I think you are hitting the nail on the head when you are saying that it is unlikely that by simply opening the barrages the Lower Lakes will revert to a healthy estuarine system. My reason for this is covered by an article from D. J.Walker who talks about the hydro-dynamics of the Murray Mouth. The key feature is that the effective head of the Southern Ocean is about 500 mm above that of the sea, because of the strong Southern Ocean swells and the wind action of waves pushing sand up through the channel to produce a spring tide delta.

The only way to overcome this is to have a pressure head on the landward side that can overcome the net forces of the tide + wind + swell action. Nature has done this over the millennia by periodically flooding the river system and it is those times when the shape has been sculpted. Between these flood times, the tidal action as you say has its effect but over time without the strong force of flushing by a flood, the mouth would close over.

Have a look at what happened on the Glenelg River this year = the mouth closed over and the river flooded the town of Nelson before the river managed to burst through and re-open the channel to the sea. This is what had happened in the Lower Lakes and Coorong for thousands of years and would go on doing so but for mankind taking away the floods and building barrages to alter natural cycles.

I agree totally with you that by merely opening the gates will not make any long term difference and that is why I dreamt up my solution published on the above page. Please read about it and let me know what you think. It is a heavy engineering solution I must admit, but it may just work because it recognises the operational dynamics and has elements that deliver on the parameters required to kick start this moribund environment again.

Hoping for increased inflows from upstream is a bit of wishful thinking. Government action is proving to be impotent at doing anything in this regard and it is high time we accept the mess we are in and make something good out of it all.

Thanks mate – I’ve been there and checked it out and I think it would be useful for you guys to check out the info on the situation in QLD and Northern NSW and what has happened there and the differences between there and the Lower Lakes – the logic put forward here and in some of those letters doesn’t stack up.

I stick by the last paragraph of my previous post and add a few links to check out for your info
http://www.nrw.qld.gov.au/land/ass/ – simple easy to explain info on coastal ASS (different to our problem here where it is a freshwater lake)
http://cat.inist.fr/?aModele=afficheN&cpsidt=16632997 (scientific journal paper outlining how the Trinity Bay problem has been managed in a similar way to what you are proposing and what impacts that had regardless – worth noting my points about tidal flux would mean the tidal flushing here needed to make it work wont occur)

Sebastian

By turning the system back to what it was pre-barrages will rectify a massive problem confronting the lower Lakes and Goolwa Channel.
The greatest mistake was to build the barrages in the first place. Sadly back in those days our understanding of putting barriers in front of nature wasn’t fully understood.
Should our current managers of the lower lakes resources have been approached with a a similar proposal today, then it wouldn’t make it past the first base.

The barrages would be tossed out of the equation because of the enormous environmental impact and the lakes as storage would be doomed to failure as they are too shallow in relation to the very large surface area where evaporation loss is far too high. In recent consecutive years, the evaporation rate from Lake Alexandrina has been more than what the river holds between Wellington and the north -eastern border. With a national water failure through drought and overuse, we cannot and should not waste a drop in the lower lakes. Backtracking the lakes to become estuarine again will give nature back what it had before. The evidence of a previous lakes estuary is bountiful. Just the samphire alone has survived to tell the story.
May I suggest that you check Under Letters in “lakesneed water.org further details on this crisis.

Ken

Look at the tidal levels at the Goolwa Barrage as opposed to Victor Harbour and see how different they are – this is the tidal ratio and the information available in reports on dredging the mouth show you the ratio is very small – insufficient to allow water movement in and out of the lakes to make it an estuary – it would quickly become similar to the South Lagoon, just on a larger scale with a fresh bit at the top.

This place is so different to estuaries in NSW I cant go on to explain that in enough detail here but if you look at the info about Trinity Bay (I think it is) you see how it should work. Because of the restricted mouth, the system does not work that way and instead you end up with a hypersaline inlet and you dont get additional alkalinity generated so it will probably just end up hypersaline and acidic.

Instead of us just assuming what we want it to be, please spend the time to read the information that is out there and bring it together to have an informed debate. The DEH (SA) website has lots of info and so does the MDBA/MDBC and DWLBC websites…

It is important that everyone know that the lakes were not marine since about 7000 years ago (the last ice age) when the coastal dune system that create the Coorong were formed. A range of sources show this including analysed soil cores and explorers journals. We only remember a generation or so and because water was being extracted before the 1930s drought flows resulted in a river that dried up to a series of pools and the lakes became to salty to drink. Its not that I’m saying salt water never entered the lakes, I’m just saying it is not as simple as some people think – a clear example of thus is the idiot Rann doesn’t even support the idea of the lakes always being freshwwater because he is ill informed, not having spent the time to find out the information himself.

Changing the system to a marine one rapidly now will not only affect water quality for people but is likely to wipe out the entire ecology of an INTERNATIONALLY important wetland. Letting in seawater as a long term concept and transitioning the site to a more estuarine lake system I agree is sensible – its the timeline we might differ on because of the impacts on the place and its people (not forgetting the Ngarrindjerri) but also because introducing seawater into an acid sulfate soils affected previously freshwater wetland might exacerbate acidification not improve it. If you spend the time to read the information about other sites in Australia affected by this issue you will find it is both very different but also saline water causes pH to drop not stabilise or increase by preventing oxidation of the sulfides in freshwater lakes.

Lastly The restricted mouth and more importantly narrow channels that connect the Southern Ocean to the Lake via the mouth and Coorong will mean that the tidal signature is significantly reduced. If people took the time to read the information that is out there on the sand pumping (dredging) project they would see that opening the barrages and expecting the tide to maintain the mouth and sufficiently flush the system are wrong. I know it sounds stupid but read the reports and then tell me I’m wrong. The present EIS that SA now has to put together will summarise this and help all of us to understand the facts better (hopefully).

This action of “re-connecting the Coorong” unless planned properly will just result in the lakes becoming a hypersaline, acidic wasteland that will cost significantly more to re habilitate

Sebastian

http://www.abc.net.au/news/stories/2009/06/12/2597202.htm

Change of direction in lower lakes acid fight
Posted Fri Jun 12, 2009 8:25pm AEST

Pumping to end in favour of different strategy (ABC: Matthew Abraham)
A change has been announced by the South Australian Government in the environmental fight to save an area at the mouth of the Murray where prolonged drought has led to acid sulfate soils.

Pumping of water into Lake Albert from neighbouring Lake Alexandrina is to cease.

The pumping had been a part of efforts to overcome the rising acidification.

A meeting of the Murray-Darling Basin Ministerial Council in Sydney has considered a report which says it is highly unlikely the water levels can be maintained in Albert and Alexandrina due to low river flows.

SA’s River Murray Minister Karlene Maywald says a major bio-remediation program will be used instead of pumping.

She says this will include putting micro-fine limestone into the lake and planting shallow-rooted cover crops to reduce acidification risks.

“Now it’s never been done on this sort of scale before,” she said.

“It’s a very enormous area Lake Albert so we will be monitoring it extremely closely to determine whether the bio-remediation is actually successful in mitigating the acid sulfate soil and we will be ready to implement other options if we find that this is not working.”

If you have the time, this would enable you to calculate the volume of each main tidal inflow (ie from low level to high) for each day and post it on your site for comparison with the fresh water option.

For example, today, Sat 30th May low tide is 0.40m at 0723 hours and high tide is 1.16m at 1630 hours for a total inflow of 0.76 metres. This 0.76 is 30.4% of total lake volume (0.76/2.5m) but the easiest way to calculate volume is to multiply the total lake area behind the barrages (in hectares) by the 0.76 metres but expressed as 7.6 megalitres/ha.

There seem to be two numbers bandied about for the area of the lake, one is 65,000ha and the other is 86,000ha. But total tidal inflow will also include the area of river surface within the tidal influence (ie, between 0.40m and 1.16m in this case). If 86,000ha is the correct number then todays maximum inflow will be 86,000ha x 7.6ml = 653,600 megalitres.

An updated and progressive table that compares daily fresh water inflows from the Murray, with augmented flows from the buy back (and adjusted for actual rather than the gross allocation), and compared with the tidal flow, would rub the noses of the fresh water advocates in the full extent of their mediocrity and the uncontestible logic of the return to natural conditions.

I was raised on Mulloway. Lets hope they all come back.