2018
About the document
This report is the product of the third year of monitoring and evaluation in the Lower Murray River under the Commonwealth Environmental Water Office’s Long Term Intervention Monitoring (LTIM) Project. The report evaluates the contribution of Commonwealth environmental water to environmental outcomes in 2016–17, complementing the first two years of LTIM Project monitoring and evaluation work undertaken in 2014–15 and 2015–16, and previous short term monitoring and evaluation work undertaken between 2010 and 2014.
The Lower Murray River LTIM Project identified a number of key environmental outcomes achieved through the use of environmental water in 2016–17:
- A natural flood event travelled down the Lower Murray from October to December 2016. Commonwealth environmental water was delivered at the end of this event. This helped to slow the drop-off in water levels, extend the period of connection between the river and floodplain and maintain flowing habitat for fish. For example, over a two to three week period, environmental water kept the river 70–90 cm higher than it otherwise would have been.
- Environmental water contributed to over 500,000 tonnes of excess salt being exported out the Murray Mouth. This is the equivalent of 25,000 semi-trailers each carrying a full load of salt (around 20 tonnes). Reducing salinity levels has benefits for native plants and animals, as well as for stock, domestic and irrigation purposes.
- Environmental water also moved nutrients through the river system. Nutrient inputs are important for aquatic plants and underpin the food chain for animals in the Lower Murray, Lower Lakes, Coorong, and Southern Ocean, adjacent to the Murray Mouth.
- Environmental water maintained oxygen levels in the Rufus River, during a time when oxygen levels were dangerously low as a result of floodplain material breaking-down in the water at the end of the natural flood. Maintaining oxygen levels in localised areas can provide refuge habitats for aquatic organisms.
- Environmental water delivery contributed to the range of micro-invertebrates (tiny animals that are food for fish) by bringing species from the northern Murray-Darling Basin and other tributaries to the Lower Murray, and transferring them between the river, lakes and wetlands.
- For the third consecutive year, small Murray cod were found in the Lower Murray. While the conditions that supported this response remain unclear, this is a promising sign of improving population health of Murray cod.
- While golden perch spawned during the natural flood event, few were detected as having survived to autumn 2017. It is likely that the low-oxygen conditions created by the flood affected the survival of eggs and larvae. This is something to further explore in coming years.
The results highlight key areas for maintaining and improving Commonwealth environmental water delivery and are also important for adaptively managing how water is delivered for best environmental effect. For example, useful ‘rules of thumb’ will inform how best to target water delivery to create flowing habitat for native fish in the River Murray.
Water delivery in South Australia is connected and coordinated. Environmental water delivered to the Lower Murray provides benefits for the river channel as well as low-lying floodplain, particularly areas that are inundated by weir pool raising events. This is complemented by wetland watering via a range of partners including non-government organisations, irrigation trusts and at the internationally-important Banrock Station wetlands. As the environmental water moves downstream, it is providing benefit to the Lower Lakes and Coorong.
The environmental outcomes detected by the LTIM project complement the results of other monitoring projects, such as those focused on wetlands: Monitoring South Australian River Murray wetlands and floodplains and monitoring at the Coorong, Lower Lakes and Murray Mouth through The Living Murray program: The Living Murray - Icon site condition report.
The report is presented in three parts:
- An executive summary;
- A non-technical synthesis report; and
- Technical appendices which provide detailed methods, analyses and results for each indicator.
The data and evaluation report from this project are being combined with those from six other LTIM Project Selected Areas within the Basin, as part of a Basin-scale evaluation of the contribution of Commonwealth environmental water to the environmental objectives of the Basin Plan being led by the Murray-Darling Freshwater Research Centre.
In addition to assisting the Office to demonstrate environmental outcomes, the LTIM Project is designed to allow adaptive management of the water holdings. As such, identified outcomes and limitations are used to inform environmental watering in future years leveraging the best available, contemporary scientific knowledge.