Mountain Buzz banner

Oroville Spillway is failing with enough rain dam may break

12K views 36 replies 18 participants last post by  Andy H. 
#1 ·

Attachments

See less See more
2
#28 ·
Hi,

It's the erosion at the bottom right in the picture of the emergency spillway that ought to be most worrisome.

If that continues to cut back and undercuts the concrete apron -- and they can't release fast enough from the other damaged spillway -- then the next thing to stop the flow in that location will be bedrock.

I'm amazed they are not reinforcing that area. Or maybe they are, and the photos just haven't been showing it.

FWIW.

Rich Phillips
 
#29 · (Edited)
Rich, yes, that's my understanding. Once the Emergency spillway starts to erode, they estimate that it could downcut about 30 feet into the rock. If this happened, then the entire top 30 feet of the reservoir would be released in very short order as the water rushing through tore out the concrete apron and began scouring and plucking the fractured metamorphic rock.

Here's my back of the envelope calculation:

I just looked up that the reservoir has a surface area of 15,500 acrea
Assuming the emergency spillway were downcut by 30 feet, the volume released would be about 465,000 acre-feet
If that volume were released evenly over one day (big assumption), this would equate to a flow of 235,000 cfs. This is over twice the outflow they're trying to release down the main spillway.

It's pretty likely that there would be a catastrophic failure and the majority of the water would be released within a shorter period. For perspective, if it all went evenly in a 12-hour period, that would be 470,000 cfs.

Holy shit.

Here's a good blog that I've been following as these storms have been coming ashore. He gets into the FERC relicensing issue also.

Geotripper - Liveblogging the Deluge This is written by a geologist, so you know it's spot on! :)
 
#30 ·
They are dropping bags full of boulders from helicopters into those erosion caused gullies. Hard to believe that is anything other than a desperate stop gap. Considering the next storm is now less than 48 hours away I doubt there are any other options.

Curious, on the main spillway they built up features to diffuse the power of the water before it hits the river. But the emergency feature is a straight drop ( i have heard 30') right into the base of the concrete foundation. Why vertical?

Thx for the blog, Andy. Will dive into it.
 
#34 ·
The photos of the damage to the main spillway after they shut off releases yesterday are phenomenal. The scale of that spillway was lost on me until I saw the helicopter in the photo. Such a massive structure.

How do they fix something like that? Not to mention all of the dredging and cleanup of the river channel so the lower power station is protected for operation.

http://www.mercurynews.com/2017/02/...stop-flow-down-spillway-see-extensive-damage/
 
#36 ·
Followup on Oroville

Here's an HCN article on the expert report on the Oroville Dam incident in 2017, when the dam was nearly lost due to overfilling:

What went wrong at Oroville?

From the article:

[The report]...describes the physical factors that caused the spillways to crumble, problems like unstable rock foundations and cracked concrete that allowed water beneath the main spillway.

The report also highlighted human and organizational errors, including faulty design details, shortsighted inspections and “overconfident and complacent” management by the California Department of Water Resources. The department “take(s) the findings very seriously,” said then-director Grant Davis in a statement. “We will … incorporate the lessons learned going forward.”
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top