Ten Million Misplaced Megalitres - Ian Mott
Murray-Darling water policy ignores the huge increase in water yield from past clearing.
A recent report has advised that current runoff volumes in the Murray-Darling Basin may be more than double the volumes that occurred under natural conditions. Farmers in the basin have long been accused of over exploiting this water resource and the government has been under intense pressure from green lobbyists like the Wentworth Group to take back 1,500,000 megalitres to "restore" so-called "environmental equity" to the system.
But rural think tank, The Landholders Institute, has found that the increase in water yield from past clearing has been completely ignored in the flow analysis. Yet, this very same increase in water yield has been almost universally claimed to be the cause of rising water tables and a "salinity crisis". And this salinity threat was used as the primary justification for new clearing controls in Queensland and NSW.
The report, "The implications of adjusting runoff values from land clearing on water yield in the Murray-Darling Basin," has found that under the most plausible scenario the volume of this increased runoff is equal to the volume being recaptured by downstream irrigators. And this can only mean that the volumes that are currently flowing to the sea or being used by wetlands are little changed from the historical range of variation.
And this partly explains Dr Jennifer Marohasy's discovery, in "Myths and the Murray", that salinity levels in the Murray at Morgan SA had halved over the past 20 years. Salt interception schemes have helped but farmers have also been using more of the water surplus that they created by clearing in the first half of last century and the system has come back closer to historical equilibrium.
Institute Secretary, Ian Mott said, "After we had completed the work we were surprised to learn that the CRC for Catchment Hydrology had already done a similar study that concluded that about a third of current flows in the basin were surplus flows produced by land clearing. The science is very clear that above 500mm rainfall a reduction in forest cover produces a rise in water yield and, more importantly, a rise in stormflow runoff peaks. And this suggests that the flooding of some riverine wetlands may actually be more frequent today than the historical norm".
"The increase in yield from clearing varies according to rainfall totals, intensity, frequency and season but it also varies with replacement ground cover. In this study we used conservative scenarios based on a normal pasture profile and we excluded the added boost in runoff that comes from over-grazed pasture or showers that fall on recently watered crops with a full moisture profile. We also restricted our scenarios to 100%, 150% and 200% average yield increases when the weighted average yield increase for the NSW part of the basin, based on official cleared land data, came in at 285%."
"Yet, the recent House of Representatives Inquiry into future water use was presented with a "fact sheet" from the Murray Darling Basin Commission that stated that the current runoff volume in the basin, 23,850 Gigalitres per annum, was the same as the "natural" runoff. Half of this total was then assumed to have flowed to the sea under natural conditions while the other half was assumed to have been transpired and evaporated from wetlands. And it was for the so-called 'restoration' of this exaggerated natural use that calls have been made to take back allocations from farmers and punch a $billion a year hole in the basin economy."
"Of greatest concern to farmers everywhere", said Mr Mott, "was testimony provided to the Parliamentary Inquiry, by Murray-Darling Basin Commission senior executives, that appeared to confirm that this gross misrepresentation of fact was deliberate. And in light of the collective defamation and demonisation that farmers have been subjected to for more than two decades on this issue, it is essential that all relevant Ministers investigate the part played by their own departments in this disgraceful sequence of maladministration."
[see CRC report at www.catchment.crc.org.au/pdfs/technical200108.pdf ]
For a copy of "The implications of adjusting runoff values from land clearing on water yield in the Murray-Darling Basin - Mott. I.A. 2005" with supporting spreadsheets, please email
Ian at firstname.lastname@example.org
The reports Conclusions were:
The volumes of water that constitute the natural flows of the MDB have been wrongly assumed to be unchanged from pre-settlement days. The very substantial increases in runoff that are a by-product of clearing have been deliberately ignored.
This assumption has allowed the volumes and frequencies of water that have been used by wetlands and flood plains within the natural range of variation to be grossly exaggerated.
This assumption has allowed the volumes and frequencies of water that have flowed to the sea within the natural range of variation to be grossly exaggerated.
Most, if not all, of the water being diverted from the Murray-Darling Basin is drawn from a man made surplus yield that the science is clearly capable of predicting but which the policy/science interface either refuses to recognise or has selectively applied.
This has allowed the policy process to ignore the fact that most water capture takes place in the middle levels of the catchment in major storage facilities. And this obscures the fact that vast areas of the Murray -Darling Basin above these storage facilities are in robust good health from significantly enhanced volume and frequency of flows.
And the failure to recognise this man made surplus has seriously distorted the current degree of departure from the natural range of variation in river flows and has seriously distorted the character, scale and extent of adverse environmental impacts in the Murray-Darling Basin.
The assertion that natural flows within the Murray-Darling Basin have been seriously over-allocated or seriously over-utilised has no basis in fact.
This is not to say that water is not wasted in the basin. At least 2000GL is wasted from evaporation of fresh water from a converted tidal estuary and the maintenace of fresh water "values" in that artificial system. But this "wasted" water has still delivered all the ecological services that nature expects of it as it flowed the length of the river system. But it could also make a much greater economic contribution.
The issue of man made surplus water yields is a "relevant consideration" within the meaning of Section 5 of the Commonwealth Administrative Decisions (Judicial Review) Act 1977, which, by way of informing questions of best practice governance, may not be ignored by any policy process.
This material is of such magnitude and relevance that any discussion of water usage or balance in the Murray Darling Basin that omits this material is worse than bad science or policy, it is a misrepresentation of fact to the policy process that may also constitute official misconduct.
The Government has a clear duty to refrain from taking any actions on decisions that have already been taken without informed consent, and under inappropriate circumstances, and to fully investigate the matters raised in this report.