LDC’s fifth large gully repair will benefit two properties

LDC’s fifth large-scale gully remediation site is at Havilah Station. Works are expected to start in July.

The Havilah gully site has been selected as a priority project, based on the work completed by the Griffith University project team as part of the LDC project to characterise and prioritise gully remediation across the BBB catchment. 

The works consist of two main gully systems within the gully site and bounded by a proposed fenced area about 1800m long (west-east) and 650m wide (north-south).  A proposed 5000m fence boundary will enclose 110ha of the revegetation plan. 

The majority of the site is located on Havilah Station, with a portion to the east on Gattonvale Station. This partnership between the two properties will mean the effort on one property to halt the gully expansion will be of benefit to both.

The first gully is elongated and the proposed works include two grade control rock chutes, one about one third along the gully and a second about two thirds along the gully. 

An overland flow bund will be constructed to assist with directing water flows to the upper chute. The lower chute will hold the water to encourage sediment deposition.

Reshaping works are proposed at the head of the gully to assist with overland flow and revegetation.

Proposed works on the second gully include a 4m wide rock chute to remediate the gully head cut and to prevent further propagation towards the road. Two bunds either side of the chute will assist with directing road runoff to the design grade control rock chute.

The lower part of the gully will be remediated to remove tunnelling to scalded lower sections of gullies. Gully reshaping works will be completed in the head cuts adjacent to the chute.

The technical designs have been prepared by engineering firms Alluvium and Veterra, and Veterra will project-manage the works. Local contractors will carry out the work.

Onsite inspections of the proposed works have been conducted and final agreements with the landholders completed.

NQ Dry Tropics is working through the final approvals required by the State Assessment and Referral Agency to meet the required State Development Assessment Provision State Codes.

Construction is expected to start in July 2021. 

Progress photos, and before and after works photos will be shared with the BBB community in the Summer edition of The Grit at the end of this year.

Work at Mt Wickham complete, waiting for the first rain.

First large-scale gully was at Mt Wickham

Alluvium and Veterra partnered with LDC to rehabilitate the project’s first large-scale gully remediation site at Mt Wickham Station. 

Read about it, and check out the progress photos in the LDC’s Landscape Remediation Halfway Update

They also worked with LDC to rehabilitate a large-scale gully on Strathmore Station. You can read about those works in this story.

The work stood up well against some of the heaviest rainfall in the district for many years.

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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.

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*GLMWW = Grazing Land Management Wire and Water

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*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.

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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.

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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.
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