WATER authorities in Brisbane are refusing to release the flood emergency plan detailing exactly when and how much water should have been released from Wivenhoe Dam to manage the Queensland disaster.

Yesterday a spokeswoman for South East Queensland Water Grid said the plan could not be made public and refused to say when it was last revised.

''[It] is a not a publicly available document and is owned and operated by SEQ Water Grid,'' the spokeswoman said. ''An independent commission inquiry has been announced into the Queensland floods and we are unable to comment further at this time.''

Professor Hubert Chanson, an engineering expert from the University of Queensland, said he could make an ''educated guess'' about what was in the Operational Procedure Manual for Flood Mitigation at Wivenhoe and Somerset Dams, but he had never seen the document.

He believes the plan is ''adequate'' and had been revised about seven years ago, about the same time that Wivenhoe's emergency spillway or ''secondary spillway'' was built, to address larger rainfall predictions.