riverman wrote:
.........snip
A second way is to lower a gate over the opening of the collapsed
tube. Its impossible to put a solid steel plate in front, as the water
pressure jams it against the dam long before it covers the opening.
But a louvered steel gate can be lowered while it is open,

The louvered panel is what failed. I have photos of it I'll put online
tomorrow. I have a photo of 50' long 20" diameter steel pipe that
was lowered down the shaft. Then they built a roughly 20' x 20'
panel made from I-beams welded together between a massive steel border.
This was supposed to reduce flow, but not stop it.

But the whole rig vibrated so violently it threatened to topple the
crane that lowered it down. That much steel, vibrating inside a
75 year old vertical concrete tube--with almost 4000cfs flow
inside--would threaten to bash the tube apart. Actually I don't
know if the attempt was inside or outside the tube. There was a lot of
big equipment there and dozens of tense-looking hard-hat faces. I asked
a dozen or more questions. But they were clearly told not to speak to
the public. Every one I asked said "I have no idea" or "couldn't say"
"don't know" "not sure" "don't ask me"

Lots of brand new 'danger keep out' signs. Which I ignored
I wore boots blue jeans and a plaid work shirt....I looked stern and did
my best to look like I belonged there.
Got good photos, but not one question got answered.