I have been a reader and minor contributor at your blog over the last few months.
A few weeks ago I was discussing the Coorong with another commentator in relation to the Prime Minister’s new $10 billion National Water Security Plan in particular the hyper-salinity aspect.
With all the talk of the Murray “dying” I had thought the hyper-salinity was due to lower flow from the Murray River, the direct implication being less dilution of the Coorong as well as not being able to keep the mouth open.
As an irrigation farmer it is not pleasant to be accused of being partially responsible for destroying the Coorong.
Having been across the barrages and seeing the Coorong first hand late last year, meeting affected stakeholders and talking to South Australian government officials, I couldn’t help but feel it is the right thing to send the Coorong more water and thus that I should support the $10billion plan in its aim to buy back water for the river.
However, if my interpretation of this report ‘A Paleaecological Assessment of Water Quality Changes in the Coorong, South Australia’ is correct, the actual water from the Murray River has had no noticeable influence on the Coorong.
In fact, according to the report:
“Before European settlement the northern lagoon of the Coorong was dominated by tidal input of marine water. Marine flushing also strongly influenced the southern lagoon but less
frequently or to a lesser extent.
At no time in the 300 years before European settlement has the Coorong been noticeably influenced by flows from the River Murray.
The northern end of the southern lagoon occasionally experienced hypersaline conditions in the 300 years before European settlement. Elsewhere in the Coorong, the salinity was typically at, or below, 35,000 mg/L. In the southern lagoon the presence of diatom and ostracod taxa preferring salinity levels ~ 5000 mg/L suggests regular freshwater input. This source is likely to have been from the south-east.” [end of quote]
The report also states that “the extended presence of marine diatom taxa in Lake Alexandrina suggests the tidal prism regularly extended into Lake Alexandrina throughout the last 6000 years”, which I take to mean long periods of low flow where the mouth evidently did not close but rather was flushed by the sea.
What few people now realize is that there are barrages, construction completed in 1940, across each of the five channels connecting the lakes with the Coorong. These barrages restrict tidal flow into the lakes and stop freshwater flowing out of the Murray River’s mouth.
So effectively we might spend billions taking water from upstream irrigators and in the process displace jobs/communities and achieve nothing for the Coorong.
I do realise there are other “iconic” sites on the Murray that will benefit from more water, but they benefit already from the environmental nature of water deliveries prior to extraction, and don’t require 1000GL of fresh water evaporation from the lakes in low availability scenarios.
I now wonder if the most natural thing we can do for the Coorong is to remove the barrages and allow tidal action to do it’s business in particular flushing the Coorong. If this study by Adelaide University is correct the fresh water from the Murray River is not what the Coorong needs. It needs to be flushed by the ocean and this would be facilitated by the removal of the barrages.
Using stored fresh water from upstream to keep the mouth of the Murray River open, as currently advocated by various environment groups and the federal government shouldn’t really be an option.
There is currently a proposal to build a weir on the river at Wellington which is upstream of the lakes.
Irrigators currently dependent on the Lakes would have to be supplied from water upstream of this proposed new weir, much to their benefit by getting better quality water. Funding under the new $10 billion water plan could allow this to happen.
If we don’t get significant inflows the weir at Wellington will be built, the lake levels will fall and the irrigators won’t be irrigating anyway. But the situation at the Coorong will not improve unless the barrages are removed or opened.
If we do get substantial inflows, what was the problem again?