As the painstakingly slow recovery continues for flooded communities across parts of Australia, a land management group says it's possible to take more than 2 metres off the flood peak by slowing the flow of water across the landscape.
Stuart Andrews, whose father Peter pioneered natural sequence farming (NSF) more than 40 years ago, hopes to get the chance to prove his father's theory on the north coast of New South Wales.
The CSIRO's interim report on the causes of the Lismore flood disaster found there was a need for a better understanding of how effective nature-based solutions could be in managing a flood.
The report's team wants to look at the whole of the catchment, including the role of vegetation in slowing and reducing the flow. The Lismore Council hopes some funding will be available to trial that approach in the region.
The federal government has allocated $150 million for flood recovery projects, and parts of the community are demanding work get started now.
But the government is waiting on a final report from the CSIRO before deciding whether to prioritise new dams and infrastructure or other approaches like this one.
What is natural sequence farming?
Peter Andrews argued that significant areas of Australia had been seriously degraded by clearing and grazing along the rivers and streams.
He experimented with techniques to slow down the flow by diverting streams into chains of ponds across the flood plain and revegetating the landscape.
Now his son Stuart Andrews is working with landholders and councils in the Lismore region to see if those techniques will work there.
"We're working on what we can do in the landscape high up in the watershed to manage water to reduce flooding, [and] build resilience back into our landscape so that we have less of an impact when we have these big rain events," he said.
"If we do that, then we have the potential to take, we think more than 2 metres off the peak of that flood, which can be the difference between houses being flooded or not."
Mr Andrews said that high up in the landscape, water used to be stored in the ground, and we needed to return to that.
"Water only ran off when there was nowhere else to put it, but even then, it would spread it [the water] out across the flood plain, spread it out across the landscape, so that it came down over a longer period of time," he said.
He warned against planting trees lower down on the flood plain itself.
"We've got this obsession with planting trees in all the flow lines thinking that we're going to save the towns from flooding, but it doesn't, the trees just get washed away," he said.
Flood reduction claims questioned
Southern Cross University professor of sustainable forestry Jerry Vanclay said while there were methods that could reduce the speed and volume of water, he doubted 2 metres could be taken off the peak of a flood as big as the one Lismore experienced.
"The flood we had last February [in 2022] was a massive amount of water, and floods like that are not easy to prevent," Professor Vanclay said.
He said he thought it was more realistic to talk about taking half a metre to a metre off the peak.
"I think anything above that you want to do some pretty careful computer simulations to be sure that your claims can be supported by evidence."
Professor Vanclay said trees could slow the speed of floodwater.
"There's very good data to show that bands of dense tree planting can lower the speed of water, and we know that with the right kind of vegetation, we can slow the speed of water to one-third."
He said he did not think planting trees higher up the slopes was useful but that pecan trees could play a role on the flood plains.
"It's very difficult in steep country to slow the water with tree planting, but on the flat flood plain above Lismore, I think there really is scope for tree planting to slow the progression of the water."
Proposed flood trials
So while there is disagreement about where to plant trees, Mr Andrews said the evidence behind the impact of Natural Sequence Farming was clear from the body of work that had been done.
"We've been doing this work in my family for 40 years, the results are in. We shouldn't need to do any more trials," he said.
There is, however, no study to verify his claim about reducing the size of a flood by 2 metres.
However, Mr Andrews pointed to research conducted by the Mulloon Institute and a study done in the United States to illustrate how it works.
A spokesperson for the Northern Rivers Reconstruction Corporation (NRRC) confirmed it had had initial discussions with Mr Andrews, and there was "interest in finding out more about their work and nature-based approach".
"Led by the CSIRO, the NRRC is working with a range of agencies and stakeholders on potential flood mitigation and adaptation measures in the Northern Rivers," the spokesperson said.
Kate Steel from Lismore City Council said the next phase was to conduct trials, but that was dependent on council receiving another grant.
She believed that working in the top of catchments, building contours and leaky weirs as well as planting trees, could slow the movement of water.
"Even if it only was 1 metre, [I] imagine 1 metre less in that peak flood would have made a difference to quite a few properties in the flood plains and in Lismore, but we don't know really," she said.
CSIRO Northern Rivers Resilience Initiative project leader Jai Vaze said the best way to test the feasibility of mitigation proposals, such as using farming techniques, would be by using the full hydrodynamic Richmond River Catchment model.
This model is being developed by CSIRO as part of phase two of the project and is due for completion at the end of 2024.
Researchers will use this model to undertake scenario analysis and testing to recommend long-term flood mitigation actions, so it may be a while yet before the community will know if Natural Sequence Farming could make a difference.
