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Return flows: Independent review

Concerns have been raised that recent increases in groundwater sustainable diversion limits and irrigation efficiency projects may lead to significant reductions in river flow and offset the benefits of surface water recovery for the environment.

The Murray–Darling Basin Authority (MDBA) commissioned an independent review by eminent hydrology experts of the risks posed by reduced return flows. As part of the project, the MDBA’s Advisory Committee on Social, Economic and Environmental Sciences (ACSEES) convened a workshop to review the technical aspects of the independent review. The workshop was hosted by Professor Mike Stewardson of the University of Melbourne. 

The independent review sought to answer the following questions:

  1. Is it likely that the Basin Plan groundwater sustainable diversion limits will have a material impact on river flow volume?
  2. Is it likely that irrigation efficiency projects, carried out to achieve Basin Plan environmental water recovery targets, will have a material impact on return flow to rivers?

The review found that generally we’re on track. The scope for future reductions in surface water return flows is relatively small, and many of the ways that surface water re-enters the system are already accounted for in the Basin Plan water accounts. It is more difficult to precisely quantify groundwater impacts, however much less water is taken directly from groundwater systems than is allowed under the Basin Plan. The risk that future growth in groundwater use poses to surface water flows was found to be relatively small, and would take many years or decades to have an effect.

The review has found:

  • reduced return flows are not undermining the outcomes that can be achieved through the Murray–Darling Basin Plan
  • we need to continue to monitor and improve our understanding of return flows so that we can reduce the uncertainty of the estimates.

This review is not the end of the process—the MDBA will continue to incorporate new science into the management of the Basin’s water resources, through the Basin Plan.

    This work is another example of the MDBA’s commitment to be open and transparent about the science and analysis that informs our decisions.

    More information


    Independent review: Potential impacts of groundwater sustainable diversion limits and irrigation efficiency projects on river flow volume under the Murray–Darling Basin Plan
    Updated: 14 Oct 2020  •   Independent reports