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| Mark Babister |
The revised figures, formulated by a key witness to the inquiry, found the river could have peaked up to 1.3m lower at Moggill and 1.2m lower at Jindalee, upstream from Brisbane.
But hydrologist Mark Babister's new figures, which allow for a scenario where engineers began releasing huge volumes of water pre-emptively, ultimately find the strategy would have been "unreasonable" because such moves "would have required foresight beyond that obtained from a measured consideration of weather forecasts".
Mr Babister, the director of hydrology firm WMAWater, is expected to front Queensland's flood inquiry today.
He is regarded as the leading source of independent modelling of Brisbane's flood, which inundated thousands of homes and businesses. The commission has reconvened to review the management of Wivenhoe Dam after The Australian revealed a string of inconsistencies in the dam engineers' evidence, suggesting Wivenhoe was operating in the wrong strategy in the days before the disaster.
Mr Babister was last month asked by the inquiry to model two new scenarios. The first, G1, supposes release strategy W3 was invoked at 8am on January 8 as the engineers say they did and releases are then ramped up to achieve a total flow at Moggill of 4000 cubic metres a second.
The second, G2, also supposes W3 is invoked on January 8, with the floodgates opened as fast as permitted to maintain a release rate at the dam of 4000 cubic metres a second.
The greatest flood peak reductions were achieved under G1, with the figures projecting 60cm could have been shaved off at Brisbane and 90cm at Oxley, southwest of the city.
Under G2, 1m of flood could have been avoided at Moggill, 80cm at Jindalee, 60cm at Oxley and 30cm at Brisbane.
He concludes the scenarios are "unreasonable" because "there would generally be no grounds to release large flows from Wivenhoe Dam during a flood event that are greater than the inflows received".
"Although hindsight indicates a better flood mitigation result could have been obtained ... it would have been unjustifiably risky using the information available at the time," the report reads.
10.2.12
