Hundreds of flood-affected residents on the NSW north coast are threatening to sue the state and federal governments over concerns the new Pacific Highway made the recent floods worse by acting as a "dam wall".
The February 28 disaster surpassed all previous flood heights on record, damaging thousands of homes and businesses across the Northern Rivers region.
Residents in towns downstream of Lismore like Woodburn, Broadwater and Wardell say they were hit like never before.
Many are questioning the impact the newly completed Pacific Highway upgrade has had on flooding.
The 657-kilometre dual carriageway between Newcastle and the Queensland border was finished in late 2020 after 24 years and a cost of $15 billion.
Residents interested in class action
Lyndall Murray, who is one of the Woodburn residents behind the push for a class action lawsuit, said the community had questions about the way the highway was built.
Ms Murray said she saw firsthand the highway acting as a "dam wall" during a helicopter flight on day seven of the flood disaster.
"Visually from the air I could see on one side of the highway the water was banked up and it couldn't move and on the other side it was drained," Ms Murray said.
She said the town was fully behind a class action, with 280 of the 360 houses in Woodburn registering within the first 24 hours, and 475 registering from the broader region.
Ms Murray said the community's preference was for government action over a court case that could span years, but they would not hesitate given the extent of the damage.
"The impact meant the water was inundating people's houses for up to 12 days where in other areas, that didn't have the new dam wall that the highway is, [it] went up and down within two or three days."
Fellow Woodburn resident Vanessa Allport said her 80-year-old house, which had previously never flooded, was inundated by two metres of floodwater.
"I think the highway was definitely a factor," Ms Allport said.
Flood model review underway
The government agency responsible for the highway upgrade, Transport for New South Wales, said there were limits during the design phase on how much impact the new highway could have on flood levels.
North regional director Anna Zycki said the highway was not allowed to impact flood levels by more than 50 millimetres or extend the flood duration by more than 5 per cent.
"We had to do quite a number of flood studies [and] there's quite a lot of information that was gathered as part of that process to demonstrate that we could keep our impact on flood levels back to those minimum standards," she said.
Ms Zycki said there would now be a review into whether the floodwaters behaved in line with the flood modelling.
She said the organisation would review the data on any individual cases raised to see if the floodwaters behaved differently from expectations.
Concerns raised before highway built
Woodburn Business and Community Chamber secretary Pam Bellingham said "something definitely made it a very different flood" this time.
"In a normal flood we have some time after Lismore floods for the water to get to Woodburn and be a problem to us," Ms Bellingham said.
"Something was obviously holding back the water that had already fallen in Woodburn and the Bungawalbin catchment, so the whole lot came at once.
Long-time Woodburn resident Bert Plenkovich was part of a community liaison group when the then Roads and Transport Authority (RTA) was planning for the new highway.
Mr Plenkovich said a number of residents raised concerns about the new highway being built on a low-lying floodplain.
"Those of us that have lived here that long and been in the area said why would you put a highway in the lowest possible area on the floodplain when you've got an option to put it on higher ground?" he said.
Both Ms Bellingham and Mr Plenkovich said they raised concerns about insufficient draining along the new stretch of raised highway, but were told all the relevant modelling had been done.
