Environmental flow targets set under the Murray-Darling Basin Plan have not been achieved, according to a new report.
The Wentworth Group of Concerned Scientists report, which analysed flows for the northern and southern basin individually, found that ‘‘excluding natural flood events, annual average flows can be up to 40 per cent to 50 per cent smaller than expected under the basin plan’’.
The Murray-Darling Basin Authority acknowledged the report contained ‘‘useful pieces of analysis’’ but said it could not be expected that flows would fully reflect basin plan modelling just six years into the plan.
‘‘This is because eight years’ worth of measurement, in the context of a highly variable climate, is not long enough to draw statistically significant conclusions in comparison to basin plan modelling that used 114 years of data,’’ the authority said.
‘‘The MDBA agrees with the Wentworth group’s assessment that full implementation of the basin plan is necessary to achieve the environmental goals.’’
The Wentworth group’s report was critical of the MDBA’s modelling, stating that the models had not been updated in a decade and had failed to be released publicly. The group said the basin plan figure for the amount of water that needed to be returned, per year, to achieve an environmentally sustainable level of take, should be ‘‘well above 4000Gl’’.
There was also concern in the report that the effectiveness of water recovered for the environment had not been measured to ensure best outcomes.
The MDBA said the basin plan was now moving into its next stage.
‘‘Most of the water that needs to be recovered to return the system to a sustainable footing has been achieved and now changes to the rules about how water is managed are needed,’’ its statement said.
‘‘In the southern basin, that means working with the states to overcome constraints or barriers to water delivery.’’
The report found that to match the amount of water in the basin plan modelling, an additional 129Gl of water would need to be recovered for the environment.
‘‘The observed results are compared to MDBA-modelled outcomes and are likely to be far less than expected if compared to the original basin plan water recovery target of 3200Gl,’’ the Wentworth report concluded.