Hebgen dam
 

I haven't posted anything in a long time because....I didn't
have much to say. But here's an interesting story:

Sarah Palin is a space alien, oops, no, that's the wrong story.
What is interesting is Hebgen dam right now.
About a week ago a vertical square tube of reinforced concrete,
that forms the output flow for the dam, imploded insward, suddenly
allowing 3500cfs flow out the tube.

Montana Power made a press release saying they appologized, but they
would have it all under control soon. There was no danger, they said.
But in the mean time all campgrounds downstream of the dam are closed,
and the fishing sucks. This is peak late June flow level.

I started thinking about it, and I suspected this was a lot worse than
they were letting on. The collapsed outflow tube is a good thing for
the fishery. I sucks the water off the bottom of the lake, so the
outflow stays cool in summer. Without the tube, the damn would
have to flow out over the top, using emergency overlow channels.
But any over-the-top flow in summer would be a fishing disaster, because
it would turn the Madison into a smallmouth bass fishery.

Mt Power said not to worry. They would lower a heavy steel
somethingorother down around or into the tube to restrict the flow.
Today they announced they'd given up on that idea: it was too dangerous.
Trying to manipulate equipment and heavy metal plates in deep turbulent
water just wasn't working out the way they wanted it to.

So what happens next? They'd better figure something out fast.
If 3500cfs goes over the damn all winter, ice jams will wash out
every bridge between Quake Lake and the dam at McAllister.
Uncontrolled ice dams might knock the willy off that damn dam too.

I worked a winter on an oil rig once, when I was young. At one point
we did a "work over rig" where we cut off a crumpled casing 2500 feet
down, rethreaded the casing and re-cased it, all with natural gas
leaking around us the whole time. No smoking within a mile of the rig
and they had special spark arresters on the big V-12 diesels that ran
the rig. That was bad, but possible. But if you add huge swirling
currents and water pressure into that mix, then you begin to understand
how difficult it would be to fix an outflow tube deep down at the bottom
of a lake. They could plug it in various ways. But then the water will
go over the top, which would be summer time fisheries disaster.

To fix the tube, they might have to drain the lake. They didn't say
that. But I did.

Hebgen dam
 

So what happens next? *They'd better figure something out fast.
If 3500cfs goes over the damn all winter, ice jams will wash out
every bridge between Quake Lake and the dam at McAllister.
Uncontrolled ice dams might knock the willy off that damn dam too.

Okay, wouldn't Quake Lake take the brunt of this? Quake is right
below Hebgen. I'm trying to figure out the dynamics here.
Frank Reid

Hebgen dam
 

Frank Reid © 2008 wrote:
So what happens next? They'd better figure something out fast.
If 3500cfs goes over the damn all winter, ice jams will wash out
every bridge between Quake Lake and the dam at McAllister.
Uncontrolled ice dams might knock the willy off that damn dam too.

Okay, wouldn't Quake Lake take the brunt of this? Quake is right
below Hebgen. I'm trying to figure out the dynamics here.
Frank Reid

This isn't a dam collapse story. It's all about flow levels.
What ever flows into quake lake will also flow (at that rate)
out of quake lake. The Madison is currently high and muddy and not
fishing at all.

3500cfs has never happened in winter. The riverbed isn't big enough
to handle it in cold weather. 3500cfs in February would build up
ice jambs 50 feet high.

They need to figure out a way to restrict the uncontrolled flow (now
feeding out off the bottom of the lake). They probably will figure out
how to plug that tube, temporarily. But they will have to fix it
eventually. To do that--without draining the lake--would be an
engineering miracle, the way I see it.

Hebgen dam
 

Just my .02 slide a huge metal plate down the lake side of the dam
blocking the hole.........Open up the side gate so water flows around
and not over build a new tube on the river side slide into hole secure
problem solved...........Tell them to send me the check...........

Hebgen dam
 

Mike wrote:
Just my .02 slide a huge metal plate down the lake side of the dam
blocking the hole.........Open up the side gate so water flows around
and not over build a new tube on the river side slide into hole secure
problem solved...........Tell them to send me the check...........

That might be what they have to do.
The radio had a few more details an hour ago.
They tried to poke a metal rod down the inside of the output
tube. That rod was supposed to guide a metal plate down the
inside of the tube, down to the rupture. That would restrict flow.
But the rod started shaking so violently (because of deep, powerful
turbulence at the bottom of the tube) it threatened to collapse
the crane that was lowering the rod.

Now they're back to head scratching.
They did mention the lake is dropping by 5" per day.
That's 150" or 12.5' per month.
Or roughly 50' drop in four months.
In other words, if they don't get it plugged, the lake
will drain by winter's end.

I assume they WILL get it plugged, one way or another.
And then (as you suggested) the best approach might well
be to build an new outflow tube, rather than fixing the old one.
That will take at least a season.

That would probably mean a lot of 75 degree water going over the top
of the damn dam next summer. Better hope they get it fixed in one season.

Hebgen dam
 

salmobytes wrote:
Mike wrote:
Just my .02

I drove down there today, jumped the fence when nobody was looking
and shot a bunch of photos. It's quite a sight. There is a huge amount
of water geysering out of the 75 year old (Hebgen Dam) syphon tube.
At the current rate, the lake will be empty (or at least down
to the bottom of the outflow tube) by the first of the year.
That seems to what they're waiting for now.....in other words,
hurry up and wait. Fix it next year. So we might have to buy
some pitch forks, for all those big browns in the soon-to-be-empty
lake. Actually I don't the think the bottom of the syphon tube actually
drains the lake. But there will be some very long steep and muddy banks
to Hebgen Lake next summer......I think.

Hebgen dam
 

On Sep 11, 7:33*am, salmobytes wrote:
salmobytes wrote:
Mike wrote:
Just my .02

I drove down there today, jumped the fence when nobody was looking
and shot a bunch of photos. It's quite a sight. There is a huge amount
of water geysering out of the 75 year old (Hebgen Dam) syphon tube.
At the current rate, the lake will be empty (or at least down
to the bottom of the outflow tube) by the first of the year.
That seems to what they're waiting for now.....in other words,
hurry up and wait. Fix it next year. So we might have to buy
some pitch forks, for all those big browns in the soon-to-be-empty
lake. Actually I don't the think the bottom of the syphon tube actually
drains the lake. But there will be some very long steep and muddy banks
to Hebgen Lake next summer......I think.

One way they can address this is to build another dam 50 feet
upstream, then once this dam is isolated and dry, they can repair it.
Common strategy in canyon regions, including digging a hole around the
damaged dam.

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, allowing
the water to pass through, then once its positioned, the louvers are
shut, sealing the hole. They did this in Maine a few dozen years back
when the ice had frozen the 'in' side of an outlet tube shut, and the
engineer opened the 'out' side. The external air pressure crushed the
30' diameter tube flatter than a toothpaste tube instantly, and they
had to seal the dam to replace it.

In any case, Dam Engineers and the Army Corps are highly skilled in
dealing with such things.

I hope.

--riverman

Hebgen dam
 

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.

Hebgen dam
 

Here are some photos I took yesterday.....

http://montana-riverboats.com/Robopa...es/Hebgen-Damn

Hebgen dam
 

On Wed, 10 Sep 2008 20:33:29 -0600, salmobytes
wrote:

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.

If the tube is vertical, why not lower a "bung plug" of lightweight
re-enforced concrete into it - it might not last forever, but it would
seemingly last long enough to work on the tube below the plug/packing.

And speaking of which: on the gas well thing - why didn't you guys have
a packer downhole? How did y'all cut the casing without one?

TC,
R