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Adjustment to sustainable diversion limits

Please be aware the proposed northern Basin amendments, including the groundwater and minor practical changes, have been disallowed.  For more information read the media release.

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

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.

Sustainable diversion limit adjustment determination

The MDBA has determined the same Basin Plan environmental outcomes can be reached with less water meaning there will be 605 gigalitres (GL) additional water available for communities through the Adjustment Mechanism and the package of supply projects, if the recommendation is adopted in Parliament.

In October 2017, the MDBA determined that a further 605 gigalitres (GL) of water, on average, would be available for consumptive use, if the suite of projects proposed by Basin state governments through the Adjustment Mechanism were implemented. Additional water for the environment would also be available through the efficiency projects, which will operate across the Basin through to 2024, subject to these projects having neutral social and economic impacts.

The Sustainable Diversion Limit Adjustment Mechanism: draft determination report outlines the MDBA’s recommended adjustment across the southern Basin and also at a catchment level.

The draft determination report also provides an overview of the Adjustment Mechanism and its role in the Basin Plan, the methodology developed to assess projects and a description of each of the projects nominated by Basin state governments.

Adjusting the Sustainable Diversion Limit

The Adjustment Mechanism works in two parts – the package of supply projects aims to achieve the equivalent environmental outcomes that 605 GL of water would achieve. Efficiency projects are real water savings for the environment, made through improving water delivery systems, including on-farm infrastructure.

The Basin Plan limits the amount that Sustainable Diversion Limits can be adjusted. The Basin-wide Sustainable Diversion Limit is 10,873 GL and this can be adjusted up or down by 5 per cent (approx. 543 GL).  The assessment of supply projects has determined the Sustainable Diversion Limit can be adjusted up, so that 605 GL of water can remain available for communities. To ensure this water remains available for communities, a minimum of 62 GL of additional water savings through efficiency projects is required to pass the 5 per cent rule. The Sustainable Diversion Limit program also requires efficiency measures to be progressively developed until 2024. 

Public feedback

The MDBA sought feedback from the public on the Sustainable Diversion Limit Draft Determination from 3 October to 3 November 2017. Throughout this period, 3185 submissions were received. In September and October 2017 there were 29 public information sessions held, with over 700 people across the Basin attending one of these sessions. The MDBA welcomed this substantial contribution and recognises the feedback will be important in designing, implementing and evaluating supply projects. 

The MDBA’s Summary of Feedback report outlines comments from both the face-to-face sessions and written submissions received, as well as recommendations for the design and implementation of the projects. Individual feedback can be viewed through the MDBA submissions platform. This feedback has been used to make a recommendation to the Commonwealth Minister responsible for Water and will also inform the next stages of design, implementation and evaluation of the projects.

Revisions to the Draft Determination

No new information or evidence was put forward during the public comment period to change the MDBA’s conclusion on the determination of the adjustment volume.

In the MDBA’s Draft Determination, the 5 per cent limit on the proposed adjustment was considered to be 544 GL. To remain in line with the 5 per cent limit outlined in the Basin Plan, the determination included a revision of 543 GL. The 5 per cent rule is explained in detail in the Summary of Feedback report.

Next steps

The adjustment to sustainable diversion limits passed the Senate in May 2018. This is just the start of the process. Basin state governments have until 2024 to work with communities, industries and engineers to further design and complete projects. View the list of projects.

The MDBA has made a number of recommendations, including ongoing consultation and engagement from all Basin governments over the coming years. Basin state governments are committed to meaningful consultation with communities and experts in the design and implementation of projects, to ensure local and project-specific concerns and issues are considered throughout this process.

The MDBA will play a key role in monitoring the integrity of the Sustainable Diversion Limit Adjustment Mechanism and the package of projects. To achieve this the MDBA will establish transparent regular reporting processes to communicate with Basin governments and communities on the progress of individual projects, and on the package of projects as a whole.



Key documents

Sustainable Diversion Limit Adjustment Mechanism - Draft Determination

The MDBA has assessed a suite of projects to determine an adjustment to the Sustainable Diversion Limits. The following report outlines how the MDBA has administered the assessment framework, designed in collaboration with Basin governments, to assess the state projects and calculate how much water these projects will contribute towards any change in SDLs.

Benchmark conditions of development for assessment of the SDL supply contribution

The Benchmark outlines a model of a fully implemented Basin Plan. The report describes how changes were included into the Basin Plan Benchmark scenario to produce the Sustainable Diversion Limit Benchmark scenario. This represents the implementation of the Basin Plan to achieve 2750 GL of water recovery for the environment. This model was agreed to by all Basin governments.

Modelling assessment to determine SDL Adjustment Volume

The Modelling Assessment report describes the implementation of the supply measures package in the modelling framework. The report explains how the model represents and assesses the supply measures to achieve maximum supply contribution. The report lists the results of three equivalence tests (ecological elements score tests, limits of change in environmental outcomes, and reliability of supply targets) to compare environmental outcomes and reliability of the Sustainable Diversion Limit Adjustment scenario to the Sustainable Diversion Limit Benchmark scenario. 

Independent Review of Hydrologic Modelling for SDL Adjustment (by Bewsher Consulting)

The Independent Audit of Modelling report details the findings of the independent review of the Sustainable Diversion Limit Benchmark and Adjustment scenarios. It gives a detailed evaluation of the modelling framework, outlining the methodology and criteria used to assess the Sustainable Diversion Limit Benchmark and Adjustment scenarios. The independent audit lists a number of suggested improvements to ensure the modelling framework is an appropriate representation of the system and remains fit for purpose. 

Independent Expert Panel Murray–Darling Basin Plan SDL Limits of Change Review

Prior to the Sustainable Diversion Limit adjustment determination, early MDBA modelling indicated the potential for a number of limits of change rules to breach. The MDBA commissioned an expert review panel to undertake an independent ecological analysis of the potential breaches likely to occur across several possible Sustainable Diversion Limit adjustment model runs. This report outlines the independent expert panel's assessment.

The SDL adjustment assessment framework for supply measures

The MDBA has developed and trialled the way the assessment framework will assess projects under the Basin Plan's Sustainable Diversion Limits Adjustment Mechanism in 2016. The framework brochure explains the key concepts, how the Sustainable Diversion Limit Adjustment Mechanism assessment works, and results from trialling the method using just seven of the supply projects submitted by Basin state governments in 2016 for the purpose. The framework includes the use of an independently-developed (by the CSIRO), scientifically-robust scoring method (test) for environmental equivalence. An Independent Review Panel has found the framework and test to be fit-for-purpose.

Advice from the Basin Officials Committee

The Basin Officials Committee has reviewed the draft determination and provided its advice to the MDBA on the proposed adjustment to Sustainable Diversion Limits. This includes advice from the New South Wales, Victorian and South Australian governments.