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Sustainable diversion limit adjustment mechanism

The Basin Plan sets sustainable diversion limits, which is how much water can be used in the Murray–Darling Basin, while leaving enough water to sustain natural ecosystems.

To provide flexibility, the Basin Plan includes a mechanism to adjust sustainable diversion limits. The mechanism requires a suite of projects to be implemented – some projects allow Basin Plan environmental outcomes to be achieved with less water. This means that more water can remain in the system for other users, including households, industry and irrigated agriculture. Other projects improve water use so it's more efficient.

The Basin Plan limits the amount that sustainable diversion limits can be adjusted. The adjustment mechanism means the limit can only be adjusted up or down by a maximum of 5% (approximately 543 gigalitres (GL)).

The sustainable diversion limit adjustment mechanism

View a short video on what it is and how it works.

The adjustment mechanism works in 2 parts:

  • Supply projects, which include some constraint projects, aim to improve water infrastructure and river operating rules.
  • There are also efficiency projects, which improve water delivery systems, including urban and on-farm infrastructure.

How the adjustment to sustainable diversion limits is determined

The Basin Plan includes a default method that the Murray–Darling Basin Authority (MDBA) must apply to assess how much water is being saved through the Sustainable Diversion Limit Adjustment Mechanism supply projects. This assessment framework has been used to calculate and recommend a new sustainable diversion limit.  If agreed by both Basin Government and the MDBA, an alternative method can be used.

The default method was used to calculate and recommend a new sustainable diversion limit in 2017.

The method is complex and includes components such as: 

  • computer (hydrological) models
  • hydrological indicator sites
  • limits on hydrological change 
  • ecological equivalence scoring.

The method compares project outcomes with the Basin Plan and applies tests during the comparison, to ensure the equivalent environmental outcomes of the Basin Plan are achieved.

During its development, the  method was trialled and thoroughly reviewed by independent experts and found to be scientifically rigorous and fit for purpose. 

Basin governments were also extensively involved in the development of the method and the Basin Officials Committee agreed it was fit for purpose to undertake the determination in 2017.

In undertaking the determination in 2017, the MDBA  received independent expert advice which noted that the modelling process and application of the assessment framework was technically sound.

Sustainable adjustment mechanism timing

Sustainable adjustment mechanism timing timeline from 2017 to 2024

Date Stage of process
  • Basin governments nominated supply projects – 30 June 2017
  • The MDBA completed assessment of proposed package and developed the final sustainable diversion limit adjustment amounts – July 2017
  • Sustainable diversion limit adjustment released for public consultation – October 2017
  • Proposed adjustment to the sustainable diversion limit tabled in Federal Parliament
  • The adjustment to sustainable diversion limits was passed by both houses
  • Basin governments will consult with communities on the design and implementation of the projects
2020 to 2024
  • Approved projects are progressively implemented by 30 June 2024
  • The MDBA will undertake a reconciliation process and determine revised sustainable adjustment limit amounts if required
Updated: 22 Nov 2022