Of all the 2500 km of river, the 8 km stretch next to the iconic Barmah Forest will attract an inordinate amount of scientific, stakeholder and political interest.
The debate is likely to be around management of the Barmah Choke, a narrow stretch of river which has a notional capacity of only 9000 Ml/day.
“While the total volume of irrigation water use in the whole system below the choke has remained relatively constant over the past 25 years, in total, more water is being delivered to the lower Murray to meet the combined irrigation and environmental water demand,” a recent report to the Murray-Darling Basin Association found.
“This was not the expected outcome of water recovery for the environment, irrigation use was expected to decline in proportion to the recovery, leaving the combined demand relatively unchanged.
“Irrigation water use over the peak summer period has been maintained by supplying high volumes from intervalley water trade accounts in the Goulburn and Murrumbidgee river systems. In some years environmental water is also released over this period.”
The MDBA says the choke is getting narrower, although the science is a little hazy.
The most recent report, from Water Technologies, said the capacity had reduced in recent decades, but also found "no evidence of a continuing decline in capacity".
River authorities and stakeholders interested in the river system are becoming increasingly concerned at the risk that water required downstream, for either irrigation or environmental needs, may not be able to be delivered at the optimum time.
This has been described as "delivery risk".
Basin governments have agreed to develop a feasibility study to understand options available to deliver water downstream of the Barmah Choke.
The MDBA says this study will include consideration of infrastructure options to bypass the Barmah Choke, but it does not imply that any such options will be pursued but is to inform policy choices for future management of the system.
The authority says the study is currently being initiated and is expected to take 12 to 18 months to complete.
Recently, the MDBA and basin states have jointly developed a paper exploring delivery risks and how they have changed over time.
This paper is now available on the MDBA website at: https://www.mdba.gov.au/publications/independent-reports/deliverability-risk-river-murray-system.
The paper concludes that the risk of shortfall in the Murray River downstream of the Barmah Choke is increasing and considers options for reducing or mitigating this risk.
The problem has been talked about for more than 10 years.
A 2009 report to the MDBA stated:
“The restricted ability to meet the demands of irrigators and other water users may result in rationing of peak demands in Torrumbarry and Sunraysia and restrictions on supply to South Australia.
“The restricted ability to manage high summer flows through the Barmah-Millewa Forest is leading to changes in forest vegetation communities, threatening Moira grass plains and red gums.
“These problems are likely to persist into the future, including under climate change conditions which are expected to lead to an increase in shortfalls, which may increase the frequency of demand rationing to Torrumbarry and Sunraysia and restrictions on supply to South Australia.”
The 2009 report identified a range of options to address the problem of the Barmah Choke, including:● Enlarging the storage capacity at Euston.
● Storage at ‘The Drop’ on the Mulwala Canal.
● Construction of a mid-river storage.
● Upgrade of existing bypass capacity options.
● A Bullatale Creek bypass.
● Victorian forest channel bypasses.
● An increased diversion through the Wakool River.
● Increased escape capacity to the Edward River.
● Increased escape capacity to the Broken Creek.
● A Barmah bypass channel.
● A Murray-Goulburn interconnector channel.
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