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Tsunami prevention

Undersea explosives to dissipate Tsunami
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Hi All.... tell me how idiotic or ingenious this may be.

With recent Tsunami's such as that which occured in indonesia and nearby countries late last year I have been thinking about protection mechanisms from such disasters.

I live in Australia and the biggest Tsunami threat for the eastern Australian seaboard would likely come via an earthquake off New Zealand. I recently read of how a Tsunami might come into Sydney harbour and wash around inside the harbour for quite some time creating much destruction. Tsunami that travel into semi enclosed bay areas are extremely dangerous due to the funnel effect.

I propose a frontline defence system of underwater explosives that would be placed at the heads of any semi enclosed bay such as Sydney Harbour. The explosives would be lined up at set intervals across the sea floor of the mouth of the bay within scallop shell/dish shaped enclosures of extremely thick concrete reinforcement and angled out to sea. There would be several lines of explosives each spaced a few hundred metres back from the first line.

Once a tsunami was detected as being within a set distance (500metres to 1 Km perhaps) the explosives in the front row would be set off together sending a shock wave mostly forward and out to sea due to the shape of the concrete enclosure. The shock wave would hit the tsunami hopefully with enough force to at least dissipate the wave somewhat before it reached the shore.

Generally there is more than 1 wave in a Tsunami and this is where the additional lines of explosive would be used once the first line had been exploded.

I basically got the idea of this from watching backwash waves at the beach and how they affect incoming waves.

The explosives would need to be extremely powerful to counteract the effects of the Tsunami.

Yes I realise that the force of an incoming tsunami is immense but you would only be trying to protect a small area of coast and hence might stand some chance at least.

Yes I realise that the explosions would destroy anything in its path, sea life, small boats etc. But thats probably an acceptable loss when compared to the possible damage from a major Tsunami.

Yes I realise that it will be near impossible to send all the explosive force forwards towards the Tsunami and that you will get at least some of the force back into the harbour itself, hopefully the shock waves would only be small though.

Yes I realise that it would take 32 billion tonnes of TNT to have the same effect as a magnitude 9.0 earthquake but you are not trying to dissipate the entire tsunami, just a small section of it.

Yes I realise that having a huge amount of explosives stored under the sea at the opening to a busy sea port may be very dangerous due to accidents and terrorism risks, naturally this would need to be accounted for with safety mechanisms.

So..... whatcha think??

By the way, a mate of mine has just launched a new "Earthquake watch" website so I may as well give him a free plug since it is directly related to this invention and well worth a visit. http://www.earthquake-news.net

Cheers,

Graham Jupp

gjupp, Jul 20 2005

Tsunami energy http://www.timesonl...690-1418302,00.html
Article explaining scale of tsunami [oneoffdave, Jul 20 2005]

Ripple Simulator http://www.falstad.com/ripple/
Simple ripple simulator, touch to creat waves... [JuJuHound, Jul 20 2005]

[link]






       Seems unlikely that a single explosive event could disrupt a tsunami. These aren't ordinary waves with wavelengths of a few tens of metres - they have wavelengths measured in tens if not hundreds of kilometres - they just go on and on - there is a massive weight of water to deflect.
I heard that a small tsunami did hit Sydney some years ago - it did tens of millions of dollars worth of improvements. <g>
coprocephalous, Jul 20 2005
  

       sorry unabubba I just mistakingly deleted your first post, didnt realise that it would actually work. Yes you are right that wavelengths are extremely long and as such this idea may be flawed.
gjupp, Jul 20 2005
  

       I think you need to say "Yes, I realise..." more.   

       Can't see how this would work. The disruption created by the explosives would need to fundamentally change the water level, and it couldn't accomplish this to any degree of impact.   

       Plus I think the idea of having these massive amounts of explosives sitting around in the water during non-tsumani time periods is asking for trouble, regardless of 'safety mechanisms' utilized.
waugsqueke, Jul 20 2005
  

       If you send one wave at another, don't they pass straight through with minimal influence on each other?
david_scothern, Jul 20 2005
  

       David's right. I used to play in my kayak just off a breakwall, and can attest that waves go right through each other. Much fun on good days, but dangerous on others--clapotic waves are just like hands clapping.   

       Gjupp maybe might be able to shape his waves to blast clear down to the sea-floor, which might have some effect, but I doubt it. Most tsunamis pull a lot of the water out from the shore, so there is no telling under what conditions his explosives will be going off.   

       I will withhold my fishbone if we can arrange to have the system computer-controlled, and designed such that a reasonably-bright fourteen-year-old can hack the program. I'd just like to see what happens.
baconbrain, Jul 20 2005
  

       Depends on the phase. If they are in opposite phase then they will have negative interference and cancel each other out. Waves bouncing off a reflector will be in half-phase and have no effect on wave amplitude.
Minimal, Jul 20 2005
  

       [admin: [gjupp] - please don't put advertising in your posts]
hippo, Jul 20 2005
  

       Some interesting comments here guys and girls... thanks for the feedback. When it comes to backwash at the beach, Ive often seen the backwash wave hit the incoming wave and create a collision effect rather than pass right though each other unnoticed... naturally the oncoming wave is stronger and continues to surge forward but i would guess that at least some of the oncoming force would have been dissipated in the collision.   

       waugsqueke: I agree that security and safety is a major issue... and the "yes I realise" repetition was intentional.   

       coprocephalous: This is not a single explosion, but rather a chain of explosions side by side and with multiple chains exploded at a set time after the initial chain explosion.   

       baconbrain: Its unlikely that the explosives would be high and dry from drainout caused by the oncoming Tsunami, that would mean that Sydney harbour would have to have been drained completely as the explosives would be placed across the heads in deep water.   

       minimal: Interesting facts, so are you saying it will have no effect at all on an oncoming wave? Under what situation would the waves have an effect on each other? Do you know of any sites that offer a wave/ripple simulator?   

       Hippo: Sorry for putting a link to my own website in my signature, I cant find anything on your site that mentions I was not permitted to do that.
gjupp, Jul 20 2005
  

       You flatter me! It's not my site, it's Jutta's - read the "About" and "Help" pages for background (see the links under the croissant logo on the left). Regarding advertising - advice on this topic is under the "Inventions" heading on the "Help" page.
hippo, Jul 20 2005
  

       //This is not a single explosion, but rather a chain of explosions side by side // I still don't think you'll get the wavelength or the energy to disrupt an incoming wave. Beer mat calculation coming up - imagine a 1km wide front of a tsunami in open ocean. Swell is maybe 0.5 metres, backing say 100km. That's 50 million tonnes of seawater.
coprocephalous, Jul 20 2005
  

       You would have to generate a wave in antiphase to the incoming wave, with the same wavelength. as [coprocephalous] says, this would involve moving 50 million tonnes of water.
Minimal, Jul 20 2005
  

       Maybe you could tow South Island a little closer, and use it as a tsunami barrier.
AbsintheWithoutLeave, Jul 20 2005
  

       Hippo.. thanks for the heads up regarding posting website.   

       Minimal and coprocephalous: Either of you know how much TNT is required to displace 1 tonne of water? Also do you know the equivalent TNT force of the most powerful non nuclear warheads such as those used in the first weeks of the IRAQ war?   

       Even reducing the force of the oncoming wave by 25% percent is going to greatly reduce damage and casualties in a major harbourside city such as Sydney.   

       Oh... There is a wave/Ripple simulator at the address below, although I cant get it to run with Sun JAVA. :(   

       http://cpucips.sdsu.edu/tlt/   

       Im probably clutching at straws here, but if this idea is even vaguely achievable it may be worth considering.
gjupp, Jul 20 2005
  

       Best conventional blast is achieved by fuel-air bombs, but obviously, that isn't going to work here. A MOAB has an equivalent yield of about ten tonnes of TNT or 42 GJoules - work out how high that would lift a tonne of water. High explosive is probably not what you want to move water - a nice sustained blast is better.
AbsintheWithoutLeave, Jul 20 2005
  

       I'm thinking something shaped like a snowplough that can be erected quickly in front of the harbour may be better, that diverts the force of the waves into large whirlpools. Diverting the direction if the wave is easier than cancelling it out.
Minimal, Jul 20 2005
  

       Im finding conflicting data for MOAB yield. One site mentions that they are around equiv to 15 tonne of tnt?? 0.015 kiloton?   

       minimal: Snow plow idea is interesting although you would meet major resistance from residents whose homes were in the path of the redirected wave. The threat of the wave would suddenly have become even more dangerous for them. The whirlpools would be a managable evil I would guess but I think that a large amount of the water would simply be deflected to other areas of the shore line.....but it would probably save the harbour. The snowplough shape would need to be an enourmous structure though and would possibly be required to move upwards during the Tsunami. Good to hear someone adding some ideas to what is a very real problem for populated bay areas.
gjupp, Jul 20 2005
  

       What i'm about to say sounds whacky, but it is a serious suggestion because of course this is a serious matter.
What would happen if an asteroid was towed into orbit, then actually deliberately crashed into the ocean at the appropriate time place during a tsunami? I imagine it would also have to be fragmented along the course of the tsunami. Couldn't such a series of impacts provide the necessary movement of a sufficiently large volume of water to counteract it?
nineteenthly, Jul 20 2005
  

       slowing and capturing an asteroid would be near on impossible I would think since they are not just sitting stationary out in space, they are moving at great speed. Even if you could capture it and get it into position for entry into the atmosphere in time, crashing it into the ocean would result in shockwaves in all directions, not just towards the Tsunami. I just read somewhere that a small meteor collision of just 32 feet across (landing in the sea between Australia and NZ) would result in waves over 100feet high off the Japanese coast. Seems extreme.. but hey I read it on the net so it must be true ;) Good to hear your suggestion though.
gjupp, Jul 20 2005
  

       Thanks, [gjupp]. There are many asteroids whose orbits are close to being in harmony with ours. If one is orbiting in the same direction and has a mass of around seven million tonnes, i.e. if it were cubical, one hundred metres on a side and made of iron, it would be quite a bit easier to steer than something like Eros or Amor. How big was Toutatis and how fast was it moving relative to us? Alternatively, how about rounding up meteoroids and putting them into orbit round the Earth?
I'm not clear about this, but i don't see how an explosion could prevent shockwaves from travelling out in undesirable directions either. Maybe i just haven't read your idea closely enough.
nineteenthly, Jul 20 2005
  

       I think in the same way that noise-cancelling technology only works when it tries to cancel the noise at a point (e.g. an ear) tsunami-cancelling technology would only work at specific points (e.g. important coastal cities). Trying to cancel the entire tsunami would never work. One side-effect of cancelling the tsunami at a single point (the important coastal city) might be that the tsunami and the cancelling wave together increase the impact a little further down the coast. Inherent in this idea is the assumption that you're prepared to save big coastal cities and sacrifice a few more small coastal towns.
hippo, Jul 20 2005
  

       The 28/12/04 Tsunami was triggered by a magnitude 9 earthquake and the energy release has been estimated at around 190 megatons TNT equivalent [link]. In order to have significant effect, you'll have to put slmilar amouts of energy into the counter wave.
oneoffdave, Jul 20 2005
  

       //Do you know of any sites that offer a wave/ripple simulator?//   

       In response to [gjupp]'s question, I have searched exactly what he requested on google - "wave ripple simulator". I have added a link to a simulator. It may not be the best, but it was the first result I tried honestly.
JuJuHound, Jul 20 2005
  

       Jujuhound.... nice ripple simulator.. and it actually works on my PC unlike the other one I linked to in a previous annotation. Thanks.   

       Oneoffdave: You would only need similar amounts of energy to the original quake if you intended to dissipate the entire Tsunami.... my proposal was to protect just a tiny section of coastline and as such the amount of energy required would be greatly reduced.   

       Nineteenthly: my proposal was to direct the force of the explosion using scalloped shaped concrete semi enclosures, there would be some leakage of the shock waves but I would imagine the majority of the force to be heading in the right direction. Maybe this is bad science, Im not sure.   

       Im now thinking that the amount of energy required is just too great and Minimals idea of an undersea plough shaped walls might be more appropriate. What I would like to find out is how such an object might affect the wave if the wall was completely submerged and was never actually raised above sea level, this way it could be completely passive, an artificial reef that still allowed sea traffic over the top of it. Yes you would get some of the wave force spilling over the top of the undersea wall, but at least some of the force would be redirected (but possibly towards smaller towns which is the obvious downer).   

       I have another question about how waves work... when in deep water a wave is not actually moving water forward to any major degree, its not until it reaches shallow areas that it starts to surge and actually is pushing water forward (correct me please as Im not sure on this). So what we are actually trying to achieve is to push water back (and up into a peak perhaps) rather than trying to cancel out or disrupt the "wave frequency"? So do the normal wave cancellation rules apply here? Just a thought and quite likely incorrect.
gjupp, Jul 20 2005
  
      
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