The rootballs of trees are part of a new engineered solution for erosion along the Herbert River near Ingham.

About 180 metres of flood-damaged riverbank has been repaired using five rootballs combined with more than 2000 tonnes of rock – for a rockwall with a difference.

Strengthening riverbanks, creating fish habitat

Terrain NRM’s Lana Hepburn said the result would both strengthen the riverbank and create fish habitat.

“The hardwood is wedged trunk-first into the lower riverbank so the rootballs are in the water, with rock benching holding them in place,’’ Lana says.

“The rootballs add complexity to the waterway, creating eddies and different flow rates which moves the fast-flowing water away from the toe of the streambank to prevent more erosion. They also create places for fish to rest and feed.

Erosion since 2009 wet season

She said the riverbank had been eroding at the site since 2009 and the 2021-22 wet season had worsened things, with more riverbank vegetation lost to flooding.

“Since 2009, the riverbank has retreated 20 to 40 metres on average across the site. The toe of the riverbank – the point where the riverbed meets the bank and supports the weight of the bank –became completely unvegetated. So when the 12 metre high bank was hit by fast water, it was eroding at the toe and collapsing, sending soil down the river and fine sediment out to the ocean.”

Cane farmer Mark Zatta, whose land borders the river, says he’s “stoked”.

“Originally we had about 50m of rainforest along the river but we were losing it over time. All of a sudden, in one river rise, a whole lot was gone. Once the first wall (of riverbank) dropped, it just kept collapsing. It’s on the outside of a bend in the river where the river pushes around.

Less soil is being lost to creeks and rivers on the southern Tablelands thanks to changed grazing practices and to solutions like rock chutes for eroded gullies.

Seven farming families have been working with not-for-profit environmental organisation Terrain NRM and grazing and soil health specialists for the last seven years on changes that range from dividing paddocks up and rotating cattle differently to building up vegetation coverage where rock chutes and bund walls have been built to stop gullies from eroding any further.

Graziers say the results include better pastures

“What we’re seeing is more feed and better-quality feed,” Woodleigh Station’s Pete Waddell says. “We’ve fenced to cut paddocks up and we’re now running bigger numbers of cattle on smaller areas rather than the reverse, which is the traditional approach. I’ve seen a marked improvement in the condition of country.’’

Preventing 4,500 tonnes of fine sediment from reaching the Reef annually

Terrain NRM’s Duncan Buckle says the combined impact of 10 erosion-control structures, and grazing management changes across six cattle stations, is keeping thousands of tonnes of soil on the land each wet season and stopping an estimated 4,500 tonnes of the really fine soil particles (the equivalent of 225 semi-trailer loads) from becoming sediment on the Great Barrier Reef each year.

“Fine-tuning grazing management practices and making the land more resilient has been a big part of these two projects,’’ he says.

“It’s the key to reducing erosion in the Herbert River catchment. We’ve been working with graziers to improve the health of grassland ecosystems and cattle, and to improve production.

Managing cattle to improve soil health

“We look at ways to manage cattle to promote soil health because improved soil health results in thicker, healthier, more nutritious pastures. And getting more roots in the soil means the soil can absorb water better and hold together better.”

Grazier Curtis Archer says changes on Glen Ruth Station are creating better pastures and making it easier to handle cattle and control weeds like lantana with fire.

Splitting paddocks for a three-paddock rotation system

“We’ve split paddocks in half and gone to a three-paddock rotation system in the river country and another three-paddock system to manage the creek flats,’’ he says.

“It’s making the cattle work the country better, rather than just sitting on creek flats and always hammering them. It’s giving paddocks a more even graze and we’ve seen the dominant species take over – good native grasses. We’ve got three times the volume of grass in these paddocks, which means we can add a few more cattle now. I think there will be more and more benefits over the years.

A new $2.53 million project will reduce streambank erosion in the Ingham area of the Herbert River catchment.

Terrain NRM will be working with landholders bordering Herbert River and Stone River on projects to improve both their land and the water flowing through this catchment to the Great Barrier River.

This project is part of a $6 million investment by the Queensland Government to stem the flow of sediment into the Great Barrier Reef. Funding has been provided for projects in the Lower Burdekin, Herbert River and Fitzroy River catchments.

Building on five years of work with landholders

Terrain NRM’s CEO Stewart Christie welcomed the news, saying the project would build on five years of work with landholders in the Herbert catchment.

“With a range of engineering solutions and improved land management practices, our sediment reduction projects have prevented several thousand tonnes of sediment from reaching the Great Barrier Reef each year,’’ he said.

Herbert a priority for sediment reduction

“The Herbert catchment is a priority for sediment reduction in Queensland’s Great Barrier Reef zone. We’ve been remediating gully and streambank erosion sites through engineering work including rock walls, pile fields and rock chutes.

The top six inches of soil is an incredibly valuable resource for us as it supports our soil microbiome and grows the food, forests and grasslands we all depend on. Unfortunately, exposed topsoil can be easily lost to wind and water erosion, and the processes that create new soil can take hundreds of years.

Terrain NRM’s Landcare Leader Sally Fields says that using cover crops, mulch and holistic grazing practices are important tools we can use to fast track the soil building process and protect soil from erosion.

“Many farmers are incorporating these tools to improve soil health and farm fertility. Increasing organic matter and keeping a living root in the ground maximises water infiltration and also ensures the sunlight energy is converted into sugars for the plants and the soil microbes they rely upon,” she said. “It’s a living system – bare ground is akin to shutting shop and we need to avoid it at all costs”.

John Gargan is a grazier and horticulturalist and has planted sunn hemp into an existing perennial pasture as part of his soil building process to improve pasture health. “In just one year the topsoil has increased from about 6cm to 17cm. The pasture’s looking really rich and nice – it should have high protein levels in it so the cattle will do well,” he said.

Healthy, covered soil also acts like a sponge that soaks up the water and keeps it there for crops to access, whereas bare soil has no protection and becomes hydrophobic. Rain will run off it, taking the topsoil with it.

Rock chute a tool to improve land and Reef

The Great Barrier Reef is a long way from the Mt Garnet region – but the world’s largest collection of coral reefs is benefitting from work on cattle properties there to repair eroded gullies and keep topsoil on the land.

A 40-metre rock chute is the latest project. Built on Woodleigh Cattle Station with an accompanying 500 metres of bund walls, it is stopping the spread of a gully complex that’s now several hundred metres long.

Reducing sediment loads on the Reef

The structure is expected to save almost 200 tonnes of fine sediment from reaching the Great Barrier Reef each year and, just as importantly, prevent the loss of more productive land to erosion.

Terrain NRM is working with Woodleigh’s Waddell family as part of the Upper Herbert Sediment Reduction Project, funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.

The rock chute is the first engineered structure for a project that’s heavily focused on grazing management practice changes. Woodleigh Cattle Station’s Kate Waddell says the combination is working well on her family’s property.

“Even with good grass cover and light stocking rates, some of our soil types erode easily during heavy rainfall so there has been quite a bit of erosion over the years,’’ she said.

“It’s important to keep our soil on the property – it’s our lifeblood.”

Slowing and channelling storm water

Terrain NRM’s Jen Mackenzie said the new rock chute was slowing water and channelling it into a nearby creek.

“This is an area with historical erosion that’s several hundred metres from a creek and getting worse over time,’’ she said. “The chute was built in the worst of a series of gully heads. When it rains, the bund walls now channel all the water into the chute, and on into a pre-existing channel to the creek.”

What a difference 18 months can make – that’s the feeling at Tash and John MacPherson’s cattle property where a swag of changes is rejuvenating the land and waterways.

The family is working with natural resource management organisation Terrain NRM on a property overhaul that includes earthworks, fencing, tree-planting, alternative water sources for cattle and a fresh perspective on grazing the land.

Tash Macpherson said the results were a win for cattle pastures and the overall environment.

“When we bought this property in mid-2020 we de-stocked it for a year,’’ she said. “The land really needed a break. There was bad erosion – big wash-outs along the waterways where the cattle had been, and springs that were a boggy mess.”

Through the project, three creeks have been fenced-off, smaller grazing paddocks have been created, 5000 native trees have been planted to strengthen creekbanks, and an off-stream watering system has been installed with a bore, water tanks and troughs.

Zuni bowl, fencing, tree-planting, off-stream watering solutions…

A Zuni bowl was also constructed to stop erosion advancing in one of the paddocks.

Terrain NRM’s Vanessa Drysdale said the bowl was a carefully designed lining of rocks at a steep drop in the gully erosion.

“This was an active gully system that had eroded several hundred metres in wet seasons over the last few years, and wasn’t going to slow down without intervention,’’ she said. “The traditional solution is a rock chute, but Zuni bowls are a more cost-effective treatment method that has proved its worth on Tableland and Daintree farms over the last few years.”

Saving sediment from reaching the reef

She said the combined work on the MacPherson property would save an estimated 180 tonnes of sediment from flowing to the Great Barrier Reef each year. It’s one of 11 properties where earthworks, tree-planting, fencing and off-stream watering infrastructure strategies have provided long-term solutions to erosion issues.

Timber pile fields will help to protect the Mossman River and two of its bridges in the upcoming wet season.

Flood-damaged riverbanks at Foxton Bridge and Anich’s Bridge in Mossman have been repaired using pile field structures, bringing a new approach to erosion solutions to the Far North.

Terrain NRM has been working with Douglas Shire Council, landholders and Neilly Group Engineering on the two river projects, which are jointly funded by the Australian and Queensland governments under Disaster Recovery Funding Arrangements.

Terrain’s Jen Mackenzie said floodwaters had stripped back 80 metres of riverbank at Foxton Bridge and 30 metres at Anich’s Bridge.

“A monsoonal event in early 2019 left trees hanging by their roots and changed the river’s course,’’ she said. “Now the erosion is progressively threatening these bridges and the rail corridor. Without enough land for rock battering or vegetation on the banks themselves, timber pile fields are a good option.”

What are pile fields?

Pile fields are multiple rows of piles, designed to slow down water and build up sediment, to protect and repair damaged riverbanks. They are used in southern Australia and in other parts of the world, and one was recently constructed in the Herbert River catchment near Ingham as part of disaster recovery work.

“The challenge, when building these fields in the Wet Tropics, is the high volume of rain,’’ Ms Mackenzie said. “In this region more robust engineering and modelling is needed, for designs tailored to our weather conditions.”

To create the pile fields, seven-metre hardwood poles were driven five metres into the riverbed and bank. The work in Mossman also included riverbank re-profiling, rock buffers and revegetation with native trees.

Fifteen thousand young trees are sinking their roots into Tableland soil as part of a $2.3 million project to fight erosion, improve farming land and better protect the Great Barrier Reef.

Graziers are working with Terrain NRM to repair eroded creek banks.

“Trees are the long-term solution, and they work well when they are combined with earthworks in the worst erosion hotspots,’’ Terrain project manager Vanessa Drysdale said.

“Root systems hold banks together and slow water down in heavy rain events, decreasing the chances of topsoil loss and of further erosion.”

Ten thousand trees were planted in March and April, bringing the total to 15,000 since the project began three years ago.

Ms Drysdale said the latest batch of trees went into the ground at two cattle properties with waterways feeding into the Johnstone River. A new cattle crossing was installed at one of the properties and sections of streambank were fenced off at both spots to prevent more erosion while the trees gain a hold. New off-stream watering points were also installed.

The work follows creek-side revegetation projects last year at two Tableland properties – in a landslip area at Jaggan and along an eroded creek system at Malanda.

Rock chutes have been put through their paces on cattle properties in the Herbert River catchment – and they’ve been given the ‘thumbs-up’ as solutions to gully erosion and topsoil losses.

The first La Nina wet season sent floodwaters down chutes and through other rock structures that were built over the last three years on properties in the Mt Garnet and Innot Hot Springs area, and monitoring work was recently completed.

Terrain NRM project manager Jen Mackenzie said rainfall over the past five months had given the engineered structures a solid testing period.

Four rock chutes have been constructed on cattle stations, along with bund walls, and different rock structures were installed at tailings dams from historical mining ventures on cattle properties.

The annual monitoring also includes inspections of native grasses, planted at these sites as part of the projects.

“It’s all about improving the land for graziers, as well as the quality of water flowing through the Herbert catchment and out to the Great Barrier Reef lagoon,’’ Ms Mackenzie said.

Together, the four rock chutes will each year prevent an estimated 1,200 tonnes of sediment – the equivalent to 50 semi-trailer loads – from reaching the Great Barrier Reef.

Chutes range from 20 metres to 100 metres long.

Erosion takes many forms, so a range of techniques can be used to repair it and prevent it from happening again. Different solutions are used to fix gully, streambank and road erosion on farms and grazing land. They improve the condition of the land, increase production, and reduce fine sediment flowing into waterways and out to the Great Barrier Reef.

Download our Erosion Remediation Brochure.

Rock chutes are used to repair gully erosion.  They are short and steep and lined with quarry rock.

When to use them:

Rock chutes are effective in a number of situations. They stop gully erosion in catchment landscapes by controlling and slowing the water flowing over a gully head. This also prevents the headward/upward progression of erosion. Rock chutes are also used for over-steepened sections of waterway where there is high water flow and ongoing erosion. Chutes reduce the elevation while using natural waterway processes.

Things to consider:

• A well-constructed engineered rock chute typically provides longer-term erosion control.
• This is a higher-cost erosion control method, and the distance of the erosion site from from accessible quarry rock will further impact cost.

Gully complex reshaping creates smooth, gradual slopes that reduce runoff and ongoing erosion. Soil treatment and revegetation are essential parts of this technique.

When to use:

Reshaping is used on many forms of erosion gullies. It is particularly useful for stand-alone gullies caused by rain falling on steep, exposed areas with susceptible soils, i.e. where there is no catchment upstream delivering rainfall runoff to the gully. Reshaping creates smooth and gradual slopes with treated and covered soils.

Things to consider:

• A relatively low-cost technique compared with other methods.
• Some ongoing maintenance may be needed to ensure long-term success.
• Capping the finished area with topsoil is essential for the regrowth of grasses and other vegetation to hold the soil in place.

Bank battering creates a flatter, more stable gradient for steep and eroding streambanks. It is sometimes combined with quarry rocks (well-graded and suitably sized), beginning at the toe of the bank and extending to a height based on the flow of water. Planting trees and grasses is also part of the process, to stabilise the bank batter in the short and long-term.

When to use:

Bank battering and revegetation is used – without rocks – when waterways have a lower flow or when there is a tighter budget. In high-flow waterways, rock toe protection is also needed. The type of soil can be a factor too. Looser soils such as sandy loams are more likely to erode and a waterway with a lower flow may still need rock protection.

Things to consider:

• This is a higher-cost remediation control technique when rock is needed, and a lower cost technique when rock isn’t used.
• Timing of the work: If a major flooding event happens too soon after construction, it could compromise the project. The rock needs to settle, and vegetation needs to establish itself.
• Location: How far away is the nearest quarry and supply of trees for revegetation work?
• Follow-up work is needed, from watering to weed control, so the trees can get established.

Timber pile fields slow down water to better protect eroding or at-risk stream banks. They are multiple rows of numerous timber piles, of a specified diameter, driven into the streambed and bank. Timber pile fields also trap sediment, helping to build the area up to support vegetation that can eventually replace the piles as the bank’s protection.

When to use

Timber pile fields can be used when bank protection is not the only desired outcome. Other outcomes may be improved or restored instream habitat and riverside vegetation.

Things to consider:

• The stream’s sediment load: The higher the load deposition, the more likely it is that vegetation will establish and succeed the piles.
• The availability of suitable timber e.g. size, durability and strength.
• Ongoing maintenance is needed if woody vegetation does not occur naturally.
• Timber pile fields might not be suitable in estuarine or tidal areas because of marine borers.

Zuni bowls are used to repair gully erosion. They are a step fall followed by a plunge pool, lined with carefully selected and placed rocks.

When to use them:
Zuni bowls are effective in situations where a rock chute would be too large or expensive. They stop the upward progression of a gully head by stepping the water down through a rock-lined pour-over. The water is slowed further by the plunge pool at the base of the pour-over.  Zuni bowls are used for smaller sections of gully erosion, typically in relatively small and steep flow paths.

Things to consider:

• The selection and placement of rock is critical to the function and design life of a Zuni bowl. It is strongly recommended to use a machinery operator trained in Zuni bowl construction.

Whoa-boys are earth bunds/diversion banks constructed across tracks or roads. They need to be high enough to divert run-off water, and low enough for safe vehicle use. Approach and exit ramps are part of construction.

When to use

Use on existing tracks with signs of erosion or gullying, or in construction plans for new tracks.

Things to consider:

• The slope of the track and the catchment up-slope. The steeper the track and the larger the catchment, the more whoa-boys should be constructed at regular intervals.
• Some ongoing maintenance is needed so whoa boys remain intact after rainfall events.
• A relatively low-cost technique that can be undertaken by landholders, ideally with some training in whoa-boy placement and construction.