Here are the inspection and damage photos better registered. It does appear that the failure is related to the area of prior concern.
View attachment 24442
I sent my engineer friend this post and this is his response:
Man! What a good source. Excellent if fact. I enjoyed it, got me thinking.
We Hams, we know about standing waves? These would be Long wave, subsonic waves. Meters in length.
The start of the spillway in the feed, the power terminator is the speed bumps at the bottom. There's Kilowatt, (Megawatts) of acoustical energy emitted as noise.
To examine the entire spillway, it looks like a Transmittion line. Energy feed, Energy terminator, containing a lot of Raw power in between.
Frankly, I think the failure was caused by resonance. Something not planned for? Not cheap construction, or some terrorists. Time will tell? Hope it wasn't just a big leak.
I know acoustical wave travel backwards in a flowing column of water. If they are strong enough, they will reverse the flow, and I can prove this. I can well imagine the vibrations building up in a rigid flat plate until it breaks. I'm sure, they must have a seismometer there.
Wonder what seismic data, during the course of failure, would revile? Bandwidth of the detectors?
Super link. Sign up? Mick West sounds grounded.