More trees could make Macquarie-Wambuul River more resilient during floods

Researchers at Macquarie University found that continuous streamside revegetation by a local community over decades had helped the Wollombi Brook - which flows north into the Hunter Valley - hold up "remarkably well" during its biggest flood on record in 2022.

Professor Kirstie Fryirs, of the School of Natural Sciences at Macquarie University, said though there had been widespread inundation during the flood, the waters were slower and the vegetation prevented large-scale erosion and sediment movement.

READ ALSO: 'History repeating itself': How council could have prevented erosion along the Macquarie River

"All the hard work that a very active community put into nature-based rehabilitation for more than 20 years, such as continuous streamside revegetation, played a role in this outcome," Prof Fryirs said.

According to Prof Fryirs, it was one of the best examples in Australia of sustainable environmental restoration in the management of rivers.

A number of organisations run rehabilitation projects along the Macquarie-Wambuul River, including Dubbo Rivercare Group, Inland Waterways Ozfish River Repair Bus, and Wellington Community Progress and Action Group.

Daryl Green, Rivercare Group member, said the small group of volunteers has been planting trees, cleaning-up garbage and managing weeds along the waterway for 21 years.

"Primarily we pick up rubbish and control weeds ... and we try to keep the plants natives - red gums, casuarinas, callistemon ... we also plant trees," Mr Green told the Daily Liberal.

Mr Green and the Rivercare Group agreed more native plants along the riverbank could help ease the damage to the banks, such as occurred during the 2022 floods.

READ ALSO: Duke of Wellington Bridge erosion could have been prevented, Soil Conservation Service report shows

The group has written a submission to Dubbo Regional Council's Macquarie River Corridor North and South Precinct Master Plan recommending the nature corridor is extended along the river to mitigate erosion during future flooding events.

"One of the things that came to the fore with the recent floods, was the intensity of the stream flow," Mr Green said.

"We've put a submission to council under their recent riverine plan. We reckon that floods were that intense ... that the erosion of the river bank, here [in Dubbo] and in Wellington ... our thin strip of trees and shrubs - an undisturbed area along the river - needs to be extended 50 metres from the high bank of the river."

Mr Green said extending the tree corridor would give the bank "broader stability". He also said "one of the real problems" was the ground species in the area had "almost disappeared".

"One of the things that's really missing from our habitat along the river is the under-storey species, the ones that are one or two metres tall - they've all disappeared. There are large trees, but that's about it," Mr Green said.

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He said planting more trees at this level, including wattles, Australian blackthorn and bottlebrushes, would not only benefit the riverbank, but provide habitat for smaller birds and tree-dwelling marsupials including possums.

"We might even get koalas back into the system as they're further west than here. There's only one line and sometimes two lines of trees - it's not really good for stability as a river system and not good as habitat value," he said.

Mr Green is calling for more support from council as well as more volunteers to help the Rivercare group continue their important work along the river.

Dubbo-based water campaigner and community organiser with the Nature Conservation Council NSW, Melissa Gray, applauded the rehabilitation work performed by local groups, and said nature-based solutions were needed over engineering solutions to manage the river.

"For this valley, we have large engineered dams, and the environment wears the cost," Ms Gray told the Liberal.

She explained the Macquarie-Wambuul is a regulated river system from below Windemere and Burrendong dams all the way to downstream of Warren, meaning "there's only so much that can be achieved through the amazing volunteer led, nature-based rehabilitation work that is done" on the river.

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"This community decided mid last century to construct large in stream dams, and mitigate the impacts of flooding in communities including Wellington, Dubbo and Narromine," Ms Gray said.

"This means water in the river channel runs high and fast for extended periods, instead of floods spreading out over the landscape and receding back into the river over a short time.

"Despite the efforts of WaterNSW to minimise the impact, a lot of erosion, scouring, vegetation loss and sedimentation happens when the river is operated this way, like it was for 15 months during the recent series of floods. Refuge holes are filled in with sediment, river red gums are torn out of the banks, and the river is channelised."

During the 2022 floods, the low-level Duke of Wellington Bridge was eroded away almost completely by heavy rainfall and flooding.

Dubbo council will spend $150,000 from a Severe Weather and Flooding grant on works to fix the Lady Cutler South sporting fields side area.

Their works will include moving a section of Tracker Riley walkway away from the bank retreat scarp and establishing a vegetated buffer to assist in bank stabilisation.