Scientists look to Indigenous history to manage flood risk in Hawkesbury-Nepean Valley

Australia Broadcast Center

25-07-2025

Accounts of floods recorded in Aboriginal oral history centuries ago could provide vital clues to how climate change will affect flood risk in the future.
Scientists working on a disaster adaptation plan for the Hawkesbury-Nepean Valley in Sydney's north-west are looking into the past to help predict the future.
Stephen Yeo, senior flood risk specialist at the NSW Reconstruction Authority, said records at Windsor go back to the early days of European settlement.
"On this river system, we have the longest record of floods in Australia from the early 1790s right up to the present," he said.
"That's actually pretty short in geological time."
The biggest flood recorded since European settlement was in June 1867.
But there are early colonial accounts of Aboriginal elders describing an even bigger flood that happened eight years before the arrival of the First Fleet.
"During that flood it apparently poured in torrents for seven nights and seven days," Dr Yeo said.
He said this event changed what scientists know about the magnitude and frequency of flooding in the river system.
"It suggests that the flood in 1780 was perhaps 2 or 3 metres higher than what we currently think is the record flood in 1867.
"So that's actually really valuable information from that Aboriginal storytelling."
Waterway scientist Daryl Lam is part of a team searching for traces of pre-settlement floods.
"History is telling us what has happened before really can happen again, so if we can find evidence of big floods from the past, it gives us some understanding of what we can potentially see in climate change," he said.
Samples of sediment have been collected from three locations high above the river bank.
These samples will be taken back to a laboratory and analysed to pinpoint exactly when the sediment was deposited.
Measurements taken at the site will allow researchers to calculate how high the floodwaters rose.
"Here in the Hawkesbury-Nepean, we have gauge records that go beyond a hundred years," Dr Lam said.
"If we take into account oral history, we might be able to push it out to 200 years or 500 if we are lucky.
"With paleoflood reconstruction, we will be able to work out a longer timescale."
Archaeologist Bec Chalker said evidence of Aboriginal occupation can be found in caves all along the river.
"We find tools that are hidden up on crevices in the shelters, just like we would put our tools and kitchen utensils on a shelf at home."
She said Indigenous knowledge built up over generations was proving to be a valuable resource.
"We have a lot to learn, and I think people are more open to learning now."
Climate change is adding to the flood risk with every degree of atmospheric warming increasing rainfall in the catchment by 8 per cent.
Between 2020 and 2022, the area flooded six times.
With 114,000 people now living on the flood plain, the NSW Reconstruction Authority is considering whether building levees and improving evacuation roads will help mitigate the risk.
"Climate change is here, we have to factor it into today's decision-making," Dr Yeo said.