Small scale landscape remediation update
The LDC is helping landholders in the Bowen, Broken, Bogie (BBB) develop cost-effective designs to remediate small-scale gullies to reduce soil erosion and improve water quality.
Technical experts have been visiting properties to determine the most appropriate on-ground solutions.
They have worked alongside graziers to design and deliver the treatments, using local contractors where possible and sharing resources to help reduce costs.
We recently completed six small-scale gully projects in the BBB, trialing options such as diversion banks, water spreading structures, sediment traps, and within-gully structures.
Alluvium and Verterra have established an Unincorporated Joint Venture (UJV), known as the Landscape Restoration Joint Venture, with the purpose of collaborating to provide high quality, integrated, evidence-based solutions for surface water, soil and vegetation management services that aims to deliver a range of environmental and economic benefits.
The UJV is overseen by a management committee whose role is to ensure the purpose and objectives of the UJV are implemented.
This Landscape Restoration Joint Venture has been commissioned by NQ Dry Tropics to provide gully and erosion technical design services as part of the LDC project.
THE gully catchment has an area of about 14.7 ha, the aim of the remediation design is to divide the runoff within the catchment and direct it into two chutes.
The catchment area for each of the chutes is about 60 per cent of the total area, or 8.8 ha.
On ground works were completed by local contractor Colls Earthmoving.
The design was undertaken by Alluvium Verterra and included two rock chutes and a bund wall which diverts water off the gully and directs the water into the chutes and down into the more stable outlet of the gully.
The earth bund was constructed with material from the gully, so the gully was reshaped and smoothed as part of the design. Gypsum was used in the construction to stabilise the bund wall and area around the chutes.
An electric fence has been put up around the site to exclude cattle and the site has been seeded with a revegetation seed mix.
Alluvium Verterra undertook a gully toolbox assessment of the sediment savings at the site and it is estimated that this project will save 120 tonnes of fine sediment per year.
With this saving, the total cost effectiveness of the project was $341.6 per tonne per year and final works came in $6500 under budget which improved the cost effectiveness.
PROJECT design was undertaken by Damon Telfer of Fruition Environmental and included the construction of two earth banks with adjacent level sills to spread potential by-wash flows into stable grassed areas.
The banks are designed to capture and slow the flow of water through the open channel and allow sediment to settle out of the water column.
Their purpose is to:
- Increase the time of flow concentration by lowering runoff velocity
- Increase the length of travel of runoff flows
- Increase water infiltration and absorption of runoff flows in the catchment
On ground works were carried out by the landholder.
The landholder will also implement a grazing management plan to ensure the banks are well grassed and not impacted by cattle padding.
Fruition Environmental undertook an assessment of the sediment saved at this site and estimated it to be 4.6 tonnes per year.
Due to using the landholder’s machines and NQ Dry Tropics staff undertaking the set out of the site, the project came in $3000 under budget making the total cost effectiveness of the project $2210 per tonne per year.
GLEN BOWEN STATION
THE project site is in a broad natural depression that drains runoff from the natural levee formed on the Bowen River bank.
On ground works included the construction of two earth banks to help control event runoff.
Damon Telfer, of Fruition Environmental, developed the design and local contractor Colls Earthmoving completed the works.
It is estimated that the earth banks will save 11 tonnes of sediment annually.
The banks are 250m and 350m long, designed to capture and slow the flow of water through the open channel and allow the sediment to settle out of the water column.
Both banks had level sills constructed to allow the safe release of the water once the bank capacity was reached.
The total cost effectiveness of the project was $3052 per tonne per year.
The Strathbogie project includes remediation of two sites with the goal to:
- stop gully head cut erosion;
- stabilise gully floor and side bank erosion;
- reduce catchment run off; and
- reduce silt escaping from the catchment project area to near historic natural levels.
The project was designed by soil conservation adviser John Day, of Emu Ridge Pty Ltd, and on ground works were carried out by local contractors On Property Management Solutions.
The design consists of a number of diversion banks with level sills which are used to slow and spread the water on the black soil flats and allow the sediment to be trapped in the banks borrow pits and level sills.
There is also a grade controlled rock chute at the outlet of the site which protects against scour.
There has been extensive ripping undertaken as part of this project which will also allow the water to be slowed and captured in the landscape, improving infiltration capacity in the soil.
Permanent fencing has also been put up as part of this project to exclude cattle form the project site and the control gully.
The site is also monitored by CSIRO for water quality using a control and design gully.
This site has been estimated to lose 100 tonnes of fine sediment per year which gives this project an overall cost effectiveness of $450 per tonne per year.
THE target gully has a catchment area of 27.6ha and the actively eroding sections of the gully extend for about 600m.
There are numerous active nickpoints and headcuts with the main process driving erosion being overland flow.
The gully width is on average 6m (ranging from ~4m to 10m), with a depth of 0.4 to 1.2m.
The landscape remediation project at Riverview was designed by Damon Telfer of Fruition Environmental, and constructed by local contractor On Property Management Solutions.
The design consists of a rock chute at the top of the catchment to stabilise the headcut and four earth banks with level sills.
The banks are between 40 and 75m long with level sills ranging from 30 to 50m long.
The design is estimated to save 17.2 tonnes of fine sediment per year by holding water up in along the diversion banks and spreading it over the landscape which will also improve infiltration.
The cost effectiveness of this site is $1778 per tonne per year.
THE landscape remediation project at Tabletop is an extension to an existing NQ Dry Tropics’ Reef Trust IV project.
The design was undertaken by soil conservation adviser John Day, of Emu Ridge Pty Ltd, and Sheyanne Frisby for NQ Dry Tropics and LDC.
On ground works were completed by local contractors On Property Management Solutions.
The project included designs for four sites, LDC contracted the construction of two of these sites, and the landholder will be undertaking works on the other two sites.
The design consisted of a series of earth banks and ripping at one site, and rock checks placed in the main channels of a scalded gully at the second site.
Construction of the project is almost complete, however the estimated sediment saving is 15 tonnes per year giving the Tabletop project a cost effectiveness of $640 per tonne per year.
THE delivery of The Reef Trust is coordinated jointly between the Australian Government, including the Great Barrier Reef Marine Park Authority (GBRMPA), and the Queensland Government.
Established in 2014, the Reef Trust was a component of the Reef 2050 election commitment to develop the Reef 2050 Plan and establish a Reef Trust.
The Reef Trust is one of the key mechanisms assisting in the delivery of the Reef 2050 Plan, and focuses on known critical areas for investment — improving water quality and coastal habitat along the Great Barrier Reef, controlling the current outbreak of crown-of-thorns starfish, and protecting threatened and migratory species, particularly dugong and turtles.
The fourth phase of action focuses predominantly on reducing key pollutants — sediment and nutrients — to strive towards the Reef 2050 Plan’s ambitious targets for improved water quality entering the reef lagoon.