The Mary and Burnett rivers are two of the five highest contributors of fine sediment to the Great Barrier Reef (GBR). Streambank and gully erosion from the Burnett and Mary catchments impact on the Great Sandy Strait Ramsar Site, Fraser Island World Heritage Area and GBR marine and coastal ecosystems.
Modelling of streambank erosion in the Burnett Mary indicates that it is responsible for approximately 62% of the end-of-basin total suspended sediment.
Grazing is the dominant land use in the Burnett and Mary catchments and is one of the main contributors of human induced fine sediment through sub-surface erosion (i.e. gully erosion, direct stock impacts on streambanks and low groundcover). Catchment runoff, with the resulting pollutant loads and poor water quality, is considered to have the greatest overall impact on coastal and marine assets in the Burnett Mary region with the catchment sediment loads assessed as very poor – ‘E’ under the Reef Report Card 2016.
Based on our current understanding, the Mary catchment poses the greatest challenge to the marine ecosystems of both the Great Sandy Strait and the GBR.
The Burnett catchment covers 3,304,000ha and is the largest in the region. Record-breaking flooding in the Burnett River in 2013 exacerbated concerns about sediment being delivered downstream and ultimately to the GBR. In the Burnett River, bank erosion was found to be largest contributor of sediment from this catchment, representing around 44% of the total annual sediment budget. The dominant land use in the Burnett catchment is grazing, across 2,500,000 ha, or 77%, of the catchment area.
The Mary catchment covers 930,000 ha and is the fourth largest contributor of anthropogenic total suspended sediment (TSS) to the total Reef TSS load (estimated 301,000 tonnes / year). The dominant land in the Mary catchment is grazing, representing 472,000, or 51%. Sediment from this catchment has been identified as a key threat to the ecological character of the Great Sandy Strait Ramsar site3, with flood plumes delivering large sediment loads to the GBR lagoon and impacting on World Heritage Outstanding Universal Values.
The lower Mary River catchment (Susan River) is hydrologically complex and contains significant interconnected coastal wetlands. BMRG is increasing effort in this sub-catchment because of a greater understanding of its importance for end of system water quality. Grazing in coastal wetlands (saltmarsh ecosystems) is widespread throughout the Susan River, whilst other land uses include including sugar cane and peri-urban / urban development.
In the 2016 Reef Report Card, the Burnett Mary was assessed as a ‘D’ for grazing practices progress against best management practice systems, which indicates there is room to improve management practices for water quality outcomes. Currently there is an estimated 46% of area under best management practice systems for pasture (groundcover) management, 49% for streambank and 30% for gully management.
Through this project, BMRG will partner with the Burnett Mary community to build resilient streambanks and restore coastal wetlands at priority sites to reduce the export of fine sediment to the Great Barrier Reef.
BMRG will work with landholders between 2018 and 2022 to implement innovative protection measures and improved land management practices to rehabilitate streambanks and wetlands, reducing sediment discharge to coastal waters. This work will contribute to targets of the Reef 2050 Water Quality Improvement Plan.
BMRG will also prepare two river management plans (Burnett and Mary) to identify priority streambank erosion and riparian vegetation rehabilitation sites and prioritise remediation actions to halt sediment loss.
The project will also improve community and industry skills, knowledge and capacity via meaningful project involvement, training and demonstration.