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Published: 23 July 2019   •   Opinion pieces

Complex modelling is a pillar of Basin Plan development and the community justifiably expects that the models used are the best they can be.

The model for the Victorian and New South Wales Murray Systems, the Lower Darling River and the South Australian Murray, together known as the Source Murray Model, has been calibrated and tested for a range of uses and scenarios over the years.

In the past couple of years we commissioned two independent reviews of the Source Murray Model. Given it was developed by the MDBA, an impartial review process was essential.

Professor Tony Jakeman et al from the Fenner School of Environment and Society at the Australian National University in 2018 and Bewsher Consulting in 2017 were asked to assess whether the model gave us the necessary capability to determine baseline diversion limits and to calculate the annual permitted take of water each year. These factors are fundamental to the Basin Plan's implementation.

While some improvements were recommended, the reviews concluded that the model represents a significant advance in the understanding of the Murray and Lower Darling systems and is fit for the Basin Plan's purposes.

Both reviews concluded that ongoing collaboration between the MDBA and state governments provided confidence that the model accurately reflects water sharing arrangements. At a more granular level it can show water sharing between states, allocation by the states to entitlement holders, the operation of dams and delivery of water to meet forecast demands. All this adds up to increased assurance that we can manage the system and monitor Basin Plan settings.

The model's reliance on 114-year climate data, which captures significant flood and drought experience, assists robust policy analysis. There's no doubt however that the impact of climate change is placing additional pressure on water resources in the Basin and is the focus of a new work program the MDBA is developing for the 2026 Basin Plan review.

It's for reasons like this that we must continually update and improve the model and maintain our flexibility to take on new data and new understanding to improve the scope, timeliness and accuracy of our analysis. There is also work to do to build the model's usability, supported by rigorous documentation and practice notes.

The Water Act required the MDBA to build an integrated water model for the Basin that would consider all aspects of water management and support the development and implementation of the Basin Plan. There was also a need to bring consistency to modelling, which led to a COAG-driven initiative to introduce daily time-step software. The Source Modelling System was the result and is now being rolled out to the Murray–Darling river systems by state governments and the MDBA.

In the interests of transparency, we've published the two reviews along with other Source model reports on the MDBA's website so you can read what they have to say about our processes.

Often considered as 'behind the scenes' work, our approach to modelling will remain collaborative and transparent to give water users and the community confidence that the best possible information is supporting the careful management of our precious water resources.


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