Oroville Dam Spillway Failure

Discussion in 'Oroville Dam' started by Mick West, Feb 8, 2017.

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1. Eric BarnesNew Member

Thanks for the interesting posts/commentary Mick! Came here from Dr. Roy Spencer's site. It will be interesting to follow events in the next few weeks/months.

Based on:

The CDEC lake level figures have 1AM with 902.58 and 11AM at 902.30. I'm going to assume they are just using a simple equation

Flow = K * (h-D)^1.5

The -D is the height of the spillway, you'd expect 901, however, solving:
12600=K*(902.58-D)^1.5, 8000=K*(902.30-D)^1.5 for K and D

Gives K=11357.8, D=901.508

So based only on those two data points it looks like they are using

Flow = 11357.8*(height - 901.508)^1.5

However it's entirely possible they are using a more complex formula to account for the variations in the lip height and shape

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3. Norman Braithwaite P.E.New Member

It is a little more complex. The crest of the ogee section is at elevation 901.0 and the crest of the parking lot spillway section (a short wall) appears to be about one foot higher. Further clouding the calculation is the fact that the weir coefficient of the parking lot spillway section is very different than that of the ogee section. These differences (two more unknowns) make it impossible to back into a reliable equation. Going forward from established weir flow knowledge, two weir equations can be superimposed to estimate the stage discharge relationship but other ambiguities (at lease to me) still limit the result to an estimate.

Well I assume they have better measurements than we do. That equation fits the two data points, and the curve would be similar (^1.5) so it's probably a reasonable estimate for <2 feet. Hopefully it will never get higher!

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5. Norman Braithwaite P.E.New Member

Also subtracting the controlled spillway and powerhouse releases from the downstream river flow may not be a very good estimate of emergency spillway flow. Before the emergency spillway was in operation I noticed that the estimate of downstream river flow was consistently exceeding the sum of the controlled spillway release and the powerhouse release. Sediment in the bottom of the river channel from the controlled spillway failure may cause this inconsistency by causing the water in the river to be higher than normal for the actual flow.

6. Carl LeoanrdNew Member

There is an emergency evacuation order for low lying areas from Oroville and down stream. There is undermining of the emergency spillway.

This is from the Sacramento TV stations.

7. dafogleNew Member

Last edited by a moderator: Feb 12, 2017

http://www.sacbee.com/news/state/california/water-and-drought/article132332499.html

This is the worst case I wrote about in the OP.

Not the same as the dam failing, however it's very bad. 30 feet rapid release will create major flooding if it happens.

10. Norman Braithwaite P.E.New Member

Yes. Failure of the emergency spillway would be very bad. If the ogee spillway is lost, flow through the breach may be in the multiple hundreds of thousands of cubic feet per second. Outflow may reach 100,000 cfs per 100 feet of lost spillway.

Last edited: Feb 12, 2017
11. Graham2001Active Member

Just checked the 'latest' videos and the scare-mongers are out in force, King Truth LoganLLC ran a video with a close up of the emergency spillway and the following title "OROVILLE DAM WASHOUT !!! BETTER EVAC NOW". I have also seen one video which I will not link to which uses footage from a flood either in China or a nearby region and claims this is happening in California.

On the other hand here is a more recent and less alarmist video of the overflow, though some of the commenters seem to be claiming that 'the government' is censoring YouTube videos on this event.

A failure of the spillway will be a significant disaster in itself. It would then raise the spectre of an possible failure of the dam itself which would be ten times worse. My "why the dam will not collapse" diagram says it won't because of the rock ridge. But the geology can't be 100% relied upon. It's not something anyone is going to rule out.

Downstream areas are already saturated with high rivers and some local flooding. And that's with actually reduced flows.
There's a range of possible outcomes here. None of them are good, some of them are disastrous.

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13. deirdreModeratorStaff Member

its not really scare mongering if it's really happening.

14. deirdreModeratorStaff Member

did they at least open the main spillway full force once it was running clear?

Said they put it to 100K

16. rkt88edmoNew Member

DWR Tweets E-spillway failure before 6pm (tweet from around 1640hrs)

• Informative x 1
18. rkt88edmoNew Member

So, there is the very strong horizontal line below the e-spillway, is that really the base of the non-earthen spillway lip, or do we know how tall/deep the concrete portion of the e-spillway is?

19. Carl LeoanrdNew Member

They are talking the top 30 of the lake being drained, so I'm guessing that it is 30 ft.

I'm just estimating as I'm only on my phone, but the top 30 feet of the lake has about 350k acre feet. That is a disaster on a huge scale.

20. Spectrar GhostSenior Member

Is there a possibility that a failure will cause upstream flow and damage the base of the dam proper?

21. Max FeferNew Member

Top 30ft of the reservoir is roughly 350-400k acre feet. Back of the envelope calculation shows that if it takes 1 day to drain that 350k, this would increase downstream flows by 200 kcfs (above current levels). From what I heard, downstream levees around Marysville are designed for 150k cfs. I think it unlikely to have a large effect on Sacramento given the current information, but these situations can evolve quickly.

The dam is unlikely to fail due to the hard rock ridge separating the spillways and the dam. If the normal spillway fails, this could cause a more catastrophic failure of the emergency spillway.

This isn't a tried and true analysis, so please comment if any readers see inaccuracies.

I'd not rule it out. There's quite a bit of elevation up the road to the power station, but the level would certainly rise.

What's the 350K figure? If the emergency spillway holds they will drain it with the broken main spillway at 100 to 150K.

If the emergency spillways fails then they would probably shut off the main spillway. The failed emergency spillway flow could be anything of a huge range of numbers.

Plan is now to use helicopters to drop bags of rocks into a hole that is forming near the emergency spillway.

Hole was eroding up the hill towards the weir, but advance has slowed.

2" of water going over the emergency spillway. Dropping

They sound relatively hopeful.

27. RedNeckGeekNew Member

Apparently there was "boil" on the auxiliary spillway at around 3PM today that is now rapidly eroding back into the hillside. In order to slow the flow into the auxiliary spillway, flow through the main spillway was increased to 100K CFS. However, it was decided to issue an evacuation notice for all people south and west of the dam in the Feather River drainage. That includes low lying areas of not only Oroville, but several communities south along Highway 70 and the Feather River. It was just announced that an Oroville city councilman had been told that the rate of erosion is not as high as originally thought, but the evacuation orders are still in effect.

• Informative x 1
28. jwchesnutNew Member

New conference reports head cutting has slowed. Spillway has been raised to 100K cfs. Lake level may drop quickly enough to dry out the emergency spillway.

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29. RedNeckGeekNew Member

DWR personnel are said to expect that the auxiliary spillway will stop flowing within one hour.

Estimates are that 500,000 cubic feet of water would be released from the reservoir if the auxiliary spillway fails.

Traffic is jammed northbound on Highway 70 north out of Oroville, but several evacuation centers are open in Chico.

There will be another news conference at 9PM Pacific Time.

30. Graham2001Active Member

Meanwhile the scare-mongering channels on YouTube are continuing to spread as much fear as is needed to generate the hits.

This is part of the write up for a video posted on YouTube channel NewsChannel428 which seems to specialise in alarmist material of all kinds. It makes the channels intent pretty clear.

• Informative x 1

Oroville emptying out earlier:

33. Eric BarnesNew Member

The weir must be getting undercut? It looks like much more water is going over the top than earlier this AM, but the actual water level is lower now?

There was a similar helicopter operation in New Orleans with the flooding there. However they used sand bags, as the water was not moving much. Oroville will likely have to be large rocks. Interesting and unorthodox engineering coming up.

They say it's down to a couple of inches. Should stop within a few hours.

36. RedNeckGeekNew Member

I thought I heard during the news conference that the boil was at the bottom of the hill near the river.

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Well that's not going to make the weir collapse. It must be near the top.

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38. dafogleNew Member

so they will be dropping large rocks into that boil/hole ??

39. LeiferSenior Member

True....searching YT for "Oroville dam"......the mass of individuals creating alarmist videos is amazing (or is it ?). It looks like they are competing for "hits" by creating extreme YT video titles....adding to more and more incorrect inflated information....and basically turning into clickbait. This might be a sign of how many people get their news from YT.
I gave-up youtube for any current helpful information on this topic, and I'm watching the KCRA live news feed.

http://www.kcra.com/nowcast
click on "Live Now" icon at the top if you don't see a live feed.

Hard to find with a simple YT search, there is Cal EOS live feed on youtube, but other than press conferences, there's not much info to be found there.