The sheer magnitude of rainfall, not man-made features, caused the floods in the Lockyer Valley in southeast Queensland that killed 12 people and destroyed more than 50 homes, a commission of inquiry has found.

The inquiry was investigating whether a breach at a local quarry or railway line embankments in Grantham exacerbated the flooding on January 10 2011.

“Quarry or no quarry, railway line or no railway line, if there is ever another sudden dump of water in the upper catchment of Lockyer Creek of the order that fell… the same thing will happen again,” the inquiry concluded.

Walter Sofronoff QC led the $2.5 million inquiry and has made no recommendations in his 236-page report, putting the event down to an act of nature.

The report was presented to Queensland Premier Annastacia Palaszczuk earlier this month.

Mr Sofronoff says quarry owner Denis Wagner and his family were unfairly targeted as culprits for the flood.

“I think they were unjustly blamed by some people and I think they were viciously blamed by some elements of the media, and they shouldn’t have been,” he said.

It was the second probe into the disaster, with the first one part of the wider Queensland Floods Commission of Inquiry in 2012.

Some residents campaigned for a specific inquiry into the Grantham flood, believing the quarry was to blame.