Authors / CoAuthors
Anderson, J.R. | Morison, A.K.
Abstract
Saline groundwater intrusions into lowland reaches of the Wimmera River, western Victoria, accumulated under low-flow conditions and formed stable saline pools. An extensive area of river downstream was affected, and almost all water in the channel during flow stoppages appeared to be of groundwater origin. Water in these saline pools had conductivity up to seawater level ( > 50000 EC units) , stable temperature of 14-20°C, low dissolved oxygen (< 10% saturation), and low pH (6.1 - 6.4), in contrast with surface water (conductivity < 4000 EC units, oxygen level >60% saturation, and temperature 8- 12°C in winter and over 20°C in summer). Halocline, oxycline and thermocline depths generally coincided, especially in winter. Salinity-related density stratification was very stable even in winter. The stratification pattern remained stable under low to moderate discharge (mean daily discharge < 1000 ML / day) , although major flow events (> 3000 ML / day) mixed or displaced most of the saline bottom layer. Saline pools which re-established within two months of flow decline had similar depth, temperature and conductivity to those found six months before. Under the prevailing intermittent flow regime, saline pools would be expected during the 7-month low-flow period (October to May) in most years. Stable stratification and associated severe hypoxia rendered much of the water in the pools uninhabitable by fish and other aerobic organisms; hypoxia rendered bed substrates and organic debris inaccessible for cover, feeding or resting, and probably reduced secondary production. The habitable area in many pools was confined to upper layers and shallow pool margins. Severe deoxygenation and rapid short term changes in salinity and temperature occurred with a first flush, and displacement of partially mixed saline water produced secondary stratifications in deep pools downstream. Vertical conductivity gradients of < 1000 EC units were associated with persistent deoxygenation at many sites as a result of this process. The total area affected by saline groundwater intrusions extended downstream far beyond the immediate area of the intrusion. The Wimmera River provides a model for other rivers in the Murray-Darling Basin where saline groundwater from rising water tables drains into them. The low-land sections of many rivers and streams proposed as sites for the disposal of saline water might have flow regimes and channel morphology conducive to the formation of stable saline pools. Further studies are required to develop management and control measures to prevent large-scale environmental degradation of riverine habitats in the Murray-Darling Basin through rising water tables, increased groundwater drainage or deliberate disposal of saline water into rivers and streams.
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document
eCat Id
81255
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
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2601
Australia
Keywords
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- GA PublicationJournal
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- VIC
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1989-01-01T00:00:00
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geoscientificInformation
Series Information
BMR Journal of Australian Geology and Geophysics 11:2-3:233-252
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Unknown
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[-37.52, -34.59, 141.13, 143.99]
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