The installation of the barrages across the bottom of the Murray River is the greatest single change that has adversely affected the health of the Coorong.
Prior to 1940 Lake Alexandrina, at the bottom of the Murray River, was a mix of seawater and freshwater, and was under tidal influence through the Murray mouth, and fully connected to a much healthier Coorong.
The Murray River barrages were completed by 1941 and separated the Coorong from Lake Alexandrina and Lake Albert.
Before the barrages, fish could move between the lakes and the Coorong. Lake Alexandrina was an important fish nursery for replenishing the Coorong. After the installation of the barrages the Coorong was cut off.
The barrages have shut off 90 percent of the tidal effect, and as a result have made the Murray mouth much more prone to closing over.
The barrages have caused much greater deposition of silt above and below the barrages, and have caused a sand island called Bird Island to form directly in front of the Murray mouth on the landward side.
The barrages were designed to hold Lake Alexandrina up to a maximum of 75cm above previous levels, and as a result shoreline erosion has accelerated. The higher level of Lake Alexandrina has prevented an enormous quantity of fresh water reaching the Murray mouth.
But now, because of the drought, sea level is 45cm above the level of the lake with plenty of sea water leaking into the lake despite the barrages.
The salinity at Goolwa is currently around 20,000 EC units. This is very high. The sea is about 45,000 EC units and the upper limit for drinking water is just 800 EC units.
In short, the barrages were designed to turn a saltwater lake into a freshwater lake, but they weren’t successful.
At best Lake Alexandrina remains brackish, with current salinity at Milang which is about the centre of Lake Alexandrina is about 4,000 EC units.
Furthermore, the barrages that were meant to hold Lake Alexandrina at a higher water level, have resulted in a requirement of up to 1,000,000 megalitres annually just to cover the evaporation loss. This loss has to be supplied from Hume and Dartmouth Dams and at times from Lake Menindee. If the barrages were to be opened, this quantity of water would be immediately saved annually.
Whether our climate scientists are correct or not, the need for this quantity of water to cover evaporation is simply unsustainable.
The value of that water to irrigation at the end of last season was in the order of $400 million.
The South Australian government should now open the barrages, particularly the Goolwa barrage, which is responsible for regulating 70 percent of the Murray River flows, and the Mundoo barrage which is responsible for 10 percent, as these two barrages would have the greatest impact on keeping the Murray mouth open, and improving the health of the Coorong.
In summary, just because the barrages were put in does not mean they have to stay there. It is wrong for South Australians to keep demanding the upper states of Victoria and New South Wales empty their dams to unsuccessfully keep a saltwater lake fresh.
Peter Martin
Finley, NSW
Re white noise. The actual water yield per hectare of catchment varies considerably to the point where localised changes in yield in the Vic NE can completely negate a broad trend over the rest of the basin. Hence the generalised yield data tells us 3/5ths of sweet FA.
And correction to the letter from SA, Adelaide had hoped to get its water from the new lake but it proved to be far too brakish due to the history of tidal flow.
I have a friend in Clayton who's brother lives in Milang and this what she wrote in reply to my email.
The results of the Lake being down haven't been all that grim....the wildlife are feeding off a lichen that has been growing on the mud flats...the birds have returned, the swans have lost their breeding ground between Milang and Clayton...but they have moved to Lake Albert that has been filled again from Lake Alexandrina.
The fish haven't been affected by the salinity rise...the local fisherman are still sending supplies to the market in Adelaide. Clayton water supply was from the Lake and they are now on town water from a holding tank in the Hills. Hindmarsh Island has been affected...they are having water delivered...however the Goolwa Shire regulated that all houses built on the Island have rainwater tanks so things aren't too bad there either.
The heathlands are dying and the frogs have had to go underground to hibernate...the results will be known spring as to their survival.....however the turtles have developed a shell disease, a worm gets into their shell and calcifies until they can no longer carry it, move into it and they are dying in great numbers....apparently the Education Dept are onto the problem and school kids are everywhere on the foreshore rescuing the turtles. Hopefully there will be a good outcome.
Apparently when the lake was saltwater, it was fished to the max and a thriving industry existed..whereas now only one fisherman survives from the lake.
I'd like to keep freshwater because in bad drought it has kept Adelaide and districts in water supply. Adelaide is now building a salinity plant...but until that gets underway I dont think there is an argument to open the barrages. They built the bloody things out of wood, and they seep saltwater anyway.
David,
Let's start with the first written record?
I've suggested it is Charles Sturt.
I've indicated Sturt observed that the lower lakes were full of water and salty in about 1830.
Do you accept the observation of this British Officer as relevant to the issue?
>The catchment wide runoff data is so generalised as to constitute white noise.
This makes no sense at all. A record is a record. We are setting records in spades. Further, stream flow is actually very red (not white).
PS Jen, any luck with that salinity or lake level data?
The catchment wide runoff data is so generalised as to constitute white noise. The important point is what is happening in the high yield catchments of NE Victoria. These supply most of the meaningful volume and they are all in a state of major forest regrowth after the 2003 wildfires.
This burst of vigorous regrowth has, according to the detailed modelling and ground truthing of the former CRC for catchment hydrology, more than halved the total water yield. And this halving of water yield has almost entirely taken place on publicly tenured land, either State Forest or, more likely, National Parks.
The prescription for ensuring the continuity of runoff volumes is neither new or complex. It is to thin the vegetation. And to thin it early and often so that the retained stems do not exceed the 'natural' or normal extractive capacity exhibited by pre-settlement vegetation.
The (titter, titter) custodians (guffaw) of the Parks and Wildlife estate have made a conscious management decision to do nothing about the impact this entirely foreseeable ecological process is having on river flows.
In doing so they have breached both the letter and the spirit of their own environmental planning legislation. Their failure to act has caused a material change in both their own and the entire catchment community's resource use. And they have given effect to what is clearly "development" without any formal process to consider the full environmental impacts of their development.
This situation has also been replicated in NSW with the failure to consider the impact on river flows of more than 14 million hectares of dense regrowth forest on what was originally open woodland <12%FPC.
Once again we have this extraordinary double standard where a farmer can be prosecuted for building farm dams without approval to catch his own water, or cutting a single tree, while the public sector avoids all responsibility for acts and omissions of the grossest, criminal negligence.
Just another reminder, if anyone needed it, that these people are not 'partners' in resource management, nor are they 'custodians'. They are the worst form of third world parasitic thugs, their incompetence matched only by their underlying malice towards, and contempt for, those who occupy the catchments.
PS The Murray and Murrumbidgee were also flowing.
David,
The first record of water quality in the lower lakes is from Charles Sturt in about 1830.
In his diary, which I read a few years ago, he described the lower lakes as estuarine.
Sturt wrote that the Murray River's mouth was at Wellington and that the River then emptied into a large estaurine lake system.
At the time there was no drought as such, at least Sturt described the Darling and Rufus River's as running strongly.
I understand that there has been an attempt, that was successful for a period of time, to make the lower lakes artificially fresh by building the barrages.
Do you have any evidence to suggest that this is not the case?
Janama, June runoff was the lowest on record across the Basin (http://mdbc.gov.au/__data/page/29/Drought-Update-July-2008-MR.pdf). Rainfall for the January to July period was 206mm which is (about) 30% down on the average of 302mm. Last year was the hottest we have observed across the basin, while the last decade was the hottest decade on record. The inflows over recent years have set records on almost any time scale you care to look at.
BTW Jen, do you have any salinity or water level data to support the view that the lower lakes turned saline in previous historical droughts? I would love to see it.
I suppose you'd have to take the fresh water barrier further back up the river, like the barrier in the Tweed is back at Murwillumbah and the Clarance is salty all the way back to Grafton and above.
I suppose the original barrier was created because they thought a fresh water Alexandrina had more value than a salty Alexandrina.
It's questionable which would have the greater value today, what with oyster and salmon farming etc. but unfortunately it's not a primary problem for the river, water allocation is.
If you check the catchments for the inland rivers you'll see that most areas have had average rainfall this year. The problem with the Muarray/Darling is not water input but water output. Left to itself the system would be fine, we just over exploit it.
"the upper limit for drinking water is just 800 EC units."
Depends how thirsty you are.
You can't get blood out of a stone but if you wait long enough the horse may talk.
That seems to be the philosophy of the MDBA.