Qld rail line increased flooding: report

A new rail link contributed to dangerous flooding north of Brisbane but heavy downpours would have flooded dozens of homes anyway, a report has found.

More than 300mm fell on the Moreton Bay region in less than 24 hours on May 1, inundating scores of homes and causing the deaths of five people who tried to cross flooded roads.

About 100 Deception Bay homes were damaged and residents blamed the new Moreton Bay Rail (MBR) link.

An independent report has found that while the rail project contributed to the flood's severity, 85 homes would have been flooded anyway.

"It should be noted that 85 residential properties are located in the area where flood levels were increased by MBR works during the 1st May 2015 storm event," the report said.

"All of these properties would have experienced flooding on the 1st May 2015 even without the influence of the MBR project works."

Deputy Premier Jackie Trad said the weather was unprecedented and akin to a one-in-1000-year rain event.

"To put that into perspective, the rain event triggered by Cyclone Marcia in February 2015, which caused devastation in central Queensland, was estimated to have been slightly larger than a one in 50 year event," she told parliament.

"No one could have predicted the severity of the storm."