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Barrages a bar to basin at best

10, November 2010

Jennifer Marohasy The Age October 31, 2010

AT THE bottom of the Murray-Darling river system are five large steel and concrete barriers blocking 90 per cent of the natural ebb and flow between Lake Alexandrina and the Southern Ocean.

To the north-west of the largest of these barrages is Hindmarsh Island, a new golf course and housing estate where retirees are encouraged to buy their piece of paradise on the edge of a freshwater lake.

The Lower Lakes were not always fresh. Before the barrages were built they filled with seawater in periods of drought but now enjoy continual flows of fresh water from the Hume and Dartmouth dams. The Lower Lakes, Coorong and Murray mouth will be the main recipients of all the proposed environmental flows in the Murray-Darling Basin Authority's controversial new Guide to the Proposed Basin Plan.
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The guide says the equivalent of four Sydney Harbours of freshwater must be delivered to the Lower Lakes yearly by taking water from irrigators as far away as the Namoi Valley in north-western NSW. When representatives of the authority attended a meeting in the Namoi recently, 200 irrigators wore T-shirts with the slogan "Save the Murray: remove the barrages".

In response, the authority told the meeting there was no scientific evidence to support removing the barrages.

The authority apparently accepts the argument that there was before the development of upstream irrigation, Lake Alexandrina was always fresh, but this is nonsense and ignores scientific studies published in the peer-reviewed literature, as well as accounts from early settlers and explorers. An assessment of the palaeoecology of the region by Peter Gell and Deborah Haynes details how the barrages have changed the ecology of the Lower Lakes and affected the adjacent Coorong.

There is an argument, put forward by Tim Flannery of the Wentworth Group of Concerned Scientists and Greg Hunt, the federal opposition spokesman on climate, that if the barrages had not been in place during the recent drought, salt water would have penetrated an unnatural distance up the Murray River.

These opinion leaders seem to ignore that there was more water travelling down the river during this drought than in either 1914-15 or 1945-46, so there is no reason to suppose the intrusion would have been any worse than back then – before the completion of the Snowy Mountains scheme. The bottom line is that the guide is about taking water from our best food-producing farm land and sending it down to the Lower Lakes, which were never a totally freshwater system and are degraded by European carp and housing developments.

Not so many years ago Bob Brown, leader of the Greens, was saying it had been "scientifically proven" that 1.5 million megalitres were needed to solve the problems of the Murray-Darling Basin. Since then at least 1 million megalitres have been bought back.

During the drought the river did not run dry and the world's largest environmental flow release of 513,000 megalitres was made into the Barmah-Millewa Forest. During this past year the basin has enjoyed flooding rains.

There is no new science to justify the demand for 7.6 million megalitres of more environmental flow.

If the authority were serious about improving the natural environment of the most stressed part of the system it would remove the barrages blocking the natural ebb and flow between the Lower Lakes and the Southern Ocean.

Dr Jennifer Marohasy is a biologist, research scientist and commentator on environmental issues.

Published in The Age

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