Tree rootballs part of erosion solution Herbert River

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.