The Murray Darling Basin Authority (MDBA) is proposing a major amendment to the Murray Darling Basin Plan based on its Northern Basin Review, conducted over four years. The amendment would reduce the water recovery targets for the Northern Basin from 390 GL to 320 GL per year, a reduction of 70 GL.
This 70 GL reduction will impact how much water is available for downstream users and the environment in South Australia and also Menindee Lakes and the Lower Darling River, the source of Broken Hill’s drinking water. Estimates of how large this impact will be have been changed many times, but the justification for these changes is unclear.
Initial versions of the Northern Basin Review estimated the impact on Menindee Lakes and South Australia at 35 GL and 20 GL respectively. Such a large impact on South Australia was rejected by the South Australian Water Minister. The estimated impacts revised down to under 10 GL just days later, even though the Northern Basin Review had taken four years to complete.
After spending four years on better science, MDBA changed the end of system numbers several times in the final weeks of the Northern Basin Review and again in the months following. The reasons for these changes and the working behind them are unclear and aren’t publicly available. Importantly, there are no differences in other numbers published by the MDBA, which might justify the reduced impacts on the end of system flows. Whilst the impacts on South Australia were claimed to be reduced, no upstream data was changed. Without clarification, they appear to be changed to avoid objections from South Australia. The reasoning and working behind the changes should be fully transparent to give all stakeholders confidence in the work of the MDBA and the process of the Basin Plan.
The amendments to change the Sustainable Diversion Limit (SDL) for the Northern Basin are currently the subject of a disallowance motion in the Australian Senate. Given the importance of this issue for the Basin Plan and the lack of transparency around the impacts on downstream stakeholders, the amendments to the Basin Plan should be disallowed by the Senate in its current form.