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Shifting the Watermarks

By Tim Stubbs

The draft Murray-Darling Basin Plan is confused at best and deceptive at worst.

The latest draft Murray-Darling Basin Plan is part of a reform process that will cost taxpayers an estimated $8.9 billion to establish environmentally sustainable levels of take (ESLT) for the rivers of the Basin.

Currently it appears that the money will be spent but the outcome not delivered because the draft plan is a confusion of politics, opinion and misrepresentation. This is illustrated by one of the draft plan’s supporting documents in which the Murray-Darling Basin Authority (MDBA) states that “through considered judgement” it established “a range of sensible ESLT options for further and more robust analysis using the hydrologic models”.

The critical factor is how these “sensible ESLT” numbers were selected. The MDBA used three “studies” to guide its selection.

The first was an analysis undertaken in the Guide to the Basin Plan in 2010, a document released 13 months before the current draft plan. The analysis showed that raising the average annual end-of-system flows by 3856 GL would have a high uncertainty of achieving environmental objectives, while raising average flows by 6983 GL/y would have a low uncertainty of achieving those objectives.

However, for the purpose of selecting its “sensible ESLT options” the MDBA chose a range of 3000–4000GL/y because “reductions in current diversions above 4000 GL/y have been judged to be beyond the range of acceptable reductions”. This is a judgement, not the result of analysis.

The second source was preliminary and incomplete hydrologic modelling done by the MDBA. Its own reports conclude that the results are “considered to have a high level of uncertainty” and do not include environmental water requirements of the Coorong, Lower Lakes and Murray Mouth.

The third source was two Wentworth Group reports published in 2008 and 2010. The MDBA incorrectly used these reports to give a Wentworth Group range, but the 2010 report utilised new data that was unavailable in 2008 and thus superseded the earlier report. To compare the two is like saying that an economic analysis pre-GFC is the same as an analysis post-GFC.

Some crude averaging of these misrepresentations was the MDBA’s last step in its quest to find “sensible ESLT” numbers to model.

If you were starting to worry about the process for selecting “sensible ESLT” numbers, hold on to your seats as it gets even worse when groundwater is considered.

The three studies referenced in the table either do not include any groundwater analysis or assume a decrease in groundwater extraction in the Basin as recommended by CSIRO Sustainable Yields. However, the draft Basin Plan recommends increasing groundwater extractions by 2 600 GL/y.

So it appears that those “sensible ESLT” numbers have been justified using studies (misrepresented in at least two cases) that take no account of a 2600 GL/y increase in groundwater extraction. How can these “sensible ESLT” numbers have any relevance when there has been such a large change to groundwater extraction?

The MDBA appears to be confused at best and deceptive at worst given that they acknowledge a “growing recognition that surface and groundwater systems are connected”.

The Wentworth Group raised this issue, along with a number of others, in a statement on the draft Basin Plan. This work subsequently appeared in the Mythbusting section of the MDBA website, which aims to “help dispel some of these myths, as without correction these untruths take on a life of their own”.

It is a little concerning that in the public consultation phase of the draft Basin Plan the MDBA chooses to publicly ridicule analysis of its work on its website. Its response to the groundwater issue on its Mythbusting page was: “In setting the groundwater limits, the Authority has assessed the rates of recharge and the risk of increases in groundwater use to groundwater dependent ecosystems, river flows and the productive base”.

It is not clear what the Authority means by “assessed”. Maybe it is like the process used to set “sensible ESLT” numbers.

Tim Stubbs is an environmental engineer with the Wentworth Group of Concerned Scientists.