The flood event that occurred in the South Australian Lower River Murray between November 2022 and February 2023 was the third largest such event in recorded history, and the largest flood in nearly 70 years. New scientific research undertaken through the Goyder Institute for Water Research has highlighted how the environment responded to this significant flood.
Teams from CSIRO, Flinders University, the South Australian Research and Development Institute (SARDI) and the University of Adelaide set out to investigate the immediate environmental impact of the flood waters in the Riverland region as well as the longer-term responses in the Coorong, Lower Lakes and Murray Mouth region, including the impacts of the flood waters on marine habitats and species.
Goyder Institute for Water Research Director, Dr Alec Rolston, said “Funding from the South Australian Department for Environment and Water allowed our researchers out onto the river and floodplains as soon as it was safe to do so. The results show that while there were both positive and negative environmental responses, many were short lived, with conditions returning to those similar to pre-flood conditions relatively quickly. For important environments like the Riverland floodplains and the Coorong and Lower Lakes, this highlights the ongoing need for freshwater flows to maintain the region’s social, cultural, environmental and economic values.”
The immediate environmental response in the Katarapko and Pike floodplain areas included a reduction in the salinity of shallow groundwater, with some saline groundwater discharging from the floodplains into the river at specific locations. Dissolved oxygen levels, which are vital for fish and other aquatic animals, did not reduce to critical levels and any low oxygen events that did occur came into South Australia from further upstream.
There was a significant carp breeding response to the flood event as floodplains and wetlands were inundated, creating good conditions for spawning at the right time of year. It was the largest carp breeding event seen in the Lower River Murray for over 20 years. At the same time, many thousands of carp were washed out of the Murray Mouth into the Southern Ocean, washing up on the beaches of the Fleurieu Peninsula.
A plume of freshwater extended at least 40 km from the Murray Mouth into the Southern Ocean. The floodwaters transported nutrients and carbon from the Murray-Darling Basin into the Southern Ocean, providing energy sources for marine plants and animals. This increased phytoplankton productivity and sparked positive responses all the way up the food chain. The sediment and reduced salinity that the flood brought to the marine environment did however impact negatively on some marine organisms.
Dr Rolston said “The positive environmental outcomes observed in the Coorong during the flood event included reduced salinities, as well as increased and more widespread numbers of plants, fish and invertebrates. However, some species that are more sensitive to salinity changes couldn’t cope with the rapid reduction in salinity as the floodwaters passed through the Coorong and into the Southern Ocean.”
Dr Ryan Lewis, Principal Advisor for the River Murray in the South Australian Department for Environment and Water said “Understanding how the environment responds to a flood event of this magnitude highlights the importance of high flows to the plants and animals which inhabit these systems. How they respond to changes caused by events like the flood is critically important for the management and conservation of these important ecosystems”.
Further Information
For more detailed information on the results of the research, a number of fact sheets and a technical report are available on the Goyder Institute website and the South Australian Government website.
A non-technical summary of the research is also provided through a storymap.
Funding acknowledgement
Funding for this research was provided to the Goyder Institute for Water Research by the South Australian Department for Environment and Water, along with the South Australian Government’s Healthy Coorong, Healthy Basin Program which is jointly funded by the Australian and South Australian Governments.
Research Team
Lead researchers that delivered this work were: Dr Eddie Banks (Flinders University), Dr Chris Bice (SARDI), Professor Sabine Dittmann (Flinders University), Dr Emily Leyden (University of Adelaide), Associate Professor Luke Mosley (University of Adelaide), Dr Jason Nicol (SARDI), Ms Cassandra Urgl (University of Adelaide), Professor Michelle Waycott (University of Adelaide), Associate Professor Qifeng Ye (SARDI) and Dr Brenton Zampatti (CSIRO).
