Queensland’s Crime and Misconduct Commission (CMC) has cleared three Wivenhoe Dam engineers whose actions were questioned after last year’s floods.

It removes the threat of prosecution for John Tibaldi, Terry Malone and Robert Ayre, who provided a report and oral testimony to the Queensland Floods Commission of Inquiry describing their operation of the dam during the flood.

As their evidence appeared contradictory, the inquiry referred the matter to the CMC, to investigate whether the engineers colluded to produce a false report.

But QC John Jerrard found the engineers did not intend to make misleading statements.

Instead, the men “honestly attempted to follow the [dam] manual’s instructions, without grasping at that time that there was an essential inconsistency in those”.

Any prosecution for perjury or official misconduct would be “oppressive”, Mr Jerrard says.

The retired judge found the “conflicting” and “badly drafted” dam manual led to the engineers’ confusion about when different flood strategies were in place.

He found contradictions in the manual’s instructions on the different stages of water release during flooding – stages W1 to W4 – which depend on the flood’s severity.

The first aimed to protect downstream bridges from inundation. The last was intended to prevent structural failure of the dam, which the manual says would be catastrophic.

Mr Jerrard identified problems with one definition prescribing “combined peak river flows”, which he says made it “almost irrelevant to contemplate using strategy W2”.

Further, two different definitions of stage W2 appeared on different pages of the manual.

“This contradiction in the manual would provide an explanation for all of the engineers’ inconsistent statements and descriptions of what they had done at the time of the January 2011 flood event and is not evidence of either the commission of a criminal offence or official misconduct,” Mr Jerrard said.

“Recommendations made by the flood inquiry… request [water utility] Seqwater to review/create a new manual, with the assistance of experts such as technical writers and legal review, to ensure compliance with the manual during any future flood event.

“Implementing these recommendations should remove any inconsistency or ambiguity.”

A Seqwater spokesman told insuranceNEWS.com.au an interim review of the manual has been finalised and the manual was updated last November.

“A longer, more comprehensive review will follow, which will involve a number of government agencies, local councils and consultation with the community,” the spokesman said.

Law firm Maurice Blackburn last month confirmed it is close to filing a class action lawsuit against government-owned Seqwater for the dam’s mismanagement. No court date has been set.