Posted on 02/15/2017 5:59:22 PM PST by Mariner
Oroville
Crews worked into the night Wednesday to shore up the emergency spillway at troubled Oroville Dam, racing to fortify the structure before the next series of storms, the first of which was forecast to hit before midnight.
Three storm systems will move into Northern California during the next six days, according to the National Weather Service. The first system will drop about an inch of rain in the Oroville area between 10 p.m. Wednesday and 4 p.m. Thursday. Greater amounts of precipitation will fall in the mountains northeast of the reservoir.
Forecasters are confident that the first two storm systems will not cause huge inflows into Lake Oroville. They are less confident about the third system, which is due sometime Tuesday. That storm could be bigger and warmer, meaning more rain and snowmelt streaming into the swollen reservoir.
“The third wave is looking like our problem child,” said Michelle Mead, warning coordination meteorologist at the National Weather Service in Sacramento.
Oroville Dam, about 65 miles north of Sacramento in Butte County, holds the state’s second-largest reservoir and serves as a crucial flood-control structure for the eastern Sacramento Valley. Wednesday’s all-out effort to bolster the dam before a new round of storms capped an anxious week that has seen serious malfunctions in both its main and emergency spillways, hobbling the dam’s ability to release water in the midst of an unusually wet winter.
(Excerpt) Read more at sacbee.com ...
Very true! Where water seeks the path of least resistance erosion slows down. When you disrupt that path you get lateral erosion and many times sub erosion. Water always wins!
.
The rock they are placing is in the emergency spillway, but is reinforcing a vulnerability of the headworks of the main spillway, as assessed by a structural engineer’s report.
.
.
The concern is not water going over the weir in general, but the potential of errosion in the portion against the main spillway.
.
>> “Water always wins!” <<
But not if you can establish laminar flow in the areas of concern. Then engineering wins.
.
.
We don’t have carpet in our house any more either!
Carpet is a filthy source of disease.
Put a mat at the doorways.
The good news is it did not rain as much as forecast last night.
But there’s still a couple of storms lined up that appear to be quite wet.
.
Present precipitation patterns are quite normal. This is the heart of our rainy season.
.
>>reinforcing a vulnerability of the headworks of the main spillway, as assessed by a structural engineer’s report.<<
Greetings, was this “structural engineer’s report” done after the assessment of the erosion from observation of the results of the first ES overtopping?
Actually, I believe it was done from about 1500 miles away.
(by an engineer intimately familiar with the short-comings of the original design)
That reply puts me in mind of a favorite book...
To Engineer Is Human: The Role of Failure in Successful Design, by Henry Petroski
.
Yep, we are witnessing an enactment of Petroski’s principles.
Sounds like this “engineer” is well respected (i.e. to be 1500 miles away & “sought out this advice”).
Engineers have stated that the large MS concrete crest structure & sluice gate is anchored in bedrock. This seems to infer that the “vulnerability” is to protect the sub structure of the main spillway (slabs & sidewall system).
Using over the road dump trucks that have a capacity of about 23 tons that’s 52 trucks per hour. Where is the pit for the rock and what is haul distance?
.
I believe that is exactly correct.
The issue has apparently been the subject of heated debate on multiple occasions in the past.
.
>>heated debate<<
If the “debate” was instances in the past, why couldn’t they have done a few test drills to answer their questions? (assuming the importance was high enough as stated by “heated”)
>>The issue has apparently been the subject<<
So, I’m assuming the overspill erosion (crevasse/hole nearest the MS side) swayed people’s minds (i.e. confirmed one side’s viewpoint in the heated debate).
>>I believe that is exactly correct. The issue has apparently been the subject of heated debate on multiple occasions in the past. <<
Sorry to pepper you with questions...
You seem very well connected & knowledgable in terms that are unique to this situation.
I believe you are familiar with Scott Cahill’s analysis. Scott’s articles and podcast interviews have provided specific engineering issues the dam is facing at this moment.
Correct if you have a different view:
(1) One of the issues Scott described was the existence of the fractured rock. The swift erosion of this fractured rock revealed its depth (how deep it exists) from the overspill flow. Survey elevation of the before and after at this location reveals that this fractured rock depth is lower than the foundation area of the main spillway.
(2) Another issue brought up was “migrating water” under the main spillway slabs. Scott stated that the “jets” of water on the spillway sidewalls reveals just how much of this waterflow exists underneath. He said a properly maintained system would not have such a vigorous flow - that this flow may cause an erosion risk & thus potential failure stresses on the concrete slabs (in time).
(3) Scott also discussed Emergency Spillway: wherein the subject of this spillway also rested upon this fractured rock. (btw: the original blueprints of the ES “encasement” is an aggregate filled concrete shell. The depth of the grout footing was not clearly stated).
This gets to the rock & quick set concrete surface repairs to the Emergency Spillway (fixing the recent erosion gashes & trying to establish a better “rough version of a controlled, but ugly laminar flow”)... Have you heard about the news chopper video footage (Fox10) of “car sized” air bubbles coming up on the water side of the ES? These huge bubbles were coming from 2 locations. This would infer that notable amounts of water (bubble equivalency translation) was penetrating somewhere. At the time of the footage, this was a few days after the overspill. Seems quite a bit of time for any trapped air in the dry sediment to suddenly come out that late.
IF this penetrating water was getting into the foundation of the ES, has there been any action to identify this? (Scott stated that he was not sure if the dam will survive (in time) and that a “V” breach is his greatest concern. He was speaking with respect to the areas resting on the fractured rock - which to me identifies it as the Emergency Spillway. Elevation erosion of the crevasse hole bottom yields a known (easiest to achieve by proven erosion - if the reinforcements are scoured again) low point of the “V”. If you take the 901ft upper part of the “V” then the low point of the “V” comes to near 100ft.
Scott did not mention anything about news on the penetrating water issue. I would assume he would have something to say about this issue potentially defeating the re-inforcements as this is a stability & undermining problem.
.
For the most part, the geology at the dam is the same as all the rest of the Sierra foothills until they intersect the Tehachapi.
California’s geologic past is one of constant pressure and collisions. The foothills are also riddled with limestone caverns.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.