'The Flood Report' repercussions

Wivenhoe Dam manual breached in Queensland flood strategy, inquiry finds

• Hedley Thomas
• From: The Australian
• August 01, 2011 3:24PM

An inquiry has found the Wivenhoe Dam's flood engineers breached their operating manual when deciding on water releases during January's floods. Picture: David Kapernick. Source: The Courier-Mail

The Wivenhoe Dam's flood engineers breached their operating manual by failing to take into account "forecast rainfall information" when they were determining the volume and timing of water releases from the dam at a critical stage, the floods inquiry found today.

The finding that they did not comply with the manual opens the door for potential damages claims as the legal indemnity for the dam's operators, SEQWater, relies on the manual being followed at all times.

The inquiry's interim report states that the evidence of the flood engineers admits “only one conclusion - forecast rainfall was not used for this purpose” of predicting the lake level at Wivenhoe Dam.

This finding could have significant implications, as affected residents and business operators may try to show that a failure to rely on forecast rainfall meant the dam was permitted to store too much water in the early stages of the flood, ultimately forcing SEQWater to release huge volumes at a peak rate of 7,500 cubic metres a second, which is twice the flow rate known to cause damage to low-lying Brisbane properties.

The inquiry heard in its public hearings that the flood engineers in the January flood event determined their releases based on a “without forecast” prediction of the likely lake level of the dam during periods of heavy rainfall, and with the Bureau of Meteorology predicting continuing heavy rain.

 

The flood engineers strenuously defended their approach, which appeared to be in conflict with the requirement of the operating manual. Many residents were incredulous that “forecast rainfall” was not used to determine the strategies for operating the gates of Wivenhoe.

The flood engineers, however, said that irrespective of how the Wivenhoe manual might be read by others, “they were in fact at liberty to ignore or give `zero weight to' forecast rainfall for the purposes of making predictions as to the level of the lake”. SEQWater told the inquiry that “if the manual is perceived by others to be ambiguous, the fact is of little moment”.

But in her interim report, inquiry head Cate Holmes, a serving Supreme Court justice, rejected the argument of SEQWater and the flood engineers.

“It can, therefore, be said that in relation to the requirement that the flood engineers' prediction as to lake level be made using the best available forecast rainfall information, and that the subsequent choice of strategy should depend upon that prediction, there was a failure to comply with the Wivenhoe manual,” the inquiry reported.

The report said that its finding must be qualified by the following observations: “The flood engineers were acting in the honest belief that the Wivenhoe manual did not, and ought not, compel choice of strategy to be made by reference to forecast rainfall”.

It added: “On the evidence, it is not possible to articulate a method by which it would be possible to predict lake level with any precision or confidently change strategies on the basis of rainfall forecasts. The existing science suggests that such forecasts lack the reliability which would be necessary before they could be incorporated into such a process.”

The inquiry said it had not identified a “particular consequence flowing from the breach”.

However, this is likely to become the subject of detailed analysis by independent hydrologists who will try to determine the beneficial difference that earlier releases of water would have made to the levels of inundation of properties.

This breach, described as a “technical breach” today by Premier Anna Bligh, was identified before public hearings had begun by Michael O'Brien, an engineer who has strongly criticised the operation of Wivenhoe Dam during the floods.