Decades of tree clearing for urban and agricultural development is worsening erosion during our wet seasons – and because of this we’re losing productive land and sending more sediment to the Great Barrier Reef.

That’s one of the reasons local landcare groups, powered by volunteers from right across our region, are working hard on revegetating river and creek banks.

Holloways Beach Coast Care has been restoring a site on Thomatis Creek, a tributary of the Barron River, for several years. Riverbank erosion was identified as a major issue there way back in the 1980s. It’s a classic example of the impact of clearing forests – big rainfall events flush much more quickly through the landscape, exposing the community to more flood risk and increasing erosion.

Sarah Sims, organiser of Holloways Beach Coast Care, says the site near Tamarind bend was cleared of native vegetation for sugarcane farming over 60 years ago.

“The site’s creek bank lost its ability to withstand wet season flows and has been eroding and receding ever since”, she says. “Without vegetation to shore it up and act as a buffer, farm land and soil would continue to be lost through erosion.”

“In 2017 the area was flagged as significant fish habitat, and an initial funding injection from the Department of Agriculture and Fisheries kickstarted the rehabilitation project. To date, we’ve planted nearly 7000 trees.”

Fluvial geomorphologist Michael Cheetham says river systems are dynamic and constantly moving.

“Channel deepening and widening are natural processes, but they are exacerbated by things that we do,’’ he says. “Riverbank erosion is almost always located where there’s no vegetation.”

Scientists have been predicting for decades that Thomatis Creek will eventually become the Barron River’s major river mouth. Rivers are constantly searching for the quickest and easiest route to the ocean and Thomatis Creek is three kilometres shorter than the main river and has a gradient advantage.

It has been shown that once tributaries carry 40 per cent of a river’s water, this triggers a migration process – and Thomatis Creek carried an estimated 35 per cent of the Barron River’s water in a 1980 study.

Sarah says the revegetated site stood up well to the floods after Cyclone Jasper in December.

“There have been some minor losses in the younger trees, but that’s to be expected in a flood event of that size. We were also pleased to see the riverbank hold strong. The trees are doing exactly what they’re supposed to do. If you look upstream at the erosion on the riverbank going through agricultural land where there’s no riparian vegetation, it clearly demonstrates why we need trees.”

Fast facts:

• Dense, wide, continuous vegetation on riverbanks helps to prevent erosion.
• Corridors should ideally be 30m wide from the top of the bank (or as far as you can go).
• Thin tree verges are not enough to withstand floods.
• For advice on the best trees for your waterway, talk to nursery staff and your local landcare group.