The Murray-Darling Basin Authority released its Constraints Relaxation Implementation Roadmap to guide governments in delivering projects that will maximise outcomes from environmental water use across the basin.
The issue has been a controversial one, as landholders were fearing that a relaxation of constraints would lead to over-bank flows which would flood their properties.
The MDBA suggests that consultation with the community include a focus on the following for the Goulburn River:
- Goulburn below Eildon: Exploring what benefits can be achieved by flows up to 12,000 Ml/day with infrastructure built to higher rates (such as about 14,000 Ml/day) to incorporate adequate freeboard. (Freeboard is the height above the base flood elevation used to determine the level at which a structure's lowest floor must be elevated or flood-proofed.)
- Goulburn River below Goulburn Weir: Exploring what benefits can be achieved by flows up to 21,000 Ml/day with infrastructure built to 25,000 Ml/day to incorporate adequate freeboard.
For the Murray River, the MDBA report suggested discussions around the following:
- Hume Dam to Yarrawonga: Exploring what benefits can be achieved within existing flow easements (25,000 Ml/day) and up to 30,000 Ml/day.
- Yarrawonga to Wakool: Exploring what benefits can be achieved by flows between 30,000 and 35,000 Ml/day with infrastructure built to higher rates to incorporate adequate freeboard.
The report also suggests a new, independent panel be established to advance discussions on constraints.
“The panel arrangements offer a bipartisan approach that ensures we have the right skills to work with community,” the MDBA report said.
“The panel would ultimately provide advice to the joint governments on the best approach to move forward Murray and Goulburn systems including flow rates and other information that could support a joint business case.”
The panel would initially be time-bound, focused on connecting with communities and First Nations peoples to test flow rate options and mitigations and associated benefits and costs under a climate future.
The panel would need support of the NSW, Victoria, South Australia and federal governments, and would provide advice to governments on preferred flow rates by the end of 2026.
Federal opposition water spokesperson Perin Davey said the report acknowledged that many of the flow targets contained in the original Murray-Darling Basin Plan were too high in a managed flow scenario.
Senator Davey said the MDBA still hadn’t gone back to adjust the original models to reflect that.
“We are still in a race against time to deliver a basin plan that was predicated on flow targets they now accept they cannot achieve.”
Senator Davey said the state water ministers must work together to determine a methodology to recognise constraints offsets as recommended by the roadmap.
What the science says
According to the MDBA, constraints relaxation would result in:
- Significantly greater extents of wetland inundation — for the Murray River (Hume Dam to Wentworth), there could be up to 97 per cent increase in the area of wetlands inundated and nearly two-thirds of floodplain wetland habitats could be inundated in the mid-Murrumbidgee.
- Up to 294 per cent increase in the area of native vegetation that can be reached by environmental flows in the Murray (Hume Dam to Wentworth).
- A 114 per cent increase in river red gum forests and woodlands remaining healthy during drier years in the Murrumbidgee.
- An increase in long-term average golden perch populations by up to 29 per cent, and minimum populations by up to 45 per cent during dry periods in the Murray River (Hume Dam to Wentworth).
- The inundation of two-and-a-half times more water-dependent vegetation communities in the Goulburn.
- A 572 per cent increase in area of river red gum in good or moderate condition in the Goulburn, subsequently protecting 6000ha of the species.
- Improvements to in-stream productivity with increasing level of constraints relaxation.
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