Rainfall in Wivenhoe catchment higher than 1974 yet flood lower.
Hard to compare floods. Rainfalls were higher and lower depending on where your comparing. This flood had rainfall coming from the further reaches of the catchment, whereas 74 had heavier rainfalls more locally. There were isolated rainfalls in 74 that were much much higher than anything this time. Also, In 74 there was a storm surge blocking the Brisbane river from entering the bay, caused by the cyclone. This added a metre or so to the heights in Brisbane.
Evidence is that Wivenhoe certainly lessened the height of the flood. Unknown quantities of water from Lockyer Creek (below Wivenhoe dam) where the water gauges were at record heights before being washed away, also from the Bremer River.
Marg
The evidence I see is that wivenhoe was releasing 8000 tonnes per second of water roughly 36 hours before the peak at Brisbane. The peak in Brisbane was not much more than this in total, so wivenhoe releases contributed most of the water at the peak. They had no choice of course, as the dam was full and was in danger of setting off an uncontrolled release.
In hindsite, if wivenhoe had of had 100% storage capacity left for when the main storm hit, the peak would have been lower. This would have ment the floods were bigger in the days before the peak. But surely the main aim is the lowest total peak, to flood the least houses in Brisbane and cause the least damage?
I still reckon it was a balls up. A dam built 30 years ago to stop Brisbane from flooding? Waits patiently for 30 years to be used. It's flood mitigation capacity is 100% full right as it is really needed because it was allowed to fill in the days before the peak to stop minor flooding rather then being kept for the 'big one'.
I made a comment on this thread, the 10th, Monday morning, just hours before the Lockyer disaster happened, where I was surprised at how full the dam was in the lead up, in posts above. And rainfall totals of many 100's of mills were still being forecast for the coming days.
Perhaps the rules need to be looked at as to how wivenhoe is operated.
See ya's.