Dredging Lake's Political Barrage

I was in Adelaide a couple of weeks ago and drove over to Lake Alexandrina.

The lake is part of a huge lake system covering some 86,000 hectares at the bottom of the Murray River.

While the dams at the top of the Murray-Darling are very low -- or basically empty -- there was plenty of water in Lake Alexandrina.

Taking a drive around the western perimeter of the lake, the countryside was green, and I was surprised by the extent of new housing development.  There is also a new marina on Hindmarsh Island.

I visited the town of Wellington, where there has been some talk about a new weir to save water for Adelaide.

At Wellington, the Murray River enters the large lake system where some estimated evaporation in an average year exceeds 800 gigalitres of water -- that's 800,000 megalitres!

When Charles Sturt sailed down the Murray in 1830 he considered Wellington the river's mouth.

It took him two days to get across Lake Alexandrina and then he couldn't get his boat over the sandbars.

There are still sandbars at the bottom of the lake system, except that now there is a dredge working to maintain a narrow channel.

South Australians use the "blocked Murray mouth" as an excuse to call for more water complaining irrigators in NSW and Victoria are taking all their water.  Never mind that there was no deep channel at the bottom of the lake system in 1830 -- long before irrigation.

In fact, without the water infrastructure build for irrigation, including the Dartmouth and Hume dams collecting runoff from the Snowy Mountains, there would have been no water flowing down to South Australia given the severity of the recent drought.

If a weir does go in at Wellington, it will be interesting to see if anything is done about the large network of barrages build at the southern end of Lake Alexandrina.

The barrages were built in the 1920s to stop freshwater from the Murray potentially flowing out to sea.

If South Australia was fair dinkum about more water for the "Murray mouth" it would dismantle the barrages and let water flow out the narrow entrance.

But, if the barrages were removed, the lakes might become salty and that would affect the many irrigators growing various crops around the lakes.

But if more farmland ends up as housing estate and marina, the new residents might demand the barrages be dismantled anyway, so they can catch saltwater fish species in what some now consider an artificially fresh evaporation basin.

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