Landholders help track sediment in key waterways
The Landholders Driving Change (LDC) Community Water Quality Monitoring Group has been active for six wet seasons, since 2018.
Nine properties in the Bowen-Bogie-Broken catchments make up this group which was established to better understand the water quality variations throughout the BBB catchment, with a focus on sediment and nutrient concentrations throughout a range of flow events.
BBB graziers have collected 297 water quality samples from their local waterways to track how sediment flows from the land into key waterways.
Scientists analyse water samples to give graziers insights on how, when and where sediment moves during rainfall events into key waterways.
This data strengthens sediment and nutrient models and identifies hotspot areas for targeted land management.
The road trip provided an opportunity for James Cook University’s (JCU) TropWATER scientists Zoe Bainbridge and Steve Lewis and graziers to discuss the sample results they had taken and delve into learning more about how, when and where sediment moved throughout a range of flow events.
It was also a chance for graziers to ask questions and to hear about the latest science around water quality in the Great Barrier Reef, and how local on-ground actions in the Burdekin were helping to improve water quality.
The three-day tour included visits to Kirknie Station and Amberkolly Station, and information sessions held at Collinsville and Nebo.
Why Bowen, Bogie catchments are a focus for fine sediment source
The Bowen and Bogie catchments have been identified as the dominant contributors of fine sediment to the end-of-basin.
Catchment modelling has also identified them as having the largest area-specific fine sediment contribution to the Great Barrier Reef of all the catchments that drain into the Great Barrier Reef lagoon. The Bowen and Bogie catchments produce six times the average contribution across the region.
This is why significant investment from the Federal and State governments has been targeted to the Bowen and Bogie catchments to improve erosion control and to improve understanding of sediment sources.
A recent scientific paper has been published to explain this, Refining fine sediment source identification through integration of spatial modelling, concentration monitoring and source tracing: A case study in the Great Barrier Reef catchments (Bainbridge et al., 2023).
You can read the report here.
How data strengthens sediment modelling
Scientists use broad catchment modelling tools to understand sediment and nutrient levels across the Great Barrier Reef catchments, but they need local data to identify specific hotspot areas. That’s where community monitoring fits in.
The data collected by landholders helps pinpoint these areas, improving how sediment movements are tracked. Local waterway samples collected feed into catchment modelling for the Queensland Government’s Paddock to Reef program.
This program provides vital data across the Great Barrier Reef catchment, tracking sediment and nutrients across the landscape.
This partnership strengthens the science and trust between landholders and water quality experts.
Sampling results (provided by TropWATER, JCU)
Rainfall and river discharge
- Average to above average rainfall occurred across the BBB catchment area during the 2022-23 wet season.
Wet season rainfall (1 Oct-30 April) ranged from 610mm (Myuna) to 970mm (Strathbogie). - Below average rainfall occurred in the most recent 2023-24 season.
- Wet season rainfall across the BBB ranged from 385mm (Gattonvale) to 630mm (Strathmore). Strathbogie recorded 465mm.
- Across the two wet seasons the Myuna flow gauge recorded average (2022-23) and below average (2023-24) discharge.
Sampling and suspended sediment results
- BBB samplers have collected 297 water samples in six wet seasons since 2018.
- All sample results for each site are plotted above, with the average site concentration displayed in blue text on the graph.
- Suspended sediment concentrations measured across sites have a large range, with the Broken River site average of
- 25 milligrams per litre consistently low across all six wet seasons sampled.
- The highest concentrations were measured at the three Little Bowen sub-catchment sites.
Sediment yields
by sub-catchment
The local waterway data is now part of a peer-reviewed scientific journal, showcasing the robust study design and dedication of the sampling network.
The research highlights the value of the samples, with extensive analysis including sediment concentration and grain size, and geochemical tracing.
The paper shows sediment contributions by each sampled site, using calculated sediment loads normalised to upstream catchment area.
Key findings across the BBB include:
- Broken River contributes the lowest sediment yield (0.08 tonnes/ha/year). This sub-catchment receives the highest rainfall, and contains steep, forested headwaters.
- Rosella and Pelican Creeks each contribute ~1.8 tonnes/ha/year), and the Little Bowen River contributes >3.3 tonnes/ha/year.
The Landholders Driving Change Program is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.
