Lower Lake Situation Near Crisis Point

By K. Jury, Journalist, Marine & Aquatic Ecology and I. Rowen, BSc

3 May 2009 

The Lower Lakes of the River Murray cover approximately 800 sq km and were on average only about 2m deep with a water level of +0.7m AHD artificially maintained by a series of barrages between the lakes and the Southern Ocean.

After several years of low rainfall, drought and with over-allocation of water for irrigation upstream, the water level has dropped to -1.0m AHD.

The impact of this has seen many dramatic changes.

For example:

Why is this so? The drawn out decisions of both the state and Federal governments in wanting a freshwater answer to the crisis puts much of the lower system in peril.

How? Delays in building the weir at Pomanda Point is causing difficulties in dealing with the drying out of acid sulphate soils, estimated to be in the order of 500 million tonnes in Lake Alexandrina alone. Some of this acidic soil has already progressed into sulphuric acid.

And so: The only solution available is to keep the exposed silts and soils of the 800 sq km lakes and channels etc covered, to halt acidification and to maintain water coverage throughout.

What will further delays do? We are witnessing sulphuric acid out-breaks where acid sulphate soils have dried and cracked. There are now extreme acid soil and silt dust problems causing extensive public health difficulties and infrastructure damage. At the request of residents in Goolwa and Clayton, EPA is now introducing additional air monitoring devices as an emergency measure. We have to flood the effected areas immediately.

The Government’s fresh solution! The government has always maintained a ‘freshwater solution’ for the lower lakes regions. Even today, when the Murray Darling Basin is at its lowest levels since records began, within ministerial levels, there is an enduring belief that enough rain will arrive and save the situation. However, there are many scientists who don’t agree. Long-range forecasts and improved science says otherwise and even if it did rain enough, there are those within the scientific community advising that not even a 56 flood would reach the border, let alone the lower end of the system. A most recent report concerns stored river water earmarked for South Australia for 2010. The Murray Darling Basin Authority said during the past week that there isn’t enough water in the system to transport the allocation into SA.

The decision makers then embark on a minor-localised, quick-fix solution.

To contain acid and acid silt dust throughout the lower Goolwa Channel and to provide a measure to contain the lower estuaries of Currency Creek and Finniss River, three temporary regulators will be installed. While the structures across the lower end of Currency and Finniss will possibly give some relief upstream in those systems, success is highly dependant upon eastern Mount Lofty Ranges catchments. Some landowner-farmers are suggesting that the catchments would not likely be great enough to make much of a difference.

Insofar as Goolwa Channel, work will commence on May 24th this year on a temporary regulator to span between Clayton and Hindmarsh Island. The government has decided that this barrier, when completed will provide some protection and remediation to the lower Goolwa Channel by transferring 30 gigalitres (as a one off) of fresh, heavily salt-laden, acid contaminated water from Lake Alexandrina to top up the Goolwa channel from Clayton to the Goolwa barrage. For future years, they say there will be enough runoff from the Finnis River and Currency Creek to top up the Goolwa Channel.

No, this is not a long term solution!

Moreover, taking water from the lake will create a ‘balloon effect’ where they rob Peter to pay Paul. It will further increase the level of sulphuric acid exposure in Lake Alexandrina, which contains an estimated 500 million tonnes of acid soils.

Some is already exposed through drying and is producing sulphuric acid. All Australian scientific papers including those from the SA Department of Environment & Heritage (DEH), when dealing with dangerous acid soils and solutions for remediation, have one thing in common.

DEH says, “as long as the soils are covered by water they are harmless to the environment, but if water levels drop and the soils are exposed to the air they react with oxygen to form sulphuric acid (the same acid in your car battery) and can release heavy metals from the soil. The acid can also cause toxic metals such as manganese, aluminium, and arsenic to be released. When the soils get wet again, through rainfall or increased river flow, the acid and metals can spread and affect large areas.” (Dept Environment & Heritage brochure ‘Acid Sulphate Soils in the River Channel and Lower Lakes’ 4 March09).

Taking the official view?

In building three temporary flow regulators at the mouth of the Finniss River, Currency Creek and from Clayton to the island, the government reports that “this will help keep soils moist and prevent acidification and irreversible ecological collapse of the area.”

So, what happens when the lake dries out? The question of pumping 30 gigalitres from Lake Alexandrina into the Goolwa Channel can only mean that more acidic soils in the lake will dry out and likely turn nasty. Keeping in mind the official view of a ‘freshwater solution,’ does this mean that the 800 sq km lake will be left to dry as the remaining water evaporates and recedes. Does this imply that nothing will be done with the lakes until it rains enough to fill the Murray Darling Basin, with a large enough supply to reach the lower lakes?

Looking further into the potential, its worth noting that a tonne of Pyrites-rich soil can produce a tonne and a half of sulphuric acid. When one considers a lesser example of 500 sq km of lake currently remaining wet and with acid to only, say a metre deep, then there is a potential of 500 million tonnes of acid-producing soils that, in the right conditions, could produce sulphuric acid at levels beyond our comprehension.

Should a massive acid attack occur, what then? In the event that the system did return to its former freshwater glory, it would then be necessary to exhaust the lakes and the Goolwa channel system and rid them of any exposed sulphuric acid and all of the pre-mentioned heavy metals, out to sea.

What would that do? To leave the lakes to dry out now would be devastating in a number of ways.

It could cause Australia’s largest ecological disaster. It would likely mean that the exposed steel stanchions supporting the Hindmarsh Island Bridge would be further damaged. It would more than likely attack and destroy the foundation of Calcium Carbonate Shell of the St Kilda formation, which naturally forms the foundations for most of the barrages. It would also badly corrode the barrages given the age of those structures and the quality of the weaker concrete used during the early nineteen hundreds.

And when this unwanted waste reaches the sea? It flows into and may have a destructive effect on the newly recognised Encounter Marine Park and its marine animals including fish life and the significant Goolwa Cockle industry. It would likely contaminate the marine food chain within the immediate area.

What options are there? To leave the lakes dry now would be devastating in a number of ways.

The only option available is to inundate the system below the Weir at Pomanda Point with seawater and exchange that water with tidal flow.

We do not believe that other remedial works on such a large scale can be anywhere near successful. The size of the problem in the Lakes and Coorong historically, is this countries largest.

Is this a precedent? No, there were at least two precedents in this country with some similarities.

In one report, at Trinity Bay near Cairns in QLD, disturbed acid sulphate soils released something like 50,000 litres of sulphuric acid into the sea every day over a period of more than 4 years. Locals reported that an estimated 120,000 tonnes of the acid escaped in that period from only a relatively small disturbed area.

The other is more recent and concerns extensive eutrophication of the Peel- Harvey Estuary near Mandurah in WA. The lake-like estuary and its Coorong-like leg suffered badly from algal and weed infestation caused by lack of freshwater flows from its three main rivers and from a lack of suitable and natural seawater intrusion.

The system is said to be Australia’s largest inland waterway which also featured sediments high in organic matter, similar to the Lakes and Coorong. The newly cut Dawsville Channel was the redeeming feature here, by providing further access from the Indian Ocean. Moving 180,000 cubic metres of acid sulphide soils while keeping it below water was also a major factor in achieving spectacular end results.

K. Jury & I. Rowen