Why the Oroville Dam Won’t Fail

February 12th, 2017 by Roy W. Spencer, Ph. D.

While it is said, “never say never”, after researching this issue I’m pretty convinced that it would be nearly impossible for the Oroville Dam to fail.

Even though it is an earthfill embankment dam, which can be destroyed if the dam is topped, the following Metabunk graphic demonstrates why the Oroville design is virtually foolproof:

The emergency spillway (which is now in use) drains excess water along its 1,700 ft length when the lake level exceeds 901 ft. At this writing the lake level is 902.5 ft, which is 1.5 ft. above the lip of the spillway.

The water level would have to rise another 18.5 feet (!) in order to reach the top of the dam itself, which would never happen because the emergency spillway flow (which occurs over a natural ridge made of bedrock) would handle the excess flow long before the lake level ever reached that point.

Now, is there any scenario in which this might happen? I’m not a hydrologist, so I can’t answer that. But if there was a sudden warm spell in the next few weeks with say, 10-20 inches of rain over the watershed melting most of the mountain snowpack, adding tremendously to the inflow into the lake, I’m sure we would see a much greater flow over the emergency spillway. But I suspect it would never reach the top of the dam itself. Nevertheless, there would be a massive flooding event downstream in the Feather and Sacramento Rivers.


164 Responses to “Why the Oroville Dam Won’t Fail”

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  1. Curious George says:

    Fullproof?

  2. ren says:

    2017 WY Precipitation Summary
    provided by the California Cooperative Snow Surveys

    For the period Oct 1, 2016 to Jan 31, 2017
    Report generated: 02/09/2017 10:52
    https://cdec.water.ca.gov/cgi-progs/precip/PRECIPSUM

  3. ren says:

    Daily Precipitation Summary
    February 11, 2017
    24-hours ending at midnight
    for selected automatic-reporting rain gages
    (Provisional data, subject to change)
    Report generated: 02/12/2017 08:09
    https://cdec.water.ca.gov/cgi-progs/precip/DLYPCP

  4. ren says:

    Daily Snow Sensor Report
    February 10, 2017
    Provided by the California Cooperative Snow Surveys for selected automatic reporting snow gage sensors
    Report generated: 02/10/2017 08:46
    https://cdec.water.ca.gov/cgi-progs/snowsurvey_sno/PAGE6

  5. Ric Werme says:

    That’s pretty much my thinking. There could be problems if erosion of the main spillway climbs all the way uphill, but it looks like if it reaches the low slope portion, there’s likely bedrock under it. If it gets above that, the water will have a lot less erosive force.

    What may be a problem is that the reservoir has pretty much lost its flood control utility for a while. However, while the outflow is impressive, it needs to double before the immediate down stream towns would be imperiled.

    It might still be a good week to leave town.

    It’ll be impressive to see what it all looks like when the spillways are no longer in use.

  6. Pete Mack says:

    The dam could never fail directly, it’s true. But the hillside next to it could fail–water with that kind of energy can easily erode rock, via ‘hydraulic mining’, and rock in the Sierra is not good quality–mostly shale.
    If the rock were to erode back to the spillway, the spillway superstructure would collapse, leading to an uncontrolled breakaway; in that case, the entire hillside would eventually wear away. It’s happened before. It wouldn’t be quite as catastrophic as a dam collapse–there’d be plenty of time to evacuate. But it still would do massive damage downstream.

    Presumably the emergency spillway has been judged adequate to a sustained load. But with continuous use, it would eventually go down. It’s how natural water gaps open in the first place.

    • Beyond Concerned says:

      If hillside erodes enough then the spot where the dam is attached to it would be compromised. First it would cutback up the spillway and then the whole thing would go.

    • Pete Mack says:

      Well, that didn’t take long. So much for ‘judged adequate for a sustained load.’

    • wendy davis (@BabylonIdeas) says:

      Land fill created the walls of this dame. It was packed down. As anyone who goes to lake knows, the critters have left a maze running hundreds of miles in the california foot hills. My dogs have spent many a day chasing them up and down the hill sides or their head in a hole and butt in the air trying to get one. Squirrels. The local park pumps poison into the holes where we walk and they fill holes (sprained ankles) but I do not think they fill the holes around the lakes.

      Well, I just cannot believe grown men in power positions seeming so very inept or lackadaisical (one actually laughed when describing how the valley would end up if the spill way gave out). Strange and dangerous if the neglect was intentional, as spawning fish/salmon, transgender, and illegals seem to take precedence in sunny California. Taxes at local level are very very high.

  7. dp says:

    The natural area the spillways are built on form a part of the dam – just not the man-made part. If the main and auxiliary as it is now called spillways erode that hillside sufficiently that the spillway lip is undermined the entire reservoir is jeopardized. There is already water coming down outside the main spillway well above the damaged section when the gates are open. That can’t be helpful.

    • dp says:

      Some days ago I told my wife if the water reaches the parking lot area the whole mess was going to come down. That is now happening. There have been better times to evacuate but now is time to get to open the gates for livestock and get the hell out.

      • K Lee says:

        Unbelievable. Hang on to their ass’es till a quarter to get the hell out & gridlock us to point we cant move

        • Tom O says:

          There is no excuse for a “this is not a drill, get out now” evacuation. There are more than enough police and national guard to have been able to have a controlled evacuation of the area. It all comes down to is there any planning ever done about anything anymore. It would seem the answer is “in our state, everything is on a moonbeam, and no one should ever think.”

      • Dawn Dawson says:

        Old graphic/picture since, has not been that much land on the lake side of the emergency spillway for some years at least 2005. Water is flush up to it and what’s left of the parking lot.

  8. Pete Mack says:

    As an aside, saw your article on feedback in the climate model. One question: if the system really has negative feedback towards warming, why isn’t earth’s temperature much closer to it’s virtual black body temperature of 254K (-18C)?
    Greenhouse amplification is the usual explanation for the preexisting temperature. So what is different about the regime above current mean temperature?

    • Roy Spencer says:

      the earth’s effective radiating temperature is just a mathematical construct…in reality the IR emission that balances absorbed solar radiation comes from all altitudes…the surface and lowest atmosphere (which is “warm” than the average emitting temperature, from the greenhouse effect, which produces a high level of IR radiation…but most of which is absorbed by the atmosphere before it can escape to space), up through the whole atmosphere, which is colder than the average emitting temperature (also due to the greenhouse effect). If the “greenhouse effect” increases, the lower atmosphere warms, and the upper atmosphere (the stratosphere on up) cools, but the total amount of infrared emitted to space remains the same. Does that answer the question?

  9. Mac says:

    I get it, the dam will not likely fail. I also get that the dam people knew from experience with the local conditions that the inflow would subside when it did. They must have also known all along that the emergency spillway would be topped. So why did they say it would not? As you mentioned Roy, that eliminates their credibility in my book.

    And what about the water flowing under the main spillway, that caused the failure there by undermining the concrete, where is that coming from? The sides of that spillway are back filled with large gravel, likely as drains, which spill water through hole into the spillway when the gates are open. All of that can be seen in the photo’s posted everywhere. What’s with that?

    • Almost certainly, the water will have got there through construction joints in the concrete apron. if the concrete has moved only a little bit so that the downstream slab is a little bit higher than the upstream slab, water will jet through underneath the slab and wash it away.

      Modern spillway designs have the upstream slab projecting above the downstream slab and also let air in. Much safer.

    • From what I’ve read, the spillway (being concrete) is poured in sections. After 50 years, if water finds its way through the cracks (especially if the edge of the downhill slab is slightly above the uphill slab), water can be forced through and wash out the material underneath. Extra water pressure underneath can further lift the downhill slab, and then it fails.

      • papertiger says:

        Roy – you were right the first day when you brought up their not expecting the emergency spillway to be overtopped.

        While they removed vegetation on one side of the emergency spillway, on the other side next to the parking lot they had crews dumping concrete to shore up that end of the dam.

        You know that didn’t cure, or have time to dry.
        https://www.youtube.com/watch?v=oQxVmKnBgvc
        Check out this video.

        At the dam itself, they stopped the flow due to backwash from the broken spillway, so now what water used to going through the powerhouse and pipes is going over the top of the emergency spillway instead. The parking lot has become part of the overflow.

        The water level is seven feet over the emergency spillway, and it will be at this level for another two days.

        • papertiger says:

          Emergency evacuation order was just sent out for Oroville, Gridley, and other downstream low lying areas in Butte County; dam failure is imminent.

          I wish this were a drill. THIS IS NO [edit].

          • papertiger says:

            Not important enough for CBS to break into their Grammy Award program.

            THat’s a hopeful sign right?

    • Ric Werme says:

      That video starts out downhill – “Update Oroville Dam Overtops” and only gets worse. I watched some of it earlier, the only thing that’s worrisome is the one thing he doesn’t dwell on, and that’s a claim that the parking lot beyond the emergency spillway is flooded.

      If you’d like to be useful, look for a drone video from today that shows the parking lot, especially the down stream side.

    • Windsong says:

      The GFS graphic at 8:08 does not look helpful to the current situation.

  10. papertiger says:

    Here’s a photo of the “ski jump” section of the normal spillway from 2013.
    http://fcdn.mtbr.com/attachments/california-norcal/1120603d1486695238-ot-oroville-reservoir-situation-16508579_1212016275513733_1512733581637597118_n.jpg

    Obviously having the water go airborne by design is an engineering flaw.

    The good news is that this critical level discharge is “sanding off” the high spot in the ski jump.
    THe more material the water removes the easier it will be to install a more gradual slop design purposely built to avoid water leaving the deck. They want a more gradual slop, like a whale’s snout, that the water slides along, rather than the million gallon pounding the old design took.

  11. barn E. rubble says:

    Some drone video here:
    <>

      • papertiger says:

        Notice how the Bee is already trying to down play the event.
        Two times the apologist press refers to the emergency spillway as “the auxiliary spillway”, as if this is just a normal bit of the operating procedure rather than a glaring example of the state experts completely loosing their [edit].

        Apparently no one in the planning stages ever thought to test the expected force of a full level water discharge, how fast the water would get at 55,000 fps, or what sort of force would result from a 30 degree drop off.
        One hopes that the same people who designed the spillway weren’t involved with the design of the dam proper.
        But chances are, being this is California works…

  12. Dodgy Geezer says:

    The problem is back erosion. If you let water play on soft earth, it will carry the earth away until it has eaten its way back to the point where it is falling from.

    You can see this in the spillway – it is not only eroding downstream from the fracture, but also upstream. If they keep using the spillway, eventually the erosion will hit the dam wall.

    Similarly for the emergency spillway. This is not lined – it was only intended for occasional emergency use. It will start to carry the side of the hill away if it is used constantly, and the hill supports the dam.

    Both these processes have the capability to impact the dam if they continue. If they stop soon, the damage will be repairable and the dam will not be harmed. The question is: ‘How long will the excess inflow continue?’…

    • R. Thiry says:

      Excellent assessment.
      It is my understanding that the core wall inside the berm/ dam is clay based, designed to handle seepage. A hard flow will cut through that like a hot knife through butter, rapidly draining the impoundment & probably leaving an intact dam, more or less. It will be a “slow motion” event, like New Orleans during Katrina.

  13. Dr No says:

    It is amazing to read the analyses of the Oroville event from the armchair experts here.
    They seem to have panicked unnecessarily in the face of the advice from the real experts who maintained there was no risk of a dam collapse nor of any serious flooding downstream.
    Their comments reflect the level of informed debate that surrounds climate change.

    • dp says:

      Wasn’t it the “real experts” that built this abomination? The same “real experts” that claimed for days the aux spillway would not be reached? The same “real experts” that built the parking lot in the flood zone?

      • papertiger says:

        The same experts who inspected the damage in 2013 and shrugged?

        Counting on the “endless co2 caused drought” to cover their heinies, no doubt.

  14. Mike Flynn says:

    “The ship’s designers were so certain that the ship could not sink that they did not leave room for enough lifeboats for everyone on board.”

    The real experts designed the Titanic to be unsinkable.

    “Insurance on the World Trade Centre’s twin towers will pay out for the loss of only one tower because experts believed that the collapse of both towers simultaneously was too far-fetched to be worth insuring . . . ”

    The real experts believed . . .

    It’s a good thing there are no real experts in the faux science practised by so called climatologists. Otherwise, people might listen to them.

    Good thing nobody’s panicking unnecessarily about their nonsensical ramblings, apparently based on the bizarre belief that thermometers can be heated using CO2! How odd!

    Cheers.

    • Jack Spratt says:

      I’m sure sufficient prayer will save the dam. Maybe if everyone thumps in unison it will get God’s attention.

  15. Milton Hathawaay says:

    I had planned to do a little reading this weekend, but not about dam failures! Interesting topic.

    I’ve gone the opposite way as Dr. Spencer, now thinking the total failure of the Oroville dam is more likely than I first thought, although it still seems unlikely.

    It comes down to a topic that experienced engineers come to know very well, the difference between “designed-in” reliability versus “tested-in” reliability. Sometimes the design phase is cut short in a rush to get to the testing phase, typically (in my experience) because the project manager is grasping for more visibility into the project schedule.

    Early testing will indeed reveal problems, and often reveal them more efficiently, than an extended design phase. But a consequence is that problems that go undiscovered in the testing phase tend to be extremely subtle.

    Humans have been building dams for a very long time. Dams have been failing for just as long, and continue to this day. This is an example of ‘tested-in’ reliability. Many causal factors for dam failure are well known now, and addressed in dam design. But since dams still fail, clearly there are still unknowns involved, and presumably some are very subtle.

    In the analysis of a failed dam, an official conclusion is always reached, even if there remains uncertainty or disagreement among the experts. One could hypothesize that this has resulted in some unwarranted public overconfidence in dam reliability.

    There appears to be a human element at play here, even among the experts, which could be called “above-ground thinking”. For example, the failure in the Oroville dam spillway. The first explanation I heard that I thought made sense was that years of water splashing over the sides of the spillway eventually undercut some of the fill placed on top of the underlying bedrock.

    Further reading has convinced me that such explanations are preferred (and common in stories about failed dams) because they minimize/localize the cause, and because we can visualize the cause.

    The fill and underlying bedrock in the Oroville dam and spillway are not impermeable. Given that the local climate swings from very dry to very wet, one can assume that the materials that make up the dam and underlying support cycle from relatively dry to saturated (i.e., the local water table goes up and down dramatically). For reliability, the properties of all the materials in the dam and related structures, whether pre-existing in-situ or added during dam construction, should be fully understood when dry, when saturated, and when in transition.

    I’m guessing now, but I suspect that the dam has always had a certain amount of leakage that has been considered normal, given that the component materials are not impermeable. Was the spillway designed by the same engineers as the dam? Was the spillway constructed directly on bedrock, or was a different fill material used in the space between the spillway and the bedrock? If fill material was used in the spillway, where else in the dam structure was the same or similar fill material used?

    • papertiger says:

      THe emergency notification service has been activated from Sacramento. They are evacuating Oroville as I type.

  16. papertiger says:

    It says on the scroll that the main spillway flow has been increased to 100,000 fps to bring the lake level down quickly, and that the emergency spillway is in danger of collapse.

  17. (snip) if you would have stuck to criticism of my post, I would have let it stand…but I’m not going to put up with insults about the quality of my “day job” work…take it elsewhere. -Roy

  18. papertiger says:

    LAKE OROVILLE, Calif. – There is a mandatory evacuation order in place for low-lying levels of Oroville and areas downstream. It is an order for IMMEDIATE evacuation.

    A hazardous situation is developing with the Oroville Dam auxiliary spillway. Operation of the auxiliary spillway has lead to severe erosion that could lead to a failure of the structure. Failure of the auxiliary spillway structure will result in an uncontrolled release of flood waters from Lake Oroville.

    In response to this developing situation, DWR is increasing water releases to 100,000 cubic feet per second.

    Immediate evacuation from the low levels of Oroville and areas downstream is ordered.

    http://www.actionnewsnow.com/story/34485995/mandatory-immediate-evacuation-ordered-for-low-lying-levels-of-oroville-and-areas-downstream

  19. Beyond Concerned says:

    The spillway is about to fail. Oroville is being evacuated. The dam is going to fail. Please find out how long before Sacramento and West Sacramento flood.

    • papertiger says:

      The dam itself isn’t expected to fail.
      The Emergency spillway concrete barrier is being undermined.

      Don’t know exactly how much water it’s holding back.

      Could be a monster though.

      • Pete Mack says:

        It doesn’t matter where the breach occurs. When it occurs anything short of granite polders would not hold it back. The lousy shale that makes up most of the Sierra will not hold. By Thursday, it’s all she wrote.

      • Warming Skeptic says:

        What do you mean that isn’t part of the dam?

        Are you drunk?

        It’s holding back the same man-made lake. It *is* part of the dam.

  20. Oroville resident says:

    The dam is now failing, the emergency spillway is crumbling and is expected to drop at least 30 feet

    • Pete Mack says:

      30′ is wildly optimistic. That much back pressure may well lead to a runaway catastrophe. The only hope is if the back side of the break is an extremely shallow grade. I very much doubt that’s true.

  21. Warming Skeptic says:

    Only a couple hours after your comment and the assurances of the “experts” (like yourself)…

    People are running for their lives in a mandatory evacuation.

    https://www.facebook.com/bcsonews/posts/781255845358029

  22. SteveT says:

    But if the emergency spillway fails it a moot point…

    S

  23. lokenbr says:

    They are right to evacuate. But within 2 hours, the water will cease going over the emergency spillway. If they make it to 9 p.m. tonight, they may have dodged a bullet. FOR NOW. The problem becomes, with both the main spillway and the emergency spillway compromised, the ability to get through the next 4-5 months .

  24. Pete Mack says:

    Looks like things are good til Wednesday. Water is only 4″ over the spillway crest, so I suspect that’s not enough to drill a hole through the rest of the way. All bets off after another rainstorm, though. Historical evidence shows dam running high for another two months. Presumably they freewheel the power plant until then to reduce the load.

  25. Pete Mack says:

    @lokenbr — great minds etc

  26. Rick says:

    Does anyone think that Sacramento can flood or am I the only one? Sacramento is surrounded by Three Rivers, the American River, the Sacramento River, and the Consumnes River, and they are all maxed out. Folsom Dam is open right now and flowing heavy so that way if necessary they can close Folsom Dam completely for a little bit which will allow the Sacramento River to handle some surge water from Lake Oroville. All it will take is a 5 foot wave coming down the Sacramento River for levee’s to breach. Most of Sacramento will be under wayer. The Consumnes River has already breached in several locations. I think anything along the Sacramento River is at risk these next few days.

    • Pete Mack says:

      Not catastrophically. The Sacto valley can swallow 5 cubic km without a hiccup. It’d certainly add to the existing flood, but no chance of flash flooding outside of the mountains and foothills.

  27. Paul W says:

    They’ve indicated they can not freewheel the plant – it must be connected to the grid to run.

    Also the outflow stream from the power plant is blocked by the debris from the spillway, causing a backup, and they do not want to flood the power plant.

    And… a tower for the power line going to the plant is right in the emergency spill area.

    There sure is a lot of “we didn’t expect” going on. That’s unacceptable when you have responsibility for these things.

    Down here in southern CA they tested the outflow channels at full flow for two dams, at least one of those started to erode and they had to fix it.

    I’m not an engineer, but I wonder if they could have welded some big steel plates together over that hole when they first noticed it.

    • Steve says:

      So what was being done over the last 5 years of drought in terms of inspections? Methinks they may have at least noticed some degradation in the concrete such that they could shore it up. whomever is in charge should be canned.

  28. Jeremy says:

    I find this article to be quite disturbing as it seems to delegitimize the authority of public officials who are working against the clock to evacuate a large populous that are under immediate threat of losing their lives. Authorities are evacuating under an abundance of caution, sure, but if this damn fails, it will be a matter of seconds or minutes before areas downstream are inundated with a tidal wave of water. This boarders on the line of recklessness as people reading it may disregard the evacuation order because a former NASA scientist said it was safe.

    The graphic used is misleading to me as it seems to suggest the threat of failure comes from water cresting over the top of the dam. The issue in this case is that water is eroding the very ‘ridge’ that is supporting the dam. The dam itself may not crack or crumble, but the very earth that supports the dam is. If enough of the ridge is eroded away, there may not be enough of it left to support the dam. Then there is a problem. Please be careful.

    • lokenbr says:

      Well, the whole dam is made of earth. The only thing holding the system together now is a plug of rock between the dam and the lower part of the auxiliary spillway.

      Roy was the first to predict publicly that the emergency spillway would be overtopped – to the hour, despite official statements to the contrary, and was one of the first to suggest that dam failure was possibility. He also has a more recent post up to the effect that spillway failure is imminent. Sadly – by the time the order went out, they were within a few hours of it going one way or the other.

      Besides dumping as much water as possible – Job 1 will be getting as much rock fill under the emergency spillway as possible. Job 2 will be re-evaluating emergency procedure.

  29. Jane F says:

    Care to put some money on it Mr. Spencer?

    There now appear to be multiple seeps that have formed, and the compromised functionality of both spillways is cause for great concern.

    Agreed that release of water will alleviate the hydraulic pressure and reduce risk, but I think the possibility for significant failure is quite real.

    Very aggressive management of the reservoir in accounting for additional rains and the coming snow melt will be required to maintain a level beneath the weakened areas for a very long time.

    It will require more than helicopters dropping boulders into the crevice, like some bad Godzilla movie to provide an even moderately successful “band aid” repair.

  30. Tony says:

    With another big storm moving in from the pacific more rain is on the way. Add to it all the snow melt that is going to contribute run off, and it is going to be a serious inflow. Clearly, the emergency spillway cannot handle any flow as it is quickly eroding. Once that erosion undercuts the concrete lip it would be game over. So the only option is to dump all the water through the damaged main spillway and lower the reservoir which is what is being done tonight. Without the concrete armouring in place, the only unknown is how quickly erosion beneath the upper intact portion of the spillway will move upstream. The pictures appear to show some rock in there which will be less prone to erosion than soil, but at more than 100,000 cfs flow, even soft rock will quickly erode. Hoping for the best, but I would get out of Dodge.

  31. Jeannie Vickery says:

    I am at a loss as to why after noticing these problems days ago, why it took until today to start throwing rocks on the spillway! This started 7th, today is day 6 ppl . Who is running this state?

  32. Listen to the Evac ORDER!! says:

    going to be honest. Don’t really care what people “think” or want to try and “prove” scientifically.

    If you are so freaking sure there isn’t a problem, you can be tossed out of helicopter to rescue people who didn’t believe that flooding will be an issue instead of my brother.

    Like the ones he had to rescue a few weeks ago trying to drive to a flood to get to a casino. Its not worth it, and please stop using science to gamble with the lives of people you don’t know.

    You are more than welcome to come back and say “I TOLD YOU SO” afterwards, but in the meantime? EVAC!

  33. lokenbr says:

    EVAC for sure. Should have been done 2 days ago in my opinion. This thing is very vulnerable now. Stay out until water is WAY down and/or repairs are complete.

  34. tlo login says:

    I whipped up a quick little model that estimates the hourly change in lake level based upon the difference between hourly inflow and outflow rates. By extrapolating the observed downward trend in inflow, and assume outflow remains constant, I get overflow of the emergency spillway tomorrow morning….but just barely….peaking at less that 902 ft. (It overflows above 901 ft.) So, I see why they are now saying it might not overflow. Gonna be a full reservoir though!

  35. db says:

    Yet the dam is now overflowing from the main lip. Your wrong already and the spillway overflow is eroding the hill you say cannot be eroded.

    What have you actually got right so far?

  36. Roy, a hydropower engineer stating that the damage is at left in on the spillway would mean the left hand end looking down stream.

    The primary cause of this problem is the failure of the slab and the main spillway chute. It should not have happened.

    But, if it is true that your emergency spillway is failing with only a very small overflow then it indicates a serious design failure by the civil engineers and geotechnical engineers. Imagine what would happen if, instead of one or 2 feet if that there was 15 to 20 feet of water going over the emergency spillway!

  37. Martin A says:

    Just out of curiosity, how much power does 50,000 cuft/sec of water falling 900ft [I think that is the height of the dam] represent?

  38. Matteo says:

    “Why the Oroville Dam Wont Fail”

    “Now, is there any scenario in which this might happen? Im not a hydrologist, so I cant answer that.”

    Sometimes the best choice is to not talk.

    Are you a NASA scientist? Really??!?

  39. Brian Gallia says:

    Who ever said anything about the water level rising above the actual dam?

    The problem was erosion of earth under the secondary spillway which would let the top 30 feet of so of lake water rush off.

  40. lothair says:

    I generally respect your work Roy however one of the biggest causes of Earth Dam failure is from erosion at the emergency spillway . In this case the car park is lower than the spillway and water although only 1.5ft above the emergency spillway is working around the edge. also are you assuming its all bedrock…..have you seen the plans. there is severe erosion at the base of the emergency spillway because they didnt think to at least put a bottom concrete curve to deflect water away from the spillway base…..this is really stupid and obvious. I at the age of ten with a bucket and spade playing in small rivers making and breaking small dams could work that out. Sometimes academic analysis severely lacks any practical knowledge and this dam has been poorly maintained. there was problems discovered with the main spillway actually in 2013 but nothing was done. there were environmental groups asking for the emergency spillway to be concrete lined years ago but this was rejected, fingers crossed that the next two systems don’t produce an atmospheric compression event that dumps rain that is already above average for this time of year. I just know some one is going to start going on about global warming and CO2 etc at some…cringe!

  41. joanne says:

    Before you lump all Californians onto the same boat, perhaps you should recognize that northern California did not vote for nor subscribe to a leaping liberal agenda. And it is the residents of northern California in jeopardy, NOT San Francisco or LA. Your judgmental comment puts you squarely on the Ship of Fools deck you are commenting about.

  42. Ryan DeMont says:

    I neither am a hydrologist, but I am someone with a basic understanding of literature and the effective use of argument in order to prove one’s point. This is pertinent to this reply due to my issue with the title of your post: Why the Oroville Dam Won’t Fail. No doubt titled as such for purposes of Google searches, but no less irrelevent to what followed. Your article doesn’t speak for one moment as to why you think the Dam won’t fail, but rather to how it’s impossible for the water to go over the top. Itself being a completely unnecessary article neither to be written nor read, as anybody who understands basic gravitational pull and it’s relation to water and elevation would inherently know that the water won’t go over the highest rim of the dam. Not with the emergency spillway 20 feet below it’s banks. Your article would be more accurately titled ‘Why the Oroville Dam Won’t See Water Flow Over It’s Highest Banks For Those Who Don’t Understand Gravity’. Or something akin to that. If you truly want to make the argument that the Dam won’t fail may I suggest a re-write? And also maybe throw in some facts that I, not to mention anyone who is working around the clock at the moment to make sure it doesn’t fail, aren’t aware of. Cause they’d be pretty helpful. Assuming you are not able to supply those things, I’m just gonna suggest that you re-title your post to more accurately represent what it embodies. I’d say it’s a common mistake, that of offering an argument completely unrelated to your thesis, but I can’t offer such a condolence. In fact It’s not common at all. Bad arguments are very common, but this. You may have well followed that title up with an article on the historical data supporting your thoughts on Mickey Mouse actually being a Rat. You still would’ve gotten those clicks, after all. May your next post be better and waste less peoples time. Good luck to you. Ryan

  43. Tim says:

    The dam itself may not fail, but that’s of little consolation to those downstream if the hillside below the spillway disintegrates. Who will really care exactly where the flood broke through?

    • Richard says:

      Exactly. Anybody with half a brain can see with their own eyes where the failure is likely to be, the emergency spillway. Once its integrity is compromised beyond a certain point, and the top section collapses, all hell will break loose.

  44. Dirk says:

    Donna, another dumb and ignorant religiosity zealot. Two points: Titanic wasn’t made of bedrock, which is why this damage will not fail, and two your God is fake and you live a lie

  45. Richard says:

    Reading all the above comments has been fascinating. However, the overriding sense is of too little to late, in terms of the warning signs and lack of planning for a timely evacuation. Seeing those images of 100,000 CFS tearing at the emergency spillway, the staggering power of 3,000 tons of water per second of hydraulic force, is more than enough to convince me that something never tested, in 50 years that severely, could fail with little further provocation. The fact that this spillway would not be constructed as it was then now, surely no further discussion is required as to just how perilous the situation still is, especially given that more heavy rain and snow melt are predicted for later in the week.

    Had I been a resident below the dam, and knowing this information before the water even got close to over topping the main dam ridge or the huge erosion damage done to the spillway, you wouldn’t have seen me for the now long gone northern Californian dust. I’m no engineer but my instincts would’ve shouted, “Runs for the hills”, long before before any expert would’ve convinced me otherwise.

  46. Richard says:

    Reading all the above comments has been fascinating. However, the overriding sense is of too little to late, in terms of the warning signs and lack of planning for a timely evacuation. Seeing those images of 100,000 CFS tearing at the emergency spillway, the staggering power of 3,000 tons of water per second of hydraulic force, is more than enough to convince me that something never tested, in 50 years that severely, could fail with little further provocation. The fact that this spillway would not be constructed as it was then now, surely no further discussion is required as to just how perilous the situation still is, especially given that more heavy rain and snow melt are predicted for later in the week.

    Had I been a resident below the dam, and knowing this information before the water even got close to over topping the main dam ridge or the huge erosion damage done to the spillway, you wouldn’t have seen me for the now long gone northern Californian dust. I’m no engineer but my instincts would’ve shouted, “Run for the hills”, long before before any expert would’ve convinced me otherwise.

  47. Richard says:

    Sorry, accidental double post.

  48. David says:

    Who knows the nature of the construction of the dam beneath the concrete wall at the top of the emergency spillway?

    Does the concrete go all the way down to the bottom?

    Or is it an earthen barrier against the reservoir?

    If it’s the latter, it’s easy to imagine the emergency spillway eroding to the point of a breach in that area, while the concrete dam itself remains sound.

  49. paul w shafer phd says:

    Dr Spencer is correct. This dam will not fail even with 30 inches of rain. Evacuation unnecessary. Evacuation routes were in correct. People should have been directed East toward dam to higher ground, to the North to higher ground. Not jam south and west. Ridiculous.

  50. Skeptic says:

    The “emergency spillway” is a section of dam that is lower than the main dam. Not paved, it is just rock and soil.
    With prolonged use, soil and rock will wash away and the rest of the dam, behind this soil will erode, leading to at least a partial failure.

  51. Ghx says:

    This issue is not the failure of the dam, but the failure of the emergency spillway (which is lower than the dan crest). If the emergency spillway fails, the dam crest will be hugh and dry.

  52. Plumas Laked says:

    How stupid do you feel or should feel? That emergency spillway started failing at 5% of its designed. A bunch of people claiming it didn’t fail. It didn’t fail because the whole thing came down? There’s multiple reasons why we lucked out in this situation. This article, and comment section, prove that the people that we’re trusting are so busy being super smart that real world things make them look stupid. If it was raining today as apposed to Wednesday night there would be bigger things to complain about than the bad evacuation orders or why the dam has bad parking lots. I love the people that add their engineering background into a comment section. If you are so smart go to Oroville and fix it. I’m sure they would appreciate it.

  53. Rocketman says:

    The complex levee and canal system around New Orleans wasn’t “expected” to fail in a Hurricane, but it, like so much of our nation’s infrastructure, was at best neglected although detailed analysis clearly projected the potential risks. Our inner cities have been neglected by Congress and Presidents for ~70 years, Republican and Democrat alike. Now we have an abrasive President who tells it like it is. Will we, for the first time since the Apollo program, stand behind our President and, this time, begin to address the REAL ills of the nation? You want jobs, higher tax revenues and a sustainable budget? The “manufacturing jobs” are gone forever, due to technology and global market realities. Put our people to real work, rebuilding our damns, bridges, highways, power grids, etc., and begin a real, multi-decade program to re-locate and educate the permanent under-class and totally alter the landscape of our dreadful inner cities. Rebuild Detroit, once the bellwether of the nation, to look more like Nagasaki (2017, not 1945).

  54. paul w shafer phd says:

    The emergency spilliway will not release a 30 foot wave of water. Impossible with possible flow rates down slope. Evacuation routes should have had half of people moving toward east, north and southeast. Ridiculous evacuation procedures jamming roads toward west. Imagine 30 foot water wave hitting those jammed up cars!

  55. Newark Guy says:

    I have not heard ANYONE claim that the dam might fail, that is not the issue.

    The BIG concern is that the Emergency Spillway will fail, the top 30 feet washing away, causing a rush of water to flow downhill……

  56. paul w shafer phd says:

    Apparently they are using the main spillway while they put bags of rock spillway in hole below the emergency concrete coffer dam on emergency spillway to try and shore it up. Hopefully 200 foot hole in concrete on regular spillway one third the way up will not erode undetlying fill material causing lower third of spillway to disinttegrate.

  57. Colin Pittendrigh says:

    The main dam may well be safe right now. But the earth filled overflow/spillway sections might fail, potentially releasing top 20 to 40 feet of the reservoir.

    No one has addressed the glaringly obvious question: Why did the spillway fail in the first place?

    The cave in the lower part of the primary release spillway has been described as “a sink hole.” Sink holes are assumed to be caused by a subterranean flow of some kind. Any such flow is unwanted and unexpected in any earth fill dam structure. The entire North end overflow area may or may not be compromised already. If water is flowing there already, and if that water’s source is the reservoir there is no fixing it without draining the reservoir.

    • dumb bo says:

      for the record, i do not have a doctorate degree in anything, nor am i a civil or hydrological engineer, but i do have a degree in mechanical engineering. the gigantic gorge that has become completely visible now that the spillway has been shut down is not the result of a “sinkhole” caused by subterranean water flow, rather it is the result of a phenomenon known as cavitation. cavitation results from high speed turbulent flow of water which will create ares where the water pressure becomes lower than the vapor pressure of water at given temperature and pressure conditions which causes liquid water to flash to vapor. a common place to observe cavitation is around a motor boat propeller. the bubbles you see around the prop wash from a boat propeller is not air that is being mixed in, it is actually water vapor. as these tiny water vapor bubbles collape they create shock waves in the fuid which can be very destructive. any boat owner can attest to this because it can and does destroy boat propellers. cavitation also can and will cause localized damage to even the strongest of concrete and can erode through solid rock in a remarkably short period of time, as you can see at the oroville dam spillway. a prolonged or sufficienly large flow of water over the spillway could erode the mountain back to the edge of the dam and subsequently cause a total catastrophic failure of oroville dam. people should be worried, in my opinion.

  58. S R says:

    Your analysis is partially right. The Dam wont fail but if the hole beneath the concrete emergency spillway starts eating into the erath and waters seeps in, we are looking at a catastrophic failure of that concrete emergency spillway bunker. Basically 30 feet of ‘lake’ will cascade down that emergency spillway causing unprecedented flooding. But yeah the Dam wont break.

  59. paul w shafer phd says:

    Evacuation Over. Emergency spillway and coffer dam safe. No further erosion damage to 250 foot hole in main spillway.

    • Rachelle says:

      The evacuation is not over, we are still under evacuation, it is just not ORDERED! You spill things that sound more like ALTERNATE FACTS!

  60. Wayne Tyson says:

    The exposed rock is highly fissured. You need a good geologist. Upon what rock doth the “emergency” spillway stand?

    If the spillway goes, the part of the ridge behind the spillway could erode much as it has downstream–or more. The exposed rock looks pretty “rotten,” and I’d be willing to bet that there’s a pile of rocks in the stream channel at the foot of the slope. It all depends on how solid the rock is. If my speculations are correct, the water level could go down farther than the height of the spillway. If it’s “rotten” all the way down, then there could be a major catastrophe.

    Then there is the issue of the lateral erosive force. If that were to occur far enough in a southerly direction, the dam structure of compacted unconsolidated material could go–and that would go all the way to the bottom.

    These observations are based solely upon photos, and are not intended to be alarmist. But all realists are called alarmists, eh?

  61. Robert says:

    No one is afraid of dam failure. It’s the emergency spill way that may fail. They are afraid of a 30 foot wall of water, not 700 feet. It will be enough to break levies and destroy homes

  62. paul w shafer phd says:

    There will be no emergency spillway break because of underwater topography and bedrock. There is no way a 30 foot wave would occur. It would rapidly dissipate as river turns about 2-6 miles downstream and enter huge north floodplain.

  63. paul w shafer phd says:

    People are worrying about nothing. The spillways will not break. The concrete coffer dam on emergency spillway is secure. Look at pictures of drained Oroville Lake and you can clearly see how thick the natural dam at emergency spillway really is.

    • Plumas Laked says:

      Seriously, at first I thought you were just arrogant now I realize you are the smartest guy in the room. How many times in life do people like you fail with confidence so high? Always respect power bigger than you especially mother nature. Using the fact they lifted the evacuation is stupid because people like me were checking in on Sunday when their story changed one hour apart. Do you really think their families are sleeping in that town?

  64. paul w shafer phd says:

    The huge natural dam (hill) below the emergency spillway cannot break before the dam breaks. Water pressure behind main dam much higher than emergency spillway hill due to much deeper lake behind main dam (Feather Riverchannel).

  65. MAC says:

    Concrete erodes easier than bedrock. The Achilles Heel in all this is the concrete spillway. What would happen if the breached concrete spillway continues to erode and give way all the way up to the base of the concrete dam? After all, the concrete spillway is built on top of the earthen dirt which sits on bedrock.

  66. paul w shafer phd says:

    If the water flowing down concrete main spillway continues to gouge out a larger hole, it is possible to undermine thr lower half of concrete but will NOT erode the very thick hill on which the concrete spillway is suported for many months if years.Remember half the hill dam is underwater on the lake side, mostly submerged now with high water.

    • Tim says:

      The hill has nothing to do with the probable dam failure mode. The distance from the emergency spillway to the left abutment is only 200 yards (across the main spillway) at the top. Probable failure is from the top. A failure of the emergency spillway either from overtopping or the main spillway consuming itself over the next 4 months will likely destabilize the main spillway structure. The main spillway structure is directly connected to the left abutment, problems with the main spillway structure would likely lead to the beginning of erosion of the left abutment which would likely be catastrophic.

      The second that main spillway was damaged, operation of this dam deviated from design criteria and we have now seen multiple structure failures at small percentages of design flow. Slurry over bare wet ground will only buy a small amount of time if the emergency spillway is overtopped again. DWR is operating this facility purely in a reactionary mode and is at the whims of both mother nature and geology. Any minute the stability of the structure could dramatically change, the structure simply is not safe and the failure of the state to accurately portray the risk to the downstream public is absolutely stunning.

      • paul w shafer phd says:

        This dam and associated spilllways will not degrade in a catestrophic failure like Teton dam or Saint Francis dam. The tallest dam in the world at 900+ feet is a dam with similar design as Oroville with similar natural hill abutements and has survived monsoon rains over 45 inches in a day.

  67. Linda says:

    California is so far in debt, they are an embarrassment to the union. Dependent completely on its debtors. And worse, there is no excuse for it.

  68. Robert Andrews says:

    The worst case scenario is playing out, even as I type. The weather people say this will probably be the wettest rainy season on record. There is already double the normal snow pack. This means runoff well into July and more pressure on earthen dams in particular. One seismic event, and there have many in the Central California Area, could easily trigger catastrophic failure. The original specification, for reinforced cement, was changed when Southern California water authorities objected to the then Reagan Administration that a concrete dam would make water rates too expensive. Profits were put before public safety when the dam was built of earthen material and merely sheathed in cement. During the San Francisco Quake of 1906, every structure built of or on fill (earth) was destroyed. Everything but solid bedrock actually liquefies during a major earth tremor. That’s why major dams have always been made of reinforced concrete and the latest with built-n strain gauges to monitor stresses. Now we have record amounts of water from snow melt over a longer period than ever recorded. If I were living around or below the Oroville Dam, I wouldn’t be.

  69. paul w shafer phd says:

    A reinforced concrete non gravity dam that is 700 feet tall with water behind it would be just as vulnerable as the current gravity dam in a major seismic event.

    • paul w shafer phd says:

      During the Wenchuan seismic event 2 concrete dams over 350 ft tall and 1 rock/earth fill dam over 350 ft tall all failed. It took the gravity dam longer to fail and it failed halfway.

  70. Jason says:

    Any water going over the aux. spill is an uncontrolled failure. The soil below is not engineered and the recent flow showed the soil to erode very easily. Not a good thing. Aux. spill is seriously weakened/undermined on the hillside now.

    Worst scenario, the aux. spill will get eroded and the water may erode the main spill structure. Through undermining or shear force. This is the only way the main earth dam will start to erode and requires continuous rain. Earth dam is directly connected to main spill and will be a controlled/engineered failure. If the main spill is gone the earth dam will at most be partially eroded across down to the top of coffer dam level. I don’t see the coffer dam going without extreme rain. See Auburn dam failure on youtube.com for a earthen dam failure.

    • paul w shafer phd says:

      This scenario is possible for any type dam. Could happen at Oroville over a couple of months flow, but not instantaneously. The St Francis dam failure is an illustration of ICOLD.

  71. ShaAnn says:

    I live in the North part of Oroville called Thermalito…our jail was totally evacuated on or before Sunday night. All the inmates were transported to Alameda. They are still there. Why transfer to Alameda? I would think Sacramento would be a better location and have the room to house several hundred inmates. I then was informed that the National Guard had set up pockets of high water rescue vehicles including men and emergency supplies all along the Sacramento Valley from Oroville to Merced…..why? I believe it is to prepare for the tidal wave that will happen when Oroville Dam goes….I have a storage shed in Chico and plan on staying in Chico for a week starting Monday morning. Schools are closed….I am feeling very unsettled…there is a dark heaviness of impending doom that is descending upon us.

    • paul w shafer phd says:

      They were smart moving cons to Alameda, so they do not have to feed cons. Also if cops left area and a 100 foot wave hit jail and cracked it open, cons would have had a field day robbing and looting the town.

  72. paul w shafer phd says:

    If you are really worried, camp out at the Gold Country casino and hotel or camp grounds near there in the hills.

  73. paul w shafer phd says:

    Lake Oroville Rec Area and Bidwell camping resorts east of town would be very safe too.

  74. paul w shafer phd says:

    There are a number of excellent motels to the north, east and southeast of oroville on high ground in mountains.

    • robert says:

      We evacuated east..above the damn…Hotels in the mountains were FULL….We were out of town in 30 minutes…and already the lines at gas pumps etc…were outrageous..My only alternative was to go higher or into Nevada…

  75. robert says:

    In the event of the emergency spillway failure, what elevation in Oroville is considered safe and above the areas that would flood…Does anyone know the answer to this question…I am at 346 elevation…the Feather River is at 162 feet…..I am disabled and unable to evacuate if we have another mandatory relocation….The last one nearly killed me….I will not go again….and will take my chances at my elevation…RM
    Email me at [email protected]

  76. paul w shafer phd says:

    Did you try motels and hotels in Old Station, Chester and Westville areas in the mountains nearby?

  77. paul w shafer phd says:

    There are 19 motels and hotels within Quincy and surrounding villages.

  78. paul w shafer phd says:

    We spent a week at Pine Hills Motel Cottages. Very beautiful any time of year.

  79. David Dewey says:

    My home is above the lake; although I was in Davis at the time of the evacuation order–it took me 4 hours to get home via Auburn/Grass Valley and back roads. We were fine staying at home, although by Tuesday I was reaching the point where a trip to Grass Valley for gasoline and groceries was looming.
    First, IF the spillway had failed, and hit downtown Oroville, we would likely have lost phone service (my house area has no cell coverage) the main switching station is downtown; and likely power too, as the power lines come from the downtown area.
    If the emergency overflow (calling it a spillway is a misnomer, it is just an emergency “safety valve” for a worse-case scenario–which happened!)occurs, it would send an increasing amount of water and debris down the hillside to the river bed below,increasing as the water cuts through the hillside until it reaches bedrock (how far down is that?). The debris fills the bottom of the riverbed (which it has already done, cutting off the outflow from the power-plant), if it doesn’t carry it along with the water, it will form a small dam, holding back some water until it lets go again. This mess barrels down the canyon, makes a left turn into the Fish Barrier Dam reservoir where it likely takes out the Union Pacific Railroad trestle, then the the fish barrier dam itself. This mass of water, concrete, mud, rocks, and trees then hits a right curve under the green bridge, knocking it out and probably over-breaching the over-100-year-old levee protecting downtown. The velocity of the water etc. will carry it right down to the highway 70 bridge, likely knocking it over too and then there’s a Hard Left turn with Thermolito on the bluff above.How far up the bluff it goes, I don’t know; but it’s likely to be all the way up. Now the water has reached a large fairly flat expanse to the Sacramento Valley, so some of the velocity will be reduced, as well as depth.
    That’s as far as I’ve thought over the scenario.
    Is it possible that the emergency overflow will be used again this spring? Depends on the weather, but obviously the experts think it might, or they wouldn’t be spending all this money doing these emergency repairs. And, downtown is still under an Evacuation Warning. We are not “out of the woods” yet!

  80. paul w shafer phd says:

    I would head for the Gold Country Casino and forget it.

  81. Patrick r burgess says:

    jesus is the way truth and life he will protect his people and jesus is more than a story heis my savior and lord and hopefully yours becuase without him we will all perish and die and go to hell repent and turn to christ before its to late he loves u all look to him and live pastor burrgess jesus is the ark run into him and be safe he is our shelter all those who trust in him that is

  82. noone says:

    Only because of the appetite of the rest of America for porn and drugs.

  83. paul w shafer phd says:

    Boy did this blog change direction.

  84. paul w shafer phd says:

    Things looking good at Oroville dam and Feather River.

  85. David Dewey says:

    They expect to finish the emergency overflow repairs on March 1. The folks living near the project supply center may finally get some sleep now! You should see what all the truck traffic has done to the roads around here. There will be a lot of road repair work when the weather dries out.
    They are working hard to get the river bed cleared of debris so they can run water through the powerhouse again. Once they can do that, they can turn off the main spillway and still control the lake level, providing we don’t get a lot of rain or excessive snow run-off. Then it will be time to figure out how to repair or re-engineer the main spillway.
    BTW, yesterday they opened one of the Shasta Dam drum gates, mostly to test it, as they haven’t had water over them since the late 1990s. It’s really quite dramatic to watch, and it usually works right!
    Of course everywhere else in CA seems to be flooding right now.

  86. A L Girard says:

    My father is one of the best operating engineers in the state of California. He worked on the dam, he said don’t worry the dam is solid like a rock. Earth and rock dams are better than concrete, they are packed solid. I wish everyone to be safe.

  87. ray reedy says:

    y’all are missing a few real big problems here.the engineers on that piece of shit all lied.the owners of that piece a shit all lied.there is no way you can trust their words or reports.for years they knew it was bad and wrote it as good.for years these blood suckers lied and stole the money.EVERY DAMNED ONE OF THEM MUST BE MADE TO PAY.EVERY DAMNED ONE OF THEM IF ONE PERSON LOSES THEIR LIFE FROM THIS BULLSHIT THEY MUST BE MADE TO FACE MURDER.THAT GOVENOR IS A REAl bastard.his ass needs hung.CALIFORNIA HAS ALOT TO ANSWER FOR.AFTER ALL Y’ALL WANT SUCESSION WANT MUSLIM ENEMY INVADERS.THIS IS NOT GOOD.MAYBE GOD IN HIS INFINATE WISDOM HAS DECIEDED ALL OF YOUR ASSES ARE UNWORTHY.EITHER WAY ALOT OF YOU WILL DIE FROM THIS.AND STOP,THINK,WHO EVACUATES THE DIRECTION WATER RUNS?WAS THAT ON PURPOSE?ARE YOUR AUTHORITYS ATTEMPTING TO KILL YOUR ASSES OFF?SURE LOOKS THAT WAY.THIS WHOLE DAM IS A PIECE OF SHIT.THEY KNEW IT THEY ALLOWED IT SUE THEIR FUCKING ASSES OFF ALL THEY WAY TO THAT COMMIE GOVENOR.EVERY PERSON INVOLVED IN THIS HAS THE RIGHT TO SUE.AND IF IT WERE ME I’D DAMNED SURE DO IT.i’m sorry i have no sympathy for people who turn traitor and treasonous to their country.and cali has done exactly that.good luck your gonna need it.if the dam dont getyou americans probably will.

  88. A L Girard says:

    This reply is for Mr.Ready my father being a operating engineers MEANS DIRT AND ROCK MOVER, he has worked on Lake Castias dam, Piru dam, flood control and forest fires throughout the state of California. I know the engineers you are talking about. Let’s keep them separate.Take care to all who live there.

  89. Pete says:

    I still think they are feeding us full of shit did anyone else notice at first they were pouring the supposed fix to the temp.spillway on the raw dirt.that should have been taken down to bedrock and sandblasted that fix can be eroded .i worked on the spillway in 97 chipping and pouring bad spots in the mainspillway right about where the huge failer was i chipped out a big cold joint it just kept going i was told to stop and not go further but should have kept going the joint went to the bottom of the concrete there is no telling how big the bad section was..all this crap is a horse and pony show for the cameras and public.what is realy going on

    • Pete says:

      This is absolute truth no bullshit i was there its kind of funny right where i was told to stop is where it failed a few years later that should have been addressed then 20 years ago.ive often wondered about that maybe the high and mighty smart educated people should have listened to the laborer who was doing it instead of dismissing there concerns.YA THINK HUM?M

  90. Roy Avran says:

    Here is my 2 cents: The main Oroville dam CAN fail and WILL fail. This is the scenario. A late and warm Pineapple express hit NOCAL in April or May with copious rain fall. High Sierra in NOCAL has one of its highest snow cover of around 150-200% in many years. Only 80 cal is needed to melt 1 gm of snow. The warm rain water has enough specific heat to over come this latent heat to melt lot of snow. As Oroville dam catchments is surrounded by High Sierra on all 3 sides, the rain and the snow melt and the resulting flood will rise behind the dam very fast.
    In last one year, the fluctuation of the reservoir level changed many times(26% to 101% and then back to 40% now). This is causing tremendous increase and release of pressure on the underlying rocks, susceptible for dam induced seismicity. In 1975, Oroville dam area had an earthquake of 5.6 on Richter scale after a similar reservoir fluctuation. In the event of an earthquake of 6 on Richter scale for 1 minute or longer will cause liquefaction on the upstream saturated slope of the dam. The resulting slope failure will cause the top of the dam to cave in, resulting over topping. In such a scenario, it doesn’t matter whether the free board is 20 feet or more. Liquefaction also create high pore pressure beneath the dam and subsequent piping and eventual differential settlement of the dam.

    About me: (I WAS a civil engineer with bachelor’s theses on Design of earthquake resisting structures during dynamic loading, Masters thesis on Design flood forecasting of a river basin during PMP and PhD on weather forecasting using ECMWF spectral model). To understand dam failure one should be proficient in Meteorology, Hydrology, Geology, Civil Engineering and good old Math and Physics). I am no longer any one of them now. As soon as Pornographic left and war mongering right took over our good old science, I left. When the elephants fight, the last thing you want to be is a grass ! This is one of the reason our kids no longer want to study science and our country is doomed. Although not part of institutional science, I still study and enjoy science in my basement.