Darling River flood forecast: 500GL to reach Menindee

Moderate to major flooding is forecast along the Barwon River this week, as southern irrigators await news of just how much will reach the Menindee Lakes.

Much of the floodwater that swept across the NSW-Qld Border Rivers region and Gwydir Valley will be lost out on vast floodplains.

A BATTLE is looming between NSW Murray irrigators and the Menindee Lakes community in the wake of northern NSW and border rivers floodwater hitting the Barwon-Darling over the coming weeks.

Menindee local and community leader Graeme McCrabb said he was confident the Lake Menindee gates would be opened once again, allowing water to flow back across a lake bed that has been dry since late 2018, given early estimates that 500GL was on its way.

As it stands only two of the four Menindee Lakes – Wetherell and Pamamaroo – already hold almost 300GL, with the capacity to take another 310GL.

The dilemma for the NSW Government and Murray Darling Basin Authority is whether it puts excess water into the large shallow basin of Lake Menindee or lets it flow down the Lower Darling to be allocated to Murray irrigators.

Letting the water flow out onto the dry Menindee Lake bed would mean at least 100GL lost as dead storage, with past work by the NSW Office of Water showing a further 300-400GL would be lost to seepage and evaporation.

Alternately the water could be released down the Lower Darling to be stored in Lake Victoria to meet South Australia’s needs, leaving more water in the Murray and its tributaries to meet NSW Murray irrigators’ needs.

NSW Murray irrigators need every drop they can get to help repay 314GL they borrowed from the Barmah-Millewa Environmental Water Account over the past four years.

The NSW Department of Industry’s last allocation statement warned: “any further resource improvements this year must be assigned to the BMEWA until the borrow is fully repaid”.

In the meantime Northern NSW floodplain harvesters are reporting the past week’s rain has created a “two-flow event”.

Gwydir Valley Irrigators Association executive officer Zara Lowien said the region was first hit with 100-200mm that delivered rainfall runoff straight into irrigators’ on-farm storages, via their tail-water systems.

Ms Lowien said a second flow followed, via falls further up the catchment that reinforced the flood surge. But she warned much of the water would be lost as it hit the Gwydir raft, a natural choke in the system, that pushed the flow out onto the floodplain.

Water is still forecast to make its way down to the Barwon-Darling system, via the Gwydir Valleys northern Carole and Gil Gil Creeks, but Ms Lowien said it was virtually impossible at this stage to estimate the volume, due to water bypassing gauges as it spread out onto the floodplain.

Further north McIntyre River irrigator Brendan Griffiths said the floodwaters stretched 60km south of his place, all the way to the Gwydir Valley.

“The flood peaked on Saturday morning at about 20cm below the 2011 (flood) event,” Mr Griffiths said.

Now that the peak has passed the Border Rivers Food and Fibre NSW vice-chairman and university lecturer said he harvested about 1400 megalitres, about twice his annual licence volume, which is allowed under NSW floodplain harvesting framework that accounts for the ephemeral nature of the northern rivers.

“It’s times like these you realise the amount of water that could be extracted is so insignificant that it would hardly register (compared to the total),” Mr Griffiths said.

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