At the height of the crisis helicopters dropped bags of rocks to fill the breach. Both Oroville and Wivenhoe are made of rock fill and compacted earth; both rely on secondary spillways to protect the main dam in an emergency. Queensland's dam regulator has also identified an erosion risk at Wivenhoe. Greg McMahon, a consultant who was the chief flood expert in Queensland's local government department until the early s, says attitudes to dam safety became compromised during the late s when "political skulduggery" led to an effective lowering of standards.
He explains that when Wivenhoe was first conceived in the s, Australian design standards for large dams made of earth and rock required them to be able to contain the flood created by the largest possible rain event in the catchment, the "probable maximum precipitation".
But soon after Wivenhoe was completed in , meteorologists realised they had significantly underestimated the size of this epic deluge. But rather than raise all the dams, Mr McMahon says, authorities changed the standard. For the first time they assigned a probability to this massive rain event, even though the new national dam design manual in acknowledged a fundamental scientific problem with doing this:.
Mr McMahon believes this was an effective softening of standards and it happened because governments, including the Bjelke-Petersen regime under which he worked, balked at the cost of upgrades. At this stage it can't - and I'm not sure the population at risk has been sufficiently consulted in this decision. The Australian National Committee on Large Dams sets the guidelines for dam design across the nation, but says it does not monitor compliance of Australia's dams with them.
But Mr Fox says Australians "can be confident that Australia's dams are well designed, are responsibly managed and that where incidents occur elsewhere the learnings are incorporated into Australian best practice".
Another veteran engineer, Ken Pearce, was involved in the design of Wivenhoe in the s and later worked in a range of state government roles in flood and drought planning. I designed the walls, along with others. I looked at the Probable Maximum Flood PMF and I designed the walls for that level because every wall has got to stand up when it's got water against it, particularly in a major flood," he says. Mr Pearce says he then watched with horror as a de-skilling of senior civil servants, with fewer and fewer having relevant professional qualifications, and increasing political meddling caused decades of paralysis across Queensland government departments dealing with water management.
McMahon, Pearce and Max Winders, one of Queensland's most experienced hydrologists, see the same fundamental problem in the approach to dam management in Australia: risk management techniques that allow for uncertainty in decision-making, common in other fields, are absent.
Mr McMahon says it was amply demonstrated during the height of the January Brisbane flood in the way Wivenhoe Dam was operated. He takes up a position at the centre of the goal or moves back to the centre of the court because until the ball is struck, he doesn't know which way it's going to go.
What they did during was all the engineers and managers took up a position at one of the goalposts. Mr McMahon says that during the flood, although the manual for the operation of Wivenhoe dam required engineers to take account of the best available rainfall forecasts, later testimony at the floods inquiry showed they couldn't decide what this meant and had instead chosen to ignore forecasts. More on:. ABC Radio Finder. Top Stories Liberal backbenchers call for more ambitious emission reduction target.
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Al Jazeera demands the Sudanese military release arrested bureau chief. Flood events in lower Lockyer Creek, in the lower Bremer River and in the lower Brisbane River were dwarfed by the subsequent water level rise associated with releases from Wivenhoe Dam. The report does not apportion any blame to dam operators, pointing out Wivenhoe was forced to collect massive inflows from surface runoff from the upstream catchment area, releases from Somerset Dam and direct rainfall. The report outlines the responsibility of insurers to assess flood-affected properties individually rather than declining claims based on the definition of the flood, as homes further away from creeks and streams may have been subject to initial flash flooding from heavy rain.
Follow Environment on Twitter. Wivenhoe Dam release caused Brisbane flood: report.
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