What happens when you re-start a dry river - the Northern Fish Flow (#88)
Mark Southwell
1
,
Darren Ryder
1
,
Lindsay White
2
,
Gavin Pryde
2
,
Matt Elsley
3
- University of New England, Armidale, NSW, Australia
- Wetlands, Policy and Northern Water Use Branch, Commonwealth Environmental Water Office, Canberra, ACT, Australia
- Eco Logical Australia, Armidale, NSW, Australia
- In 2019, the northern Murray-Darling basin was in severe drought, rivers had stopped flowing and weir pools along the Barwon-Darling River were at their lowest water levels in 50 years. To improve water quality and prevent fish kills, an environmental flow (the northern fish flow – NFF) was delivered from the Macintyre and Gwydir Rivers down the Barwon-Darling River. We monitored conditions before, during and after the NFF to initially inform a risk assessment and then monitor temporal changes to water quality.
- Spot water quality samples were taken in 5 weir pools from Mungindi to Bourke along the Barwon-Darling River. Dissolved oxygen (DO) and temperature loggers were deployed over 5 months to measure continuous changes during the NFF.
- Initially some of the deeper pools showed signs of thermal stratification and low DO (<2 mg/l) at depths below 3m. Detailed sampling at several pools suggested the volume of low DO water was relatively low (~10% pool volume). Water quality was more consistent through the water profile within shallower pools (2-3m deep). Ongoing monitoring suggested that the NFF was successful in replenishing weir pools and improving their water quality.
- Pool stratification was also influenced by atmospheric conditions, with cold snaps appearing to reduce stratification. While this was not always reflected in improved DO at depth, it does suggest that if flows are timed to coincide with cold fronts, then potentially less water might be needed to break the already weakened stratification and promote full water column mixing.
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