Oral Presentation Australasian Groundwater Conference 2017

The Lamington and Main Range Volcanics in Qld and NSW: their significance as preferential recharge areas in the Clarence-Moreton Basin (#142)

Matthias Raiber 1 , Russell Crosbie 2 3 , Tao Cui 1 , Mat Gilfedder 1 , Steven Lewis 4 , David Rassam 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
  4. Groundwater, Geoscience Australia, Symonston, ACT, Australia

The Lamington and Main Range volcanics form a major regional fractured rock aquifer system (more than 12,000 km2) within the Clarence-Moreton Basin in south-east Qld and north-east NSW. Although widely recognised as an important hydrological feature, there has been no systematic or comprehensive basin-wide assessment of their significance as a major preferential recharge area.

Within the Clarence-Moreton bioregional assessment, an integrated hydrogeological assessment of basin-scale aquifer systems involved developing a 3D geological model, groundwater recharge and regional stream flow assessments, and characterising aquifer hydrochemistry (within the volcanics and neighbouring aquifer systems). The 3D geological model yielded a median thickness of approximately 130 m for these volcanic aquifers, and a maximum thickness of ~800 m near the crest of the volcanics in elevated areas. However, borehole lithological data confirmed that these volcanic rocks do not consist of a single homogeneous basalt flow nor form a single aquifer, but instead consist of many thinner overlapping basalt flows (up to ~10 m thick). The groundwater recharge assessment (using chloride mass balance) indicated recharge rates that can locally be more than 1000 mm/yr, with recharge rates to the volcanic aquifers at least one order of magnitude greater than recharge rates for most sedimentary bedrock units. However, a large proportion of groundwater recharge to the Lamington Volcanics discharges locally with short transit times (days to months) into the alluvium or streams, whereas only a small proportion percolates to deeper aquifers.

Based on this integrated approach, we have developed conceptual models that describe the relationship of the volcanic aquifers with alluvial aquifers and streams as a primary driver of alluvial groundwater and surface water quality in the Clarence-Moreton Basin. This conceptual understanding provides important knowledge for assessments of any future coal seam gas or agricultural development activities within the Clarence-Moreton Basin.

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