The current Draft Basin Plan, and comments by the Chair of the Murray Darling Basin – Craig Knowles, pay a lot of attention to the health of the Lower Lakes, and ensuring end of system flows. Why does this one part of the Murray Darling Basin get such a lot of attention?
The Lower Lakes and Coorong extend over approximately 140,000 hectares. It is a surprising diverse environment, with 23 different wetlands types, from very fresh to saltier than the sea. It is one of the 10 major havens for large concentrations of wading birds in Australia, and is recognised internationally as a breeding ground for many species of waterbirds and native fish. The Coorong is ranked among the top six waterbird sites in Australia, based on the diversity and number of species found there. Both the Coorong and the Lower Lakes are listed as part of the Ramsar Convention, and international agreement which aims to protect the worlds most precious wetlands. The area is a an important feeding and breeding grounds for birds who then travel throughout the Murray Darling Basin, and in some cases, all the way to Japan and China. We have international agreements with these countries to maintain suitable habitats for birds which are part of our joint natural heritage. Japan and China are of course, our largest trading partners, which makes this connection pretty special. The Lower Lakes and Coorong are particularly important during periods of drought, and act as a refuge for fish and birds when other parts of the river are dry.
But the maintenance of these habitats is not the only reason that scientists and the MDBA think it is important to keep the River Mouth open. Australia is an old and saline environment. The River Murray flows across an old sea bed as it makes its way through South Australia and as a result, picks up a lot of salt which need to be flushed out of the system. A report from the Goyder Institute identifies that at least 3,500 GL of end of river flows are required (on average) to ensure there is not a build up of salt throughout the River system. Under careful management, the average flows suggested by the Basin Plan will achieve the salinity targets in the SA reach of the River Murray (see below). With no changes to the current extractions from the Murray Darling Basin, these salinity targets will not be met. This will have a major economic consequence for Adelaide, will reduce irrigation efficiency in other parts of the River system, and risks Australia’s current brand as a clean and green source of food products.
So you can see that it is not just South Australia that benefits from a healthy Lower Lakes and Coorong. But South Australia does benefit in a very important way. The city of Adelaide, home to one million people with $60B of economic production, relies on the River Murray for its water supply. Because of its limited water storages, Adelaide draws up to 90% of its water requirements from the River Murray in any one year. Even with the construction of a large desalination plant in Adelaide, one million people and $60B of economic output is reliant on the River Murray for potable water. How is this linked to the Lower Lakes? In the severe drought during the 2000′s, the Lakes water level dropped so far, there was a major risk that the Lakes would turn acid sulphate. Within a week, the acid, and released heavy metals would have moved back up the River Murray to beneath the inlet pipes for the water that is pumped to Adelaide, cutting off Adelaide’s water supply of last resort. Furthermore, increases in salinity in the River have a major impact on the lifespan of expensive infrastructure in Adelaide, so there are some important targets for salinity in the off-takes for Adelaide’s drinking water that have been agreed to, for economic reasons as much as anything else.
What is we removed the Barrages?
It is sometimes suggested that the Lakes would have been saline much more before that Barrages were put in to maintain Lake levels, and so the barrages should be removed. Such people I find are unwilling to use the same logic (ie. let’s make things how they used to be) to argue for more water for wetlands along the River, but nevertheless, lets follow the logic. The Lakes were almost exclusively freshwater (sorry, paper is behind a paywall, I can email if you want a copy), meaning that those who argue for things to return to ‘normal’ are asking for the Lakes to remain as freshwater systems. Those who say removing the Barrages would return the Lakes to an estuarine environment would also have to argue for all of the water currently diverted to be put back into the River to maintain the original estuarine condition. The argument is a red herring. There may be reasons to remove the barrages, but to return the Lakes to their original condition is not one of them.
Proposed reductions in evaporative losses from the Lakes
Ever since I can remember, there have been proposals to reduce the size of the Lower Lakes. These have been explored and usually rejected as returning poor value for money. The net evaporation from the Lower Lakes is 750 GL to 800 GL per annum. This is already built into South Australia’s long term, historic entitlement flows. This compares with total evaporation and ‘consumption’ by wetlands across the MDB system of 11,000 GL, nevertheless it is a large amount.
The MDBC explored options to reduce evaporation in the Lower Lakes. The savings identified were relatively small (10GL – 60GL) and incurred both significant costs, and some potential major benefits, including more habitat for wader birds. These options should be explored but they do not make much difference to the overall size of buybacks suggested by the MDBA in the Basin Plan.
The Murray Mouth impact on the health of the Coorong
Another argument bandied about with little scientific evidence is that the health of the Coorong is only dependent on flows from the South East. As a matter of fact, these flows are being restored to the Southern lagoon of the Coorong, but the scientific consensus is that an open Murray Mouth is required to ensure that the Southern Coorong continues to exist as a site of high ecological importance. Any suggestion to the contrary is simply wishful thinking.
The impact of the Basin Plan on the health of the Coorong and Lower Lakes
A recent scientific review of the impact of the Basin Plan on the health of the Coorong and Lower Lakes identifies that while not all environmental water requirements are met under the Guide scenarios (3,000, 3,500, 4000 GL), they represent an improvement on baseline conditions and, in some cases, they represent a large improvement. Obviously, more environmental water requirements are met under the 4000 scenario than under the 3500 scenario, and under the 3500 scenario than under the 3000 scenario, respectively. This is a useful starting point.
I would note personally, that the existing environmental water requirements, while entirely defensible scientifically, will need further refinement. I am sure there is a lot we don’t know about how water could be managed differently to achieve the same ecological outcomes. Just as I am sure that with a renewed effort to improve irrigation efficiency in Australia, we could make another big improvement as we did in the 70′s and 80′s when we spent a lot on R,D & E in this field. These outcomes are, I am confident, what the MDBA has in mind when they say that local communities will have a say in the adaptive management of water to balance environmental and economic outcomes. A lack of perfect knowledge is no reason to hold back reform, but it is a reason to ensure review points in the reform process, more research, and for all parties to retain an open mind and be willing to adapt their positions over time as new knowledge becomes available.
Socio-economic impact of Basin Plan
The Goyder Institute also undertook a socio-economic impact assessment of the Basin Plan. It misses a major component of the socio-economic impact (irrigation!) but argues that it did not have the skills to do the regional input output modelling. I would love to see some regional input output modelling of the Basin Plan. Please post a link if you see something. Nevertheless, the Goyder Institute does a fascinating analysis and comes up with some surprising results.
Some of the key papers quoted:
Salinity in the Lower Lakes and Coorong ( SA Government report)
Murray Darling Water Resources Fact Sheet (MDBC report)
Scientific review of Basin Plan and its implications for South Australia (Goyder Institute)
Palaeolimnological evidence for the independent evolution of neighbouring terminal lakes, the Murray Darling Basin, Australia, Fluin et al, Hydrobiologia, 591, 117-134
