Authors / CoAuthors
Halas, L. | Tan, K.P. | Lawrie, K. | Apps, H. | Clarke, J.
Abstract
The Murray River is known to display great complexity in surface-groundwater interactions along its course, with 'gaining' sections of the river identified as sites of regional saline groundwater system discharge to the river and the adjacent floodplain. 'Losing' reaches of the river occur where river water infiltrates through the base of the river and recharges underlying aquifers and/or where adjacent aquifers are recharged through lateral bank infiltration. Recent studies have shown that recharge is not-steady state, with surface-groundwater processes promoted after river bank scouring during major flood events. 'Losing' reaches of rivers are hard to identify hydrochemically, while only airborne electromagnetic (AEM) methods provide 3D spatial mapping of salinity and hydrostratigraphy at depth beneath the river and across the floodplain. In 2007 a regional airborne electromagnetic (AEM) survey (24,000 line km @ 150m line-spacing in a 20 km-wide swath) was acquired along a 450 km reach of the Murray River in Victoria from Gunbower Island in the east to near the South Australian border. The AEM survey was calibrated and validated by drilling and complementary field mapping, and lithological and hydrogeochemical investigations. Holistic inversions of the AEM data were used to map key elements of the hydrogeological system and salinity extent in the shallow sub-surface (top 20-50 m). The survey successfully mapped key elements of the hydrogeological system including previously unmapped salinity discharge zones and significant losing 'flush' zones. Significant 'flush' zones to depths of 25m and up to 1.5 km in width have been identified at Turrumbarry Weir, with other significant zones identified in parts of Gunbower Forest, and between Liparoo and Robinvale. Elsewhere, flush zones are smaller, and occur at depths of 5-10m in narrower zones associated with locks, weirs and irrigation districts. Salt mobilisation associated with the flush zones at weir pools may be an issue in terms of salt load delivery to the River Murray and floodplain. Reaches of the river where the flush zones are absent and /or significantly constricted, and similar zones in tributary creeks in the adjacent floodplain, are at higher risk of saline groundwater inflows.
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nonGeographicDataset
eCat Id
75827
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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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