A quarry owned by a prominent Queensland businessman stemmed, rather than intensified, the deadly floodwaters that surged through Grantham in 2011, a report has found.
Residents blame an embankment wall at Dennis Wagner's quarry for causing a devastating wall of water that engulfed the small southeast Queensland town in January 2011, resulting in 12 deaths.
But a report conducted by experienced engineer Dr John Macintosh has found that it is more likely the quarry slowed down the deadly flow of water.
"I consider that it is most likely that the primary effect of the presence of the quarry has been to delay the time on inundation of the Grantham area," the report said.
"The primary reason for this is due to the time it takes to fill the quarry pit."
However, the delay was likely between just one and three minutes, the computer-simulated study found.
It also evaluated the possibility that the flooded quarry sped up the flow of water by providing a slick surface for incoming torrents to traverse.
But this was, in Dr Macintosh's view, founded on an "unrealistic" appraisal of the disaster.
Instead, the report contends a railway embankment running east-west through Grantham increased the intensity of the water's flow into the town's west and central districts.
This is because the embankment, which reaches up to two metres, effectively intercepted the natural flow of the water that would have spilled onto the Sandy Creek floodplain.
Dr Macintosh is expected to elaborate on his findings when he fronts the Grantham Floods Commission of Inquiry in Gatton next week.
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