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
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
“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.
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.
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.
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?
PS The Murray and Murrumbidgee were also flowing.
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.
>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?
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?
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.
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.
You dont think there is an argument to open the barrages Janama? How About that it is an artificially created freshwater lake that evaporates/wastes half of SA’s water allocation each year. The barrages have resulted in the mouth silting up thus needing constant dredging due to the lack of tidal flow and have destroyed the ecology of the coorong. The coorong and lower lakes are just as much a part of the ecological system of the ocean as the river. It is only during recent times of severe drought and resulting lack of flow from the river that the true disaster of these barrages has become evident. I can see no good reason for leaving the barrages closed. The government needs to spend some money on a weir at wellington and some pipes around the lakes to provide freshwater for people who rely on it and return them to their natural state of a tidal estuary. This would benefit the ecology of the lakes, the coorong stop the mouth silting up and save loads of water. I do not beleive that Adelaide derives any of its water from these lakes as you suggest.
Jennifer,
By accepting Sturts observations (those of a British Officer too!) you must also accept all other ‘observations’ (Flinders Uni say that the last time that saltwater was present was 1,700 years ago)
Sturt 1838
“During my late visit I never observed the sea running in, but a strong current always setting out of the channel. From what I observed, I am led to think, that the level of the lake is above high water mark. The narrowness of the channel preventing the body of water thrown into it, by the Murray from being thrown out in the same proportion. The immense body of back water in the chain of lagoons, would be an argument in favour of this supposition.”
Can we aford to waste 1,000,000 megalitres of fresh water which evaporates from this lake every year. South Australians like to claim how efficent they are, they should include this evaporation in their water use figures.
Richard – I was only passing on what my friend said on the matter as she lives there and is aware of the problem locally – that’s all.
One correction, Richard, the lakes evaporate 2/3rds of SA’s allocation, not half.
Funny how few of the so-called ‘concerned ecologists’ demanding more fresh water when the system can least spare it seem to give a rats arse about the extensive salt water ecosystem that was destroyed by the barrages. A system this size would have had a huge prawn stock that formed a large part of the food chain for the entire coastal fishery in the region.
The destruction of this would have left the Coorong to serve the entire food chain from only 25% of the original resource, and without the regular tidal flush on which so much depends.
And the only possible conclusion to be drawn from it is that this impact has been far more significant than overfishing could ever have been.
The irony is that a floating house on this degraded estuary would prevent 1.6 tonnes of evaporation for every metre of roof or deck area while the total annual runoff from each metre of that roof into a rainwater tank would only be a third, or 0.5 tonnes a year.
All cities in low rainfall zones should be maximising the amount of housing that floats on their water storages. This competitive advantage remains the same regardless of drought or flood while runoff dependent systems exhibit major variations in yield.
david,
An Adelaide Uni study: http://www.dwlbc.sa.gov.au/assets/files/USE_CoorongWQChangeDraftNov05.pdf
It talks about a 6000 year history of the lakes, and the affect of sea water and how far upstream it went during drought.
I think the barrages very existance are proof that sea water incursions were a problem well before widespread irrigation.
“coastal lagoons that were formerly
saline have been converted into freshwater lakes by construction of barrages to exclude sea
water. In the estuarine lagoons at the mouth of the Murray, in South Australia, barrages were
completed in 1940 to seal off gaps in the enclosing barriers and exclude sea water.
Previously, the sea entered Lake Alexandrina and Lake Albert freely, particularly during dry
summer periods when fresh water discharge from the Murray was low. The building of
barrages were stimulated by the evidence that during droughts brackish water was spreading
into the Lower Murray and invading irrigation works. Late in summer of 1938 – 39, surface
salinity in Lake Alexandrina reached 28.5º/oo, the salinity of the open sea being a little above
35º/oo. There were extensive tracts of salt marsh bordering the lakes, liable to inundation by
the brackish water. In 1940, after the completion of the barrages, salinity dropped sharply to
1.42º/oo, and it has continued to decline, falling to a lowest annual maximum of 0.08º/oo in
1955 – 56. The lakes are now sufficiently fresh to be used as a source of water for irrigation
of adjacent pastureland, and the freshening of the lakes has been followed by the
development of reedswamp”
http://www.dpi.vic.gov.au/dpi/vro/egregn.nsf/0d08cd6930912d1e4a2567d2002579cb/0da8459bb6f7a4ecca25730600149cc7/$FILE/geomorphology%20gipps%20lakes%20shoreline%20erosion.pdf
During the 30’s and 40’s extraction was well below half that of the 90’s(3000 GL vs 10000 GL approx).
Charles Sturt found salt water in the lower lakes. I would think that Sturt’s observations are evidence that directly challenges rog’s assertion that “Flinders Uni say that the last time that saltwater was present was 1,700 years ago”.
See for yourself at:
http://www.jennifermarohasy.com/wiki/Historical_Records_of_the_Murray_River#Charles_Sturt.27s_Diary_of_his_Expedition_down_the_Murray_River
the above site has links (in the references section) to the full text of Sturt’s diary
Given that the normal average depth of the lake today is about 3 metres and this is at least 0.5 metres above mean sea level, then it is a physical impossibility for sea (salt) water to have not penetrated a very long way into the estuary for at least part of the year.
A full moon tide is usually about 1 metre and this volume represents 40% of the original 2.5 metre average depth. Ergo, in the absence of any river flow the tidal flush would introduce sea water to at least 40% of the estuarine area.
Furthermore, as the total area is in the order of 68,000 hectares, this tidal surge would involve an influx of 680,000 megalitres each day over the week of full moon tide.
And it follows that the only days on which no sea water would penetrate at all would be those days when the flow of the Murray was GREATER than 680,000 megalitres. Just to put that in perspective, this volume, if averaged over a whole year would amount to 248 million megalitres, or 10 times the current average gross annual inflows and 25 times the current net flows after extractions.
The numbers behind the claims that the estuary spent any significant time as a completely fresh water body prior to the barrages simply do not add up.
And I challenge any of the proponents of this absurd notion to prepare a simple flow model that is capable of incorporating historical flow cycles and known tide cycles. But they will not do so because this model will clearly demonstrate that the entire annual volume of extractions from the basin amounts to only 22 days worth of tidal volume.
Ergo, neither the natural flow nor the reduced extracted flow had any significant effect on the extent of tidal penetration in the estuary.
And will someone drown that moron they have elected as mayor down there. The guy is dumber than duck $hit.
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