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September 19th 2010 print

Jennifer Marohasy

The Murray: a fresh perspective

Few understand how different ecologically the Murray Darling Basin was before European settlement and the impacts of agriculture and the construction of barrages designed to keep salt water out.

Save the Murray, remove the barrages 

The release of a new Murray Darling Basin plan on October 8, 2010, 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 as a debate over how to fix the two very large freshwater lakes at the very bottom of the Murray River rages. 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 impacts of agriculture and the construction of barrages designed to keep salt water out. Oral histories from local families and the diaries of the first European explorers paint a different picture of the Lakes than that shaping the debate today. If we look back to what the river was like before the barrages then there is a much different solution than that currently being proposed. A solution that may not be as palatable to the South Australian Government or those communities who have grown used to life behind the barrages but a much cheaper and more environmentally sustainable solution in the longer term.   

Many academics and bureaucrats deny that the lakes were ever estuarine. But families that 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 River Murray as far as Mannum with the sightings of a shark at Tailem Bend and a dolphin at Murray Bridge.

Since 1941 and the completion of the barrages blocking 90 percent of flows between the lakes and the South Ocean a new history and geography of the Lower Lakes, Coorong and Murray mouth has been created. 

These barrages were built to regulate the river flows improving it for local irrigators, boating and recreational activities 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 move to the sand bars beyond the barrages, rather than 52 kilometres upstream at Wellington where the river empties into Lake Alexandrina. Farming, urban development and recreational use over the past seventy years has 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 South Australian Government to argue for more environmental flows.

In order 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. The British explorer Charles Sturt travelled down the Murrumbidgee then the Murray in a whale boat arriving at a 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.

Captain Sturt described the waters of Lake Alexandrina as initially "sweet" but by the morning of the second day, as they headed to the south western 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, 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 fourth day at Lake Alexandrina that Captain Sturt conceded that it would be impossible for his men to drag the whale boat any further over the sand bars and sand flats. He eventually changed plans heading back across Lake Alexandrina and up the River Murray because it was futile to try and break through to the ocean.    

When his diary was later published Captain Sturt included comment that: 

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 also Lake Menindee a near constant water level of 0.75 metres 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 were two solutions to this problem. The Dutch who know all about dykes have for centuries limed regions that were once exposed to tidal flow to avoid the creation of acid sulphate soils providing one solution. The other was for the South Australian Government to open the barrages and let sea water back into the Lakes as had happened before European settlement.

The entrenched history and development of this region, however, now sees the only solution as more environmental flows from the Murray Darling.  During the drought, the South Australian Government consistently arguing 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 returning the lakes to a more natural state or liming the areas to prevent acidification as the Dutch have done. 

Next month the Murray Darling Basin Authority will release a new plan for water sharing in the Murray-Darling Basin. Various organisations have lobbied hard during the development of this plan in particular to get more water for the Lower Lakes some claiming up to $8.5 billion of tax payer dollars needs to be spent buying more water as environmental flow.

It is seven years since the last 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 generated models were used to claim salinity levels were rising when in fact concentrations had been falling for twenty years.

The false claims proved embarrassing for the Howard government, and it was eventually agreed that 500 gigalitres, rather than 1,500 gigalitres of environmental flow, would be bought back under the Living Murray Initiative.   

Now despite the buyback of over 900 gigalitres, this year’s flooding rains, and no salinity problem, tax payer are likely to be again expected to foot the bill for more water buy back this time ostensibly because the Lower Lakes need more freshwater.

New South Wales and Victorian irrigators worked hard to fix the salinity problem through the 1980s and 1990s. It is really 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 negatively impact on local irrigators who currently rely on the Lakes.   Provisions would need to be made to buy-back their irrigation licenses. Consideration could also be given to compensating the commercial fishermen whose business currently depends on harvesting freshwater carp.   In order to keep the river fresh and protect Adelaide’s water supply in times of drought a weir needs to be built near Wellington.   Consideration could also be given to construction of embankments on the Currency Creek and Finniss River if these wetlands are to be conserved as fresh during drought.   But all of this is very achievable and 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.  

Dr Jennifer Marohasy is a biologist and adjunct research fellow at CQ University

See also:

Bob Bourman “Life of the Murray

Jennifer Marohasy “The Murray: salt water solution