WaterNSW has predicted that 400 to 600 gigalitres will arrive in Menindee following the recent floods and heavy rain in southern Queensland and northern NSW.
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The latest update, released on Wednesday, said 650 to 850GL was expected to hit Bourke, with inflows already amounting to 155GL, while 450 to 650GL is estimated to reach Wilcannia.
It is an increase to last week's predictions (300 to 400GL at Menindee), because higher than forecast inflows have been observed from the floodplains upstream of Walgett.
The inflows are expected from the Border, Gwydir and Namoi catchments and QLD tributaries, the Culgoa and the Moonie.
The update said as channel capacity constraints in the Border and Gwydir systems resulted in water breaking out onto the floodplains, it was difficult to estimate how much of that water will return to the Barwon-Darling.
"WaterNSW has included an estimate of floodplain drainage based on historical events but the drainage has a high variation," it said.
Then once the water makes it to the Barwon-Darling they warned further overbank flows to the floodplain could occur.
"A significant volume of water can be lost between Walgett and Boorooma and downstream of Bourke," it said.
Menindee locals are hopeful there will be enough water to fill Lake Menindee for the first time since 2016.
However, although NSW Water Minister Melinda Pavey has indicated that while the two top Lakes, Pamamaroo and Wetherell, were expected to fill, she said "the decision on how to manage any water above that which is required to fill these upper lakes will depend on a range of factors including the total volume likely to reach the Lakes."
"Given the amount of water on the floodplain, providing an accurate forecast into Menindee is difficult at this stage," Mrs Pavey continued.
"Over the coming weeks NSW will be making decisions on how to manage the inflows into the Menindee system with the first objective being to improve water supplies for the Lower Darling communities and ensure the top two Lakes are filled.
"The size of the inflows will ultimately decide whether water is diverted into Lake Menindee or passed through the Lakes system to count towards NSW Murray general security allocations."
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