Time to prepare for better floodwater monitoring at Murray Mouth

South Australia’s marine ecosystems are under stress from prolonged drought and rising temperatures. Moreover, the recurring flood occurrences of the River Murray present additional challenges. The significant flooding that struck the Murray-Darling Basin in 2022-23 provided a valuable chance for Flinders University researchers to observe its impact on biodiversity and water quality in marine habitats and local ecosystems, especially in popular vacation areas south of Adelaide.

An innovative study conducted by the Beach and Dune Systems (BEADS) Lab at Flinders University, showcased in the journal Remote Sensing, has developed an insightful framework to explore how the river’s discharge surged turbidity by dispersing silt, clay, and other suspended particles over vast distances. The sediment plume extended thousands of kilometers from the river mouth, bending westward around the Fleurieu Peninsula into Gulf St Vincent.

“During phases of substantial riverine discharge, we gauged the spatial reach and intensity of the surface sediment plume,” states Evan Corbett, an environmental science honors student at Flinders. “Our satellite imagery lays the groundwork for understanding future plume behaviors, particularly crucial for shoreline-targeted monitoring.”

The study observed that the historic sediment plume within the coastal stretch achieved its maximum reach of 13,681 km in the eight-day span commencing on 11 December 2022, surprisingly over a month before the peak discharge was recorded.

Through careful observations and satellite imaging from November 2022 to February 2023, researchers quantified the water discharge, tracked turbidity levels influencing standard seawater conditions, and examined other elements such as surface winds and barrage controls.

The findings point to a recurrent clustering of the plume near the river’s outlet, often near Long Bay’s northern edge, gradually progressing westward past the Fleurieu Peninsula and through Backstairs Passage into Gulf St Vincent, with the occasional brief eastward shifts.

Water clouded or rendered opaque by fine organic and inorganic particles can have adverse effects on ecosystems when present in substantial quantities.

Pat Hesp, a Strategic Professor in Coastal Studies at Flinders University, highlighted that the study, which included collaboration with academic partners, has established a valuable dataset that could shape future research directions.

“This research underscores the vital role of riverine discharge in dictating the surface sediment plume’s spatial outreach and intensity, especially within its central core,” says Professor Hesp.

By identifying potential formation and growth periods for these plumes, the study lays a foundation for targeted monitoring, timely interventions in management, and strategic planning to mitigate the ecological and socio-economic threats linked with extreme river discharge events in the future.

Enhancing our methods of measuring and analyzing such environmental phenomena is essential to evolving better coastal management techniques. Such initiatives are crucial to ensuring greater stability and resilience of beaches and ecosystems amid the ever-shifting spectrums of climate and weather conditions.