The application and adaption of mine site rehabilitation approaches to alluvial gully rehabilitation in the Bowen Catchment
Led by: Dr Andrew Brooks, GU
This project will develop the partnerships and the institutional framework for implementing large scale innovative rehabilitation works which aim to directly reduce sediment supply from the large alluvial gullies on the lower Bowen River. These gullies are the largest single source of suspended sediment loads into the Great Barrier Reef (GBR). The project will work directly with Glencore and Q Coal, who are some of the largest grazing landholders along the section of the Bowen River with the highest concentration of large alluvial gullies. The central premise underpinning the strategy is that alluvial gully rehabilitation is more akin to mine site rehabilitation, and such techniques are more appropriate for tackling this major GBR sediment source than grazing BMPs. The strategy aims to draw upon the mine site rehabilitation experience and expertise within these two major Queensland mining companies, applying and adapting mine rehabilitation approaches to the rehabilitation of alluvial gullies.
The Burdekin River (catchment area ~ 130,000 km2 ) is estimated to deliver about 47% of the total suspended sediment load to the GBR (Waters et al., 2013), some of which is contributing directly to the Crown of Thorns Starfish (COTS) initiation zone to the north of Cairns. The Bowen/Bogie catchment contributes ~ 65% of the silt/clay load at the Burdekin River mouth from just 9% of the total Burdekin catchment area (Bainbridge et al., 2014). This equates to around 30% of the total input to the GBR lagoon, making it by far the single most significant source hotspot contributing sediment to the entire GBR.
What is it about the Bowen catchment that makes it such a dominant source of sediment to the GBR? A key factor is that the Bowen catchment enters the Burdekin mainstream channel downstream of the Burdekin Falls Dam – which traps a significant proportion of the sediment sourced from its upstream tributaries. However, this is only part of the explanation. The other key characteristic of the Bowen River; particularly along the lower 100km of the river; is that the alluvial floodplains and terraces in this section of the catchment are littered with large alluvial gully complexes (Brooks et al., 2009) which are delivering vast quantities of fine sediment directly into the main channels of the Bowen and Burdekin (downstream of the Bowen confluence), which is then transported directly out of the Burdekin catchment to the reef lagoon. Sediment contributed to the channel at this point in the drainage network has few opportunities for deposition before it reaches the catchment outlet. Hence, not only are these sediment sources akin to a series of intensive point sources, they are also highly connected to the reef lagoon.
The connectivity of the alluvial gully sediment sources was graphically demonstrated when an early wet season storm hit the area in November 2015 causing the river to become highly turbid almost instantaneously (Figure 4). By comparison, sections of the river immediately upstream, which were unaffected by the storm cells, were running clear. Clear water flow is the typical scenario for the dry season low flows in this part of the Bowen River.
Given the concentration of these large alluvial gullies along the lower Bowen catchment, and the disproportionate contribution of sediment from these sources, developing appropriate methods to rehabilitate these gullies is arguably the single highest priority sediment management task across all GBR catchments. This is especially so if serious inroads are to be made into improving GBR water quality over the next decade.
Results from initial plot trials in alluvial gullies in the Normanby (Shellberg & Brooks, 2013) indicate that sediment reductions of 75% from active alluvial gullies are achievable within a two year timeframe. The challenge now is to up-scale these results on an industrial scale to some of the highest priority alluvial gully point sources in the Bowen Catchment, and to demonstrate how similar results can be achieved on similar timeframes over entire gully systems.
The lower 100km of the Bowen River where the major concentrations of alluvial gullies are located is dominated by around ten large grazing properties. A number are owned by mining companies, although they are managed as grazing properties. Traditionally the management of sediment sources from grazing land has focused on the application of industry agreed standards for grazing “best management practices” (BMPs), which to date have not typically targeted sediment sourced from gully erosion processes. Indeed the available evidence (Bartley et al., 2014) indicates that the application of grazing BMPs fails to induce a significant reduction in sub-catchment sediment yields following 10 years of implementation. The explanation for this result is that the treatment is not targeting the primary erosion processes, which in this case are associated with hillslope gully, scald and channel erosion processes. The chances of grazing BMPs, or even complete stock exclusion, reducing sediment yield from highly active alluvial gully erosion is even less likely than the scenario described by Bartley et al., 2014.
The aim of this project is to develop a large scale collaborative project with at least two of the mining companies which are major landholders on the lower Bowen River, with a view to building partnerships to implement large scale direct action management of these key sediment sources. The project will build on connections already established as part of the NESP round one project, focusing initially on two of the large grazing properties owned by mining companies.
How Research Addresses Problem
This project will deliver a large scale rehabilitation framework in collaboration with some of the largest mining companies in Queensland which aims to adapt and apply mine rehabilitation techniques to the problem of rehabilitating alluvial gullies.
Alignment with NESP Research Priorities
This project addresses priority 1, Reducing water quality Impacts: Identify and prioritise practical management actions capable of protecting and improving water quality in the Great Barrier Reef region, and includes components which address sub-sections a, b and c :
a) Local scale identification of priority contaminant export loss (hot spots) for better targeting of on-ground works and extension activity.
b) Determining the source and marine fate of environmentally relevant sediments.
c) Develop/evaluate practical on-farm nutrient and sediment loss mitigation and capture and land management practices that will influence behavioural change and improve water quality outcomes – link to field trials.
This project will provide the basis for a strategy to make significant inroads into Reef 2050 targets.
This project will also provide information that is crucial for enabling the gully rehabilitation investments to meet their stated objective of significantly reducing sediment and nutrient yield within the next 10 years. In so doing it will provide important input into the:
- Reef 2050 Long-Term Sustainability Plan
- Water Quality Improvement Plans (implementation phases; Burdekin, Cape York, Fitzroy, Herbert)
- Great Barrier Reef Water Science Taskforce and Independent Expert Panel
Alluvial gully erosion; Mine site rehabilitation; Bowen River; Sediment hotspots; Demonstration projects.
This project is jointly funded through GU and the Australian Government’s National Environmental Science Programme.
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