This is a running commentary on the rapidly developing Oroville dam situation. Because the story developed so rapidly, there wasn’t time to write a complete report.

Oroville Dam
By California Department of Water Resources [Public domain], via Wikimedia Commons
I’ll have a tidy summary at some point, but first we have to scour and assemble the information.

The reason we cover such situations in detail as the develop is because we feel we can do a better job of condensing and presenting complex and rapid information better than mainstream news, we don’t sensationalize and go for grounded facts every time, and because such situations offer a learning moment to help orient us to the realities of the world in which we live and how we should think about preparing and being prepared.

The bottom line is that the US has many poorly maintained dams, bridges, water works and the like. Even worse, we’ve built using a form of concrete with re-bar for tensile reinforcement that will necessitate virtually 100% replacement of all concrete structures within 40 to 100 years of being built.  Here’s the article I wrote on the concrete situation.

So in this respect, the Oroville dam is a signpost for shortsighted thinking and very large future demands to pour more money into maintenance.

February 12th 2017

Post #1 9:11 p.m.

This is a pretty shocking development.  I’d been somewhat enjoying watching the spillway disgorge huge amounts of water, but apparently things took a turn for the worse.

THOUSANDS ORDERED TO EVACUATE AFTER OROVILLE DAM PREDICTED TO FAIL

OROVILLE, Calif. — Officials have ordered thousands of residents near the Oroville Dam to evacuate the area, saying a “hazardous situation is developing” after an emergency spillway severely eroded.

The Butte County Sheriff’s Office says the emergency spillway could fail within an hour unleashing uncontrolled flood waters from Lake Oroville.

The department says people in downstream areas need to leave the area immediately. It says residents of Oroville, a town of 16,000 people, should head north toward Chico and that other cities should follow orders from their local law enforcement agencies.

A major dam failure is a very rare, and possibly symbolic thing to occur at this time.  Very much not “first world.”


Sun, Feb 12, 2017 – 9:41pm

This was a very good piece of reporting by a private citizen…much better than Da Newz…which presumably didn’t want to overly concern anyone…or something.

At any rate, another great reason to keep your go bags organized, even if that means having your most important affairs in one place where you can get to them quickly.

The major issue is that the Oroville dam has too much water behind it.  There are only three ‘approved’ ways for it to be released.  I’ve pulled these three images from the above video.

1) is the hydro plant at the base of the dam.  That has been shut down because of some sort of problem.

2) Is the concrete spillway.  That is severely compromised (see pictures below) and is in danger of failing.

3) Is the emergency spillway.  The problem there is that the water got high enough that it took an unapproved route there too…the unreinforced parking area is now spilling water.

There are no good choices left for releasing additional water.   So the spillway may fail and the first, large modern dam in US history could fail.  Wild.

Here’s the damage to the spillway that was there before the additional releases had to happen…they had noticed an already weak spot in the spillway was being badly eroded, stopped the flow briefly, and found this:

 

And in this next photo you can clearly see what happened when they had to continue releasing via the spillway to avoid losing the entire emergency spillway which was also being eroded badly at the base.

 

Oops. No good choices left here.

You can clearly see that the emergency spillway is eating its way up towards the earth that is holding the water in the dam back.  Bad choice.

But the emergency spillway is eroding badly both at the parking lot end and the far right side where emergency concrete was poured at the base of the emergency spillway just a day or two before the water topped it.


Sun, Feb 12, 2017 – 10:03pm

NBC now reporting that the spillway has failed.  I have not confirmed this via a second source yet.

This is not the same thing as the Oroville Dam  failing…but it’s a step closer to that.

Hopefully the bedrock stops the process before failure.

Here’s the best (jargony, but seemingly knowledgeable and factual) account I’ve come across so far:

I have heard that the emergency spillway is eroding through cutback. This will be an evolutionary erosive failure. It will take some time for the cut back. Hopefully the erosion will be stopped at bedrock.

However, I fear that if the erosion of the emergency spillway, on the canted bedrock of the abutment communicates with the hydraulics of the principal spillway, this may result in a V notch failure.

This would be the most serious type of failure. I believe there to be a good chance of a loss of the gate structure on the left (facing downstream). I expect loss of rock and perhaps some of the weir of the emergency spillway.

The training wall between the emergency and the principal spillway is a likely place for failure of structure. I understand that significant releases, which will be uncontrolled will take place, the possibility of this becoming very serious does, indeed exist. I am sorry with all of my heart that this is taking place. This is one time that I want so deeply to be wrong. All of my best wishes are with you tonight.

Scott Cahill (update 1)

As I write the Oroville dam in California is eroding back toward a breach of the reservoir. I am a dam contractor. If you ever heard someone say “that dam contractor..” they may have been talking about me.

I have repaired hundreds of dams including ones like Oroville, which were in the process of failure. I know a lot about dams.

The spillway failure is a common type of failure, where phreatic, or surface water entered the spillway, migrating beneath the slabs. (A static element on a dynamic element, A hard element on a live element). The dam is hydrated and dehydrated as water levels rise and fall, moving, as soils swell from pressures and water mass. In times of high rain the phreatic surface (hydrated soils line) moves toward the surface, venting into the void so produced.

This creates a void. Moving water over the years has eroded soils from beneath the slab downstream and left a channel. Now, the spillway has been actuated in a high-flow event and the plates of the spillway have failed into the stream, scouring from beneath them. They will continue to fail as the water continues to flow. The hydraulic jump exacerbates this erosion.

If the flow continues for a long enough time, with sufficient velocity, the reservoir will be voided by the migration of the erosion to the pool (cut-back). I cannot tell if failure is imminent,

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