Left to sink or swim, it's our ag that could drown

I enjoyed a meal of crawfish with farmers in Louisiana a few years ago, where the locals boasted the Port at New Orleans was the fifth largest in the world.

Vast quantities of grain and oil seed, including genetically modified (GM) cotton and GM soybean, were shipped down the Mississippi and to the world via New Orleans.

Along comes Hurricane Katrina and New Orleans is no longer a busy port but a city reeling under gale force winds, a tidal surge and then a crime wave.

New Orleans is built on a delta and deltas tend to sink when the supply of sediment for delta and wetland building is less than the rate of subsidence due to natural geological processes.

Levee banks, built to contain flood waters, have significantly reduced the supply of sediment to New Orleans and surrounding wetland areas.

The levees are designed to keep the water within the main river channel of the Mississippi so the sediment is dumped at the extreme end of the delta.

It was over that meal of crawfish that I learnt that the sediment eventually slides down the continental slope to fan onto the deep ocean floor.

Among the news reports over the last few days there has been comment that New Orleans is three metres below sea level.

The farmers had joked the city could one day slide into the Gulf of Mexico.

I have previously written that the Murray-Darling Basin River drains 14 percent of the landmass of Australia and that the mighty Murray has an average annual flow, including diversions for irrigation, of 14 million megalitres.

Compare this to the Mississippi River which drains 41 percent of the United States and has an average annual flow of 405 million megalitres.

There is no equivalent of New Orleans in Australia and there is no great port at the bottom of the Murray River.

Adelaide is about 100 kms to the west.

There are holiday houses on the lake system that sits at the bottom of the Murray and then a series of barrages build to keep the lake's water fresh, and beyond that, a dredge working to keep the Murray's mouth open.

The Murray-Darling Basin is the food bowl of Australia but when you compare total agricultural production in Australia to the US we really are insignificant.  We produce about 34 million tones of what the World Resource Institute classifies as cereals;  the US produces 334 million tones.

We produce about four million tones of meat, they produce 37 million tones.

Our mighty Murray River and its dependent farming communities are puny in the global scheme of things.

And on reflection it is perhaps more likely that Australian agriculture will be let to slide into oblivion through corrosive state and federal government policies, than New Orleans will be left to slide into the Gulf of Mexico.

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