The work to determine the environmental water requirements for the Coorong, Lower Lakes and Murray Mouth region identified a range of objectives. These were:
- maximum salinity of 1000 µS cm-1 EC in Lake Alexandrina should be maintained in 95% of years, never exceeding 1500 µS cm-1 EC (with the additional condition that the 5% of years where this is not met are not sequential)
- the long-term average annual salinity in Lake Alexandrina should be 700 µS cm-1 EC, and should be the target for most years.
Investigations showed high freshwater flows only had a short-term impact on salinity in the lakes. Large flows above entitlement flows to South Australia had the ability to lower the salinity of the lakes and provide a salinity benefit for up to three years.
To meet the water quality requirements of the site and maintain the Ramsar-nominated ecological character, low and high flow requirements as well as water level targets were identified. These form the environmental water requirements for the site.
Environmental water requirements: flows targets
To maintain salinity in Lake Alexandrina below 1000 µS cm-1 EC for 95% of the time, at least 6000 GL of water should flow out through the barrages within every three year period. This is an average of over 2000 GL per year. If 2000 GL can not be achieved in any one year, salinity targets can still be met by providing extra water to make up the short fall within the next two years.
In addition to these low flow requirements, high flows of 6000 and 10 000 GL per year should be maintained at their current frequency of every three and seven years to maintain a healthy Coorong.
Environmental water requirements: water level targets
The plants and animals of Lake Alexandrina require a variable inundation regime. It is recommended that water levels vary seasonally between 0.35 and 0.75 metres above sea level.
Every three years, lake levels are recommended to remain higher to induce flooding of surrounding lake and river banks (riparian zones), and to seasonally vary between 0.5 and 0.83 metres above sea level.
This is different to the historical management of the lakes.
Reports outlining the findings of these investigations are now available for downloading:
A shorter summary report is also available:
Drafts of the full reports were independently reviewed by Professor Ed Maltby of Liverpool University and Dr Dugald Black of CSIRO Land and Water respectively as part of a larger scientific review by the Goyder Institute of the Murray-Darling Basin Authority’s Guide to the Proposed Basin Plan.
The peer review of the draft reports can be downloaded from the Goyder Institute website. The author’s response to the comments has also been published:
As this is the first iteration, more investigations are proposed to further examine the water requirements of the site.