Effectiveness of bioengineered river-bank protection in reducing erosion rates and sediment supply in a Great Barrier Reef catchment, Australia

Abstract Accelerated river-bank erosion is a major source of increased sediment, turbidity and nutrient to receiving waters, including Australia’s Great Barrier Reef (GBR) lagoon. In the last decade the Australian and Queensland Governments have invested tens of millions of dollars in programs to reduce sediment supply to the GBR. Today there is a growing demand for more natural bank stabilisation involving “bioengineering” methods including bank battering or sloping, deflection structures (such as permeable biodegradable groynes), riparian and bank revegetation, and stock exclusion. Most evaluations of the effectiveness of these expensive measures are qualitative rather than quantitative, and they have not been evaluated in the GBR catchments. Erosion in a four kilometre reach of the Mary River in SE Queensland has produced 1.9 Ma m 3 of sediment since the 1950s with two-thirds estimated to have reached the GBR lagoon. This study reports the effectiveness of a program of bioengineered bank protection in this reach. A 50 year record of erosion shows a linear relationship between bank erosion rate and flood magnitude. This relationship allows us to show that post-remediation, a large flood in 2022 produced 80% less erosion (and sediment) than would have been expected by that size flood before remediation. A before and after comparison (adjusted for flow) using LiDAR suggested an even greater reduction in effectiveness with over 90% reduction in sediment production. Similarly, up and downstream control sites experienced increased erosion during the 2022 flood whilst the treatment sites experienced dramatically reduced erosion. These results suggest that bioengineered river-bank protection can be considered an effective treatment for reducing sediment to the Great Barrier Reef and in other similar sized rivers.