Great Sandy Strait

Environmental flows into the Great Sandy Strait come from a number of sources, largely the Mary River and Fraser Island. These flows play a crucial role in sustaining the strait’s marine ecosystems and the extraordinary diversity of life they support.

Environmental flows, or flow regimes, are the key driving variable for any river’s downstream aquatic ecosystems. Flood timing, duration and frequency are all critical for the survival of communities of plants and animals living downstream. Small flood events may act as biological triggers for fish and invertebrate migration: major events create and maintain habitats by scouring or transporting sediments.

The natural variability of most river systems sustains complex biological communities that may be very different from those adapted to the stable flows and conditions of a regulated river. Water temperature and chemistry are also altered as a consequence of water storage and the altered timing of downstream flows. Algal growth may occur in the reservoir and in the channel immediately downstream from dams because of the nutrient loading of the reservoir releases. Watch Steve Burgess talk about Dam weeds and mosquitoes.

Freshwater flows help support marine fish production as many marine fish spawn in estuaries. A decrease in freshwater flow in nutrients due to dam construction would effect the nursery areas in a number of ways, including increasing salinity, allowing predatory marine fish to invade, and reducing the available food supply.

The Traveston Crossing Dam would most likely have significant impacts on Matters of National Environmental Significance all the way to the Great Sandy Strait Ramsar Wetlands and beyond. References to the maintenance of 85% of mean flows at the river mouth are deliberately misleading as the Mary River is characterized by occasional and extreme flood events. Most of the time the river has low flows and these will be severely impacted by the dam.

¨ ‘Fraser Island Freshwater Flows’ ... click here

¨ ‘Effects of Dams on River Systems’ … click here

¨ ‘Inadequate Environmental Flows—Flaws in Current Mary Basin Water Resource Plan’ … click here

¨ ‘Sediment Plumes’ … click here

¨ ‘The Trapping of Sediments and Nutrients’ … click here

¨ ‘Barrages, Dams and the Mary’s Environmental Flows’ … click here

¨ ‘Maintaining Great Sandy Region’s Environmental Flow’ ... click here

¨ ‘The Great Coorong—A Biological barometer’ ... click here

¨ ‘Geomorphology & Hydrology—The Making of the Great Sandy’ ... click here

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Environmental Flows

’In short, in the First World, we have learned that dams don’t create water; they just move it from one spot to another. Even though we may have more water upstream for the fifty-year average life of the dam, we’ll have less downstream, and a lot of other problems we never thought about before, any more than we thought about our hearts beating before we started blocking our arteries with saturated fats.’

David Suzuki, Good News For A Change

(p. 149).