Oroville Spillway Investigation and Repair

[SeanT]

DWR plans to start blasting, this is from a few days ago and I haven't heard any blasting yet (I'm 1.5 miles from the spillway), I'm assuming they'll wait until they can stop outflows from the main spillway.

Slope setback with controlled blasting
• As part of regular procedure, DWR will use controlled blasting methods to break up intact rock on the slopes along the damaged gated flood control spillway so that it can be safely excavated. The slopes are near vertical and are up to 150 feet in height. These slopes present a significant safety risk for construction workers.
• The controlled blasting produces little to no audible noise or vibrations. A whistle/air horn will alert workers near the project area prior to each controlled blast.
• Seismographs will be located throughout the project area so engineers can monitor movements and to make sure recorded vibrations are within safe levels.
• The controlled blasting will begin as early as Friday, April 21, and will continue for four to six weeks on approximately an every-other-day schedule, so that workers can start making necessary repairs to the spillway to meet the tight construction schedule.
• DWR obtained required permits for the work from its state and federal regulatory partners, as well as the Butte County Sheriff's Department.

From http://www.water.ca.gov/news/newsreleases/2017/042017_oroville_construction.pdf

 

[Dan Brekke]

...Maybe the only item of interest in this is that the DWR spokesperson repeats the comment made by Mr Croyle two press briefings ago that there was a lot more concrete used than the original construction specs refer to. She said that this was in the area of the spillway "core" without saying (or being asked) where that is. I've taken this to refer to backfill on the rock surface under the deck but if so a lot of it must have got washed away.

I asked DWR the week before last to expand on the claim about the thicker concrete. Here's part of an email exchange with the person who's been put in charge of responding to most spillway questions:

Q. Director Croyle mentioned that drilling on the upper spillway has revealed areas with 4 or 5 feet of concrete. How extensive are those areas? Earlier reports from Board of Consultants and others stated the slab was 9 to 15 inches thick (depending on placement of sub-slab herringbone drains). Were those reports essentially accurate?

A. A number of holes have been drilled in the upper portion of the gated flood control spillway and more will be drilled in order to assess geological conditions. Some bore holes show concrete that is four to five feet thick, some do not.
​

And that's all the department's communications apparatus chooses to say on that subject. I don't know if you could be less informative if you tried, but I'm guessing that's precisely the department's intention. It would be easier if they'd just say "take our word for it."

 

[Dan Brekke]

Here's Robert Bea's revised root-cause analysis document, with attributions:

https://www.documentcloud.org/documents/3676605-Robert-Bea-Oroville-Spillway-Failure-Root-Cause.html

 

[aczlan]

Here's Robert Bea's revised root-cause analysis document, with attributions:
https://www.documentcloud.org/documents/3676605-Robert-Bea-Oroville-Spillway-Failure-Root-Cause.html

He also emailed me a link to a PDF copy:
Source: https://drive.google.com/file/d/0Bz1I1mIutSEnT3J5N2ZKUHQtNDQ/view

I tried to upload it, but at 127MB, it wouldn't upload. I "printed" it with CutePDF and that dropped the size down to 60MB, but the forum still claimed that it was too big.
I then split pages 1-37 and 38-78 into two files and that worked.
They are attached as "bob bea preminary RCA rev2Pages1-37.pdf"(sic) and "bob bea preminary RCA rev2Pages38-78.pdf"(sic)

Aaron Z

 

[aczlan]

Apparently, there were some errors in some of the citations so Bob Bea released a rev3:

Happy Monday,
this morning, i discovered i had made several mistakes in the revised report photograph attributions.
i have corrected them and included the additional cited reference in the attached Rev3 of my report. please use Rev3.
Aaron, if you know how to contact EarthResearcher333 who provided the concerned photographs on the Free Republic web site, please send the report link to him:
http://www.freerepublic.com/focus/news/3524221/posts?q=1&;page=3284#3284
thank you again,
bob

Google Drive link: https://drive.google.com/a/berkeley.edu/file/d/0Bz1I1mIutSEnV05SMUVMN2lEWk0/view?usp=drive_web
I split it again and attached it as:
bob bea preminary RCA rev3Pages1-37.pdf
bob bea preminary RCA rev3Pages38-78.pdf

Aaron Z

 

[Boilermaker]

Apparently, there were some errors in some of the citations so Bob Bea released a rev3:

If you follow the link in the "Happy Monday" message, which is:

http://www.freerepublic.com/focus/news/3524221/posts?q=1&;page=3284#3284,

you open up a kind of parallel planet of observations on this incident, on which Dr Bea appears to have felt obliged to post himself because of the issue over attribution of the images he used (including one of mine, but I am not bothered about it). I had not found this other forum before.

I'm not going to dwell on the attribution issue because what caught my attention was this, posted yesterday:

BREAKING: CA Dept. Of Water Resources releasing all three independent Oroville Spillway reports (Redacted) #CBS13

another tweet says it will be on their website this afternoon

I think that I have found what this refers to here (and forgive me if everyone else on this forum already knows about it):

http://www.water.ca.gov/oroville-spillway/bocreports.cfm

These are the three independent Board of Consultants reports issued to date. On first reading, the two I hadn't seen already may not contain much that is entirely new. But it's not possible to be sure because there are several redactions. I can't figure out for the life of me why they think they are justified in redacting anything (apart of course from fear of blame/liability).

Anyway I am more interested in the forensic team's report. No news on when that will be out but as the BOC reports make clear, it's relevant to the actual rebuilding plan, which cannot be long delayed.

 

[Boilermaker]

This is the link to the second BOC memo:

http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 2_031717.pdf

Apart from many other observations, this seemingly anticipates in the passage reproduced below what the forensic team might think. I can't work out what are the three photographs they are referring to and they are not included in the report. Maybe someone else knows which/where they are; I have added the italics in the text:

4. Does the BOC have any other comments or recommendations for the Design Team?

Response

Three photos of very low flow on the upper chute taken after the chute failure, clearly show a hole on the left side of the spillway approximately at or near the construction joint near station 29+00. The second photo shows flow occurring at very small depths (probably due only to gate leakage). At this very low flow, what appear to be role waves, or possibly disturbances due to flow over construction joints or cracks are clear. The third photo shows the hole that developed shortly after initial failure. In this photo, the damage to the chute is totally downstream of the construction joint. Later photos show the damage has taken place on the upper side of the construction joint and has migrated to approximately station 29+00.

These photos show that failure was initiated at the hole at the left side of the chute near station 33+00. The failure, likely occurred as a result of high velocity flow (in the range of 85 to 90 feet per second), penetrating under the slab, causing a strong uplift force and causing the slab to lift, eventually causing all or part of the slab to break away. Subsequent erosion of foundation material caused progressive failure both upstream and downstream.

Repairs had been made to the spillway slab several times since its completion in 1968. The most recent documented repair took place in 2009. Locations of numerous existing cracks and spalls were shown in the report. The spalls were probably caused and enlarged by freeze-thaw damage. Some of these holes were quite large and extended as deep as the reinforcing steel. The hole that triggered the failure was probably of the latter type.

If cavitation damage had a role in the slab failure it was probably minor. If cavitation did occur, it would have been damped by aeration in the disturbed flow leaving the gated structure. The thick piers cause large rooster tails downstream of the thick columns downstream of the gates. The waves caused by the piers are efficient aerators. This effect has been used by the Chinese as an aeration device on their design of steep high-velocity chutes and have been found to be effective in preventing cavitation damage. In their design, the channel between the thick walls is actually narrowed slightly to increase the air entrainment. The Chinese call these spillways "Flared Chutes" or "Flared Spillways."

The BOC believes that the aeration produced by flow past the Gate-Structure walls, is sufficient for this spillway.

 

[sweepleader]

My daily work for the past 11 years has included cavitation investigations involved in the design of industrial pumps. Standard industrial criteria used by the plumbing industry is to keep water flow speeds below 8 fps. Our pumps normally operate with fluid flow speeds of 25 fps and in only several months of testing will sustain cavitation damage resulting in failure of their heavy outlet components.

The BOC says, "The failure, likely occurred as a result of high velocity flow (in the range of 85 to 90 feet per second),..." (This is the first time I have seen velocity numbers mentioned.)

They follow up with, "If cavitation damage had a role in the slab failure it was probably minor."
Question 6 for the BOC, pages 7 & 8 of Oroville Emergency Recovery – Spillways Independent Board of Consultants Report No. 2

That cavitation damage could be minor at these speeds is hard for me to imagine.

Then, near the end of the report, they go on to say "M2 – 13 The BOC recommends that an air supply slot be built into the reconstructed chute at the location where the slope changes to a steeper incline." This is a technique used to entrain air to reduce cavitation.

???? Probably like everyone else here, I am wondering what they talk about in private.

 

[Peter M]

I'm not convinced. The one place on the remaining spillway that shows significant capitation damage is damaged concrete just below the break. There is exposed rebar showing there, and the surface is toughened. All other pictures show minimal damage, even in the region where the slab separated, above the right side of the break. In contrast, there is plenty of indirect evidence of undermining--most notably the blocked drain pipes uphill from the initial break. Yes, cavitation happens in pipes, but as you say, it takes months of use to be perceptible, and is presumably in a significantly softer material than rolled concrete. In contrast, the spillway failed within days of first use. That suggests a very fast process.

My daily work for the past 11 years has included cavitation investigations involved in the design of industrial pumps. Standard industrial criteria used by the plumbing industry is to keep water flow speeds below 8 fps. Our pumps normally operate with fluid flow speeds of 25 fps and in only several months of testing will sustain cavitation damage resulting in failure of their heavy outlet components.

The BOC says, "The failure, likely occurred as a result of high velocity flow (in the range of 85 to 90 feet per second),..." (This is the first time I have seen velocity numbers mentioned.)

They follow up with, "If cavitation damage had a role in the slab failure it was probably minor."
Question 6 for the BOC, pages 7 & 8 of Oroville Emergency Recovery – Spillways Independent Board of Consultants Report No. 2

That cavitation damage could be minor at these speeds is hard for me to imagine.

 

[dario martinez]

Which federal agency is picking up the tab for this repair?

Who or what abc federal agency picks up the tab, it will be the people who will pay for this!

 

[sweepleader]

I'm not convinced. The one place on the remaining spillway that shows significant capitation damage is damaged concrete just below the break. There is exposed rebar showing there, and the surface is toughened. All other pictures show minimal damage, ...

If you reread what I said you will see 'only several months of testing will sustain cavitation damage resulting in failure of their heavy outlet components.' Perhaps it is not clear but I meant that cavitation damage to destruction often occurs rapidly, even in metal structures. The spillway has been in use for years and years and years. I was trying to point out that the BOC was downplaying a very important part of the equation, not that it was the only part. Exposed rebar is not a trivial matter, especially when there is only one layer. Once exposed it can not longer reinforce the concrete as it depends on being embedded to bond with the bulk material. I hope this makes my point more clear.

It is entirely possible that the major cavitation damage has been swept away but that is conjecture on my part.

 

[Boilermaker]

I was trying to point out that the BOC was downplaying a very important part of the equation, not that it was the only part. Exposed rebar is not a trivial matter, especially when there is only one layer. Once exposed it can not longer reinforce the concrete as it depends on being embedded to bond with the bulk material.

Looking in more detail at the BOC reports, the burden of what they are saying is directed to ascertaining the initial cause of the deck failure. They don't regard cavitation as that cause although they do think that it was a surface defect in the deck that started the whole process.

I can't locate the three photos the second BOC report relies on as supporting this conclusion despite trawling though the earliest ones here and elsewhere, including the DWR gallery. Maybe these have never been released to the public or the BOC have seen something in other photos that I can't.

However, thinking back to the earliest image of the spillway failure I can recall, namely the amateur video taken from the slope to the west of the failure point, it showed lumps of the deck being thrown skywards by the force of the water. I assume that's at least consistent with cavitation damage although at the time I simply put it down to the deck being undermined and breaking up.

Lastly I believe that the third BOC report clarifies their earlier remarks about cavitation prevention measures: http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 3_033117.pdf
This is from page 10:

Provisional Air Slot: In previous meeting comments, the BOC suggested that it could be advisable to add a designed air slot near the beginning of the steep slope. Although cavitation was probably not the root cause of the slab failure, it may have aided in the progress of the slab failure. Adding air could aid in aerating the flow on the steep slope and dampening the added damaging effects of cavitation. It may be advisable for these air slots to be analyzed in the hydraulic model tests that are currently taking place.

 

[sweepleader]

However, thinking back to the earliest image of the spillway failure I can recall, namely the amateur video taken from the slope to the west of the failure point, it showed lumps of the deck being thrown skywards by the force of the water. I assume that's at least consistent with cavitation damage although at the time I simply put it down to the deck being undermined and breaking up.

I think you are correct in regard to this video showing only that the deck was breaking up, unrelated to the exact failure initiation process.

I had forgotten the other reference you noted about air slots. Since the BOC seems to be consistently thinking of air slots they MUST think that cavitation is more important than they are letting on. My personal belief is that air slots should be added to all transverse joints so that any water that would otherwise tend to enter the joints and under slab spaces would be drawing back into the main flow by air being drawn upward into the flow. It appears to me that the "drain" system could be air pipes that empty through the joints into the high speed chute flow, not a system to conduct the leakage around elsewhere. That would solve both any cavitation issues and the under slab water question.

 

[Boilermaker]

I had forgotten the other reference you noted about air slots. Since the BOC seems to be consistently thinking of air slots they MUST think that cavitation is more important than they are letting on.

My personal belief is that air slots should be added to all transverse joints so that any water that would otherwise tend to enter the joints and under slab spaces would be drawing back into the main flow by air being drawn upward into the flow. It appears to me that the "drain" system could be air pipes that empty through the joints into the high speed chute flow, not a system to conduct the leakage around elsewhere. That would solve both any cavitation issues and the under slab water question.

I think the strong implication of what they have said is exactly as you have described. So I don't understand why they haven't just come out and said it. The redactions in the second and third BOC reports seem rather haphazard but there may be a link between them and this issue.

Regarding water penetration into the joints, one thing I got from Dr Bea's comments is that it is clear that even at low flows there was water entering those joints. The photos he borrowed from this site show this clearly when collated as he has done. The BOC has laid no small emphasis on embedding "water stops" in the joints to stop such penetration. I am not sure that this is more efficient than placing air slots at transverse joints. However, what follows is from page 8 of the second BOC report and reflects their approach of using stops in both transverse and longitudinal joints:

Both transverse and longitudinal joints will be provided with water stops. Water stops between slabs were apparently not included in the design of the original spillway and the lack of them was no doubt an important factor in the February failure of the slab on the FCO Chute. It will be very important to have constant construction inspection when slab concrete is poured to assure proper imbedding of the water stops.

This is Bea's illustration of construction incorporating the stops:

 

[Balkan]

they MUST think that cavitation is more important than they are letting on

Earlier in this thread, there was a consistent point of view on the mechanism of water impact involving (infra)sound waves. IMHO, the cavitation affect is not only superficial, though observed on the surface. It penetrates through the material via vibrations caused by water turbulence. Also, let's take into account the interaction of cavitating water over the chute with the same water in the crevices of it, and underneath.

 

[sweepleader]

Earlier in this thread, there was a consistent point of view on the mechanism of water impact involving (infra)sound waves. IMHO, the cavitation affect is not only superficial, though observed on the surface. It penetrates through the material via vibrations caused by water turbulence. Also, let's take into account the interaction of cavitating water over the chute with the same water in the crevices of it, and underneath.

I don't follow your thoughts here, cavitation damage is a surface phenomenon, at the boundary between liquid and solid in this case. Damage is not caused by cavitation impacting only liquid.

Can you cite the passages you refer to "involving (infra)sound waves."? Incipient cavitation produces ultrasound which is not audible to humans but is formed at high energy levels and can be detected with the correct equipment.

"Cavitation" by Knapp, Daily, and Hammitt, McGraw Hill 35080 is a good reference on the subject. Chapter 1 page 3 has excellent photographs, figures 1-1 and 1-2 (which I am unable to insert here), of cavitation at only 40 fps in room temperature water. This is half the speed and 1/4 the energy that the BOC refers to above.

 

[Balkan]

Thank you for your answer.

Can you cite the passages you refer to "involving (infra)sound waves."?

I will not dig back into 40 pages of discussions. Cavitation itself generates ultrasound waves, waterflow generates infrasound waves. Water isn't so simple. There was a man who lived a century ago, Viktor Schauberger.
He made great discoveries about water.

 

[deirdre]

I will not dig back into 40 pages of discussions

use the search box then.

 

[Balkan]

Sorry, I found the mentioned passage Pre-Failure Oroville Dam Spillway Historical Images

We Hams, we know about standing waves? These would be Long wave, subsonic waves. Meters in length.
The start of the spillway in the feed, the power terminator is the speed bumps at the bottom. There's Kilowatt, (Megawatts) of acoustical energy emitted as noise.
To examine the entire spillway, it looks like a Transmittion line. Energy feed, Energy terminator, containing a lot of Raw power in between.
Frankly, I think the failure was caused by resonance. Something not planned for? Not cheap construction, or some terrorists. Time will tell? Hope it wasn't just a big leak.
I know acoustical wave travel backwards in a flowing column of water. If they are strong enough, they will reverse the flow, and I can prove this. I can well imagine the vibrations building up in a rigid flat plate until it breaks. I'm sure, they must have a seismometer there.

 

[Boilermaker]

It looks like by the time that the forensic team produces its report on the cause(s) of the spillway failure, which is meant to be next month, other authorities will have already identified all the possibilities. This report from the Corps of Engineers (completed 3 weeks ago but only in the press this week) gives another detailed analysis:

https://assets.documentcloud.org/documents/3678133/Oroville-Army-Corps-Briefing-on-Oroville-Dam.pdf

Their conclusions are summarized at page 5. Note that they do not mention cavitation as a factor. The detailed list of possible reasons is followed by this text, which is broadly consistent with what the BOC has already said:

Based on these observations, the underdrain system, poor geologic conditions with compacted clay leveling fill, and marginal design details likely led to the incident. The drain pipe protruding into the service spillway slab likely caused open cracks to form, and the underdrain flows may have eroded material (possibly altered due to years of drought) from beneath the slab. If the upslope side settled relative to the downslope side, such that the downstream portion projected up into the flow, the situation would be exacerbated. When the spillway gates were opened, high velocity water probably entered the cracks and the stagnation pressures were enough to lift and break the thin slabs, given that the anchor bars were short and anchored into weak materials, and there was no steel mat on the bottom of the slab to resist bending. Once the concrete slab was gone, the underlying highly decomposed rock and compacted clay leveling fill were easily eroded down to lightly weathered rock. Deeper erosion occurred along the deeply weathered shear zones, and the water followed these pathways.

The BOC identified a surface defect in the deck as the point of origin of the failure. I've also come across this annotated photo from another forum highlighting both typical surface deterioration and water ingress between the spillway chute slabs (although this is far closer to the flood control gates than the point of failure):

 

[Balkan]

Note that they do not mention cavitation as a factor

IMHO, not accounting dynamic factor is wrong.

high velocity water probably entered the cracks and the stagnation pressures were enough to lift and break the thin slabs

Need to keep in mind the Bernoulli's Principle. The spill water in the slab is not flowing slowly as on above photo. Beside the turbulence/vibration it may exercise negative pressure onto the adjacent surface, especially in area where it accelerates (exactly where the damage occurred) - where the slope increases.https://en.wikipedia.org/wiki/Bernoulli's_principle

 

[Boilermaker]

A fourth Board of Consultants memo has now (3rd May) been released by DWR:
http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 4.pdf

Although dated some two weeks before the first three memos were disclosed on 25th April, it was not included with them nor referred to in that disclosure. Exactly why that is so is unclear. In any case, the released text of this memo appears to be more significantly redacted than that of the earlier memos.

The memo does disclose a fundamental shift in the proposals for repairing the spillway. In particular, the remaining upper part of the spillway chute will not be rebuilt in 2017. Instead, the lower chute will be rebuilt and the "scour hole" filled in that time. It is acknowledged in the memo that completing this work by 1 November 2017 will be "challenging." See extracts from the memo copied below.

Other matters referred to in the memo include differences in the foundations of the upper and lower chutes disclosed by historical records and test borings, lack of success to date in finding a rock crushing method that permits use of the spoil excavated from the river channel as aggregate for new construction concrete and work to level the steep slopes adjacent to the lower spillway section.

There is also reference to defects in the original design of the spillway but as noted below these have been redacted.

The Design Team presented a detailed review of construction documents that included photographs taken during foundation preparation of FCO spillway chute slab, the Division of Safety of Dams (DSOD) and DWR inspection reports during construction, and the results of borings and core holes drilled through the spillway chute slab during the current field investigations. On the basis of this review, the design team concluded that the foundation conditions under the upper spillway chute are different from and better than those encountered under the failed section downstream [concluding passage redacted].

The motivation for adopting such an approach is to replace the currently proposed "remove-and-replace" option of the upper spillway chute (which has been slated for the 2017 construction season), which is likely to present challenges in being completed by the November 1 deadline. This alternative option would allow completion of the reinforced concrete lower spillway chute (founded on an RCC-backfilled foundation) and the scour hole repair to be accomplished during the 2017 construction season.

The BOC considers this option a feasible alternative, provided repair measures to the existing chute consider the following measures: [All five of the BOC-recommended measures redacted]

The designs developed have corrected a number of problems that were inherent in the original design. [Specific reference to such problems/corrections redacted]

Historical photos and construction reports indicate that there were locations where the surface [redacted]. Water methods should continue to be used as well.

[T]he BOC notes that the FCO spillway will begin flowing on Friday of this week (April 14) and, except for a one week hiatus, will flow continuously until about June 1. [Redacted] to begin placing RCC in this area by the planned date of July 1. While this task appears to be doable, completing it in the time allowed appears to be challenging. The BOC encourages the development of other options to continue work to proceed while the FCO spillway flows occur.

 

[whoosh]

Although dated some two weeks before the first three memos were disclosed on 25th April, it was not included with them nor referred to in that disclosure. Exactly why that is so is unclear. In any case, the released text of this memo appears to be more significantly redacted than that of the earlier memos.

That explains the delay.

Thanks for the summarization!

 

[BakingDude]

A fourth Board of Consultants memo has now (3rd May) been released by DWR:
http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 4.pdf

Although dated some two weeks before the first three memos were disclosed on 25th April, it was not included with them nor referred to in that disclosure. Exactly why that is so is unclear. In any case, the released text of this memo appears to be more significantly redacted than that of the earlier memos.

On Friday May 5 at 10pm Pacific Time, I tried to use the link above and got an error page at DWR. I then went to the DWR BOC page:
http://www.water.ca.gov/oroville-spillway/bocreports.cfm

and I saw a list of links to 4 BOC reports, including BOC Report #4 April 11, 2017 When I clicked it, it gave the same result as clicking Boillermaker's link above - an error page. Today that link has been *removed* - on a weekend no less. The press reports (http://www.orovillemr.com/general-n...repairs-starting-from-the-bottom-up-literally) that this report was first posted on FERC's web page for the ORO incident on May 3:
https://www.ferc.gov/industries/hydropower/safety/projects/oroville.asp

and lo and behold when I visited that page the evening of May 5, report #4 was not in the list and is not today. It appears Report/Memorandum #4 has gone missing. Does anyone here have it and if so could they post the entire document somewhere? (eg Scribd, etc) Thank you in advance for any tips on locating it because it appears someone does not want it seen.

 

[bRad]

I believe this is document:
http://webcache.googleusercontent.com/search?q=cache:cuQfdTUEeVsJ:www.water.ca.gov/oroville-spillway/pdf/2017/BOC%20Memo%204.pdf+&cd=4&hl=en&ct=clnk&gl=us

I wanted to share some of my sources of locating this document, in case they will be help to anyone in the future.

----

You may try searching the internet wayback machine for changes to that page. I think I have some clues for you, but may need some more work. (moderator - some of the urls below are not there as links, they are textual urls working through finding the document BakingDude was asking about, so I have intentionally not made them links).

https://web.archive.org/web/*/http://www.water.ca.gov/oroville-spillway/bocreports.cfm
Just a touch about the Internet Wayback machines. They scan millions of sites every day looking for changes, and the archive the versions. You can query for those changes.
The view that you land on from the link above will be a calendar. That calendar has a blue circle for every day that page changed. You over with your mouse over that blue circle and it will show times that they scanned the page and detected changes. You click the day, it will take to the version of the page on that day. You hover then click on a time it will take you to a time of a change. I was not able to find the page version based on this method.

So lets do a bit of searching of the url of the pdf you are referring. BOC Memo 3 has a url like http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 3_033117.pdf. So the report you are looking for should have a url like http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 4_041117.pdf
Again ask DWR site and asked wayback. Again no luck.

So final try. Wayback has a way to query for any pages that are subpages to a url. All the docs should have a base url of http://www.water.ca.gov/oroville-spillway/pdf/2017.
That leads us to this page: https://web-beta.archive.org/web/*/http://www.water.ca.gov/oroville-spillway/pdf/2017/*
On this page you will see 5 documents. Taking the doc name from the url they are:
"a3186 Oroville Spwy Recovery_v5.pdf"
https://web-beta.archive.org/web/*/http://www.water.ca.gov/oroville-spillway/pdf/2017/a3186%20Oroville%20Spwy%20Recovery_v5.pdf

"BOC Memo 2_031717.pdf"
http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC%20Memo%202_031717.pdf

"BOC Memo 3_033117.pdf"
http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC%20Memo%203_033117.pdf

"BOC Memo 204.pdf"
https://web-beta.archive.org/web/*/http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC Memo 4.pdf

"Lake Oroville events timeline.pdf"
http://www.water.ca.gov/oroville-spillway/pdf/2017/Lake%20Oroville%20events%20timeline.pdf

"Lake Oroville Spillway Repairs general overview_022117.pdf"
http://www.water.ca.gov/oroville-spillway/pdf/2017/Lake%20Oroville%20Spillway%20Repairs%20general%20overview_022117.pdf

Unfortunately, the Internet Wayback machine does not have copies of any of these documents. If you ask www.water.ca.gov/ for those documents they all come back, except "BOC Memo 204.pdf", that one fails.

But at least we now have a fairly specific document name.

Lets see if anyone else has this document. google query "BOC Memo 204.pdf" and google has a link to it, if you look at google links there is often a little green triangle, if you click that triangle it has a "Cached". This is googles scanned history of pages. Click that and you get Memo4.

Not sure why wayback does not have these documents, or why it does not have the version of the links page with the 4 document links.

I hope this helps.

 

[StickyMockwell]

I believe this is document:
http://webcache.googleusercontent.com/search?q=cache:cuQfdTUEeVsJ:www.water.ca.gov/oroville-spillway/pdf/2017/BOC%20Memo%204.pdf+&cd=4&hl=en&ct=clnk&gl=us

Very very interesting - this version seems to be the full version (without redactions), e.g. compare the text to Boilermakers post #102. Maybe that is part of the reason the memo has disappeared

 

[whoosh]

I find it at http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC_memo4.pdf
linked from http://www.water.ca.gov/oroville-spillway/bocreports2.cfm

 

[bRad]

I find it at http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC_memo4.pdf
linked from http://www.water.ca.gov/oroville-spillway/bocreports2.cfm

That is clearly a reposted one. It is kind of a mess. That version has major redacted sections. Yet retains. "Contains Critical Energy Infrastructure Information DO NOT RELASE" markings.

I suspect if you want the undredacted you better grab it fast, it will likely be going away. Also gives you a chance to see what they redact.

 

[Boilermaker]

As of yesterday, and with no fanfare, the first report of the Forensics Team tasked with determining the cause of the spillway failure appeared. This is the text:

http://www.water.ca.gov/oroville-spillway/pdf/2017/Memorandum_050517.pdf

Note that this deals with both the emergency and main/service spillway failures but I reproduce below only what is said about the latter.

I actually found this by monitoring another forum but it can be tracked back to its source on the DWR website posted yesterday:

http://www.water.ca.gov/news/newsreleases/2017/051017news .pdf

Highlights below (italics added) - in the sense of what this memo says, although absolutely nothing in it will come as any surprise to those who have been following this story here. I will say that out of the two dozen factors listed the majority relate to original (1960s) design and construction defects whereas more recent operational and maintenance deficiencies are a ways down the list - make of that what you will:

At this time, the Team is still in the information gathering and review stage of its work, and it has not yet reached conclusions. However, the Team recognizes that the California Department of Water Resources (DWR) is in the process of designing and constructing interim and permanent repairs to the service and emergency spillways at Oroville Dam. As requested by DWR, to provide input to the repair efforts, the Team provides the following preliminary lists of candidate physical factors that are being considered as potentially contributing to the damages that occurred at the spillways in February 2017. At this time, the Team does not believe that it is likely that there are singular physical causes of the spillway damages, but rather that the damages were the results of some combination of physical factors from the lists below.

Candidate physical factors potentially contributing to service spillway damage:

1. Thinning of the chute slab above herringbone drains; these locations can promote cracking.
2. Large variations in slab thickness.
3. Limited slab reinforcement consisting of one layer of light reinforcement in the top of the slab.
4. Lack of continuous tension reinforcement across slab joints.
5. Corrosion and failure of reinforcing bars across cracks.
6. Slab joints with insufficient keys or lack of keys.
7. Slab placement sizes which were too large to control cracking.
8. Lack of waterstops in slab joints.
9. Hydraulic pressures and flows transmitted beneath the slab sections through open cracks and joints.
10. Increase in spillway discharge shortly before slab failure.
11. Plugging or collapse of drains or collector pipes, including potential plugging by tree roots.
12. Flow into the foundation that exceeded the capacity of the drain pipes, including possible flows from areas adjacent to the chute.
13. Lack of redundancy in collector drains.
14. Unfiltered drains; the gravel envelope may not serve as a filter.
15. Herringbone drains crossing joints in the slab.
16. Weathered rock and completely weathered rock that is soil-like material as slab foundation, without appropriate modification of the chute slab design, resulting in potentially erodible material beneath the slab and lack of foundation bond with concrete; the weathered rock and completely weathered rock appears to be associated with geologic features such as shear zones, and the degree of weathering changes relatively rapidly between some areas of the chute slab.
17. Less rigorous foundation preparation, resulting in lack of foundation bond with concrete.
18. Extended drought impacts on foundation materials.
19. Insufficient anchorage, due to limited anchor development in the concrete, short anchor length, inadequate grouting or grout strength, and/or installation in weak foundation material.
20. Relatively high spillway flow velocities in the lower chute for higher spillway discharges.
21. Lack of durability and effectiveness of slab repairs.
22. Spalling and/or delamination of concrete at slab joints.
23. Groundwater pressures; although current evidence suggests this may not have been a significant factor.
24. Cavitation; although preliminary analysis suggests this may not be a significant factor.

 

[SeanT]

CA Department of Parks and Rec now has a live stream of the spillway and surrounding area http://www.parks.ca.gov/live/lakeorovillesra_spillway (doesn't seem to work with Goolge Chrome)

 

[Boilermaker]

DWR has recently posted the 5th Board of Consultants' report, the text of which is here:

http://www.water.ca.gov/oroville-spillway/pdf/2017/BOC_Memo5.pdf

A fair number of passages are redacted. The Board's recommendations are mainly about construction issues and there is practically nothing new in them that sheds light on the cause(s) of the spillway failure.

 

[SaC]

Has "repair" has started? It looks like they may have started filling depressions on the lower portion of the flood control spillway?

Still from livestream here:

http://www.parks.ca.gov/live/lakeorovillesra_spillway

 

[Boilermaker]

Has "repair" has started? It looks like they may have started filling depressions on the lower portion of the flood control spillway?.

I think that you have to count demolition and also creating access to the site as part of "repair" as well as creating facilities for mixing concrete. All of those are well under way now even if they are not yet creating a new spillway surface. The truck in the foreground of the above image looks to be applying concrete to what will form the foundation of the new surface and if so that is certainly a start on replacing the spillway itself

 

[Boilermaker]

Latest DWR photos appear to confirm that the lowest level of a new concrete spillway foundation is being poured (below images and the full gallery are at https://pixel-ca-dwr.photoshelter.c...g/G00003YCcmDTx48Y/Oroville-Spillway-Incident):

 

[SaC]

Thought this was interesting given all the under-drain discussions that occurred here. All images from https://pixel-ca-dwr.photoshelter.c...CcmDTx48Y/Oroville-Spillway-Incident-Recovery

 

[KAN DAEK]

Is there anyone here who has been watching the repairs and issues currently... Today is Oct 15

 

[Boilermaker]

I am sure there are others but yes, I have kept an eye on the recovery progress and what's been said about the causes of the spillway failure.

 

[NoParty]

Love those pictures!!

Who'd have ever thought that Americans could get excited about the construction of a spillway?!?