.17
- ItemSignificance of the connection between bedrock, alluvium and streams: a spatial and temporal hydrogeological and hydrogeochemical assessment from Queensland, Australia(Elsevier B. V., 2019-02) Raiber, M; Lewis, S; Cendón, DI; Cui, T; Cox, ME; Gilfedder, M; Rassam, DWCatchment-scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing; they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant. However, in many cases, such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components, particularly in regions dominated by cycles of droughts and flooding. From a modelling perspective, such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems. In this study, we use 3D geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the Lockyer Valley (Queensland, Australia), a catchment impacted by a severe drought (‘Millennium Drought’) from 1998 to 2009, followed by extensive flooding in 2011. We also demonstrate how discharge from the sub-alluvial regional-scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams. The investigation of aquifer geometry via development of a three-dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams. Multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets. This confirmed that most sub-catchments within the Lockyer Valley have distinct water chemistry patterns, which result from mixing of different water sources, including discharge from the sub-alluvial bedrock. Importantly, in addition to the observed spatial variability, time-series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers, streams and sub-alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding, affecting both catchment water quality and water balances. Crown Copyright © 2018 Published by Elsevier B.V.
- ItemStable isotopes of lithium as Indicators of coal seam gas-bearing aquifers(Elsevier, 2015-08-21) Owen, DDR; Millot, R; Négrel, P; Meredith, KT; Cox, MEIn this study lithium isotopes were used in combination with hydrochemistry to investigate interactions between coal-seam-gas bearing sedimentary bedrock aquifers and surrounding basalt and alluvial aquifers in a large catchment in eastern Australia. Understanding groundwater transport and aquifer connectivity is critical to managing coal seam gas (or coal bed methane) developments, because large volumes of water need to be extracted in order to release the sorbed gas; however, to date lithium isotopes have not been applied to coal seam gas groundwater management problems and no information on the δ7Li of coal or coal-seam groundwater is available. Li/Cl and Li/Na ratios in the coal-bearing and sedimentary bedrock aquifers are distinct (>0.0001) from alluvial and basalt aquifers (<0.0001). Preliminary δ7Li results for coal measure samples are typically between 7 and 11‰; many of these samples also contain methane, and can therefore be expected to be influenced by coal and the early stages methanogenesis. Interestingly the coal measure with lowest δ7Li value occurs in an area where the coal measures outcrop and direct recharge is likely, with nearby basalt groundwater having much higher δ7Li values (δ7Li>18‰). Preliminary lithium isotope results show that δ7Li may be effective in distinguishing groundwater flow paths in the coal-bearing aquifer from basalt aquifers, and from a transitional zone between the alluvium and underlying coal measures. Further lithium isotope analysis is being carried out to: a) compare the δ7Li between alluvial, basalt and coal-bearing aquifers to further investigate aquifer connectivity; b) to describe δ7Li for CSG production waters with low- and high-methane groundwater in the coal-bearing aquifer; c) to describe the δ7Li from coal and basalt leachate. © 2015, Elsevier B.V.
- ItemUse 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, MERadiocarbon (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.