Oroville Dam Spillway Failure

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You don't need a flow under the concrete slab. Take a look at this typical venturi-bernoulli image. The faster fluid is generating a lower pressure, even though there is no flow underneath it (the other side of the concrete).

Think of this image as as the spillway. The top section of the spillway has low velocity, and so a higher pressure. The center of the spillway has a fast flow, and has lower pressure. And if the spillway flattened out at the bottom, it would have a higher pressure once more.

Ralph



The above diagram applies to closed conduit, pressurized flow only. The hydraulic gradient is the pressure in the pipe. Open channel flow at the Oroville Dam spillway behaves according the hydraulics of a 'free surface' - much more complex flow, and is not pressurized. The hydraulic gradient is the free surface from one point to the next. When open channel flow speeds up because of slope change to a steeper slope like at the Oroville Dam spillway, the flow depth becomes less and the hydraulic gradient is still the water surface. The water velocity increase has a force of its own, but it is not pressurized. For an interesting study, search for hydraulic papers on the Karnafuli Dam spillway failure in East Pakistan. Huge slabs of concrete were sucked off the dam because of pressure fluctuations in the spillway vents caused by the appearance of the hydraulic jump in an unexpected portion of the spillway
 
It is part of a statewide water system that benefits all. If you think this is an important point then divide the cost by the population of the state.
To add, I believe if that dam cannot provide irrigation to the central valley of California water costs and less production will increase the cost of produce for hundreds of millions if not billions around the entire planet, not a huge amount but given the production of the area it would have an effect. I wonder how much?
 


Was posted 2 hours ago, what is this new flow?


A portion of flow appears to have jumped to the other side of the main spillway for some reason. There is the muddy stream and new (to me anyway) flow along the outside of the wall.

upload_2017-2-17_14-35-26.png
 


Was posted 2 hours ago, what is this new flow?
in the bottom left of your post 908 you see the muddy flow? thats it but its down by the dental teeth...!!!! not very interesting other than those dredges will have a lot more work soon.... this is a big event something could easily "overrun" them . this new flow could further the complete daming of the feather and send the flows back at the dam.... ?
 
I would not go that far. The definitive cure for cavitation is adequate aeration of the flow as the paper indicates. Anchoring and drainage are at best secondary measures as cavitation can spall concrete regardless of how well it is anchored or drained.

These media reports are speculative in that they are insinuating there is no cavitation protection (aeration). Modern protection might be manifested by ramps or aerators in the chutes, but I don't see any (doesn't mean they are not there). It could be the radial gate outlets work in such a manner as to provide adequate aeration in the designer's and maintainer's view, or there is something else we are not privy to.

Nevertheless, your point about the age of the spillway is valid and if media reports are valid that they inspected the spillway from a distance (http://www.redding.com/story/news/2017/02/09/dam-spillway-checked-distance-last-inspection/97723936/), then they will face criticism, because any differential settlement of the panels could exacerbate cavitation as highlighted in the paper.

My point about the age of the spillway is an important one. If the drain pipes under spillway floor are rotted out, then it would be a reasonable assumption that concrete slab anchors would also have experienced similar corrosion. It has been my experience in working with older anchor installations that replacement is necessary because, as I stated in an earlier post, older installations used older methods derived from open-pit mining and were regarded as temporary, where as with a permanent structure like a dam, then permanent installation methods are called for. l agree that cavitation is a likely process that occurred. Cracking, spalling, delamination and joint offset are prime contributers and it looks like from the photos that maintenance of the concrete surface was done to the extent that it could be. But, it is difficult to look under the concrete, though it is possible with specialized tools, to see how big the voids are and the condition of anchors that hold the concrete panels in place. The USBR paper we are using as a reference here even states that once cavitation initiates, aeration is not effective to prevent structural damage. At that point, the only way to prevent damage is to limit spillway discharge volume and velocity, which was not possible here. In other words, something was going to break no matter what.
 
t
More on concrete slab control joints from the American Concrete Paving Association.

http://www.acpa.org/wp-content/uplo...oint-Design-and-Construction-FINAL-100214.pdf

A concrete slab WILL crack as it cures, no matter the reinforcing within. The trick is to control the cracking to locations that are planned, and design for load transfer between the now independent slabs with dowel bars.

https://www.fhwa.dot.gov/pavement/concrete/pubs/07021/07021.pdf

These joints are sealed to retard water infiltration, and is a continuous maintenance issue on concrete paved highways.

http://wikipave.org/index.php?title=Joint_Sealing

The purpose of joint sealant is to minimize infiltration of surface water and incompressible material into the joint system [1][2][3]. Sealants also reduce dowel bar corrosion potential by reducing entrance of de-icing chemicals. Pavement engineers have recognized the need for concrete pavement joint sealants for many years. Sealant use dates back to the early 1900's [4][5]. Today, nearly every agency building and maintaining concrete roadways or airports requires joint sealing.

Appreciate the references. Thanks
 
My point about the age of the spillway is an important one. If the drain pipes under spillway floor are rotted out, then it would be a reasonable assumption that concrete slab anchors would also have experienced similar corrosion. It has been my experience in working with older anchor installations that replacement is necessary because, as I stated in an earlier post, older installations used older methods derived from open-pit mining and were regarded as temporary, where as with a permanent structure like a dam, then permanent installation methods are called for. l agree that cavitation is a likely process that occurred. Cracking, spalling, delamination and joint offset are prime contributers and it looks like from the photos that maintenance of the concrete surface was done to the extent that it could be. But, it is difficult to look under the concrete, though it is possible with specialized tools, to see how big the voids are and the condition of anchors that hold the concrete panels in place. The USBR paper we are using as a reference here even states that once cavitation initiates, aeration is not effective to prevent structural damage. At that point, the only way to prevent damage is to limit spillway discharge volume and velocity, which was not possible here. In other words, something was going to break no matter what.

Good points all, except in this photo, the anchors in the hanging spillway wall footer are clearly visible and appear to be intact, whereas the material they were anchored to is gone.

upload_2017-2-17_14-51-8.png

The now missing "rock" here appears to be deficient as opposed to the anchors.
 
A portion of flow appears to have jumped to the other side of the main spillway for some reason. There is the muddy stream and new (to me anyway) flow along the outside of the wall.

upload_2017-2-17_14-35-26.png

I'm sure a bigger picture will show additional sloughing of the embankment below the electric tower which allowed the breach outside the main spillway wall to connect thru to the hillside and allow water to connect to that natural ravine. That ravine is all blue-green bedrock and I suspect will see minimal if any erosion (other than topsoil)

I also suspect this could be a direct result of the reduction in flow to 70,000 cfs ... slow the water down and it has more chance to fill into the break in the sidewall and into the void below the electric tower ...

This is silty debris and it enters the river below the still huge flow from the main spillway, which should rapidly disperse it downstream.

IMO ... of course ...
 
To add, I believe if that dam cannot provide irrigation to the central valley of California water costs and less production will increase the cost of produce for hundreds of millions if not billions around the entire planet, not a huge amount but given the production of the area it would have an effect. I wonder how much?
It is part of a statewide water system that benefits all. If you think this is an important point then divide the cost by the population of the state.

http://www.water.ca.gov/swp/contractor_intro.cfm

From my time at DWR I recall that there are 14 Water Contractors who support and use the State Water Project. The largest one is the Metropolitan Water District in Los Angeles. I had a chance to ask my State Representative James Gallagher if the Water Contractors would be on the hook for the cost of the repairs and he replied that they definitely will be paying for a portion of it, but could not say how much at this time. Of course they would likely pass on those costs to their users.
 
Good points all, except in this photo, the anchors in the hanging spillway wall footer are clearly visible and appear to be intact, whereas the material they were anchored to is gone.

upload_2017-2-17_14-51-8.png

The now missing "rock" here appears to be deficient as opposed to the anchors.
True. This is, what we called in the Geotechnical business, the best test pit you could have. Lots of forensics to keep people busy.
 
I'm sure a bigger picture will show additional sloughing of the embankment below the electric tower which allowed the breach outside the main spillway wall to connect thru to the hillside and allow water to connect to that natural ravine. That ravine is all blue-green bedrock and I suspect will see minimal if any erosion (other than topsoil)

I also suspect this could be a direct result of the reduction in flow to 70,000 cfs ... slow the water down and it has more chance to fill into the break in the sidewall and into the void below the electric tower ...

This is silty debris and it enters the river below the still huge flow from the main spillway, which should rapidly disperse it downstream.

IMO ... of course ...
the whole lookers left "gulch" is in danger now(imo)... and if that goes, its possible to dam the river sending the flow back at the dam. not trying to scaremonger but... more sediment on the downstream pile makes a reversal of flow more likely IMO. this is a big event on a massive scale... it could easily overun mans efforts to contain it.
 
The term soil is a matter of semantics. A layman would consider soil to be topsoil, aka the O horizon and A horizon. A geologist considers soil to be everything overlying unweathered bedrock. Above the green line in the figure is the topsoil, below it to some depth I would call saprolite. This saprolite recently (in geologic terms) developed in the metavolcanics.
The metavolcanics are likely composed of basalt that the sheeted dikes, composed of diabase, circled in blue intruded through during the formation of oceanic crust at a mid oceanic ridge during the Mesozoic. Hydrothermal fluids circulate through the crust, likely following pathways of least resistance. The rock in these pathways can undergo hydrothermal alteration as outlined in figure 2. The red circle around the yellowish substance, is likely weathered, hydrothermally altered basalt.
The underlying cause of the failure of the main spillway could be this yellowish, hydrothermally altered material as postulated by Dr Rocdoc. http://www.rocdoctravel.com/2017/02/oroville-dam.html.
main spillway feb 17 anotated.jpg
hydrothermal circulation.jpg
figure 1 from post #882
figure 2 from http://blogs.agu.org/geospace/2015/11/25/tracking-down-hydrothermal-vents/
 
Is this something you suspect is part of their contingency plans?

Probably easier to just call the Air Force to drop some 'bunker buster' bombs on the high spots. They'll burrow 20~30 feet into the rock before exploding, carving out a path of crushed, easily eroded, rock.
 
My point about the age of the spillway is an important one. If the drain pipes under spillway floor are rotted out, then it would be a reasonable assumption that concrete slab anchors would also have experienced similar corrosion. It has been my experience in working with older anchor installations that replacement is necessary because, as I stated in an earlier post, older installations used older methods derived from open-pit mining and were regarded as temporary, where as with a permanent structure like a dam, then permanent installation methods are called for. l agree that cavitation is a likely process that occurred. Cracking, spalling, delamination and joint offset are prime contributers and it looks like from the photos that maintenance of the concrete surface was done to the extent that it could be. But, it is difficult to look under the concrete, though it is possible with specialized tools, to see how big the voids are and the condition of anchors that hold the concrete panels in place. The USBR paper we are using as a reference here even states that once cavitation initiates, aeration is not effective to prevent structural damage. At that point, the only way to prevent damage is to limit spillway discharge volume and velocity, which was not possible here. In other words, something was going to break no matter what.

Drain pipes would have been exposed to water.

The anchors had some grout protection. Page 100:
https://archive.org/stream/zh9californiastatew2003calirich

The reinforced invert slab has
a minimum thickness of IS inches and is anchored to
the rock with grouted anchor bars and provided with
a system of underdrains.
Content from External Source
 
upload_2017-2-16_6-5-52.png

A couple of interesting things.

Note that three lines above the highlighted "Maximum release" it says "Emergency Spillway". It also says "(in saddle on right abutment)" So there was an existing saddle where they built the emergency spillway.

I have a problem with the idea that the "emergency" spillway was designed as an sacrificial plug though. Even if the Main Spillway was inoperable, the emergency spillway is designed to pass a 350,000 cfs flood. Why then would it start failing with only 12,000 cfs flowing over it? Would you really want it to wash out at that low a volume? Or even if its designed to wash out at 100,000 cfs, wouldn't you then say that the maximum release is 100k ? Also, note that the highest recorded flood was 250k cfs. If the Main spillway wasn't working at all, would you want the Emergency Spillway to fail below, say, 300k?

If you want to make sure the dam doesn't overtop there are other, more accurate ways to do it. Along the Mississippi River some of the levies have galleries built into them that can be filled with explosives to remove the levies when they need to release the overall pressure on the levy system. This was done a couple of years ago just south of St. Louis.

Edits made to correct spelling error and to make it more readable.
I believe you are misreading the information. 350,000 cfs is the maximum release from both spillways when the water level is at the maximum emergency level it can be prior to dam overtopping.
 
Probably easier to just call the Air Force to drop some 'bunker buster' bombs on the high spots. They'll burrow 20~30 feet into the rock before exploding, carving out a path of crushed, easily eroded, rock.
I think something more surgical and elegant can be done, such as controlled blasts, to shape a new topographic surface. Survival of nearby structures and lower lines is important (this is dam for Petes sake). Not saying that I agree that anything needs to be done here, but it's best not use a club when a hammer will do.
 
Drain pipes would have been exposed to water.

The anchors had some grout protection. Page 100:
https://archive.org/stream/zh9californiastatew2003calirich

The reinforced invert slab has
a minimum thickness of IS inches and is anchored to
the rock with grouted anchor bars and provided with
a system of underdrains.
Content from External Source

I believe I see grout adhering to the anchors in my picture post above. Seems like the grout was good.

The underlying cause of the failure of the main spillway could be this yellowish, hydrothermally altered material as postulated by Dr Rocdoc. http://www.rocdoctravel.com/2017/02/oroville-dam.html.

Excellent link. The confirmation of altered rock brings up the possibility of chemical processes, low pH being the most familiar to me in altered rock. The consequence could be corrosion of metal or weakening of concrete, even pulling clogging of (drain) pipes with chemical deposits.
 
Drain pipes would have been exposed to water.
True. Not sure I am getting your point. Though we don't know for sure because we have not seen an isolated close up of the drain pipes, the 1974 report says that the pipes were only wooden under the spillway gate structure and from that point down hill were round pipe. So I am presuming they are perforated metal pipe. Therefore corrosion is the issue.

The anchors had some grout protection. Page 100:
https://archive.org/stream/zh9californiastatew2003calirich

The reinforced invert slab has
a minimum thickness of IS inches and is anchored to
the rock with grouted anchor bars and provided with
a system of underdrains.
Content from External Source
True, that's what it says. But, grout surrounding a 1 inch diameter rebar of unknown depth does not by itself prevent corrosion of the bar. As I have said before, at the time, construction practice relied on open pit mine techniques. The holes drilled for the bar insertion tended to be the minimum diameter needed to fix the bar in the hole. Nowadays, we would require a minimum of 1 inch of grout cover around the entire length of the bar. We would also require sacrificial bars to be installed and pullout verification tests performed to verify the adequacy of our design. And now that there has been a failure, I would bet all the change in my pocket that all those procedures will be done when it comes time rebuild the spillway.
 
I believe I see grout adhering to the anchors in my picture post above. Seems like the grout was good.



Excellent link. The confirmation of altered rock brings up the possibility of chemical processes, low pH being the most familiar to me in altered rock. The consequence could be corrosion of metal or weakening of concrete, even pulling clogging of (drain) pipes with chemical deposits.

A question for the geologists.

If as Rock Whisperer suggests there was a degraded segment of rock, what is the possibility of that strata extending diagonally across the area of the Flood Control Spillway back to the area of the parking lot at the far end of the emergency spillway?



The above is the best image I could find. It shows the area of the damage to the FCS as a black shape on the spillway. You can also make out the corner of the upper boat launch parking lot at the point that the access road turns into it. There is a natural gully connecting these two points. This gully was further eroded when the emergency spillway over-topped.

Since water takes the path of least resistance, is it possible that the weathered rock associated with the FCS damage extends across the site and is the reason for the eroded channel originating at the parking lot corner? This channel, or gully, descends across the site, appears to create the weakness in the area of the FCS, and then continues down to the lower arm of the Feather River. This is the same pathway the water from the damaged FCS followed.

Is this evidence of a zone of poor rock extending diagonally down across the site?
 
the whole lookers left "gulch" is in danger now(imo)... and if that goes, its possible to dam the river sending the flow back at the dam. not trying to scaremonger but... more sediment on the downstream pile makes a reversal of flow more likely IMO. this is a big event on a massive scale... it could easily overun mans efforts to contain it.

Not true. The stable blue-green bedrock was completely apparent in the channel water is now flowing thru - from the top of the hillside to the river. Some topsoil will wash into the river from increased flow in this natural spillway, but there is no apparent likelihood of hillside collapse.

And as I noted, the topsoil is 'fines' material ... dirt ... which enters the river next to and downstream from the large flow from the main spillway. That flow will disperse these fines downstream.

And IF it were a problem the solution is simple. Turn flow thru the spillway off - stop the erosion ... and clean the debris
 
Probably easier to just call the Air Force to drop some 'bunker buster' bombs on the high spots. They'll burrow 20~30 feet into the rock before exploding, carving out a path of crushed, easily eroded, rock.

I think something more surgical and controlled would be preferred ... to do just the necessary amount to open to bedrock ...
 
I believe you are misreading the information. 350,000 cfs is the maximum release from both spillways when the water level is at the maximum emergency level it can be prior to dam overtopping.

Nope. Find 917 feet near top left of chart, as that's the maximum "Design Flood Pool". The curves on the right are at 350,000 for the emergency spillway and 296,000 for the main spillway individually. At that point there's about 16 feet of water flowing over the emergency spillway.

 
Note the above image has a 2x vertical exaggeration in the terrain rendering, which I did to make the ridges more apparent. It's actually more like this:
20170217-151026-qc8a1.jpg

You can also do 3x, which makes things overly dramatic.
20170217-151127-i9afz.jpg
 
I believe you are misreading the information. 350,000 cfs is the maximum release from both spillways when the water level is at the maximum emergency level it can be prior to dam overtopping.

You may be right. It isn't real clear. However, the Main Spillway is listed as 296k cfs and has a total opening of 4,620 sq. ft., whereas the Emergency Spillway has a crest length of 1,730 ft. The water flowing over the crest would only need to be 2'-8" deep to equal the same cross-sectional area. It looks like the Emergency Spillway is meant to handle 16 ft of water over the crest. (Crest elev. minus Freeboard, above spillway design flood pool minus Emergency Spillway Crest Elevation or 922.00 -5.00-901.00 = 16) So the total cross-sectional area above the Emergency Spillway would be 27,680 sq. ft. If the water is moving at a little over 12 ft./second, that would give you 350,000 cfs.

Of course I could be reading it wrong, or I might have screwed up the math. Plus the Main Spillway will have a greater head on it.
 
I believe I see grout adhering to the anchors in my picture post above. Seems like the grout was good.



Excellent link. The confirmation of altered rock brings up the possibility of chemical processes, low pH being the most familiar to me in altered rock. The consequence could be corrosion of metal or weakening of concrete, even pulling clogging of (drain) pipes with chemical deposits.

Yes. This. Standard practice is to obtain several representative samples of soil and rock to test pH and design corrosion protection, either galvanization or epoxy coating of bars and concrete reinforcement for the predicted design life.
 
Hi, new here. Lowland archaeologist without real knowledge of reservoirs. Reading and learning a lot here.

When I saw post #883, I wondered if the big concrete dents would still be there. In some pictures, the lowest part of the spillway seems not completely destroyed. I see a smooth flow, indicating a bit of concrete bed, in the upper right part of the picture in post #911, and what looks like the leftmost dent. If they're still there, would they still help lessening the impact of the water on the outflow pond and its other bank? Not contibuting to more erosion there, that might add to the build-up that's a problem for the power plant?
Or is the general water flow so chaotic that any surviving dent doesn't make a difference there anymore?

I can't put the image of post #911 here (obsolete mac with only partially functional browsers). Sorry about that.


Edit to add: https://www.metabunk.org/oroville-dam-main-spillway-waterfall-erosion-watch.t8402/page-3, post #85, new picture shows that at least three dents are still there, and it looks like they do spray the part of the wather that flows at the left side well enough that it doesn't slam into the far bank of the pond. Nor, looks like, the water from the right side. So at least that doesn't add to the problems for the power plant.

Thanks mod, for adding the picture from #911!

mod add: photo from 911
upload_2017-2-17_14-35-26.png
 
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I believe you are misreading the information. 350,000 cfs is the maximum release from both spillways when the water level is at the maximum emergency level it can be prior to dam overtopping.

You mention "dam overtopping". The graph I just posted shows that at dam-top height, the emergency spillway alone would carry 440,000 cfs. That number is not an accident, as it is the 450-year flood inflow number. Most of the dam descriptions, however, assume that the dam is being operated and never has to deal with that.

From the spillway design description, from page 100 of https://archive.org/stream/zh9californiastatew2003calirich


The flood control outlet was sized on the basis of
limiting Feather River flow to leveed channel capacity
of 180,000 cfs during occurrence of the standard
project flood (peak inflow 440,000 cfs). This limitation
applies at the confluence of the Feather and Yuba
Rivers approximately 35 miles downstream of the
Dam. It was estimated that a runoff of 30,000 cfs could
be expected within this 35-mile reach of the Feather
River during the standard project flood. Therefore,
the flood control outlet was designed for a controlled
release of 150,000 cfs. The normal reservoir water surface
previously had been set at elevation 900 feet.
To meet these criteria, a flood control reservation of
750,000 acre-feet was needed. The criteria also governed
the size and location of the flood control outlet
gates. The outlet must release 150,000 cfs at water
surface elevation 865 feet to control the flood shown
on Figure 80.
The standard project flood has a probability recurrence
interval of approximately 450 years. If data received
indicate a flood is developing greater than the
standard project flood, release through the flood control
outlet may be increased above 150,000 cfs but may
not exceed 90% of the inflow. When the reservoir fills
above elevation 901 feet, flow occurs over the emergency
spillway. The emergency spillway, in conjunction
with the flood control outlet, has the capacity to
pass the maximum probable flood release of 624,000
cfs for the drainage area (peak inflow 720,000 cfs)
while maintaining a freeboard of 5 feet on the embankment.
The maximum probable flood has a probability
recurrence interval in excess of 10,000 years.
Content from External Source
 
You may be right. It isn't real clear.

It helps me if I look at it backwards and sideways:
20170217-154258-lc1pd.jpg

Then it's just a graph of how the flow rating increases as the lake height increases. The "Combined" curve is just adding the other two together. It goes all the way to 750,000 cfs. The limit for the main spillway is 300,000 cfs (when it gets to the lip of the main dam)
 
A question for the geologists.

If as Rock Whisperer suggests there was a degraded segment of rock, what is the possibility of that strata extending diagonally across the area of the Flood Control Spillway back to the area of the parking lot at the far end of the emergency spillway?



The above is the best image I could find. It shows the area of the damage to the FCS as a black shape on the spillway. You can also make out the corner of the upper boat launch parking lot at the point that the access road turns into it. There is a natural gully connecting these two points. This gully was further eroded when the emergency spillway over-topped.

Since water takes the path of least resistance, is it possible that the weathered rock associated with the FCS damage extends across the site and is the reason for the eroded channel originating at the parking lot corner? This channel, or gully, descends across the site, appears to create the weakness in the area of the FCS, and then continues down to the lower arm of the Feather River. This is the same pathway the water from the damaged FCS followed.

Is this evidence of a zone of poor rock extending diagonally down across the site?


Water flows downhill. Water flowing downhill cannot get to the dam from the spillway damage location.

And pictures of the underlying ground conditions in the damage area show the left side of the spillway is blue-green bedrock.
 
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I also am not visualizing the process you describe as being a valid explanation. Say the layer of water flowing over the slab is five feet thick. A layer of stationary water of that same thickness would apply a pressure of roughly 310 pounds per square foot to the top side of the slab (that's not correcting for the fact that the slab is slanted in this case so the orientation of a normal force is not the same as the orientation of gravity, but the slope here is not that great so it's a close approximation). Can you really cause a certain mass of water to apply less downward force (and therefore pressure) by setting it in motion when the only downward force that originally was present was that of gravity? Pressure changes which occur relative to velocity because of conservation of energy are one thing, but a pressure that's due simply to the force of gravity pressing water against a supporting surface is something entirely different, the way I see this. Basically I am suggesting that you can't make the water weigh less simply by setting it in motion. And even if the downward pressure applied by the water could be reduced, even to zero, the upward force of the water below is only counteracting that of gravity on the slab. When you lift a gravity-supported object off of whatever supports it, does the force of support from below remain the same? No, it becomes less. I think you are making the water below the slab part of the same dynamic system as the moving water above, and I don't believe it is (this is ignoring the aspect I proposed earlier, though, that force applied to the bottom of the structure by hydraulic head pressure might be involved here, so I'm not dismissing this out of hand, just in the context you presented).

It's a challenge to keep up with this site! Perhaps this topic lies among all the pages. What role might cavitation have played in the original spillway failure? I know that cavitation was implicated in the near-failure of the Lake Powell Dam system in the 1983 floods.
 
I can think of no dam that has had It's emergency spillway tested intentionally. That is not typical for many reasons. One, you don't control the water, and you have to receive a lot of water to test, meanwhile, your users go thirsty if you are intentionally holding water. Two, you'll never get the full design flow so you can fully test. Three, emergency spillways are allowed to have damage, so why damage just to test? Four, intentionally holding water back above flood storage just to test puts people d/s at risk, as Oroville just proved.

Update: Probably the biggest reason is if you are flowing the emergency spillway, you are at maximum risk - why go intentionally to max risk level to test something if you can't isolate that something?

I am with you here. I am fascinated by dams and their engineering (bridges too), and maybe it's possible to fulfill this criterion If you think you may need it, you have to test it for some (certainly not all) of those cases. I am thinking about earthquake engineering and also tsunami engineering such as sometimes worked and sometimes failed in 2011 northern Honshu. Or what happened in Christchurch. That is, how do you test for an earthquake or a tsunami? Granted you can do lab tests and also design in factors of safety, but seems like engineering for disasters requires design beyond what can in actuality be "tested"
 
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