RIVER managers have fish on their mind at Menindee Lakes and downstream along the Lower Darling.
They are slowing the rate of release from Far Western NSW’s water storage system to give Murray cod a boost as breeding season - typically from October to December - heats up.
The Murray Darling Basin Authority (MDBA) made a splash last month when it announced a rapid water release from Menindee Lakes, destined for South Australia.
The lake system serves as Broken Hill’s drinking supply and a storage for downstream farmers.
Shooting water south at a rapid rate minimises evaporation from the scorching sun on Menindee’s relatively shallow waters. That’s good news in terms of maximising water deliver into SA, but locals are worried draining the lakes sets the Lower Darling up for a damaging dry run.
In early October Menindee held 643 gigalitres, or 37 per cent of its capacity. At that level the MDBA controls the floodgates.
Basin Plan Rules give the MDBA control of releases until the storage level falls below 480GL, which is the trigger for control to revert to NSW management. This is designed to enable the MDBA to utilise Menindee as a delivery system to SA, while NSW retains control over the lakes’ function as a critical water storage for Broken Hill.
IN announcing the water release, the MDBA said the flow rate from Menindee would peak at 1800 megalitres a day and remain high until early November, when the storage was expected to dip below 480GL and to NSW’s control.
But today a mutual agreement was announced by the MDBA, WaterNSW and the Commonwealth Environmental Water Holder (the CEWH - an agency which manages a portfolio of water entitlements to be deployed for natural assets like wetlands and floodplains).
A new flow regime would reduce flows to 700ML/day so the release event last longer, giving the the cod more time to get busy with breeding. The catch is slower for longer means more evaporation.
In return for the fish fillip CEWH will chip in with entitlements from the Murray Valley to make up for the losses.
Recent scientific work identified the stretch of river as a key nursery that spawns cod to spread right across the Southern Basin.
Local fish ecologist Clayton Sharp said the new river management regime would capitalise on a particularly successful deployment of 100 gigaltires of environment water down the Lower Darling in 2016, which spurred the best breeding event in 20 years.
“The modified flow pattern of operational water currently being delivered aims to support both the spawning of Murray cod this year, by removing overt flow variability, and the growth of Murray cod and golden perch produced last year” Mr Sharp said.
WaterNSW has staged the release so the majority of water remaining after the 480GL trigger is tripped sits in Menindee’s upper lakes for future needs.