Up to 37Gl will be delivered along the lower Goulburn River this month in an environmental flow designed to benefit golden and silver perch populations.
The flow will see Goulburn-Murray Water release about 5Gl to meet minimum river operation requirements with a maximum of 23Gl of environmental water needed with the aim of triggering native fish breeding and improving overall river health.
Commonwealth Environmental Water Holder David Papps said it was important to continually use science to understand how plants and animals were affected when environmental water was delivered, describing native fish as a ‘‘barometer’’ of river health.
Monitoring shows that the best spawning response by golden and silver perch was usually later in spring during a higher flow when water temperatures had started to rise.
‘‘Over the years we have refined the timing of flows to get the best spawning response, with mid to late spring being the most effective,’’ Goulburn Broken Catchment Management Authority’s environmental water manager Simon Casanelia said.
‘‘The last time we were able to deliver an environmental flow at this time of the year was 2014 — as last year natural flooding was occurring, and the previous year due to the very dry conditions and low water availability the environmental flow was cancelled.’’
Water for this spring’s environmental flow will peak at 5.5Gl/day and is due to be released from Goulburn Weir from November 15.
The increased flows will take about four days to reach McCoys Bridge near the Murray River with rivers to gradually rise to about 2.9m at Murchison, 4.1m at Shepparton and 3.8m at McCoys Bridge before slowly returning to current levels (0.8m at Murchison, 2.8m at Shepparton and 1.5m at McCoys Bridge) by late November.
These increases in river flow and height will be well below minor flood level.
In the event of heavy rain, the timing and size of the environmental flow could change or not go ahead at all.
The environmental flows will also act as a trigger for other native fish to move, breed and find shelter; provide increased shelter for water bugs; and improve water quality.
‘‘This all helps crayfish, shrimps, water bugs and native fish continue to recover after the naturally occurring blackwater event that happened earlier this year after a summer storm,’’ Mr Casanelia said.
‘‘Irrigators appreciate better water quality too and of course, now the weather has warmed up, more people will be out and about on and by the river boating, fishing, bushwalking and birdwatching.’’
Based on recent water trades from Waterpool Co-Op which valued a megalitre of water about $100, the cost of the water used in the environmental flow is more than $3million on the temporary water market in the Goulburn system.