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Saving the Coorong by restoring its native state

By Jennifer Marohasy - posted Thursday, 14 August 2008


When the Minister for Climate Change and Water, Penny Wong, recently announced that there was insufficient water in upstream dams to flood the lakes at the end of the Murray River, ABC Online ran with the headline "Government says the Murray's Lower Lakes can’t be saved." But that's not what she said, and furthermore the lower lakes can be saved. The Murray River is at far greater risk and the solution for the river is not nearly as simple.

The lakes can be saved by opening the barrages and letting the area flood with seawater. This will solve the developing environmental problem with acid sulphate soils.

Flooding the lakes with salt water will create economic problems for the communities who live and farm in the region and who have come to reply on the lakes as a source of freshwater including for irrigation. Perhaps for this reason, and for local politics, this obvious environmental solution has been treated as a taboo subject for too long.

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Most Australians, and many South Australians, have never visited the lower lakes, but they have come to believe that the region is now degraded because upstream irrigators take water which would otherwise flow to South Australia. The Australian Conservation Foundation has made the sand dredges working at the bottom of the lakes a symbol of the need for bigger environmental flows.

Arlene Buchan, a campaigner for the Australian Conservation Foundation, told national ABC radio in June 2006 that, "There are lots of problems with the River Murray, but lack of environmental flows is without a doubt the biggest one. We need to have much bigger environmental flows passing down there through the Coorong and out the mouth. A healthy river should be able to keep its own mouth open, and shouldn't need any sort of dredging or artificial assistance in keeping sand out of its mouth."

But this is not necessarily true of Australian rivers; the idea that a river should be always brimming with water and always flow strongly to the sea is a very European concept.

Indeed British explorer Charles Sturt, the first European to visit the lower lakes wrote in 1832, "Australian rivers fall rapidly from the mountains in which they originate into a level and extremely depressed country; having weak and inconsiderable sources, and being almost wholly unaided by tributaries of any kind; they naturally fail before they reach the coast, and exhaust themselves in marshes or lakes; or reach it so weakened as to be unable to preserve clear or navigable mouths, or to remove the sand banks that the tide throws up before them."  

Captain Sturt left Sydney in 1830 in search of an inland sea but instead the Murray led him to the lower lakes and the Coorong in what is now South Australia. He travelled down the river in a whale boat; a boat resembling one of the lifeboats on the Titanic but longer, oar-powered and with a dismountable mast and sails.

While many Australians who watch the nightly news on television have come to associate the narrow channel between the sandbars below the barrages at the bottom of the lakes as the Murray River's mouth, Captain Sturt described the river's mouth as being above the lakes, where the township of Wellington now lies. After 33 days in the whaleboat, he wrote, "we had, at length, arrived at the termination of the Murray. Immediately below me was a beautiful lake, which appeared to be a fitting reservoir for the noble stream that had led us to it; and which was now ruffled by the breeze that swept over it."
 
Captain Sturt described the waters of the lake as initially "sweet" but by the morning of the second day on the lake, as they headed to the south western corner of the vast expanse of water, he noted the lake suddenly became salty and "unpalateable" and that "the transition from fresh to salt water was almost immediate."

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That night they camped on the western shore of the lake and Captain Sturt wrote, "the stillness of the night was broken by the roar of the ocean, now too near to be mistaken for wind or by the silvery and melancholy note of the black swans as they passed over us, to seek food, no doubt, among the slimy weeds at the head of the lake."

On the third day, the expedition's attempt to maneuver the whale boat from the lakes to the Southern Ocean was blocked by sandbars. Captain Sturt wrote, "Shoals again closed in upon us on every side. We dragged the boat over several, and at last got amongst quicksands."

It was not until the next day, the fourth day at the lower lakes, that Captain Sturt conceded that it would be impossible for his men to drag the whaleboat any further over the sand bars and sand flats. He eventually changed plans and told his men they would be heading back across the lower lake and back up the Murray River because it was futile to try and break through to the ocean.

Captain Sturt's diary tells us three important things. Even before irrigation there was no navigable passage between the lower lakes and the ocean;.the lower lakes were not fresh; and to a British explorer the lower lakes could not be considered part of the Murray River.

Over the last 100 or so years, for mostly politically expedient reasons for South Australia, the geography of the area has been redescribed and history rewritten. Indeed by claiming the lower lakes as part of the Murray River, South Australian politicians have been able to argue for additional water allocation and by complaining that there would be a navigable passage from the lower lakes to the Southern Ocean if only there was more water coming down the river, South Australian have over the years successfully played the victim card and been allocated more and more water.

But this recent prolonged drought will perhaps be their undoing.  I am not suggesting the drought will be a disaster for the lower lakes, but simply that it is becoming increasingly difficult for South Australians to insist that the only solution to the environmental issues confronting the lower lakes is more water from upstream. At issue is the role of the barrages at the bottom of the lakes.

Prior to 1940 Lake Alexandrina was a mix of seawater and freshwater, under tidal influence and fully connected to a much healthier Coorong. The barrages were completed in 1941 and separated the Coorong from Lake Alexandrina and Lake Albert and shut off 90 percent of the tidal flow. They were designed to raise water levels in the lower lakes by up to 75cm and stop fresh water flowing out to sea. But now, because of the drought, sea level is about 45cm above the level of the lake and some salt water is leaking through the barrages into the lakes which are rapidly drying out.

As the water recedes and more of the lake floor is exposed to oxygen, an acid sulphate soil problem is developing.

Potential acid sulphate soils (ASS) are common along much of the Australian coastline. These soils formed after the last major sea level rise, which began about 10,000 years ago. The soils are harmless as long as they remain waterlogged. But, if the water table is lowered the sulphide in the soils will react with oxygen forming sulphuric acid.

In the case of the lower lakes, the barrages are stopping inundation from seawater; in the same way the dykes in Holland are used to reclaim land. Indeed the Dutch have been managing associated acid sulphate soil problems for more than four centuries.

Acid Sulfate Soils have been associated with fish kills in coastal Queensland and New South Wales when land was inappropriately drained.

For example, about 700 hectares of land near Cairns was drained in 1976, and since then it has been estimated that 72,000 tonnes of acid have flowed into Trinity Inlet. Approximately 50 percent of NSW sugarcane land is underlain with potential ASS and inappropriate drainage of these soils caused a major fish kill in the Tweed River in 1987.

NSW farmers have since largely solved the problem through the implementation of liming and less intrusive drainage. But the South Australians, instead of considering practical solutions, initially just provided money to CSIRO Land and Water to undertake a study, which included establishing the severity and spatial extent of the problem, while issuing media releases claiming that because of "imbalances in the way water has been shared between Murray–Darling Basin states" the lower lake would turn acidic.

The most recent statements from Minister Wong suggest there is a realisation that there is just not enough water upstream to save the lakes, and that the only real solution to this emerging environmental catastrophe is to open the barrages and let seawater flood the area.

If the barrages are opened, irrigators dependent on freshwater from the lower lakes would need to be compensated because they have a freshwater allocation creating a property right and the damage to their businesses from the salt water would be difficult to repair. The alternative, during this protracted drought continuing to send large quantities of water from the upper catchment to the lower lakes is no longer viable.

Some argue that if a permanent weir was constructed just upstream of the lakes at Wellington and the barrages used under "an adaptive management regime", there could be water savings in the order of 750 gigalitres (billion litres) a year. Opening the barrages would immediately take some pressure off the entire Murray-Darling system, because less water would need to be allocated to South Australia. That doesn’t mean the Murray River won’t run dry if this drought continues.

Indeed, it doesn’t matter how many activists and South Australian politicians call for more water for environmental flows, if there's ongoing drought and the upstream dams eventually run dry, there will simply be no water for the river. Thankfully the lower lakes can be saved by the Southern Ocean even if the drought continues.

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About the Author

Jennifer Marohasy is a senior fellow with the Institute for Public Affairs.

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