Popular Mechanics article

Six months before rushing water ripped a huge hole in a channel that drains a Northern California reservoir, state inspectors said the concrete spillway was sound. As officials puzzle through how to repair Oroville Dam spillway, federal regulators have ordered the state to figure out what went wrong.
Earlier inspection reports offer potential clues, including cracks on the spillway surface that if not properly repaired could let water tear through the concrete. In recent years, construction crews patched cracks — including in the area where water burrowed a huge pit last week.
 to the main spillway triggered a series of problems culminating with the first use of the emergency spillway, which quickly began eroding and threatened to unleash a torrent of water on cities downstream. On Tuesday, officials said the immediate danger had passed, and allowed nearly 200,000 residents to go home after evacuation orders scattered them for nearly two days.

The gushing waters of the Feather River, downstream from a damaged dam, draw curious onlookers Tuesday, Feb. 14, 2017, in Oroville, Calif. Workers are rushing to repair the barrier at the nation's tallest dam after authorities on Sunday ordered the evacuation for everyone living below the lake amid concerns the spillway could fail and send water roaring downstream.AP Marcio Jose Sanchez
Inspectors with the state agency that both operates and checks the dam, the nation's tallest at 770 feet, walked the half-mile-long spillway in 2014 and 2015 and did not find any concerns.
"Conditions appeared to be normal," the inspector wrote in reports from both years.
Last August, a team of inspectors did not check the channel on foot but instead from afar, also concluding that everything looked fine.
The inspection came as California was enduring a five-year drought, and the channel rarely was used to relieve pressure on Oroville Lake, which is about 70 miles north of Sacramento. An extraordinarily wet subsequent six months changed that. Dam managers were draining water from the fast-filling reservoir into the Feather River below when the pit appeared last week.
Experts said problems like the cracks in the concrete spillway and spots in nearby areas where water seeped from the reservoir through a hillside were common issues with dams. What mattered, said John Moyle, New Jersey's director of dam safety and flood control, was whether dam operators dealt with the problems carefully — patching cracks so they were watertight, and dealing with spots where water was leaking through so they didn't grow to undermine the concrete.
The Department of Water Resources declined to answer specific questions about the repair work, saying engineers were focused on ensuring public safety.
Robert Bea, professor emeritus of civil and environmental engineering at University of California, Berkeley, said it's "obvious those repairs didn't work."
"We don't have details on the repairs, but they put cement into the cracks and troweled it over," Bea said. "I call it 'patch and pray.'"
On Monday, federal regulators told the department it must enlist a group of independent consultants both to assess what went wrong and to recommend long-term fixes.
Documents and interviews show that crews were patching cracks in 2009 and 2013. A water resources department spokesman said it was normal for maintenance crews to be troubleshooting cracks in the channel during dry summer months.
One resident of the region said he saw crews in the spillway at least once a year for the past several years.
"When they have four or five trucks down there, the only thing they have to do is fill cracks," said Don Reighley, a retiree and fisherman who several times a week drives past the channel to launch his boat into the reservoir.
One of the state inspectors who went to Oroville Dam in August said authorities may never know exactly what destabilized the spillway.
"Any type of evidence that might have been there is gone," Eric Holland of the water resources department's dam safety division said. "Everything has been washed away."

Chromophobia    You can beat this, brother ...

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Ed

Could not resist.

Wonder how many $$$ they have in on this to date and how much they intend to spend before next flood season. There was an original rectal grope of quarter of a billion dollars at the beginning. Wonder of that's still in the ballpark.

They're drowning in drought.

Very nice of you!

 the awesomeness that is GD.

I bet the idiot inspector doesn't even get fired.  At most he gets reassigned to a different department.  

Guess what happened in 1997, also on a Tuesday?  The same damn thing "A gaping hole — some 250 feet long and 45 feet deep — appeared Tuesday in the lower part of the spillway, which sits on dirt."  http://usa-general.com/los-angeles/at-oroville-dam-a-break-in-the-storms-gives-engineers-hope.html

So they had this problem before yet the inspector completely missed it.  Granted that was 20 years ago but there should have been a big note in dams profile, "lower end sits on dirt and has previously failed". Then you would think after 5 years of not using that might be one thing they would check for.  Apparently not.  Government employees that their finest.

Thank you! Very humbled and appreciative.

No homo.

Aye to that!

That isn't really the way it works... That might be the weight of the volume of water, but pressure is not the same as weight of water.

They have probably spent more on half assed repairs and helo flight time then they would have had to on solid repairs done the right way a year ago...

And they are just getting started! The bottom half of the spillway will be major.

and then during the next big dry spell then can rip out all their emergency repairs and do it the right way....

CA is a beautiful state, with millions of great Americans in it.

The retardation is correlated with population density and the coasts have disproportionately large cities.

Some folks seem so angry about the stereotype they can't think straight.

Well dam!  I was thinking a bit homo

Ed

I think you misread. The article said in '97 the E-spill was nearly utilized, not that the spillway failed.

Have no doubt, voids will form in fill underneath concrete.  We had a section of aircraft parking ramp at McGuire AFB that needed to be replaced with thicker concrete that we suspected had started forming voids.  When it would rain you could see air bubbles blowing out of the seams between concrete slabs as the voids filled with water.

When those slabs were replaced there were a couple of voids large enough for cars or trucks to fall into.  Somewhere in the 8'x20' range.  Old slabs torn out, the voids filled with packed gravel instead of sand and new, thicker concrete poured on top (21" versus 11" due to new requirements for heavier aircraft).

We never could figure out where the flowing water came from that washed away the sand that had been put there in the 1940s.  But in 50 years even at he low elevations in ground that is nearly swamp at times, the water flowed enough to move tons of sand out from underneath a dozen or so 25'x25' concrete slabs.

I would agree with that.

Show me where I said that.

It was a figure offered just for its own sake, which I guessed no one had tossed into the discussion.

You read more into it than there was.

Unless they combined their visual inspections with something like a ground penetrating radar, I'm not sure how they could have noted anything other than surface cracks in the spillway.

Would that be true for any dam? If so, is it normal to do that as part of a periodic inspection?

I would think, considering the forces involved on that spillway, they would have done so when they found damage and patched it.

No I clarified what could be misrepresented when read.

I'm clearly speculating, but considering soil tends to compact, shift, move, erode, etc., I would have thought there would have been more extensive / intrusive inspections, especially considering the space / distance the spillway consumes.

dupe

Ground penetrating radar (GPR) is common enough now that most state highway departments have several towed units they do yearly surveys of the interstates in their states.  Certainly not like it was 20-25 years ago when it took us getting one brought in by a contractor to survey the MAFB parking ramp.

I can't imagine DWR not having access to a GPR unit either by borrowing one from CalDOT or by hiring a contractor.  It isn't like they are still experimental devices or something.

Have it your way, but nowhere did I use either the word "pressure" or the word "force".

Also, I "misrepresented" nothing .......... perhaps you meant could be "misinterpreted".

  Just the tip, eh?

It looks like 854 is where they want to be.

This was Disneyland on Thursady:

I realize that, two entirely different things, I was just marveling at the mass of the water, that's all.

DO NOT let your balls touch.

Thar isn't where the river boat goes, is it?  

Post #1005 over at metabunk has some good information on the spillway; 90% on bedrock and 10% built on concrete backfill.  Mick follows in #1009 with some good documents on hydraulic aspects at Oroville.

It wasn't just 1 guy with a flashlight inspecting that spillway. It would have been a team.  I'd bet dollars to donuts that there's an engineer on that team furiously forwarding his emails to a private account documenting all of his objections to the report.  If those ever see the light of day it'll get real fun real quick.

That's just Goofy!

  Kinda like what is happening in New Mexico, Right? 

I guess we were supposed to met them at the State Line, rifles in hand, and make them prove the were conservatives before letting them in.

To be honest, I expect that that limit isn't listed as a restriction for the sake of the spillway, but for flow of the river downstream.

Mike

Apparently so. Google has been reporting wrong dates all day.  Not sure what is going on but they dated that article and many other articles 1997.  With no date on the story, the 1997 date on Google, and the 1997 down stream evacuation in the article I just figured the whole thing was from 1997. 

So the theory is that is what caused the sink hole under the spillway?

They would threaten to take away his pension if he leaked it, so he will stay quiet.

When I worked building a highway 20 years ago they had some sort of nuclear density testing machine that they ran to tell if the asphalt that was laid was sound enough.  They now have the portable ground penetrating sonar systems.  One would assume that part of the inspection would have included at least a couple passes up and down the spillway with either one of those types of devices just to make sure there was no settlement under the concrete and to make sure the concrete itself was retaining the density they expected.

Someone mentioned previously in the thread.  Those weep holes in the side of the spillway are to let water in the ground drain out and not get under the spillway itself.  Apparently they run all the time which pretty much suggests water has been under the spillway the whole time.  The part of the spillway that remains must be built on rock but the part that eroded was on dirt.  When you have under ground moving water transition from rock to dirt you get a sink hole.