One of the most eroded stretches of a Queensland river has been transformed in a bid to stop valuable farmland washing away and polluting water.

Key points: A badly eroded stretch of Queensland's Mary River, once considered a "basket case" has been repaired

A badly eroded stretch of Queensland's Mary River, once considered a "basket case" has been repaired The $500,000 project to restore the banks included 9,000 native plants being put in

The $500,000 project to restore the banks included 9,000 native plants being put in Station owners say the transformation has been "overwhelming" and will help to protect the Great Barrier Reef

The environmental stakes are high on the Mary River at Kenilworth, which is the fourth-highest source of sediment, out of 35 catchments, flowing onto the Great Barrier Reef.

Tree clearing, sand and gravel mining, and the misguided farming practices of the past turned what was once a shady meandering river to a denuded waterway plagued by erosion.

"We've certainly lost a lot of land, we're told something like 600,000 tonnes has disappeared, probably over the past 70 years, from floods and from erosion," Mount Ubi Station owner Stephen Carter said.

The river repair site at the Carter's beef property before restoration began in April 2019. ( Supplied: Mary River Catchment Coordinating Committee )

"It was a straight drop of 10 metres [from the bank] right down to the river, and every time we got a rise in the river or a flood it would be cut from underneath.

"The clearing means the water gets into the river quicker when we have a flood, and because there was a lot of vegetation taken away, the water comes in so much faster.

"And then away it goes — straight down out to sea."

Looking downstream over the repaired riverbank at the Carter's farm at Kenilworth in October 2019. ( ABC Rural: Jennifer Nichols )

Fighting the tide

With the help of Federal Government funding, action has been taken to start repairing the damage and stop thousands of tonnes of sediment continuing to be lost.

The severely eroded bank by the Carter's property is unrecognisable after Alluvium Consulting coordinated $500,000-worth of works designed to reduce future sediment loss by 90 per cent.

Alluvium Consulting's Misko Ivezich at the restoration site on the Carter's property. ( ABC Rural: Jennifer Nichols )

"This project came out of a plan we developed after the 2011 and 2013 floods with a range of stakeholders, including the Burnett Mary Regional Group, who funded this site, but also the Mary River catchment Coordinating Committee, Seqwater, and the Sunshine Coast Regional Council," project manager Misko Ivezich said.

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"We basically looked at this reach in Kenilworth and it was a really, really high producer of erosion with lots of land loss and lots of roads washed out."

Earthmoving equipment reshaped the bank and rows of six-metre long timber poles were driven four metres into the ground to slow down floodwater.

The river repair site during restoration. ( Supplied: Burnett Mary Regional Group )

Nine thousand natives were planted on the site, which is protected by electric fencing to ward off marauding feral deer.

Under the Australian Government's Reef 2050 Water Quality Improvement Plan, water quality targets have been set for all catchments that drain onto the Great Barrier Reef.

The groups working on the Mary River have prioritised a list of projects that are waiting for future funding.

The Mary River Catchment Coordinating Committee's Brad Wedlock and Burnett Mary Regional Group's Nick Maclean at the site. ( ABC Rural: Jennifer Nichols )

'Basket case'

Brad Wedlock from the Mary River Catchment Coordinating Committee praised property owners for coming on board to be part of the solution.

The first river repair site before restoration works in Kenilworth in 2015. ( Supplied: Alluvium Consulting )

The repair site four years later shows the area now covered with vegetation. ( Supplied: Alluvium Consulting )

"Ten or 15 years ago this reach in particular was a basket case," Mr Wedlock said.

"It was very difficult to actually see a future in what we would do here but, with just working away, getting a couple of landholders on board who were willing to try some new techniques, it's just sort of crept up on us and probably now we say 'snowballed'.

"We can see the progress that's being made, but there's at least another 30 or 50, or even 100 years worth of work with this issue that we've got here with riverbank erosion."

A two-kilometre stretch downstream was the first to be transformed back in 2015 and has survived the test of time and nature.

"It's been through multiple floods and a few cyclones as well — previously that bank was eroding metres per annum with different floods," Mr Wedlock said.

"This is not a technique that's particularly new, all of this has been developed all around the world and it's been implemented in Victoria for 20 to 30 years and it's also been working in Central Queensland and North Queensland for about 10 to 15 years."

Aaron Brunton from Noosa Landcare with natives to be planted at the Carters' property. ( ABC Rural: Jennifer Nichols )

An 'overwhelming' transformation

Weeds and deer remain a challenge but thousands of native plants will be crucial to the long-term future of the restoration project.

"Piles will only last 10 to 20 years because the timber will rot away, so the ultimate stability will be the multiple sets of tree roots and shrubs and forbs and grasses and all those things going down onto this riverbank now and stabilising it for the longer term," Mr Wedlock said.

Over the long term, the revegetated banks are expected to help cool the water where endangered Mary River cod are currently spawning.

"It's really quite overwhelming to have this completed in our lifetime," Mr Carter's wife, Ruth Carter said.