Five rock chutes were constructed as part of phase two of the Mt Wickham gully remediation project. The chutes were designed to intercept flows and reduce flow rate.
Cost savings achieved in the management of the Landscape Remediation activity area of the LDC project have been reallocated to the maintenance of gully sites near Collinsville on Belmore Downs, Havilah (Sites 1 and 2), and Weetalaba.
Work currently being carried out includes:
- Extending rehydration banks to disperse overland flows.
- Reshaping slumping on walls to address erosion and structural issues.
- Installing rock armour at key points including at the end of banks and on level sills next to banks.
- Applying gypsum in subsided rock work to help address tunnel erosion.
- Filling in rills to address erosion.
- Tube stock maintenance.
This activity area is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.
The highly-erosive soil across these sites makes remediation difficult. This is typical of floodplains within the dry tropics catchments.
Approaches must be tailored to each individual site to ensure lasting water quality improvements for the Great Barrier Reef lagoon.
The approach involves reshaping gullies and treating the chemistry of soil to neutralise its reactivity, using gypsum or lime. Rock capping and organic mulch, along with revegetation, ensures the surface layer becomes more resilient to intense rainfall.
When it works well, it effectively shuts down the sediment supply from the remediated gully within a relatively short time frame, sometimes within a year.
Monitoring remediation work on gullies is important to deal with any issues that arise, and for determining success.
Post wet season monitoring will be carried out.
Why is gully remediation and maintenance in the BBB catchment a focus for investment?
The Burdekin catchment is the largest contributor of anthropogenic fine sediment loads of the 35 catchments that drain to the Great Barrier Reef lagoon so best management practice is essential.
It delivers, on average, 3.3 million tonnes per year; more than double the load of any other catchment. Most comes from gully erosion in grazing areas.
The Bowen Broken and Bogie (BBB) river catchment encompasses an area of 11,718km2, and is part of the much larger Burdekin River system (130,000 km2 ). Despite its relatively small size (less than 9 per cent of the Burdekin, and less than 3 per cent of the total catchment area draining into the Great Barrier Reef, the BBB catchment generates almost a quarter of the total fine sediment load into the GBR lagoon.
About 65 per cent of that fine sediment comes from gully erosion. A total of 22,311 active gullies were mapped within the BBB study area (~3,500 km2 ), with a cumulative active area of 4,620 ha.
This makes gully remediation in the BBB catchment a focus for investment activity. Gully remediation in this landscape is challenging.
The area is vast, sparsely populated and poorly serviced. The climate exhibits a pronounced wet and dry season, with most rain falling in intense falls between November and April.
Average annual rainfall is 715mm (28.1 in), with significant year-to-year variability. The window for undertaking large-scale earthworks is often narrow, and revegetation is constrained by water availability.
Many of the gullies are a legacy of historical land management, and unrelated to current land management practice or current owners. Many gully works involve high capital cost, and deliver little private benefit to the landholder.
Characteristics vary considerably between gullies, requiring tailored treatment plans for each gully.
NQ Dry Tropics’ response
For the past seven years, NQ Dry Tropics has trialled a suite of landscape interventions and land management efforts at a catchment scale to improve water quality and long-term sustainable land management in the BBB.
This work has been funded by the Queensland Government through the Queensland Reef Water Quality program, and the Australian Government through the Great Barrier Reef Foundation and the Reef Trust Partnership.
The project was born from recommendations made by the Great Barrier Reef Water Science Taskforce. It was called Landholders Driving Change (LDC).
LDC was designed from the ‘ground up’, with actions and support targeted to landholder needs in a flexible, tailored way.
LDC trialled a mix of new and conventional activities to achieve land management outcomes at a landscape scale, providing a foundation for the adoption of improved management practices for increased sustainability, profitability and for management of erosion and sediment loss.
NQ Dry Tropics understanding of where and how to remediate gullied landscapes in the dry tropics has grown from a low base seven years ago, to now having a significant body of guidance.
Work arising out of the LDC includes:
- transferable procedures for the remote sensed mapping and characterisation (including load estimates) of gullies;
- an extensive, spatially-explicit, GIS dataset that identifies, characterises and prioritises 22,311 active gullies within the BBB area;
- a framework for site selection that incorporates a range of biophysical and socioeconomic considerations; and
- a spatial prioritisation based on cost effectiveness that incorporates the biophysical characteristics and socio-economic considerations.
The Burdekin Major Integrated Project Gully Maintenance and Monitoring project is funded by the Queensland Government, through the Queensland Reef Water Quality Program. The Landholders Driving Change Program is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.
