A new report on a key mechanism used by the Murray-Darling Basin Authority to determine how much water can be taken out of the basin is critical of a model used to determine the diversions.
The report by an expert panel was commissioned by the NSW and Victorian governments in February but was kept under wraps until this week.
State Member for Shepparton Suzanna Sheed has been pressing the government for its release over the past month.
The report found that the benchmark model, used in developing sustainable diversion limits, has flaws.
‘‘The (basin) plan describes the development of an agreed benchmark model,’’ the report said.
‘‘Whilst developed in preliminary draft form, the benchmark model has not been agreed, finalised and published.
‘‘The inability to reach agreement on the benchmark parameters and publish a report has contributed to continuing uncertainty in relation to some important model assumptions.
‘‘Without a clear baseline in the form of an agreed benchmark, the subsequent calculation of the supply contribution is contested and will continue to limit the ability to assess the supply contribution associated with a suite of supply measures,’’ the report said.
On the overall Murray Darling Basin Plan, the report found there is currently a wide and fragmented range of monitoring, evaluation and reporting conducted by many parties across the basin.
‘‘Existing approaches, while largely necessary in their own right, do not provide clarity on the performance of the system as a whole and aer not building confidence for all stakeholders.
As a result, it is unclear whether the objective of the plan is being met, namely to optimise social, economic and environmental outcomes.’’
The report is likely to reinforce concerns held by the two of the basin states, NSW and Victoria, over the process used to determine what water has to be given up by agriculture from the basin.
‘‘We called for the review to provide us with greater confidence in the modelling being used by the Murray-Darling Basin Authority to assess these projects,’’ Victorian Water Minister Lisa Neville said.nf
‘‘We wanted to ensure these projects could deliver the water savings necessary to achieve the critical environmental outcomes and ensure further productive water did not need to be purchased out of the system,’’ Ms Neville said.
The independent report found the uncertainty over the benchmark model had led to an ‘‘erosion of trust and confidence in the process and a low level of confidence in the modelled supply contribution’’.
The panel comprised former Murray-Darling Basin Commission chief executive Don Blackmore, Brett Tucker, Chris Arnott and Professor Peter Davies.