Murray-Darling Basin water resources interim inspector-general Mick Keelty has told a Senate committee that 375 Gl of water is under-used in the southern basin.
Mr Keelty spoke to the Multi-Jurisdictional Management and Execution of the Murray-Darling Basin Plan hearing on May 12 to discuss his recent inquiry into management of Murray-Darling Basin water resources.
The third recommendation from that inquiry was Mr Keelty would ask the Murray-Darling Basin Authority to look more carefully at the under-use of water.
“I had a group come and see me and they presented to me ... a set of facts that pointed to an amount of water that's under-used in the quantity of about 900 Gl,” Mr Keelty told the committee.
“I was quite taken by their presentation and so I asked them to get more data and more information and meet me in Melbourne with more people from my team.
“I asked them to present those findings to the Murray-Darling Basin Authority and see if we can't reconcile what the authority was telling us with what they were telling us.
“They were educated people who delivered a very unemotive argument as to how the calculations that were being put forward by the Murray-Darling Basin Authority and others were incorrect.
“We ended up with a figure of 50 Gl of water under-used per year for the last seven years, which amounts to, obviously, 350 Gl.
“So I had 350 Gl in my mind as being the amount of water that was under-used.
“I've sent my officers over to get a thorough briefing on just exactly what this quantity is because, going back to the demonstration here at Parliament House, those southern irrigators were looking for in the order of 200 Gl of water, which would have, I think, met their demands for the upcoming season.
“We now understand, having worked with the Murray-Darling Basin Authority over the course of the last fortnight (fortnight before May 12), that the figure is much closer to around 375 Gl per year — not over seven years but per year.”
The group that Mr Keelty met with was consultancy firm RMCG, whose founding consultant Rob Rendell said the under-use could be caused by several reasons.
“The rice industry got RMCG to look at this (MDBA) data as they were concerned that irrigators weren’t getting their share,” Mr Rendell said.
“The accounting showed that the rice industry wasn’t using its share.
“However, irrigators were using every bit they have access to, except for carryover spill.”
Despite the reasons for the unused water still being investigated, Mr Rendell said the likely reasons were a combination of factors including increased spills due to carryover and a "whole stack" of policy changes.
MDBA Water Resource Planning and Accounting acting executive director Dr Peta Derham said a draft consultation report was under way into water use.
“At this stage, there may be some under-use by some water users who choose not to use all the water allocated to them in the irrigation year,” Dr Derham said.
“Some of this would be driven by user behaviour and state allocation policies.
“Over the past seven years (2012-19) there appears to be a trend of roughly 7 per cent under-use (or 375 Gl/year) across the Murrumbidgee, NSW and Victorian Murray and the Goulburn.
“There is no ‘spare’ water — the River Murray system is operated efficiently and any water that isn’t used is carried over or reallocated for use in the next irrigation year.
“The water accounting system for the sustainable diversion limit monitors water-use trends over the long-term.
“Importantly this is not the system used for allocations, water sharing between the states, or daily river operations."