Severe floods in the 2018-19 wet season left extensive damage in the Mossman region – riverbanks collapsed, trees hung by their roots and farmland was swept downstream to the Reef. Now a combination of engineered structures and trees are working their magic…
Over the last 15 to 20 years, I’ve noticed the creeks are getting deeper and there’s nowhere for the water to break out and flood the plains.
The floods in late 2018 and early 2019 were some of the worst on record. They changed the course of the Mossman River in some sections and wreaked havoc on smaller waterways, leading many farmers to voice their concerns. One of them, cane grower Richard Padovan, says the erosion on his property was ‘next level’.
“The floodwater was like a raging torrent, it took everything with it,’’ he says. “Over the last 15 to 20 years, I’ve noticed the creeks are getting deeper and there’s nowhere for the water to break out and flood the plains. Everything is concentrated down the river. It’s causing a lot of damage and erosion. You’ve only got so much topsoil and once you lose it, there’s nothing left to grow on.”
Richard is one of the farmers involved in projects to repair riverbanks in the Mossman and Daintree catchments. The restoration work is a collaborative effort from organisations including Douglas Shire Council, Canegrowers Mossman, Mossman Agricultural Services and Terrain NRM.
Jen Mackenzie, leader of Terrain NRM’s Sediment Reduction Team, says funding from the Australian and Queensland governments led to engineered solutions – from rock walls to pile fields – to stabilise creek banks in some of the most acutely affected areas.
Pile fields are multiple rows of piles, driven into riverbeds and banks. They are designed to slow down water and build up sediment, to protect and repair damaged riverbanks.
“The fields also support vegetation, so in coming years we expect vegetation to establish in and around the pile fields and in time, as the timber piles break down, this vegetation will take over as the long-term sustainable solution to holding creek banks together,” she says.
Bank stabilisation is also being embraced by Wangan banana farmers Shayne and Blaise Cini, who recently finished a project to stabilise a section of the South Johnstone River’s bed with basalt rock and build the bank up.
Shayne says his grandfather started stabilisation work more than 40 years ago. “There used to be a bit of trial and error, but over the years it has become better understood how to manage riverbank erosion and we’ve had some great success with the latest work.
The project was managed by the Cassowary Coast River Improvement Trust.
“Without repairs, erosion will just keep moving further up and down the riverbank. It’s expensive to fix and involves a lot of work pushing rock around with excavators for weeks on end, but it’s well worth the effort. Soil is one of our most important assets and putting measures in place to protect it makes sense. It’s good for the environment and for our farming business,” says Shayne.
The Australian Banana Growers Council’s Amelia Foster says farmers are very keen to maintain their riverbanks.
“We’ve a lot of banana farmers actively revegetating and increasing their riparian zones, often in conjunction with other project works. The Cini’s site was technically difficult because of the shape of the river and steepness of the erosion. The riparian zone can now be reinstated without fear of it falling in.”
Dr Michael Cheetham, a fluvial geomorphologist, says river systems are dynamic and influenced by both natural factors and human intervention.
“Riverbank erosion is almost always in locations where there is no vegetation,’’ he says. “Vegetation holds the banks together and slows the water down, so it reduces erosion.
“Planting a dense, wide, continuous corridor of vegetation along creek banks can strengthen a big portion of waterway. It’s a self-sustaining and long-term mitigation measure.
“Ideally riparian verges would be about 30 metres deep. But we understand that this is productive land for farmers, so compromises are necessary. Plant what you can, at least 6 to 10 metres. And talk to your local nurseries and NRM groups about the most appropriate trees.”