6 ms·

Remember that the sluice gates are seized. Obviously they should still drain it but it's not as simple as making the call.

foota 11y ago
How could they drain it?
- hyperion2010 11y ago
  Dig an alternate channel.
  - foota 11y ago
    I'm not sure it would be quite so simple. The article mentions the reason that they can't just open one gate is because the asymmetric draining would be harmful to the dam. It's possible that any sort of adhoc draining would adversely affect the dam. Not to mention quickly building a secure tunnel to handle the water pressure at that depth sounds like no mean feat.
  - acveilleux 11y ago
    That's called a spillway BTW and the problem with spillways is erosion and the energy of the water. So spillways have to be made of reinforced concrete or similarly strong materials when the local rock isn't hard enough and they have to be shaped to dissipate the energy. The spillway of the Mosul dam is made of concrete the problem with it appears to be that it allows too high a water level for the dam in its current shape even when fully open.
- techdragon 11y ago
  I would imagine siphoning might be a simple enough process and could be setup in multiple places along the dam to avoid the asymmetric draining issues mentioned further in the discussion here on hacker news.
  - tim333 11y ago
    You can syphon up about 30ft. The dam is 371 ft.
    - Blaque 11y ago
      Can you explain why a syphon won't work over 30ft?
      - Errsher 11y ago
        "This siphon effect relies on atmospheric pressure to allow the pressure and pressure potential energy to drop as the water travels upward inside the sealed pipe. But eventually the pressure of the rising water reaches zero and no further reductions in pressure and pressure potential energy are possible. That failure of the siphon effect occurs when the water is about 30 feet (10 meters) above the higher container. You can't use a siphon to lift water higher than 30 feet because above that height, an empty region will develop at the top of the pipe and stop the siphon process." http://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20080512104921 http://www.physicscentral.com/experiment/askaphysicist/physi...
        mikecb 11y ago
        What about running the tube over the dam and down to a lower level than it originates? Then gravity(?) does the trick?
        sangnoir 11y ago
        It would only work if the difference between the water level and the top of the wall is less than rouhgly 30ft (as per xkcd). The bottom line is, the siphon will not work if it has a vertical water column taller than 30ft (water weight per unit area becomes greater than opposing atmospheric pressure)
        taco_emoji 11y ago
        The issue is that top of the dam is (way) over 30 feet above the water level behind the dam, which prevents the suction from overcoming gravity. A siphon won't work with that much of a rise in the middle no matter what the difference is between the elevations of the ends of the tube. Also what you're describing is literally how all siphons must work--you can't siphon to a higher elevation.
rwallace 11y ago
Would it suffice to just take a stick of dynamite to one of the seized gates?
- adrianN 11y ago
  What could possibly go wrong?
  - rwallace 11y ago
    You (and at least one other) reacted as though I had claimed such an action would come with a guarantee nothing could go wrong. Which is, to put it bluntly, a rather stupid reaction given that: 1. I didn't make a claim. I asked a question. 2. According to the experts, the clock is currently ticking down on a million lives with no idea of how much time is left, so your implied suggestion of doing nothing (which is the implied suggestion when you summarily dismiss a line of thought while providing nothing in its place) is... well, how exactly would you describe the suggestion of just letting a million people die, had it come from someone else?
    - adrianN 11y ago
      It just seems to me that using explosives on a structure where collapse is imminent in order to fix it sounds like the most dangerous idea one could possibly have.
      - rwallace 11y ago
        First of all, according to what the experts are saying, the most dangerous idea one could possibly have is your idea of doing nothing - that guarantees the worst-case outcome. Second, one would normally expect the force required to break the dam to be orders of magnitude larger than that required to open a sluice gate. Obviously this isn't a normal situation, but then, what are the figures? If a stick of dynamite isn't the appropriate tool, exactly what would it take to open the gates? Third, if you could say 'we are going to try this at such and such a time, everyone be prepared' that would be far better than having it fail at an unknown time. Fourth, now that I think of it, even deliberately blowing up the dam at a known time would be better than letting it fail at an unknown time. Fifth, I'm sure there is some relevant idea or consideration I haven't thought of, that someone else could think of if they put their mind to doing so.

foota 11y ago

How could they drain it?

hyperion2010 11y ago
Dig an alternate channel.
- foota 11y ago
  I'm not sure it would be quite so simple. The article mentions the reason that they can't just open one gate is because the asymmetric draining would be harmful to the dam. It's possible that any sort of adhoc draining would adversely affect the dam. Not to mention quickly building a secure tunnel to handle the water pressure at that depth sounds like no mean feat.
- acveilleux 11y ago
  That's called a spillway BTW and the problem with spillways is erosion and the energy of the water. So spillways have to be made of reinforced concrete or similarly strong materials when the local rock isn't hard enough and they have to be shaped to dissipate the energy. The spillway of the Mosul dam is made of concrete the problem with it appears to be that it allows too high a water level for the dam in its current shape even when fully open.
techdragon 11y ago
I would imagine siphoning might be a simple enough process and could be setup in multiple places along the dam to avoid the asymmetric draining issues mentioned further in the discussion here on hacker news.
- tim333 11y ago
  You can syphon up about 30ft. The dam is 371 ft.
  - Blaque 11y ago
    Can you explain why a syphon won't work over 30ft?
    - Errsher 11y ago
      "This siphon effect relies on atmospheric pressure to allow the pressure and pressure potential energy to drop as the water travels upward inside the sealed pipe. But eventually the pressure of the rising water reaches zero and no further reductions in pressure and pressure potential energy are possible. That failure of the siphon effect occurs when the water is about 30 feet (10 meters) above the higher container. You can't use a siphon to lift water higher than 30 feet because above that height, an empty region will develop at the top of the pipe and stop the siphon process." http://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20080512104921 http://www.physicscentral.com/experiment/askaphysicist/physi...
      - mikecb 11y ago
        What about running the tube over the dam and down to a lower level than it originates? Then gravity(?) does the trick?
        sangnoir 11y ago
        It would only work if the difference between the water level and the top of the wall is less than rouhgly 30ft (as per xkcd). The bottom line is, the siphon will not work if it has a vertical water column taller than 30ft (water weight per unit area becomes greater than opposing atmospheric pressure)
        taco_emoji 11y ago
        The issue is that top of the dam is (way) over 30 feet above the water level behind the dam, which prevents the suction from overcoming gravity. A siphon won't work with that much of a rise in the middle no matter what the difference is between the elevations of the ends of the tube. Also what you're describing is literally how all siphons must work--you can't siphon to a higher elevation.

rwallace 11y ago

Would it suffice to just take a stick of dynamite to one of the seized gates?

adrianN 11y ago
What could possibly go wrong?
- rwallace 11y ago
  You (and at least one other) reacted as though I had claimed such an action would come with a guarantee nothing could go wrong. Which is, to put it bluntly, a rather stupid reaction given that: 1. I didn't make a claim. I asked a question. 2. According to the experts, the clock is currently ticking down on a million lives with no idea of how much time is left, so your implied suggestion of doing nothing (which is the implied suggestion when you summarily dismiss a line of thought while providing nothing in its place) is... well, how exactly would you describe the suggestion of just letting a million people die, had it come from someone else?
  - adrianN 11y ago
    It just seems to me that using explosives on a structure where collapse is imminent in order to fix it sounds like the most dangerous idea one could possibly have.
    - rwallace 11y ago
      First of all, according to what the experts are saying, the most dangerous idea one could possibly have is your idea of doing nothing - that guarantees the worst-case outcome. Second, one would normally expect the force required to break the dam to be orders of magnitude larger than that required to open a sluice gate. Obviously this isn't a normal situation, but then, what are the figures? If a stick of dynamite isn't the appropriate tool, exactly what would it take to open the gates? Third, if you could say 'we are going to try this at such and such a time, everyone be prepared' that would be far better than having it fail at an unknown time. Fourth, now that I think of it, even deliberately blowing up the dam at a known time would be better than letting it fail at an unknown time. Fifth, I'm sure there is some relevant idea or consideration I haven't thought of, that someone else could think of if they put their mind to doing so.