Phase two begins at Glen Bowen

PHASE two of gully remediation at Glen Bowen is about to start. Two gullies will be treated and the effect of the work will be monitored through CSIRO on-ground water quality monitoring equipment to help develop a cost-benefit analysis.

Engineering firm Neilly Group has developed the gully remediation technical design for Gully 2 and Gully 4, and will project manage the works. Local contractors will complete on-ground works and are expected to start this month.

This work follows the remediation of Gully 1 that was carried out on Glen Bowen in 2019, read about it here.

The Landholders Driving Change Landscape Remediation Activity Area is about trialing different remediation approaches to determine cost-effective solutions that can be transferred to other projects and catchments.

A number of large-scale gully rehabilitation projects are being established in the BBB with the aim of returning the catchment to a healthy functioning landscape.

Results of the study sites, including the smaller gully remediation trials being carried out across the BBB, will inform a strategic investment plan for landscape remediation.

Gully #2 at Glen Bowen Station… the gully scarp averages 2.5m-3m high.

Gully #2

THE actively-eroding footprint of Gully 2 has a perimeter of about 1km, with an internal area of 1.1ha. 

The banks of the gully scarp are on average 2.5-3m high. The drainage lines within the gully all converge to a single drainage line discharging into the Bowen River.

The Gully 2 remediation design consists of the following works:

  • Reshaping of the northern and central complex gully networks into two stabilised and free-draining basins that involves bank battering and topography reshaping through cut to fill-and-compaction earthworks operations.
  • Reshaping of the southern complex gully network into a third stabilised and free-draining basin. 
  • Reshaping of a small alluvial gully adjacent to Basin 3.
  • Construction of three rock cut-off walls at the downstream extent of each of the three basin reshaping works.
  • Construction of rock check dams in the beds of the three reshaped basins.
  • Treatment of all the reshaped surfaces to consist of:
    • application and incorporation of gypsum to all reshaped and disturbed surfaces;
    • spreading topsoil stripped from the footprint of the works; and
    • applying soil ameliorants, fertiliser and drill seeding.

Gully #4 at Glen Bowen Station… it covers an area of almost 5ha.

Gully #4

Gully 4 is about 200 metres from Gully 2.

Gully 4 differs from the other gullies of interest on Glen Bowen Station, having an upstream catchment approximately four times the size of the gully’s footprint.

The actively eroding footprint of Gully 4 has a perimeter of about 1.2km, with an internal area of 4.8ha. The banks of the gully scarp are on average 0.6m high.

The Gully 4 remediation design consists of the following works:

  • Rock chutes designed to move flows to the bed of the gully and prevent future migration of gully heads from occurring.
  • Earth bunds to be constructed on either side of each rock chute to direct flows to the crest of the rock chutes.
  • Reshape the gully network into two stabilised and free-draining basins by battering banks and reshaping land features to reduce water flows and to prevent ponding occurring on the sodic and dispersive soils.
  • The reshaping of shallow gullies and gully scarps to manage runoff.
  • Construction of a series of rock check dams to help control flow velocity and to trap sediment allowing the structures to act as drainage and sediment control devices.
  • Cover treatment will include cornet matting, hydromulch, hay or bagasse (depending on availability) to achieve 50 per cent cover of the disturbed footprint prior to the first wet season.
  • Amelioration will also include spreading of an ameliorate mix of topsoil, fertiliser and gypsum, based on soil sample results.

Traditional Owners’ cultural heritage field survey and assessment

A CULTURAL heritage survey and impact assessment was completed on Gully 2 and Gully 4 in consultation with the Birriah People to address NQ Dry Tropics’ obligations and cultural heritage duty of care under the Queensland Aboriginal Cultural heritage Act 2003 (ACHA).

Aboriginal cultural heritage surveys are conducted to identify places in the landscape which contain or embody Aboriginal heritage values, not just sites.

Michele Bird, of North Queensland Cultural Heritage Pty Ltd was commissioned, and endorsed by Birriah Cultural Heritage Services, as technical advisor and project archaeologist to assist the Birriah people in coordinating a cultural field survey of planned remediation sites.

A number of artefacts were found and Birriah Elder Algon Walsh and Glen Bowen Station landholders Christian and Melissa Cormack agreed that the Cormacks would hold the artefacts ‘on country and on homelands’ at Glen Bowen Station.

The majority of the artefacts did not appear to be in-situ at the time of their discovery due to the environmental conditions and erosion. The assessment concluded there were no impediments to accessing or traversing the project footprint.

Representatives who attended the fieldwork on Glen Bowen were Birriah Elder Algon Walsh, Birriah cultural officers James Palmer and Rasharna Prior, North Qld Cultural Heritage’s Michele Bird and NQ Dry Tropics’ LDC representative Daniel Hazelman.

NOTES BREAK… pausing just long enough to make some notes during the cultural heritage assessment of the Glen Bowen gullies are, (from left), Melissa Cormack, of Glen Bowen; Birriah Cultural Officer Rasharna Prior; North Queensland Cultural Heritage’s Michele Bird; and Birriah Cultural Officer James Palmer.


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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