Give ne back my hat!

Oroville Dam

http://www.mercurynews.com/2017/02/10/oroville-dam-crisis-eases-but-incident-highlights-risk-of-aging-u-s-facilities/

"Oroville Dam is not as glamorous or well-known as the Golden Gate Bridge, and few Californians have ever seen it. But the monumental structure, built into a rocky canyon 70 miles north of Sacramento in the Sierra foothills, is a critical part of modern California, providing water for 23 million people and vast stretches of farmland as the anchor of the State Water Project.

At 770 feet tall, the structure that holds back the mighty Feather River is taller than the Washington Monument and as thick as 10 football fields at its base. Its reservoir, Lake Oroville, is 10 miles long, the second largest reservoir in California behind Shasta Lake near Redding.

Bob Bea, a professor emeritus of civil engineering at UC Berkeley, said Friday that the partial collapse of the spillway highlights the need for the state and nation to invest the money updating its aging highways, dams, bridges and flood control projects.

“A 50-year-old person isn’t as robust as a 16-year,” Bea said. “And neither is a 50-year-old dam. Most of our infrastructure dates back to this time period. It’s now in its old age — the geriatrics phase — and we are still using a reactive approach to manage these systems. We wait until we have a big problem. It is much more cost-effective and safe to be proactive than waiting to fix something after an infrastructure disaster.”"
Permalink Grumpy Old Man 
February 13th, 2017 8:31am
In 2005, multiple groups filed a suit, saying the dam was unsafe, improperly designed, and the emergency spillway in particular, being made out of earth only, was at great danger of erosion that would lead to catastrophic collapse. Nothing to do with its age and wear, had to do with being a bad design.

The agencies responsible for the dam said that upgrading to a concrete spillway would simply be too expensive and would eat into their profits. They argued that the primary spillway had a high enough capacity that the emergency spillway would never be used anyway.

The case was dismissed.
Permalink Pegular Roaster 
February 13th, 2017 9:30am
Drone and other footage shows that discharge from the emergency spillway (which is further away from the main dam than is the main spillway) is eroding the hillside below and making it own way down to the pondage.

I think the main dam wall itself is safe but if the emergency spillway wall collapses there will be a large but relatively slow uncontrolled release which will increase until everything is gone down to erosion resistant bedrock.

Hopefully that won't be too far down. If not and it bottoms out way below the current dam water level then flooding is going to be huge.

I sure have hope it holds.  Dambuilding was already pretty well an established science back when it was built and the stability of the containing hillsides would have been assessed and this scenario worked through. But I do wonder why the ground below the emergency spillway wasn't paved to a good distance downhill.

But hey, if it goes totally we need footage. It will be like the aftermath of Moses and that trick he had with a 2x4.
Permalink trollop 
February 13th, 2017 9:40am
From that link:

>This weekend, as Lake Oroville’s level rose to the top and water couldn’t be drained fast enough down the main concrete spillway because it had partially collapsed on Tuesday, millions of gallons of water began flowing over the dam’s emergency spillway for the first time in its 50-year history.

The fuck? The only reason the main spillway is not running fucking full bore is they are trying to protect it against further damage.

They should drop the gates and let it rip down the remaining paving which will defer erosion until the torrent is well away down the hill.

Erosion undermining the emergency spillway crest is a far more dangerous possibility.

Popcorn.
Permalink trollop 
February 13th, 2017 9:51am
No, the normal spillway wasn't able to handle even 1/20 of its rated capacity. If they run it at full, it will erode away the base of the main dam face.
Permalink Pegular Roaster 
February 13th, 2017 10:05am
That's rubbish. Neither spillway is able to threaten the main dam, as a glance at any map or photo would confirm.

Well not until the whole valley below backs up to the foot of the main dam and by then it's all over, Red Rover.

The threat is to the emergency spillway crest way off to the left when facing upstream. That going would in itself be a disaster to tell your grandkids.
Permalink laptop trollop 
February 13th, 2017 10:32am
Erosion caused by the main spillway failure was threatening nearby electrical grid infrastructure. That's why they were limiting the flows. It wasn't until the potential catastrophe of losing the emergency spillway wall that they opened up the main spillway full bore to try preventing disaster.
Permalink Dam it 
February 14th, 2017 12:53am

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