Emergency: California’s Oroville Dam Spillway Near Failure, Evacuations Ordered

Breitbart ^ | Feb 12, 2017 | Joel B. Pollak1

[janetjanet998]

The California Department of Water Resources issued a sudden evacuation order shortly before 5 p.m. Sunday for residents near the Oroville Dam in northern California, warning that the dam’s emergency spillway would fail in the next 60 minutes.

The Oroville Dam is the highest in the nation.

[KC Burke]

Yes, Janet can be proud. This thing could have devolved into a dozen loose end threads.

It is like watching Katrina play out. My favorite expression for this phenomena is an “all day train wreck.” The cars of governmental poor planning just keep piling into the pile of wreckage.

[janetjanet998]

lake up 4 feet in 24 hours....inflow in the low-mid 40,000 a little above what they expected(39,000)

Juan had an update saying that they plan on putting more shotcrete on the upper portion when things dry out...but the window is closing..since they will spill again at 860-865 feet

lake at 851 feet rising a foot every 7-8 hours or so

[meyer]

The inflows should taper over the course of the day if the weather clears. They’ve had something on the order of 2-3 inches of rain over the last 2 days. Once the bulk of that comes downstream to the reservoir, inflows will back off.

Unfortunately, the spillway will still need to be used a couple of times more. Maybe even 3, but you didn’t hear that from me. There is a LOT of snow up in those mountains that will be trickling down over the next couple of months.

I hope that they get a chance to harden the area at the mouth of the surviving spillway into the plunge pool. That step alone would allow them to taper flows down below 40,000 without major erosion.

[Jim W N]

Moonbeam’s not an engineer, nor has he ever built anything in his life. Maybe he thinks he can simply order it and it will magically happen.

Isn't that how dictators work?

[Jim W N]

all day train wreck

Good one.

[janetjanet998]

yes....they only say the spillway will have to be used 1 or 2 more times more likely 2 or 3....they can only drop the lake to around 830-835ish using the spillway...

2 inches of rain fell at the dam last storm while 3-5 fell in the basin in the mountains..some of that snow which could have replenished what snow has melted so far

after perhaps 1/4- 1/3 inch in the basin today...looks like a very weak system monday morning and a little stronger one tues-weds

[abb]

They’ll probably set up the batch plant adjacent to the pile of rock and concrete they dug up from the riverbed. From there, they’ll set up a belt conveyor over to Moonbeam Canyon. As the mix is placed, dozers will spread and rollers will compact. The RCC will be a “hardened fill.”

Once the canyon is filled, then a conventional slab spillway will be built atop the concrete fill.

That’s my guess.

[mad_as_he$$]

We got 1” this am North of Reno. Already 38 degrees though. My place of business is directly impacted by another slow motion train wreck:

http://www.kolotv.com/content/news/Silver-Lake-could-rise-as-much-as-4-feet-due-to-spring-runoff-418448873.html

Silver Lake is a “dry” lake and typically only holds seasonal runoff. There is no outlet.

[meyer]

Once the canyon is filled, then a conventional slab spillway will be built atop the concrete fill.

LOL - I laugh every time I see "moonbeam canyon".

Let's hope that the conventional slab is about twice as thick as the broken one, and with a lot more rebar and anchoring.

[KC Burke]

Based on water content in the near record deep snowpack I think the lake aw will continue near full with inflow until mid to late June. I saw one area where there as over fifty feet of snowfall hat had consolidated to 17 feet of snowpack with seven feet of water content. That isn’t going to thaw on one warm May Day.

[mad_as_he$$]

The only good news is that the melt hasn’t started in earnest yet. The snow pack in the Sierra’s sublimates 1% per day. So every day the pack goes without melting significantly buys some relief. There is also one interesting aspect that I have not seen discussed outside of the Desert Research institute meetings. The freeze state of the ground is very key in how the runoff occurs. If the ground was hard frozen down to a significant depth then the run off characteristics are very different than if it was ready to absorb more moisture. General consensus is that the ground was not frozen hard in most areas prior to the snow starting in earnest. We shall see.

[KC Burke]

I had no idea the sublimation loss was that high.

It’s amazing that the east side is so dry.

[EarthResearcher333]

DWR Board Expresses Concern of Breakage of 50 year old Anchor Tendons in Spillway 3 years ago

For 3 years the Oroville DWR Board has been expressing concern of "breakage" within the array of 37' 6" steel post-tensioned Anchor Tendons (rods). Ultrasonic wave testing has been used to inspect the rods, however this technique is limited in quality of defect (corrosion, cracking) detection short of the full length of the rod. It has limitations to a quality analysis for the full length of the rod due to attenuation (signal reflection losses & other artifacts). Ultrasonic wave testing does not provide another important structural result; i.e. the remaining post-tension load "stress" that is left in these 50 year old rods. Knowing the remaining "stress" in these rods will reveal how much structural capacity the Radial Trunnion Gates may withstand in water flow operation (hydrostatic & hydrodynamic forces). Thus, the DWR Department of Engineering (DOE) has been seeking to implement a new technology to determine the stress left in the rods using "dispersal wave technique". More on this later.

DWR Board is concerned regarding tendon anchor breakage due to age and other breakages at dams of similar construction: 2014 Division of Safety of Dams DSOD Inspection report.

View of Trunnion Anchors (tendon ends, rows of dots) extending out of the Trunnion anchorage blocks. 2014 Division of Safety of Dams DSOD Inspection report.

[KC Burke]

Prestressed and post tensioned concrete have service life assumptions I am not always happy with depending upon.

[meyer]

The inflows should taper over the course of the day if the weather clears.

I may soon get to eat those words. :/

[jpal]

I can understand the use of RCC as the foundation for the main spillway. If they used any type of uncemented backfill, it would eventually consolidate and sink, causing problems. They could plausibly build a structure, which might ultimately be cheaper, but would take a lot of time and effort to engineer correctly. Laying layer upon layer of RCC which set quickly and requires no formwork appears to be the fastest method of construction.

The volume would be enormous. They would end up with a monolith of concrete more than 100 feet in every direction, which would have to be one of the biggest pores outside of dam construction in the world. You could build a couple dozen miles of freeway with that volume! I guess cost is no longer a concern. Even with RCC’s lower cement content, I think heat buildup could still become an issue that would have to be dealt with.

However, I can’t see the use of RCC to make an apron between the (yet to be constructed) cut off wall and the emergency spillway weir. They just finished dumping bags of rock and boulders cemented together with conventional PCC below the weir, leaving a relatively uneven surface. They would have to rip that out out and smooth it off before placing RCC, or fill it in with even more rocks and concrete. What would be the benefit of using RCC for this emergency spillway application?

[meyer]

Does RCC generally include any kind of reinforcement material (rebar)? Not my area of expertise.

[KC Burke]

I think the concept as mentioned above is RCC as a spillway covering below the emergency weir. That is proposed as a seamless full width cover. My concern is can it be placed sloped that much.

Something along the lines of flow-able fill could be an answer for the moonbeam canyon sub-grade. It could be delivered by chute, pump, or truck.

The whole thing is a crap shoot of choices. The design should take 12 months not 12 days.

[jpal]

You note that each anchor tendon is a 6 inch thick steel rod. That is a fairly hefty chunk of steel. Even if the outer 16th inch got corroded, which would be a lot, the rod should still maintain better than 95% of its tensile strength.

Steel in the Golden Gate Bridge, and the Brooklyn Bridge, and many other applications has been in continuous tension for quite a bit longer than the Oroville dam has existed, and that steel is still quite serviceable. Are these anchor tendons so under designed that they commonly fail?

In my experience as a civil engineer, most structures are overdesigned A minimum of 300 to 500%. Maybe with dams, it’s a whole different ballpark though. Considering the consequences, it seems like they’d want to do way better than that.

[EarthResearcher333]

"You note that each anchor tendon is a 6 inch thick steel rod."

Perhaps there is a misunderstanding of the text... The text of 37' 6" is a length - thirty seven feet six inches long. The diameter of each steel rod is 1 3/8 inches. (Oroville specs). In the Oroville Radial Trunnion Gate anchor tendons, in reference to this picture, anchor tendon (150), encased within a steel sleeve (158), anchor plate (154), nut (156) -(or in other cases a wedge type "grip nut"). Oroville's spillway has 24 anchor tendons to secure the operating loads from each Trunnion Pin (136) (forces from). note: This drawing only shows 1 anchor tendon to each Trunnion Pin. Oroville's construction emplaced grout inside the steel sleeve (158) that encapsulated the anchor tendon (150) after the tendon was tightened to load design tension.

Anchor Tendon example image - for discussion.