Government water quality targets provide the context for LDC project

In response to the ongoing water quality impacts affecting the health of the Great Barrier Reef (GBR), the Queensland and Australian governments have set ambitious targets in the Reef 2050 Long Term Sustainability Plan (Reef 2050 Plan) to reduce pollutants in key reef catchments by 2025 (up to 50% reduction in sediment run-off and up to 80% reduction in nitrogen).
The Queensland and Australian governments also released a new Reef 2050 Water Quality Improvement Plan in July this year that comprises a revised set of catchment targets that can be read here.

Mt Wickham: LDC tackles first large gully remediation

LANDHOLDERS Driving Change is conducting a large-scale gully remediation project on Mt Wickham.
In mid-August, LDC staff walked the landscape with local contractors looking to be involved in these major works.
They were joined by representatives from ecological engineering firm Verterra, a principal partner on the project, who developed the gully remediation technical design.
Vertarra informed local contractors about the design process, approach and methods being used on the Mt Wickham site.
Contractors will lodge quotes for consideration to undertake works and it is hoped that works can start by the end of September.

Why Mt Wickham was chosen as a demonstration site

The LDC project contracted gully remediation experts to develop a range of criteria to help locate a ‘typical’ large-scale sodic gully rehabilitation study site in the BBB.
Criteria included biophysical traits such as:

  • size of the gully;
  • soil type; and
  • that possessed typical erosion features the LDC project is trying to fix.

Other factors include (but not limited to) that the site can:

  • demonstrate a range of gully remediation techniques and solutions;
  • show the outcome of various remediation treatments, and if they are transferable and cost effective;
  • be easily accessible;
  • be able to host field days; and
  • a willing landholder to host a demonstration site. (We are grateful to the owners of Mt Wickham for allowing the project to undertake remediation works on their property).

On ground monitoring and integration with *NESP 2.1.4. research shows that the total suspended sediment (TSS) concentrations vary considerably between gully sites in the BBB, with the highest mean concentrations being measured at the Mt Wickham site (coming in at ~ 57,000 mg/l). This gully has highly sodic sub-surface soils.
By comparison, other gullies being monitored reached peak concentrations about 10% of those at Mt Wickham (between ~5000 and ~11,000 mg/l).
The total nitrogen (TN) concentrations follow a similar pattern to TSS when comparing the control and treatment sites.
Interestingly, although Mt Wickham has much higher TSS concentrations than the other sites, the TN values are not statistically different.
The demonstration site will be monitored and evaluated using a range of practice, vegetation, runoff and water quality measures.
CSIRO has installed monitoring stations at two gullies at Mt Wickham – the treatment gully that will undergo remediation and a control gully for reference.
Each system is comprised of the following components:

  • metal stand or frame;
  • ISCO water quality sampler;
  • depth transducer;
  • turbidity sensor;
  • telemetry communications;
  • rain gauge; and
  • camera.

Results of the study site (including the smaller gully remediation trials being carried out across the BBB) will inform a strategic investment plan for landscape remediation in the BBB.
The purpose of this plan is to provide a scientifically robust strategy for widespread implementation of cost effective landscape remediation in the catchment, and to guide transferring the learnings from the demonstrations sites at larger scales.
The strategic plan will be informed by landholder input on the practicalities of implementation, particularly for smaller erosion features across large areas.
It will involve a multi-pronged approach recognising works that can be achieved by landholders, works that will require dedicated public investment, and works that may be hybrid of both of these approaches.
*National Environmental Science Program

Principles of gully management

Sediment source tracing, erosion mapping and catchment modelling studies show that gully erosion contributes approximately 40 per cent of all fine sediment to the Great Barrier Reef Lagoon.
This makes gully management a high priority for investments to reduce sediment loads.
The principles of gully management success are:

  • to increase the efficiency of sediment trapping within gullies;
  • improve vegetation cover in gully features to improve stability; and
  • to reduce surface runoff into managing gully erosion to improve water quality in the Great Barrier Reef Lagoon


Reef regulations - grazing, standard conditions

  1. For land in good or fair condition (more than 50 per cent ground cover at 30 September), continue using measures to maintain land condition.
  2. For land in poor condition (less than 50 per cent ground cover at 30 September), steps must be taken to improve land condition.
  3. For land in degraded condition (less than 20 per cent ground cover at 30 September), steps must be taken to improve land condition OR prevent areas from further degrading or expanding.
  4. Keep records of measures taken and also of agricultural chemicals, fertiliser and mill mud or mill ash applied to land.
KEQ #8

KEQ #7
KEQ #6

KEQ #5

KEQ #4

The LDC project monitors four gully sites (represented in this table) with gold standard equipment and analysis, carried out by CSIRO.

Results have been compiled in a preliminary report from Bartley et al (2020), with the final report expected to be released by the end of 2020. The preliminary report shows all four sites have indicators of improvements, notably the Strathbogie and Mt Wickham sites.

KEQ #3

*The Exploring New Incentives activity area has provided an opportunity for graziers to adopt improved land management practices through a range of activities. For some of these properties, it was the first time they signed contracts for on-ground works.

KEQ #1

Figure 1. Total fine sediment reduction by project type and erosion source. Inset shows the proportion of the total project area for each project type.

These estimates have been calculated using two methods: 

1) The pollutant reduction component of the Alluvium/Great Barrier Reef Foundation (GBRF) investment tool for hillslope and streambank erosion management projects; 

2) The Reef Trust Gully Toolbox method for gully erosion management projects. The LDC Water Quality Report 2020 (Waterhouse et al., 2020) highlights that a number of assumptions underlay these calculations, therefore these figures should be treated as the best available estimate of sediment reductions to date.

Preventing sediment from reaching the Great Barrier Reef

Each wet season sediment is washed into local waterways and out to the Great Barrier Reef (GBR). 

Most sediment is very fine, and can stay suspended for a long time and can travel great distances. Valuable topsoil is lost from production, and increased concentrations on the reef can be harmful to seagrasses and corals. 

Landholders in the BBB have completed 69 on-ground water quality practice changes, and it is estimated that these have contributed a fine sediment reduction of 6,154 tonnes per year from reaching the GBR. 

Of this, approximately half of the sediment savings are attributable to grazing land management changes on hillslopes and streambanks, and the other half as a result of gully remediation treatments across a broad range of scales, as shown in the graphs above. 

The table below also highlights the relatively small area of intervention in the gully management projects compared to the large sediment savings that these can achieve - 60 per cent of the sediment savings over only 4 per cent of the project area.

Table 1. Estimated sediment reductions (tonnes) from projects completed in the LDC Project to date.

KEQ #2

*GLMWW = Grazing Land Management Wire and Water

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