Posted on 02/12/2017 4:26:47 PM PST by janetjanet998
Edited on 02/12/2017 9:33:58 PM PST by Admin Moderator. [history]
The Oroville Dam is the highest in the nation.
This series of photos was helpful to this lay person, ER333. What exactly does “X linear” mean? And why is the 2039’ distance significant?
Very interesting and reasonable analysis. Not necessarily obvious but understandable after your explanation.
Thanks maggief and I join the others in commending you for your research and info dissemination.
Interesting. So apparently there’s belief that the original failure point was caused by the failure of a particular slab not the dynamics of the curve in the spillway.
I find all of this interesting and worthwhile.
>>What exactly does “X linear” mean? <<
To identify an accurate location, or in this case, a linear distance “point” -measured from the start of the top of the main spillway chute - there are two linear reference distances that can be used. To keep the discussion “apples-to-apples” I used the same linear method as used in the blue line spillway plot in the second to the last image in Ray’s Post 1,735. Thus the intersecting point of interest on the blue line (spillway plot line) can be referenced using an a Linear X,Y coordinate system, but just using the X axis value. (btw- I find it extremely ironic that post 1,735 discusses a real and accurate measurement of 1,735ft - how about them odds...). Thus the “x marks the spot” is simply a vertical line (as greatly illustrated in Ray’s graphics).
The other linear reference, in full linear length, would be longer as it includes the curvature of the spillway. This second option would be equivalent to pulling a giant measuring tape down the spillway. In this case, the spillway curvature would make the length longer as it involves both the X and the Y together.
I was just trying to keep the discussion accurate in reference method, but simplified.
>>And why is the 2039’ distance significant?<<
Because this 2,039ft distance is well beyond (300ft+) the posited “inflection point” inference (1,735ft) of a causal mechanism in the context of a “failure or failure mechanism”. At the 2,039ft distance the spillway is in a linear slope - well beyond the curvature region. The extensive hydraulic flow studies of the spillway design was proven out well in advance.
side note: There are other complex factors to laminar waterflow verses a form of a “jump”. Fluid hydraulics in this spillway, while in a laminar flow state, will not separate. However, if there is any form of separation from a critically sharp bend, it would instantly convert into a damaging potential non-laminar flow.** The last thing a designer wants to occur is to create cavitation.
btw- A number of spillway models were live tested extensively in the lab before construction. Special piezoelectric sensors were extensively attached to the models to measure any pressure differentials in many different configurations, flow rates, and shapes. This was one engineering aspect that was very well done in the design of the Oroville spillway.
**There is one condition that occurs just before the “jump” into a violent non-laminar flow. It is a sharp pressure drop. The Pakistani’s learned this the hard way as their concrete slabs were “sucked away” up and outward from these sharp pressure drop differentials. Needless to say their dam failed (spillway). That is why the Oroville spillway construction design specifically shows “anchors” where the concrete slabs are anchored into the bedrock (10’ grid spacing on average).
>>So apparently there’s belief that the original failure point was caused by the failure of a particular slab not the dynamics of the curve in the spillway.<<
Exactly. See post 1,745 on the extensive fluid flow replica model lab testing. Only a super critical bend would risk a failure mode (i.e. inducing cavitation & great turbulence). None of these conditions have been observed even in the higher flow rates of 100,000cfs. The water exactly follows the results of the hydraulic model testing.
How long does it take to tear out, re-compact soil, form, tie steel and pour new concrete on a rugged hillside. ( maybe 3000 feet worth.?)
Here is the best info....http://cdec.water.ca.gov/cgi-progs/queryF?ORO
Spillway Profile
To determine the profile of the spillway I used a topographic profiling tool and then fed the data into google charts. As a sanity check I reviewed photographs and topographical maps and spot checked several points on the charted profile. I was satisfied that the profile was reasonable and posted the chart several days ago. Since then I located a November 1974 California State Water Project Bulletin which on page 96 has a profile of the spillway. I also located a 1965 US Bureau of Reclamation report, Hydraulic Model Studies of the Flood Control Outlet and Spillway for Oroville Dam, which on pdf page 140 has a profile of the spillway. The charted profile was compared to the profile in these two documents and the chart is reasonably accurate.
Spillway Measurements
According to the November 1974 California State Water Project Bulletin the length of the chute is 3,050 feet. I measured the length of the chute via google map and obtained the same figure. I located a photograph of the failure point (see further comment below). The photo was taken from a point directly vertical from this point and not at an angle. Visible in the photograph are high tension lines and a nearby uniquely shaped piece of dead wood. Returning to google map "satellite view", I located the same high tension lines and piece of wood and noted their position relative to the spillway (photo 4 in previous post). Using google map I measured the length of the chute from the gate to this point (photo 5, previous post), the length is 1,735 feet.
Failure Point
Source of Error
Referring to photo 5 in the previous post, I mistakenly considered this to be the point of failure rather than what it is, the point to which the spillway has eroded to.
Your identification of the failure point is correct.
The failure point is approximately 270 feet further down the spillway than I had originally indicated.
Re-Analysis
Comments
I agree with your comment regarding laminar flow. Although my misidentification of the failure point led to an incorrect conclusion, I believe a curved spillway is a factor contributing to failure. A curved spillway does not promote laminar flow and increases turbulence, which enhances cavitation erosion. The effect would be more pronounced at higher flow rates. It's possible that the curved spillway induces a periodic disturbance (turbulence, pressure wave, etc) which propagates along the flow before dissipating. Even if the effect of the curve is minor I think it is a factor.
No doubt there are multiple factors, we'll have to wait and see.
> I find it extremely ironic that post 1,735 discusses a real and accurate measurement of 1,735ft - how about them odds
Whoa!
It really varies based upon how much has to be dug out and mucked out below grade after you demo the lower potion of the spillway. Additionally it can be done a lot faster if you want to pay for overtime work — big money can be used to accelerate it.
I would say, four months for starters after the approved plans and access.
There are three factors to any project:
Time - Cost - Quality
Contractors can optimize any two but not all three...
-
Deliver quick time and low cost but sacrifice quality.
Deliver quick time and high quality but sacrifice cost.
Deliver low cost and high quality but sacrifice time.
Buy some time, but go for high quality. I think that if they move to a new spillway, they can harden the present one so that it won’t tear up anything more. Then use the time that buys to build the new one.
It’s seemingly simple, but it really isn’t. There is tremendous force in the water and it has to be built to withstand that for decades.
Right.
What do you see now at the emergency spillway?
Quick and cheap but low quality.
Time, by necessity, had to be sacrificed.
I have heard that often over my career. You must have messed around in the building profession.
Huge slabs like runways, giant aprons and roadbeds have special issues when placing.
It needs to be understood that if we disregard temperature expansion and contraction, which is not as severe in concrete as it is in steel and many other materials, then what we need to concentrate on is that concrete takes up the greatest volume the day it is placed. This causes reinforce concrete to have joint failure and to crack (and to curl) in almost all situations and minimization of that issue is what is attempted with good design and procedures. These involve continuous placements with very low slump mixes and/or checkerboard placements.
The spillway in the photos is very deceiving because it is actually much larger than it looks. Imagine a 12 lane interstate and you have a closer idea as to its width. This means you have longitudinal placement joints to consider as well as transverse.
Absolutely, KC. The project looks as simple as pouring a concrete driveway, but it’s much more complex. Drainage. Enormous changing pressures depending on use and quantity of water. Temperature extremes. A driveway can crack and it poses no real issues. I can lose its flatness - a corner can lift or drop and the result is really insignificant. I can drive up a bumpy driveway as easily as I can drive up a gravel road.
I think that the original spillway was well designed and built, but time takes its toll. There’s going to be a lot of discovery behind what all failed when things settle down. They will incorporate the original terrain into the design. There’s so much involved.
I have optimized all three together as a package for decades. But when a client then wants it cheaper and/or faster, quality will indeed take hit. Or if the client wants everything gold-plated, cost and/or time obviously go up.
The key is full disclosure to the client who wants to emphasize one or two of the factors what the hit will be on the other(s). And in competitive bidding situations the client had better have clear specs and get that disclosure from all bidders and question everything to enable an apples to apples comparison and fair selection.
So with all of the upper dams full, a huge snow pack that could take all summer to melt off, the time it takes to draw new plans, plan check and engineering, and the possibility of another heavy winter next year, there may be a huge logistics problem here. Plus the fact of unforeseen problems discovered after demolition and environmentalists breathing down the contractors necks about polluting the feather river.
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