Rediscovering the Past

Historical Sea Water Intrusions up the River Murray

By Ian Rowan, Goolwa

1 September 2011

I thought I was being so smart plotting the saline intrusions up the River Murray during the recent drought when the Lower Lakes were salty and when there were strong southerlies. I also thought I was very clever recording high water levels caused by a combination of spring tides and meteorological influences causing the reversals of flow.

But it has all been done before.

Professor Rainer Radok, of the Horace Lamb Institute of Oceanography, Adelaide in 1975 was not the first, but he too rediscovered the past with his observations and publication ‘Sea Water Exclusion from Australia’s River Murray’.

Saline intrusions were first observed and recorded over 110 years ago.

Observations prior to 1903 regarding the interaction between the sea and river levels were spot on in that the river dominated during high flow periods only. This goes back to at least 1850 when the first such suggestion was made.

I have just converted the data from the initial barrage investigations prior to 1903, converting from grains per gallon and elevations from the datum then used. Their data and explanation is consistent with the data observed over the last few years after allowing a bit for sea level rise. Their maximum measured water levels inside the Murray Mouth due to extreme sea levels was 1.28m AHD compared to 1.42m recently. And in the past when strong southerly winds blew salty Lake water above Welington salinities of up to 6000EC were measured compared to 4500EC in 2009 during similar events.

Going back further in South Australian Lower Lakes settlement history, you can see that everytime there was a drought period, talks about locking the river (1860's) and upstream irrigation (late 1870's and the disastrous 1880's) came to the fore.

The drought period of the 1880’s was inevitably followed by another wet period and the Murray again flooded in 1890 only to be followed by the very severe 1895 to 1902 Federation Drought and the Lower Lake farmers blaming upstream diversions and lobbying for the construction of the barrages to combat seawater intrusions.

The similarity between major changes of river flows and the ebb and flow of farmers above and below ‘Goyder's Line’ depending upon rainfall is becoming clearer. As we have seen recently these large El Nino/La Nina oscillations not only effect river flows but our mid north and northern areas.

George Goyder, Surveyor General of South Australia in 1861, first established what became known as ‘Goyder’s Line’ in 1865 during the early 1860's drought. By the time it was made law in 1872 the rains had returned (there was also a major Murray flood in 1871 and 1876) and he was ridiculed. Farmers ventured north again. But then the inevitable happened and the 1880's were disastrous and all those northern towns were deserted as evidenced by the ruins we see today.

An interesting sideline is the role of the South Australian government. In 1878 they first complained about upstream irrigators, but in 1887 they signed an agreement with the Chaffey Bros to establish an irrigation settlement at Renmark ( the first irrigation settlement in Australia) and, despite opposition, they did not stipulate extraction limits. This irrigation settlement was quickly followed by one in Mildura.

And back in the 1850’s the following description of flows through the Mouth was written:

The union with the waters of the ocean seems after all to have been accomplished

only by a sort of compromise, the understanding being that the river, during the time

of its periodical flooding, should be permitted to excavate for itself a channel just

sufficient for the passage of its waters, which seldom exceeds 15 feet in depth, while in

the interim the ocean should be at full liberty to work away at filling up the same,

which it never fails to punctually perform, generally managing before the return of the

freshes, to reduce the outlet to a depth of from 4 to 6 feet.

This description seems to encapsulate the whole variable regime of the Lower Lakes system in response to the variable flows. A more beautiful way to describe the interactions of sea and freshwater than 'seawater intrusions', and proving the Lower Lakes are naturally estuarine during times of low river flows.

Read more about seawater incursions at Ian's Corner.