New hydrology reports from the Insurance Council of Australia’s (ICA) panel of experts conclude that releases from Wivenhoe Dam were to blame for the Brisbane floods.

The reports says the dam releases were the “principal immediate cause of flooding along the reach of the Brisbane River downstream of the dam, along the lower reaches of Lockyer Creek and the Bremer River, and along tributaries further downstream”.

According to reports, Queensland legislation protects Wivenhoe Dam operator Seqwater from liability for losses caused by releases of water from the dam and subsequent flooding providing its operating manual was followed correctly.

Lawyers and engineers are now comparing the event log entries of dam staff with the operating manual for discrepancies. Should procedural deviations be found, Seqwater could be subject to professional indemnity (PI) claims from both Brisbane property owners and insurance companies.

Sources have revealed to insuranceNEWS.com.au that PI cover for Seqwater was placed by a “major international broker into Lloyd’s”.

But the matter may not be resolved without prolonged investigations and test cases, as the hydrologists’ reports stop short of blaming the dam operators and their management of releases.

It says the dam had to accommodate “massive inflows” from further upstream, comprised of surface run-off water and releases from Somerset Dam, as well as direct rainfall, all of which ultimately becomes “dam release”.

“All of this water – generated by natural meteorological processes – had to pass through the dam,” the reports state. “It may be more appropriate to assign flood causation to succeeding storm events over the catchment area of the dam, each characterised by exceptionally heavy rainfalls and massive surface run-off volumes.”

The hydrologists conclude that in order to provide a “full interpretation of the primary cause of flooding”, questions outside the scope of their report that need to be investigated include whether the flooding would have been worse in the absence of Somerset and Wivenhoe dams, whether releases from Wivenhoe Dam were unnecessarily high and whether a different pattern of releases would have reduced downstream flooding to a significant extent.

The report also concludes that flooding in the Lockyer Valley towns of Murphys Creek, Postmans Ridge, Whitcott, Helidon and Grantham was flash flooding.

“In all cases, flooding was sudden and abrupt, and occurred within six hours of the flood-producing rainfalls,” the report states. “It is thought that inflows from Flagstone Creek amplified the flood wave moving down Lockyer Creek from Helidon, so maximising the devastation brought by this flood on Grantham.”