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Title: Isoscapes: a 3D visualisation approach to study aquifer connectivity during drought and flood, Lockyer Valley, southeast Queensland, Australia,
Authors: Raiber, M
Cox, ME
Cendón, DI
Hartland, A
James, A
Keywords: Simulation
Sedimentary basins
Alluvial deposits
Groundwater recharge
Carbon 14
Issue Date: 16-Sep-2013
Publisher: International Association of Hydrogeologists
Citation: Raiber, M., Cox, M. E., Cendón, D. I., Hartland, A., & James A. (2013) Isoscapes: a 3D visualisation approach to study aquifer connectivity during drought and flood, Lockyer Valley, southeast Queensland, Australia. Paper presented to IAH 2013 Perth Australia : "Solving the groundwater challenges of the 21st century", International Association of Hydrogeologists 40th International Conference, Perth, Western Australia, 15-20 September 2013. (pp. 69).
Abstract: A 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.
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