Oroville, Calif. spillway failure - IMO absolutely can endanger dam itself.

Submitted by Jeff Buster on Sun, 02/12/2017 - 14:39.

 

The image above from the latimesgraphics makes it look (at least to me) that the primary dam is concrete - it is not concrete - it is dirt!   The prmary dam appears so vertical  (camera lense issue) that I thought it had to be concrete - no, it's "engineered" compacted dirt.  

The emergency spillway is dirt also - but the soil below the surface of the emergency spillway was never "engineered" - removed and replaced in a controlled manner.   The fact that the emergency spillway was constructed over untouched virgin soils and rock (full of faults, cracks) is totally unprofessional, even criminal. 

 

Here is a web site metabunk.org which has a very thorough and detailed review of the Oroville dam spillway failure - but  I disagree with the site's confidence that the dam itself is "not endangered".

What is not known is if there are geologic fissures or factures which will allow water to lubricate the soil and rock and thus decrease the arched concrete dam's compressive forces against it's left and right hand abuttments.   

At 770 feet tall - and the water level inside the dam now with in about 20 feet of the top of the dam, the concrete dam is getting "lighter" - the specific gravity of the water is much greater that air and thus acts to "float" the dam and the soil against which the dam is compressively braced.    

The geologic conditions in this area aren't ideal for a dam - there is soil, decomposed rock, and not much competent bed rock - look at the close ups of the spillway quite a way down on the website linked above. 

Read more good info here at AmericanRivers.org updated 2.16.17

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Both spillways at Oroville dam are jokes - look at the soil

 The geology at the site looks like a combination of volcanic intrusions (see elsewhere on line the 3 rock columns on the upstream side of the base of the main spillway), and sedimentary soils.    When water flows over this type of geologic material the erosion is instantaneous and extreme.   The more water, the faster the water, the more erosion. 

The so-called "emergency" dirt spillway is a total joke while the main spillway is a joke because the assumption was that it would not have any leaks or cracks - while being built right over the sedimenary soils.   

Other factors which may threaten the dam itself but which are very difficult to predict and to monitor are

1. the earth's crustal deformation due to the massive weight of water in the full reservoir vs the prior drought almost empty reservior and

 2. the effect of vibrations (caused by the mlllions and millions of tons of 50 mph water crashing down the sspillway) on the immediate dam area.

3. increased subteranean leakage cause by the two above factors and the record high level of the reservoir - potentally leading to wash out.   

 

when news reporters don't know what the critical issue is

 When the news helicopters fly over the spillways of the Oroville Dam, their photographers and videographers don't really know what they are looking to film - so their cameras spin around and often miss the crucial details.  

In this matter what is most important are construction and engineering failings - and not so much the flood waters running half way down the hill.  Specifically, where is the failed section of the emergency spillway?   Where is the wash out that crews are potentially going to helicopter bags of rock into?  

This could be a market for "drones for hire"....such a business would supply drones at the site and allow engineers or other experts to hire via the internet the drone and fly it via the internet right where they directed it - to obtain specific images or videos....

Did efflorescence in Oroville spillway signal failed concrete?

 

The image above with the 4 pick up trucks on the dry Oroville Dam spillway is dated 2013.  What the work that is being done isn't clear - but the whitish colored streaks flowing down the dry face of the spillway appear to be effloresence.  Read more about efflorescence here on Wikipedia.

In the image above the white streaks below the trucks all appear to be emminating from a horizontal construction joint in the floor of the concrete spillway.    Provided that the streaks were not caused by the present work being done, and are in fact a historic stain on the floor of the spillway, then the streaks would indicate potential long duration groundwater rising up through the spillway floor slab.    If water was entering the slab for years from underneight - this would lead to deterioration of the steel slab reinforcement and the concrete itself.  

This is just about the exact same area that the spillway floor catastrophically failed in February, 2017. 

 

Anti-cavitation spillway aeration design - if you aren't busy

 Here is a web site which discusses different designs for aerating the fast moving water in concrete spillways - which aeration diminishes surface cavitation and concrete destruction.     If cavitation were the problem, the rebar would be visible after the concrete was "cavitated" away....

Cavitation is not the reason for the Oroville dam spillway failure, IMO.