The River Murray mouth will be open at least 90 per cent of the time if the Murray-Darling Basin Plan is passed in its original form, but Australia could lose $805 million a year in agricultural production and 800 jobs.
The Murray-Darling Basin Authority released a guide to its controversial plan, stressing it is not “a done deal”.
The independent authority charged with restoring balance to Australia’s food bowl went with the lower end of the range that its modelling determined was needed to return environmental health.
The clawback of 27 to 37 per cent of water amounts to an additional 3000 to 4000 gigalitres of surface water annually.
The federal government has committed to buying back the water needed to meet the target, which could cost more than $3 billion.
The authority estimates the gap, based on water purchased by state and commonwealth governments to June 30, at 2295 to 3295 gigalitres.
But its chair Mike Taylor said there were other ways to hit the mark. “Purchasing water is obviously a key issue and the commonwealth government has been doing that,” he told reporters in Canberra.
“The commonwealth government has also been funding (efficiency) works and measures and they are another means by which that volume might be reduced.”
The plan in its current form would send a long-term average flow of up to 7700 gigalitres through the Murray mouth – compared to the 5100 gigalitres expected now.
The mouth would be open between 90 and 92 per cent of the time, compared to 64 per cent under current arrangements.
Declining populations of water birds would stabilise, river red gums would be healthier, as would native fish like the Murray Cod.
To protect bodies of groundwater in the basin, an additional 99 to 227 gigalitres would be withheld. But the guide says the cutbacks would reduce irrigated agriculture by $805 million annually, and admits the true impact is hard to predict.
“The effect in the short term may be greater than this due to the flow-on effects on other parts of the basin economy,” it says. It amounts to about 13 per cent of current irrigated production, or a 1.1 per cent reduction in the long term.
About 800 full-time jobs were expected to be lost. The authority wants further work to understand the likely size of the effects, but notes the rice and cereal industries will be worst hit.
The regions expected to have the worst economic impacts were the Murrumbidgee in the southern basin, and the Moonie and Gwydir in the northern basin.
It was for this reason, the authority said, that it examined the 3000 to 4000 gigalitre target range, as this was at the lowest end of the scale that would meet the environmental needs.
The uppermost target range, a 7100 to 7700 gigalitre cutback, would have provided certain environmental outcomes all of the time.
But Mr Taylor said the social and economic impacts would be “beyond management”.
The proposed basin plan will be released later in 2010 or early in 2011, the guide says, with consultation before and after.