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Add salt at the mouth to save the Murray

By Jennifer Marohasy - posted Wednesday, 6 October 2010


The release of a new Murray-Darling Basin plan next Friday is likely to reignite debate over how best to solve the problems of the Murray River. It will further pit some environmentalists and some South Australians against upstream irrigators over how to fix the two large freshwater lakes at the mouth of the Murray River.

Lake Alexandrina and Lake Albert are situated behind the narrow expanse of water known as the Coorong. Beyond the Coorong is the Southern Ocean and upstream of the lakes is the river proper.

Few understand how different ecologically this region was before European settlement and the effects of agriculture and the construction of barrages designed to keep out salt water.

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Oral histories from local families and the diaries of the first European explorers paint a different picture of the lakes from that shaping the debate today. If we look back to what the river was like before the barrages, then there is a different solution from that being proposed.

It is a solution that may not be palatable to the SA government or those communities that have grown used to life behind the barrages but one that is a cheaper and more environmentally sustainable solution in the longer term.

Many academics and bureaucrats deny that the lakes were estuarine. But families who have lived in the region for generations explain, for example, that in 1915, before the barrages and during a period of prolonged drought, sea water penetrated beyond Lake Alexandrina up the Murray River as far as Mannum. There were sightings of a shark at Tailem Bend and a dolphin at Murray Bridge.

Since 1941 and the completion of the barrages that block 90 per cent of flows between the lakes and the Southern Ocean, a new history and geography of the Lower Lakes, Coorong and Murray mouth have been created.

These barrages were built to regulate the river flows, improving river use for local irrigators, boating and recreational activities and creating the artificial freshwater environment in the Lower Lakes that people enjoy today.

This has seen community understanding of where the river's mouth is moved to the sand bars beyond the barrages, rather than 52km upstream at Wellington, where the river empties into Lake Alexandrina.

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Farming, urban development and recreational use during the past 70 years have entrenched this understanding of the lakes. It has reached the point where the once estuarine Lower Lakes have become eligible for freshwater allocations from the Darling and Murray rivers under national water-sharing plans, enabling the SA government to argue for more environmental flows from upstream.

To get a fresh perspective on the region, it is worth going back in time and considering the diary of the first European to visit the region. British explorer Charles Sturt travelled down the Murrumbidgee and then the Murray in a whale boat, arriving at the place now known as Wellington in 1830. He described this as the Murray's mouth, writing:

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.

Sturt described the waters of Lake Alexandrina as initially sweet but by the morning of the second day, as they headed to the southwestern corner, he noted the waters suddenly became salty and unpalatable and that “the transition from fresh to salt water was almost immediate”.

On the third day, the expedition attempted to manoeuvre the whale boat from the lakes to the Southern Ocean but was blocked by sandbars. Now a sand dredge works at this site to keep the so-called Murray's mouth open and its image has become a symbol of reduced flows because of upstream irrigation. But before irrigation, in 1830, 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 fourth day at Lake Alexandrina that Sturt conceded it would be impossible for his men to drag the whale boat any farther over the sandbars and sand flats. He eventually changed plans, heading back across Lake Alexandrina and up the Murray River because it was futile to try to break through to the ocean. When his diary was later published, Sturt commented:

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.

With the barrages and flows from the upstream Hume and Dartmouth dams and Lake Menindee, a near constant water level of 0.75m above sea level was maintained until 2006-07. Then, given the severity of the drought, there was not enough water in the upstream dams to supply the Lower Lakes and the barrages functioned as dykes and the lakes started to dry up.

As water levels declined a new problem emerged. Potential acid sulphate soils were exposed. These soils are harmless as long as they remain waterlogged, but if the water table is lowered, as happened in 2007, the sulphides in the soils react with oxygen, forming sulphuric acid.

There are two solutions to this problem. For centuries the Dutch, who know all about dykes, have limed regions that were once exposed to tidal flow to avoid the creation of acid sulphate soils, providing one solution. The other is for the SA government to open the barrages and let seawater into the lakes, as had happened before European settlement.

The history and development of this region, however, now means the only solution is seen to be more environmental flows from the Murray-Darling.

During the drought, the SA government argued that because of “imbalances in the way water has been shared between Murray-Darling Basin states”, the Lower Lakes would turn acidic. This ignores the possibility of removing the barrages and returning the lakes to a more natural state, or liming the areas to prevent acidification as the Dutch have done.

The Murray-Darling Basin Authority will release a new plan for water sharing in the basin. Various organisations have lobbied hard during the development of this plan to get more water for the Lower Lakes, some claiming up to $8.5 billion of taxpayer money needs to be spent buying more water as environmental flow.

It is seven years since the previous basin-wide plan was developed. At that time salinity was considered the biggest risk to the Murray-Darling Basin and salinity levels at Morgan, just upstream from the offshoots for Adelaide's water supply, were considered the best measure of the health of the entire system.

Computer models were used to claim salinity levels were rising when in fact concentrations had been falling for 20 years. The false claims proved embarrassing for the Howard government and it was eventually agreed that 500 gigalitres, rather than 1500GL of environmental flow, would be bought back under the Living Murray Initiative.

Now, despite the buyback of more than 900GL, this year's flooding rains and no salinity problem, taxpayers are likely to be again expected to foot the bill for more water buyback, this time ostensibly because the Lower Lakes need more fresh water.

NSW and Victorian irrigators worked hard to fix the salinity problem through the 1980s and 90s. It is now time for South Australians to fix the problem of the Lower Lakes and a lasting solution could be quickly achieved by the removal of the barrages and the restoration of the lakes to their natural estuarine state.

Permanently opening or removing the barrages would have an adverse effect on local irrigators who rely on the lakes.

Provisions would need to be made to buy back their irrigation licences. Consideration also could be given to compensating the commercial fishermen whose business depends on harvesting freshwater carp.

To keep the river fresh and protect Adelaide's water supply in times of drought, a weir needs to be built near Wellington. Consideration also could be given to construction of embankments on Currency Creek and Finniss River if these wetlands are to be conserved as fresh during drought.

But all of this is achievable, much less expensive and much more environmentally responsible than continuing to demand more water from upstream, particularly when supplies are limited during times of drought.

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A version of this article appeared on Quadrant Online and in The Australian on October 2, 2010.



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About the Author

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

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