The Mary River has undergone significant land use pressures since European settlement. Riparian and floodplain vegetation has been cleared and there has been extensive extraction of the alluvial sands and gravels from the channel. Within the Kenilworth reach of the Mary River these changes have resulted in significant channel widening and channel straightening since the 1950s. Following the 2013 flood this reach was considered one of the most actively eroding reaches in the GBR catchments.
In 2014-15, stakeholders worked together to develop a rehabilitation plan. The plan made costed, prioritised recommendations for the management of riparian, instream and floodplain zones based on the geomorphic and hydraulic processes and threats. Since the development of the plan, significant soft engineering and revegetation works were implemented between 2014 and 2021. The impact of these works on stream stability were analysed following the 2022 floods (the largest in 30 years) using geomorphic assessments and multi-temporal spatial analysis.
The works were highly effective in resisting major channel change during the 2022 floods. The analysis indicated the reach scale works have significantly reduced rates of lateral channel change and reduced sediment loads from this reach by between 90-95%, and saving 12kT/year of fine sediment delivery to the reef. There has also been a significant improvement in riparian condition. Additional investment is required to improve instream habitat values, however these interventions are not currently funding through Great Barrier Reef water quality programs.
The work highlights how well planned, reach scale management plans can effectively reduced sediment loads and improve riparian condition. The efficacy achieved from these works is significantly higher than the assumed efficacy used in Great Barrier Reef water quality programs.