The Risk of System Collapse
14 September 2009
It is great that the Freshwater Embassy people care so much about our environment, however there are many problems with their insistence on a fresh water only solution to the crisis of the Lower Lakes.
There is not enough fresh water in the whole system to save the Lower Lakes at the present time. Regardless of the source of the problem, whether overallocations or drought, the Lakes are facing an unprecedented crisis, with the levels predicted to fall to a critical point within the next year (-1.5m AHD) where the water in lake Alexandrina will become so acidic that very little will be able to live in it. At the beginning of the dry season, we are already at -0.76m AHD, the levels having reached -1.0m last
summer. The Freshwater Embassy constantly downplays the problem of the acid sulphate soils (ASS) which are developing, and propose "bioremediation" to counteract the "hot spots". They do not appreciate the vast extent of the ASS, both in surface area, and depth. To bioremediate this huge area, even if it did work, which is highly unlikely in the longer term, will take enormous resources and time, which we do not have.
The simple solution is to allow the Lakes to return to a modified estuarine condition, mimicking the situation before the barrages were installed. A recent meeting of international experts in Goolwa has said that allowing seawater into the Lakes will give them the best shot at recovery. Contrary to the Freshwater Embassy, there is scientific and historical evidence that the sea came into the Lakes on a daily basis with the tide, and during drought years, penetrated well up into the River. There are many benefits of this proposal, mainly
the seawater would cover the acid sulphate soils, and prevent their further development,
corrosive dust storms from the dry lake bed will be averted,
the Ramsar wetland would be restored, albeit a marine one, allowing wading birds, migratory birds, marine fish and plants such as seagrasses to create biodiversity (Ramsar has allowance for changing ecology), and
the huge amount of freshwater which presently evaporates from the surface of the Lakes (between 450 and 800GL, 2-4 times Adelaide's annual water consumption) would then be saved for restoring the River.
The building of the weir at Pomanda or nearby would be necessary, preventing the seawater penetrating up into the River, but in times of heavy flow would allow fresh water to spill over and proceed through the Lakes as of old. Circulation of the seawater in the Lakes would be needed to prevent
hypersalinity, and this is entirely possible using modified barrage gates which could be opened and closed during tidal cycles, similar to the West Lakes system. Some have said that there is not enough tidal head at the Murray mouth to effect penetration into and out of the Lakes, however tidal ranges of about the same magnitude occur at Lakes Entrance mouth. In that case magnified oscillations of lake levels occur as the result of the weather fronts that regularly cross the system. These would also occur in the SA Lower Lakes, allowing a greater head of water to be built up than what is caused by the tides alone. Removal of sand accretions which have built up inside the mouth since the barrages were installed would also have to be done, and this is something that is carried out at many estuaries around Australia. Newer technologies are now being developed by which sand can be resuspended on the ebb tide and removed before settling permanently, thereby immensely reducing the amount of dredging needed.
Those who have historically used the water of the Lakes directly for domestic or irrigation purposes have now been partly catered for by the building of "The Creek's Pipeline" and others, but there is the acknowledged need for further pipeline development to service other rural communities.
I agree that we need to be encouraging an understanding of the whole Murray-Darling system which does not treat it as an unlimited resource to be exploited for economic benefit at the expense of the health of the River and Lakes. This will come in time, but right now things are so bad that we can't wait without risking a system collapse.
Elizabeth Gordon-Mills, Phd
Retired Aquatic Biologist