28 ms·

Current Storage vs Capacity Levels: https://apps.axibase.com/chartlab/dee79515 https://apps.axibase.com/chartlab/dee79515 The overflow lasted for 45 hours. T

Current Storage vs Capacity Levels: https://apps.axibase.com/chartlab/dee79515 https://apps.axibase.com/chartlab/dee79515 The overflow lasted for 45 hours. The water level appears to be dropping quickly at the moment: https://apps.axibase.com/chartlab/dee79515/2/ https://apps.axibase.com/chartlab/dee79515/2/

anotheryou 10y ago
Overflow means the actual spilling over the top (the emergency spillway) on to hill and street below? So we still have the broken main spillway in action or not?
- hack_edu 10y ago
  Overflow over the top of a dam this size and type will almost certainly result in complete structural failure. The overflow we've seen so far is a secondary canal diverting excess water away from the main dam.
  - ChefDenominator 10y ago
    Is there an article discussing the dangers of continuing to use the main or emergency spillways? I'm not clear on why the downstream destruction is so dangerous. (And I apologize if it's completely obvious, maybe I'm just dense on this.)
    - tlrobinson 10y ago
      The spillway is damaged and eroding as water flows through it. As it erodes it opens up such that more water can flow, accelerating the erosion to the point where the entire hillside erodes away and the dam essentially fails.
      - ChefDenominator 10y ago
        I can understand those concepts just fine, but when I look at the dam in Google Maps, it is not clear to me how this is specifically going to occur. The main spillway is on the hillside next to the dam, and the emergency spillway is on the same hill, yet further from the dam.
        Naritai 10y ago
        You have to remember that the hill _is_ the dam (of the type[1]). so when water flows down that spillway, it's going to pick up dirt with it - making the hill smaller and smaller, ie. making the dam thinner and thinner. [1]https://en.wikipedia.org/wiki/Embankment_dam https://en.wikipedia.org/wiki/Embankment_dam
        ChefDenominator 10y ago
        The dam is the earth type of dam, but the portion the spillway is on is not part of the dam, at least as I am looking at it in Google Maps: https://www.google.com/maps/@39.5400137,-121.4931958,3617m/data=!3m1!1e3 https://www.google.com/maps/@39.5400137,-121.4931958,3617m/d...
        anotheryou 10y ago
        But if it eats up the spillway upwards it engangers the little part of tho damm where the vales are. If you do not have a concrete lip like on the auxillary spillway and it just flushes over the top of the hill it will quickly carve a lot deeper, so you have more water than just what was held back by the smaller wall. Also: the top 70 meters or something is still a lot of water!
        Naritai 10y ago
        You're drawing distinction between the 'man made' part of the dam and the 'natural' dam, which exists on paper but not in the static force analysis. If that natural portion of the dam becomes unable to support the weight of the water, there will be a collapse.
        10y ago
    - hack_edu 10y ago
      California's damming of the Sierras and construction of the aquifers were primarily about flood control. Supporting the growing population came secondary (that's the easy part). An enormous effort was put into diverting melting snowpack into mountain valleys. This essentially created the northern and middle parts of the Central Valley, on top of creating sustainable year-round sources of fresh water for the developing coastal cities. Downstream destruction is of concern because that entire region depends on flood control. The habitability and agricultural production of the corridor between Oroville and Sacramento relies upon, and was created by, the flood control of Plumas, Yolo, Butte, etc counties. There are a number of canals, diversions, and reservoirs both above and below the Oroville to further control flow the dam as it reaches our rivers. However, most of the re-routing is also man-made and thus untested for such an event.
    - alexhutcheson 10y ago
      The two spillways have different issues: For the main service spillway, the main concern is that the flow of water will cause erosion damage upstream of the existing damaged site[1]. If the damage to the concrete continues up the spillway to the top, it could render the spillway inoperable. For the emergency spillway, the main concern is that a continued flow of water would erode the soil off the hill to the point that the hill would no longer support the spillway (the concrete lip at the top of the hill). If this happened, the spillway would fail. The effect wouldn't be as severe as if the dam failed (because there would still be a large hill in between the water and where it wants to flow), but the erosion along the path of the water would get out of control pretty quickly. [1] https://en.wikipedia.org/wiki/Headward_erosion https://en.wikipedia.org/wiki/Headward_erosion
    - pilom 10y ago
      A picture is worth 1000 words: https://sandrp.files.wordpress.com/2017/02/screen-shot-2017-02-09-at-11-42-17-am.png https://sandrp.files.wordpress.com/2017/02/screen-shot-2017-... Dirt hillsides are not designed to have 100,000 cubic feet of water rolling down them. They tend to erode extremely quickly and can quickly turn into uncontrolable discharges if the lip erodes.
- chrishacken 10y ago
  It's not just flowing over the top of the dam; the water is channeled through an area designed to handle overflow; but the channel is damaged. See pic: http://s4.reutersmedia.net/resources/r/?m=02&d=20170213&t=2&i=1172421238&w=&fh=&fw=&ll=780&pl=468&sq=&r=LYNXMPED1C0CT http://s4.reutersmedia.net/resources/r/?m=02&d=20170213&t=2&... I believe they're worried about the erosion tearing apart the hillside and thus destabilizing the entire hill; at which point the whole hill would just collapse.
  - tlrobinson 10y ago
    LA Times has more great photos. Google "Major sinkhole on spillway at Lake Oroville" to avoid the paywall. http://www.latimes.com/visuals/photography/la-me-lake-oroville-spillway-pictures-011-photo.html http://www.latimes.com/visuals/photography/la-me-lake-orovil...
  - rebootthesystem 10y ago
    What I've been wondering is: What, if anything, did they do during all of these years of drought in order to ensure dams and all required mechanism remained sound and ready for when rains returned? The lake near my house was down 120 feet. You could see land and structures never seen in decades. Prime opportunity to get in there to inspect and maintain said infrastructure. Not sure anything was done at all. I am no expert in concrete but I would like to think the break in the Oroville spillway could have been detected and dealt with with cursory inspections over the last several years, when access was easy due to the drought. I don't like it when folks are put in danger because other folks who are supposed to be working for us don't do their jobs. Not saying this is what's happening here, I don't know, but the question needs to be asked.
    - maxerickson 10y ago
      The spillway can be completely shut during normal operation of the dam. So the drought didn't provide any increased opportunity to do inspections.
      - 10y ago
- rodionos 10y ago
  I should have used a different term, for clarity. By overflow I meant that the estimated amount of water in the reservoir exceeded its total storage capacity and they had to use spillways to drain the excess. We have a geo engineer on our team and he's saying that while primary spillways are made of concrete, the secondary (emergency) spillways are made of soil and materials and can deteriorate quickly.

anotheryou 10y ago

Overflow means the actual spilling over the top (the emergency spillway) on to hill and street below? So we still have the broken main spillway in action or not?

hack_edu 10y ago
Overflow over the top of a dam this size and type will almost certainly result in complete structural failure. The overflow we've seen so far is a secondary canal diverting excess water away from the main dam.
- ChefDenominator 10y ago
  Is there an article discussing the dangers of continuing to use the main or emergency spillways? I'm not clear on why the downstream destruction is so dangerous. (And I apologize if it's completely obvious, maybe I'm just dense on this.)
  - tlrobinson 10y ago
    The spillway is damaged and eroding as water flows through it. As it erodes it opens up such that more water can flow, accelerating the erosion to the point where the entire hillside erodes away and the dam essentially fails.
    - ChefDenominator 10y ago
      I can understand those concepts just fine, but when I look at the dam in Google Maps, it is not clear to me how this is specifically going to occur. The main spillway is on the hillside next to the dam, and the emergency spillway is on the same hill, yet further from the dam.
      - Naritai 10y ago
        You have to remember that the hill _is_ the dam (of the type[1]). so when water flows down that spillway, it's going to pick up dirt with it - making the hill smaller and smaller, ie. making the dam thinner and thinner. [1]https://en.wikipedia.org/wiki/Embankment_dam https://en.wikipedia.org/wiki/Embankment_dam
        ChefDenominator 10y ago
        The dam is the earth type of dam, but the portion the spillway is on is not part of the dam, at least as I am looking at it in Google Maps: https://www.google.com/maps/@39.5400137,-121.4931958,3617m/data=!3m1!1e3 https://www.google.com/maps/@39.5400137,-121.4931958,3617m/d...
        anotheryou 10y ago
        But if it eats up the spillway upwards it engangers the little part of tho damm where the vales are. If you do not have a concrete lip like on the auxillary spillway and it just flushes over the top of the hill it will quickly carve a lot deeper, so you have more water than just what was held back by the smaller wall. Also: the top 70 meters or something is still a lot of water!
        Naritai 10y ago
        You're drawing distinction between the 'man made' part of the dam and the 'natural' dam, which exists on paper but not in the static force analysis. If that natural portion of the dam becomes unable to support the weight of the water, there will be a collapse.
      - 10y ago
  - hack_edu 10y ago
    California's damming of the Sierras and construction of the aquifers were primarily about flood control. Supporting the growing population came secondary (that's the easy part). An enormous effort was put into diverting melting snowpack into mountain valleys. This essentially created the northern and middle parts of the Central Valley, on top of creating sustainable year-round sources of fresh water for the developing coastal cities. Downstream destruction is of concern because that entire region depends on flood control. The habitability and agricultural production of the corridor between Oroville and Sacramento relies upon, and was created by, the flood control of Plumas, Yolo, Butte, etc counties. There are a number of canals, diversions, and reservoirs both above and below the Oroville to further control flow the dam as it reaches our rivers. However, most of the re-routing is also man-made and thus untested for such an event.
  - alexhutcheson 10y ago
    The two spillways have different issues: For the main service spillway, the main concern is that the flow of water will cause erosion damage upstream of the existing damaged site[1]. If the damage to the concrete continues up the spillway to the top, it could render the spillway inoperable. For the emergency spillway, the main concern is that a continued flow of water would erode the soil off the hill to the point that the hill would no longer support the spillway (the concrete lip at the top of the hill). If this happened, the spillway would fail. The effect wouldn't be as severe as if the dam failed (because there would still be a large hill in between the water and where it wants to flow), but the erosion along the path of the water would get out of control pretty quickly. [1] https://en.wikipedia.org/wiki/Headward_erosion https://en.wikipedia.org/wiki/Headward_erosion
  - pilom 10y ago
    A picture is worth 1000 words: https://sandrp.files.wordpress.com/2017/02/screen-shot-2017-02-09-at-11-42-17-am.png https://sandrp.files.wordpress.com/2017/02/screen-shot-2017-... Dirt hillsides are not designed to have 100,000 cubic feet of water rolling down them. They tend to erode extremely quickly and can quickly turn into uncontrolable discharges if the lip erodes.
chrishacken 10y ago
It's not just flowing over the top of the dam; the water is channeled through an area designed to handle overflow; but the channel is damaged. See pic: http://s4.reutersmedia.net/resources/r/?m=02&d=20170213&t=2&i=1172421238&w=&fh=&fw=&ll=780&pl=468&sq=&r=LYNXMPED1C0CT http://s4.reutersmedia.net/resources/r/?m=02&d=20170213&t=2&... I believe they're worried about the erosion tearing apart the hillside and thus destabilizing the entire hill; at which point the whole hill would just collapse.
- tlrobinson 10y ago
  LA Times has more great photos. Google "Major sinkhole on spillway at Lake Oroville" to avoid the paywall. http://www.latimes.com/visuals/photography/la-me-lake-oroville-spillway-pictures-011-photo.html http://www.latimes.com/visuals/photography/la-me-lake-orovil...
- rebootthesystem 10y ago
  What I've been wondering is: What, if anything, did they do during all of these years of drought in order to ensure dams and all required mechanism remained sound and ready for when rains returned? The lake near my house was down 120 feet. You could see land and structures never seen in decades. Prime opportunity to get in there to inspect and maintain said infrastructure. Not sure anything was done at all. I am no expert in concrete but I would like to think the break in the Oroville spillway could have been detected and dealt with with cursory inspections over the last several years, when access was easy due to the drought. I don't like it when folks are put in danger because other folks who are supposed to be working for us don't do their jobs. Not saying this is what's happening here, I don't know, but the question needs to be asked.
  - maxerickson 10y ago
    The spillway can be completely shut during normal operation of the dam. So the drought didn't provide any increased opportunity to do inspections.
    - 10y ago
rodionos 10y ago
I should have used a different term, for clarity. By overflow I meant that the estimated amount of water in the reservoir exceeded its total storage capacity and they had to use spillways to drain the excess. We have a geo engineer on our team and he's saying that while primary spillways are made of concrete, the secondary (emergency) spillways are made of soil and materials and can deteriorate quickly.