Poster Presentation Australasian Groundwater Conference 2017

More than just a ‘tick the box’ exercise: why geology is the key to hydrogeological and hydrochemical investigations (#79)

Matthias Raiber 1 , Russell Crosbie 2 , Jorge Martinez 1 3 , Tao Cui 1
  1. CSIRO Land and Water, Dutton Park, QUEENSLAND, Australia
  2. CSIRO Land and Water, Adelaide, SA, Australia
  3. Earth, Environmental and Biological Sciences, Queensland University of Technology, Brisbane, Qld, Australia

Geology is a major driver of hydrochemical and hydrogeological processes, including recharge and groundwater-surface water interactions. However, geology remains an under-utilised resource that is increasingly only addressed marginally in hydrogeological or hydrogeochemical investigations to ‘tick the box’ of providing some background geological information. Here we provide an example from the Condamine River catchment (south-east Queensland) that highlights benefits of integrating hydrogeological and hydrochemical data with a comprehensive analysis of the geological framework. This work demonstrates how such integrated approaches can help to avoid shortcomings and misconceptions in conceptual hydrogeological models.

We have developed a three-dimensional geological model through application of state-of-the-art 3D geological modelling software packages GoCAD and SKUA (Paradigm Geophysical Pty Ltd®) using information from more than 15,000 groundwater and exploration bores. Unlike previous 3D geological model developments of the Condamine River catchment (which often focused on the characterisation of deeper sedimentary bedrock units) this newly developed model provides a more accurate depiction of the geometry of shallow and deep aquifers, focusing on the important interfaces between the alluvium, volcanic bedrock and sedimentary bedrock. The conceptual understanding forms the basis for development of an initial conceptual hydrogeological model. This hydrogeological model has been tested using independent lines of evidence, including a recharge assessment, development of potentiometric surface and head gradient maps and an assessment of hydrochemistry.

The integration of multiple techniques, the refinement of aquifer geometry understanding, and the interfaces between shallow and deep aquifers have all been used to provide new insights into the spatial variability of the connectivity between shallow alluvial and volcanic aquifers and the underlying sedimentary bedrock aquifers. The study also highlighted limitations of groundwater quality monitoring bore networks, which often do not target areas identified as likely areas of interactions between shallow and deep aquifers based on the assessment of the geological framework.

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