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Extended drought and warm weather are damaging South Australia's marine ecosystems, and periodic flooding of the River Murray poses another major risk.

A significant flood in the Murray-Darling Basin in 2022–23 gave Flinders University researchers a rare opportunity to analyze conditions that damaged biodiversity and water quality for both marine species and local ecosystems, some at popular holiday locations south of Adelaide.

A new study led by the Beach and Dune Systems (BEADS) Lab at Flinders University and in Remote Sensing provides a detailed framework for understanding how the river discharge increased turbidity (silt, clay and other suspended particles in the water) as the sediment plume expanded across thousands of kilometers from the river mouth westwards around the Fleurieu Peninsula into Gulf St Vincent.

"During this period of high riverine discharge, we measured the spatial extent and intensity of the surface sediment plume, with our satellite imagery providing a reference point for future plume behavior—particularly near shore for targeted monitoring," says Flinders environmental science honors student Evan Corbett.

"Interestingly we found the historically important sediment plume within the coastal region reached its maximum spatial extent of 13,681 km² during the eight-day period beginning on 11 December 2022, more than a month before the peak discharge occurred."

The local monitoring and satellite imaging between November 2022 and February 2023 measured the volume of water discharge, turbidity levels affecting regular seawater quality, surface winds, barrage controls and other factors.

The study found the major plume typically pooled near the river's mouth within the northern corner of Long Bay, before migrating persistently westward around the Fleurieu Peninsula through Backstairs Passage into Gulf St Vincent, occasionally exhibiting brief eastward migration periods.

Fine organic and inorganic particulate matter in water can make it cloudy or opaque, often having a detrimental impact on ecosystems when it occurs in large amounts.

Strategic Professor in Coastal Studies Patrick Hesp, who leads Environmental Sciences at Flinders University's College of Science and Engineering, says the study—in collaboration with University of Adelaide lecturer Dr. Sami Rifai—used technology which effectively built a useful dataset to direct future research.

"This study highlights the significant role of riverine discharge in driving the surface sediment plume's spatial extent and intensities, particularly within the plume's inner core," says Professor Hesp.

"Revealing when and where plumes are likely to form and evolve, this study provides a foundation for targeted monitoring, timely management interventions, and informed planning to reduce the discussed ecological and socio-economic risks associated with extreme river discharge events in the future.

"By improving how we measure and analyze these environmental events, we pave the way for better coastal management strategies, ensuring beaches and ecosystems remain more stable and resilient in the face of changing climate and weather conditions."