Case Study – Glen Bowen | Landholders Driving Change

Reclaiming eroded land on Glen Bowen Station

The Cormack family: Melissa and Christian with children Mia and Darcy

 

January

120mm

February

95mm

March

130mm

A GULLY, covering more than 3ha of Glen Bowen Station has always been “off-limits” to graziers Christian and Melissa Cormack.

That land – an extensive gully system right next to the Bowen River – was an eyesore and not contributing to production on the property.

“Ever since we came here, it’s always been something we wanted to fix, but we didn’t know how,” Mr Cormack said.

Worse than being completely unproductive, the land was rapidly disappearing downriver, contributing up to 1500 tonnes of fine sediment annually to the Great Barrier Reef lagoon.

One of four large alluvial gullies on Glen Bowen, it was selected as the Landholders Driving Change (LDC) project’s second major gully remediation project in the Bowen Broken Bogie (BBB) catchment.

Dubbed “Gully 1”, it had an actively eroding footprint of about 3.36ha. The perimeter was about 1.1km and the banks of the gully scarp were, on average, 2 – 2.5m high.

A bund wall surrounding the affected area was in place when the Cormacks purchased the property in 2006, but it did not prevent large-scale erosion every wet season.

Neilly Group Engineering was engaged to design a solution, and they worked with the Cormacks and the NQ Dry Tropics LDC team.

They came up with a plan to reshape the complex gully network into two stabilised free-draining basins by battering banks and reshaping land features using cut-and-fill techniques and compaction earthworks.

Three smaller gullies and six scalded areas were reshaped and compacted to protect the works.

Two rock cut-off walls were also constructed downstream of the reshaping works as well as rock check dams along the contours at one metre intervals in the basins, and in the reshaped, incised linear gullies.

As added protection to the site, the existing earth bund wall around the head of the gully was reinstated where necessary, and reinforced to manage any overland flow and to use excess cut from the reshaping works.

Gypsum was added to the soil in all of the works undertaken at the Glen Bowen project site to aid the stabilisation.

An average of 20 tonnes of gypsum per hectare was used to condition soil used in all works.

Earthworks were carried out by JRT Group using local subcontractor Colls Earthmoving and the area was revegetated by Revegetation Contractors.

In a unique local collaboration, members of the Bowen Women’s Prison Working Group assisted, by manually spreading hay, bagasse and coir mesh between the rock contours to protect the soil before vegetation was established. The entire site was also drill-seeded and hydro-seeded.

The Cormacks were very much involved in the project and contributed a significant amount of in-kind support including: spreading bagasse with a tractor, removing and replacing a fence, and installing the tanks, pump and pipeline to supply water to the site.

Mr Cormack said he found himself spending a lot of time at the site and encouraged others to get involved in similar projects if they were given the opportunity.

“It’s not as big and scary to do as it sounds,” he said.

Before the project began, Traditional Owners swept the site for artefacts. North Queensland Cultural Heritage conducted an assessment of the Gully 1 site and another Glen Bowen site earmarked for a future project.

Archeologist Michele Bird, of North Queensland Cultural Heritage Pty Ltd, with Birriah Cultural Officers Algon and Paul Walsh walked the site searching for possible artefacts.

They found 16 stone artefacts including some tools.
Algon Walsh gifted the artefacts to Mr Cormack on the understanding he would keep them safe while construction was underway and return them to country when the project was complete.

The effect of work on the remediated gully will be carefully monitored. In the short term improvements in vegetation, cover and biomass, and soil condition, and reductions in erosion and gully retreat rates are expected.

In the long term, there will be improvements in runoff and sediment loads.

Remediation effort is expected to save 1,482 tonnes each year, however this is also influenced by rainfall, so those trends will take longer to detect.

CSIRO water quality monitoring is being carried out on the treatment site, as well as a control site for reference. The water quality data will be the greatest indicator of success for the project.

The Cormacks are achieving positive land management practice change as a result of the gully remediation.

Through the LDC’s BBB Grazier Support program, they completed a riparian fencing project that included fencing off riverfront country and installing off-stream watering points.

This has enabled the Cormacks to implement a grazing management plan that excludes cattle from the fragile riparian areas along the Bowen River to allow the banks to restabilise and revegetate.

It also minimises the risk of cattle impact causing gullies to be formed in the future.

Another two gully sites are scheduled to be remediated in 2020.

The Cormacks are looking forward to watching the landscape transform into productive grazing land.

Archeologist Michelle Bird (sitting) and LDC Project Manager Lisa Hutchinson with Birriah Cultural Officer Algon Walsh and Glen Bowen grazier Christian Cormack (right).

Christian and Melissa Cormack (pictured, with son, Darcy) will be hosting LDC field days at the site in 2020.

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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

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 #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 #5

KEQ #6

KEQ #7
KEQ #8

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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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