The commissioner heading South Australia’s royal commission into the Murray-Darling Basin plan, Bret Walker SC, has repeatedly questioned whether the Murray Darling Basin Authority relied on the best available science.

Hearing evidence today from the Wentworth Group of Concerned Scientists, a group that includes some of Australia’s most eminent environmental scientists, Walker quizzed the group on the twin themes of whether the MDBA was fulfilling its obligations under the Water Act and whether it was relying on the best available science.

“The MDBA has issued a series of press releases saying their findings are based on the best available science. None of them condescends to particulars,” Walker noted.



The MDBA and the federal government have refused to participate in the royal commission and banned staff from cooperating with the state-based inquiry.

The issue of whether South Australia can compel federal bureaucrats to give evidence is now before the high court. It is expected to be heard in September or October.



The Wentworth group has warned that without major changes in implementation, “it is almost certain that the basin plan will fail”.

It accused the MDBA of “deliberate misuse and neglect of scientific evidence in decision making to justify a predetermined political outcome”.

It has also pointed to “secretive agreements between the commonwealth and state agencies” and a failure of the commonwealth to intervene when states failed to fulfil their duties under the plan.

“Managing rivers without a sustainable rivers audit is like trying to manage the budget without the national accounts,” said Peter Crosier, a member of the Wentworth Group.

Walker homed in on the scientific basis for the 2017 revisions to the plan passed by parliament in May and advocated by the MDBA.



Among other things, these changes will allow 605GL of the 2,750GL environmental water recovery target to be achieved through a series of projects said to improve the efficiency of water use in the environment as an alternative to buying back water from farmers.

The weir at Menindee Lakes. Photograph: Mike Bowers/The Guardian

According to the Wentworth group, only one of the 36 so-called “sustainable diversion limit adjustment projects” submitted by the states meets all the MDBA’s own criteria. In most cases there is insufficient information or scientific modelling to assess them.

“Our assessment showed that the majority of projects were not of sufficient quality to deliver basin plan outcomes equivalent to 605GL of water,” the Wentworth Group said in its submission.



The MDBA’s own analysis of the New South Wales government’s plan to reduce evaporation in the Menindee Lakes by changing their configuration, released to the Senate, found it lacked crucial scientific studies required to assess it.

Walker noted that the MDBA had essentially approved the projects even though it had concluded that the promised environmental outcomes “can be achieved with high degree of uncertainty”.



He repeatedly asked the scientists what this meant.

“I think when one looks at it, they are saying: ‘We don’t think it will be achieved’. I don’t understand how an administrator can then make decisions in favour of the projects,” he said. “I find it puzzling. I find it alarming as an administrative lawyer.”

The Wentworth Group stressed that the plan had made progress on improving the Murray-Darling Basin but that progress had stalled in recent years.

Associate prof Jamie Pittock said the plan’s failure to take account of climate change was particularly concerning.

“In a dry year the risk is borne by the environment. There was a proposal that this would be shared 50-50 by the environment and water users but this was dropped by basin authority. It has said this would be dealt with in future revisions,” Pittock said.

Walker has urged the MDBA to participate in his inquiry.

“I will have to draw a conclusion on the fitness of the MDBA to administer the plan, just as I will have to draw a conclusion on the fitness of the plan to fulfil the objectives of the act,” he warned.