Authors / CoAuthors
Lawrie, K. | Gibson, D. | Christensen, N.B. | Halas, L. | Brodie, R.S.
Abstract
The keystone element of a system is one which is disproportionately important to the workings of that system relative to its size, abundance and/or distribution. In the Broken Hill Managed Aquifer Recharge (BHMAR) Project, previously unidentified faulting of the unconsolidated sediments beneath the Darling Floodplain, N.S.W., may be considered as such a keystone element, as it is a spatially discrete and subtle element of the regional hydrogeological system that is critical to the recharge of the underlying Pliocene aquifers, and consequentially vital to the viability of MAR and groundwater extraction options in the area. Initial inversions of a regional airborne electromagnetics (AEM) dataset revealed a multi-layered conductivity structure in the top 100m, broadly consistent with the hydrostratigraphy identified in a sonic drilling program. However, initial laterally and spatially constrained inversions showed only moderate correlations with ground data in the near-surface (~20m). As additional information from drilling and complementary hydrochemical and hydrodynamic studies became available, various horizontal and vertical constraints were trialled using a new Wave Number Domain Approximate Inversion procedure with a 1D multi-layer model and constraints in 3D. The resultant improved 3D conductivity model revealed that an important Pleistocene aquitard (Blanchetown Clay) confining the main target aquifer (Pliocene Calivil Formation), has an undulating top which is locally sharply offset. The interpreted top surface suggests that it has been affected by significant warping and faulting, as well as regional tilting due to basin subsidence or margin uplift. Overall, the aquitard top surface varies in elevation by 60m. Several of the sharp offsets in the conductivity layers are coincident with lineaments observed in LiDAR data, and with underlying basement faults mapped from airborne magnetic data. The recognition of neotectonics in this area was made possible through the acquisition of high resolution AEM data and the selection of appropriate horizontal and vertical constraints in inversion procedures. Prior to the structural features being mapped it had not been possible to explain apparently contradictory data, nor develop a plausible hydrogeological conceptual model.
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nonGeographicDataset
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75741
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- External PublicationAbstract
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Geology
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2013-01-01T00:00:00
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Abstract prepared for submission to the International Association of Hydrogeologists (IAH).
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