Why are rivers running high in drought?

The MDBA explains why they ran the Murray high last summer

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A map of water's journey from Hume Dam to Lake Victoria. The MDBA said the Murray ran high in summer because less natural inflows meant more water had to travel from Hume to make the South Australian allocation in time.

A map of water's journey from Hume Dam to Lake Victoria. The MDBA said the Murray ran high in summer because less natural inflows meant more water had to travel from Hume to make the South Australian allocation in time.

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Little natural inflows caused the MDBA to turn on the tap for SA.

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Common sense would conclude that rivers run low during droughts, but last summer after well below average rains the Murray river was higher than many had seen it in some time.

The Murray Darling Basin Authority explained the reason was because it had to get more water than usual from Hume dam in the east of NSW, to Lake Victoria near the South Australian border.

The Murray Darling Basin Agreement dictates that if available 1850 gigalitres must be delivered to South Australia each year.

MDBA River Murray Operations senior director Jacqui Hickey, explained to irrigators at a recent drought consultation in Deniliquin, that last winter and early spring they waited to send large volumes of water from Hume to Lake Victoria (for South Australia) as they were holding out hope for natural inflows.

Murray water losses questioned at Deniliquin forum

"The tributaries, like the Ovens and the Lower Goulburn, typically get some good rain events and they run," Ms Hickey said.

"A flow out of the Ovens could easily fill Lake Victoria, but if we'd already released water from Hume Dam an inflow could cause a spill and would mean we've unnecessarily transferred water to Lake Victoria."

They also said MBDA did not want to keep water in Lake Victoria for too long as in hot, dry weather losses through evaporation would be significant.

But Ms Hickey said these factors were balanced with needing to push enough water through for South Australia ahead of peak summer because of restrictions through the choke and increased demand from water users downstream.

The MDBA said when the natural inflows it was hoping for did not arrive in time it had to turn on the tap as much as they could to get enough water from Hume to Lake Victoria to make the South Australian delivery in time, rising the level of the Murray through spring and early summer.

The MDBA said when natural inflows did not arrive they were forced to turn on the tap to get enough water to South Australia quickly.

The MDBA said when natural inflows did not arrive they were forced to turn on the tap to get enough water to South Australia quickly.

Irrigators at the public forum also questioned the MDBA releasing water in what they felt was an ad hoc manner during the 2016 floods.

Ms Hickey said it released water to protect the structure of the Hume and Yarrawonga dams.

"This is so we don't get unnecessary toppings that could put embankments at risk and the whole dam might fail," she said.

"Or we might do a bit of pre-release so that we can cut the top off the big peak of water when it comes through."

Ms Hickey said she was impressed by the questions asked by the irrigators at the Deniliquin meeting.

"I think as government we need to figure out better ways to inform the community so they're working off the facts rather than snippets of mistruths," Ms Hickey said.

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