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The catastrophic 2011 Queensland floods and the record-breaking deluge of 2022 - Sydney’s wettest year since 1859 - were stark reminders, with losses exceeding $6.95 billion and insurance claims sprawling across 35 river catchments over 1600 km from the north to the south.

But are these events truly unprecedented, or is our collective memory simply too short? To answer this critical question and help Australians prepare for an uncertain future, a team of researchers, led by from the University of ÌìÃÀ´«Ã½’s (UOW) Environmental Futures Research Group, have launched a groundbreaking project that reveals the in the Hawkesbury-Nepean catchment.

Associate Professor Tim Cohen conducts fieldwork in the Hawkesbury-Nepean area. Photo: Rachel Pagitz – NSW Reconstruction Authority

“Understanding the full picture of flood risk means reaching beyond what’s in written records or living memory,” said Associate Professor Cohen, a geomorphologist whose research encompasses the landscape’s past and present.

“By incorporating evidence from the past 1,000 years - even before European settlement - we’re able to identify floods that far exceed anything previously recorded.

"This knowledge is vital for making communities safer in our changing climate.”

Partnering with the NSW Reconstruction Authority, WaterTech, WMA Water, Aon Reinsurance, and Dharawal Environment and Heritage, the team uses cutting-edge technology to trace floods deep into the landscape’s geological past.

Associate Professor Cohen has worked alongside partners from NSW Reconstruction Authority to unearth the hidden history of the rivers. Photo: Rachel Pagitz – NSW Reconstruction Authority

Researchers deploy GPS-guided equipment into places like Fairlight Gorge, downstream of the confluence of the Nepean and Warragamba rivers, where they excavate soil pits and recover flood deposits perched 30-40 metres above today’s riverbed.

These layers are then carefully analysed using advanced luminescence dating methods in UOW’s world-class Optical Dating Facility - one of the leading labs of its kind globally - to reveal when these ancient floods occurred.

Looking out over the Nepean River during fieldwork in the area. Photo: Tim Cohen“Our findings show that the landscape holds memories of extreme floods stretching back centuries - memories that can fundamentally change how we understand risk and resilience in our rapidly changing climate,” Associate Professor Cohen said.

“By integrating geological records, ancient flood deposits, and local stories, we provide a far more accurate, and sometimes sobering, picture of what the future could hold.”

Associate Professor Tim Cohen, pictured at UOW's ÌìÃÀ´«Ã½ Campus. Photo: Paul Jones

The project is not only scientific but collaborative, blending statistical data and cultural oral histories, particularly accounts from the 18th century, to produce a rich and unique record of flood events.

This comprehensive approach is being proposed as a method that will inform new and existing flood models and risk assessments for the sprawling communities of western Sydney, helping to inform improved planning and emergency response.

The team hopes to replicate this research across Australia’s most at-risk river catchments.

“The more accurately we know our flood history, the better we can predict and prepare for the extremes yet to come,” Associate Professor Cohen said.

“Communities cannot prepare for disasters that they don’t know are possible. In the face of a changing climate, knowledge truly is our best defense.”