Murray Darling Basin Plan and Variability

November, 2011
John Cox has written a great article putting some hard numbers on my much repeated point about Australian river flow variability and the difference between allocations and entitlement volumes. Here is an extract.

There is no evidence that the sustainable diversion limits in this report were influenced by any social or economic outcomes, as the main thrust of the proposed report is still on satisfying environmental outcomes in the basin with environmental watering plans, water salinity targets and end of valley targets for river flows to keep the mouth of the Murray open.
Despite the Chairman’s urging that we see this revised report as “more than just a volume of water” to be cut from irrigators, the proposed Basin plan still places this single cut in irrigators allowance front and centre without any explanation on how this single figure can apply to the widely varying annual flows that we know are a hydrological feature of the Murray Darling basin.
If this 3,573 GL of water buybacks for the environment had been in place between 1984 and 2000, when irrigation diversions averaged about 11,500 GL per year, then agricultural production would have been reduced by 33% for no real reason at all, as flows over the Goolwa barrages averaged about 5,000 GL over this period.  This waste of Australia’s scarcest resource will also occur in future years of average and above average flows if these cuts are implemented.
If this 3,573 GL had been in place between 2007 and 2010, when irrigation diversions were reduced by about 6,000 GL to about 5,000 GL for these four years, then such cuts would still not have been enough, as there was just not enough water around during these drought years. 
It would seem logical to have produced a more dynamic model where irrigation allocations are not cut by a single figure but are dependent upon the water availability in the Murray Darling basin each season. 
In fact, the State water agencies have developed quite an expertise in this dynamic modelling area  during the recent drought years and progressively set percentage allocations during the season for both high security/reliability water used on permanent tree plantings and low security/low reliability irrigation water that is used on annual crops like cotton or wheat.   It is difficult to see why this system needs to be changed.
The second major problem in the report is the lack of any real discussion on the waste of scarce water from evaporation in the artificial fresh water lakes of the Murray Mouth and whether fresh water flows to keep the mouth open 90% of the time would be necessary if the barrages were kept open and the lakes revert to their natural state of tidal fluctuations.
A lock between Wellington and Tailem Bend and opening of the barrages in drought years to form an estuarine environment would not only save 800 GL of evaporation, or more than half of the 1468 GL still to be recovered between 2012 and 2019, but convert this barren fresh water monoculture of carp into a diverse, vibrant ecoculture that would be similar to the Lakes Entrance estuary in Gippsland. Not only would the Murray River have an estuary and open mouth like all of the world’s great rivers but an increase in tourism would also be an economic boost to local communities.
We should also be clear about the outcomes of a further 2,750 GL cut in irrigation allocations which would be similar to those of a 3,000 GL cut that was modelled in the draft report.  This report stated that in an average run off year, these cuts to irrigators would result in 1,000 GL being made available for environmental watering projects within the basin and an extra 2,000 GL would flow out to sea, making 7,000 GL per year in total.  Is this scandalous waste of Australia’s most precious resource what Australians really want?
John Cox is a citrus grower in Waikerie, SA

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