Today's Sinkhole

[WOM]

Today's Sinkhole

They keep saying that there's no threat to the actual dam, just from secondary flooding (or landslides, I guess) from the emergency spillway issue. But CBC radio led off with "Major dam in danger of collapse" this morning.

[Ginger Yellow]

Today's Sinkhole

And it looks like there was plenty of warning that use of the emergency spillway would cause damage but they decided against reinforcing it.

[ursus arctos]

Today's Sinkhole

Evacuations now over 180,000

But the good news is that the lake has receded to the point where water is no longer going over the auxiliary spillway. Though there is still great concern over the next storm anticipated for mid week.

Latest from the Bee

[San Bernardhinault]

Today's Sinkhole

The emergency spillway was, theoretically, rated to 250,000 cu ft/s (the main spillway rated to 100,000 although they've run it up to 160,000 in the past). There's a lot of hillside that it drains onto so the idea was that it should drain over such a wide area that there wouldn't be massive erosion.

It looks, though, as if the concrete top of the emergency overflow has a massive crevice in it (filled in with giant boulders dropped by helicopters overnight). And if that concrete overflow fails, then that's something like 30 feet of lake level that would drop in an uncontrolled manner. It's not a complete dam failure, but it would mean all the levees on Feather River, and possibly even the Sacramento River, would be threatened, and that could lead to massive flooding down as far as the Yolo Bypass.

[ursus arctos]

Today's Sinkhole

Very much so.

One of the experts interviewed by the Bee said that the Route 70 corridor "is gone" if the emergency spillway fails.

[Guy Profumo]

Today's Sinkhole

"Thermalito Diversion Pool" - BNT

[linus]

Today's Sinkhole

WOM wrote: It looks like there are two spillways, though. There's the concrete chute (with the hole in it), which is the controlled spillway. And then on the left is an emergency spillway that basically appears to be like a lowered lip on the dam. It just dumps the water onto a grassy/treed hillside. I mean, I wonder if the engineers even figured that part would ever be used.

Engineers will plan their designs according to specification, based on historic data and the magnitude of extraordinary natural disaster they have to build for, usually defined statistically by the number of standard deviations from the norm ("sigmas"). For instance, a 3-sigma design will be built to sustain an outlier event 3 times the standard deviation removed from the mean.

In this case, this looks like the wettest season since 1982-83 in CA, roughly twice the average seasonal precipitation, which is still well within the specs, the issue here is maintenance.

[Ginger Yellow]

Today's Sinkhole

Engineers will plan their designs according to specification, based on historic data and the magnitude of extraordinary natural disaster they have to build for

Yes, but apparently this dam was designed under the expectation that another dam, Marysville, would be in operation. It was never built.

[linus]

Today's Sinkhole

Water management earlier this winter was part of the problem. Normally they would not have let the reservoir levels climb to near-full in midwinter, because of the important snow runoffs that will start building up in Srping. Their decision-making was affected by the drought.

[caja-dglh]

Today's Sinkhole

Decision making in that kind of situation is challenging. Damned if you do, damned if you don't.

[linus]

Today's Sinkhole

caja-dglh wrote: Decision making in that kind of situation is challenging. Damned if you do, no more dam if you don't.

FIFY.

[linus]

Today's Sinkhole

Ginger Yellow wrote:

Engineers will plan their designs according to specification, based on historic data and the magnitude of extraordinary natural disaster they have to build for

Yes, but apparently this dam was designed under the expectation that another dam, Marysville, would be in operation. It was never built.

Not building that dam didn't make the network inherently unstable or precarious, very poor upkeep and management did. California's infrastructure had been the best in world through the mid to late 20th century, with cutting-edge civil engineering and great planning. Best university system in the world by a wide margin, superb road network, great waterworks. The system only started to crumble with the deterioration in the state's political climate, which started a few decades ago.

[San Bernardhinault]

Today's Sinkhole

The good news is that the evacuation order has been lifted, and that increasing the flow down the regular spillway hasn't appeared to have done much extra damage, and they've got the levels to about 25 feet below the top of the emergency spillway.

The moderate news is that the storm that's about to hit looks to be carrying a bit less water than was previously thought, and seems to be cold enough that a fair amount of its precipitation will fall as snow, and won't melt any of the massive snowpack up on the mountains.

The least good news is that there might be a big storm coming on Monday.

[Incandenza]

Today's Sinkhole

Los Angeles:

http://abc7.com/weather/1-person-hurt-after-cars-fall-into-massive-sinkhole-in-studio-city/1760948/

One car was already in, then the other fell in on top of it on TV.

[San Bernardhinault]

Today's Sinkhole

This is what the spillway looks like now:



Completely collapsed in the middle, which means that when they let water out it now diverts to the right in that image, and has basically eroded an entire canyon in the hillside.

And here are a couple of little video clips:

The kind of destruction
Flyover with humans, to show the scale of it.

[Sits]

Today's Sinkhole

Blimey. That will take some repairing. WOM is very good at that sort of thing.

Seriously, will it actually function, albeit through a completely wrecked course? Or is there a risk of further collapse?

[San Bernardhinault]

Today's Sinkhole

It has been functioning over the last 2 weeks as they've drained down the reservoir to 75% of capacity, and about 60 feet below the top. If they release water at the rate they have been, I'm sure there'll be more erosion - particularly in the hillside. But I'm not sure that will be particularly damaging. It'll be unsightly, but unless it erodes back all the way to the dam itself, it's not a problem.

The trouble is going to be how they're going to find time to fix it. We might have seen close to the end of the rain in Southern California, but up in the Sierras there are more storms coming. And as soon as the storms stop, the snow will begin to melt. And they have 200% of normal snowpack this year, so that will keep melting and filling the reservoir through the first parts of the summer at least. It's not clear when they'll have a good window to properly start repairing it.

[Sits]

Today's Sinkhole

Thanks SB. Interesting reading up to see there was a community proposal in 2005 to upgrade the backup slipway to a similar (but wider) concrete structure. Rejected.

[WOM]

Today's Sinkhole

Sits wrote: Blimey. That will take some repairing. WOM is very good at that sort of thing.

You're gonna need a bigger moat.

[linus]

Today's Sinkhole

The five month window should be enough to fill in the canyon and repair the spillway, provided the budget (somewhere around $100M-200M) is there.

[Gangster Octopus]

Today's Sinkhole

Sinkhole potential...

[evilC]

Today's Sinkhole

Gangster Octopus wrote: Sinkhole potential...

Kids these days! When I were a lad we had to find things out the hard way!

[ursus arctos]

Today's Sinkhole

YIKES!

Hundreds of workers at the Hanford nuclear waste site in Washington state have been ordered to “take cover” after a portion of a tunnel appeared to collapse.

The U.S. Department of Energy said it has activated its emergency operations protocol in Hanford, a small agricultural community in south-central Washington, about 200 miles from Seattle. It came after an alert at the 200 East Area, which is home to numerous solid waste sites.

Energy Department officials in Hanford said in a statement, “Officials are responding to reports of a cave-in of a 20 foot section of a tunnel that is hundreds of feet long that is used to store contaminated materials.”

[ursus arctos]

Today's Sinkhole

Mar-a-Lago!

"A 4' x 4' sinkhole has formed on Southern Boulevard directly in front of Mar-a-Lago," the traffic alert read. "It appears to be in the vicinity of the newly installed water main. West Palm Beach Utilities distribution crews have secured the area and will most likely need to do some exploratory excavation today."

[Ginger Yellow]

Today's Sinkhole

I was going to say the metaphors write themselves, but I see the Post has beaten me to it.