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Tsunami Local Warning System

Triggered by rapid sea level change
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(+3, -1)
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Those of you who saw my recent "Tsunami Prevention" proposal might be interested in this new idea as it is probably a lot more viable. I got to thinking after I read somewhere that a warning system based on "drain out" might be pheasible. As the article didnt mention any actual solution I thought the following might be a possible idea.

I propose the following:

Usually before the onset of a large Tsunami, shallow coastal areas are often drained well below the normal tidal levels. This gives a visual warning that a Tsunami is soon to follow, however if you are not within view of the ocean or if it happens to be night this effect will likely go unnoticed.

By embedding "warning pylons" into the sea floor directly in front of inhabitated areas, residents could be given an audible warning (siren) that a Tsunami is fast approaching, perhaps giving people a few extra minutes to get to higher ground, upper levels of hotels etc.

Each pylon would consist of a sealed plastic/fibreglass top section well above high tide level housing a loudspeaker and solar panel/Battery together with the necessary electronics or mechanics to provide an audible warning.

Further down the pylon below the low tide water mark would be a float at the end of a hinged arm (the float would always be under water until a tsunami occured). Whilst the water was above the float level the arm would be in the up position indicating to the alarm system that all is well, however when the water level dropped to below the low tide mark the weighted arm and float would drop and trigger the alarm system announcing imminent doom.

The float arm would likely need to be contained in a cage to prevent vandals from setting off the alarm as a hoax, possibly causing panic and accidents.

Cost to produce the units would likely be reasonably low considering the amount of lives it would likely save. As such they would be ideal for both wealthy and poorer countries.

The units would of course degrade, need regular "defouling/cleaning" and also need battery replacement over time however this is not a major issue.

Question: Does anyone know how many minutes of pre warning the device is likely to give? How long is it between when drainout occurs and when the actual wave hits?

Feedback please... :)


Graham Jupp

gjupp, Jul 23 2005

Tsunami Video Site http://www.asiantsunamivideos.com/
Amateur Asian Tsunami Video Footage [baconbrain, Jul 23 2005]

Last mile warning systems http://asia.news.ya...050807/3/259e5.html
This is what the boffins are currently working on. Interesting read. [gjupp, Aug 08 2005]


       Gjupp, this is a good one. Drainout has long been a warning sign, but one that not everyone knows.   

       There are some satellite images of the 26 December tsunami that may give you a series of time stamps, and there are sets of photos taken on beaches that may have times printed on them. I've also found videos, but not one that allows a time estimate yet. As has been said on other ideas, any warning at all is good, but people need to avoid panic.
baconbrain, Jul 23 2005

       thanks baconbrain..... both for the enthusiasm and tips.   

       It would be nice if leavers of negative scores (and positive) could leave a little comment as to why its a bad or good idea, especially the negative scorers as I know in my own head why I think its a good idea, but not sure why it would be classed as a bad one.   


gjupp, Jul 23 2005

       I don't know why anyone would think it is a bad idea either. This is a very workable idea, and could save lives. Some people think that any tsunami warning would just cause panic--they don't suggest any alternatives, though. I think they fear taking any action that may cause harm, but don't realize that taking no action causes greater harm.   

       Yes, panic is an issue, but it can be reduced with planning, practice, training, drills, information and understanding. Which is not to say that all those are needed, but to say that all those are available. Even without them, I'd still prefer a warning and a panic to no warning and a panic.   

       Some of the videos show much time between the lowering of the sea and the arrival of the waves. They also show a lot of people who didn't know what the hell was happening. (I've known what the water going away meant since I was a 10-year-old in Kansas.) You will need to do some education and informing.   

       I do not know if drain-out occurs every time. I cannot even figure out why it happens. Even if it does not, some of the videos show a wave approaching from a long distance away. An addition to your system could be a wave detector. A radar or laser system could monitor wave profiles and sound an alarm. This could be mounted on shore at a lower cost than a submerged unit. (It could even be handy for letting surfers check conditions over the web.)   

       I like this idea, and I am in a tsumani town. I want a warning system.   

       [Later] After more net-searching. Warning systems are being developed, but most are focussed on long-range detection and complex communication systems. A few have beach sirens, but they are hooked to long-range, deep-ocean sensor.   

       I only find three cases where someone saw the water draining away, realized what it meant and gave a verbal warning. Many videos show people going out to play in the exposed areas.   

       There is a need for short-range tsunami detection and warning. As the article that inspired this idea says, drain-out is a sign that may be useful. This float-arm idea should work to detect drain-out and activate a warning system--heck, float arms work in toilets billions of times a day.
baconbrain, Jul 24 2005

       Even more reliable is the technique of measurement of conductivity between two electrodes using an ac voltage system. This is common in water treatment plants. A high sea level will complete the circuit, but when the circuit is opened by a falling sea level, then the alarm can sound. Use two sets of electrodes to detect that the level has changed quickly, and for longer than the period of a normal wave.
Join several systems together for cross checking, and fault signalling.
Ling, Jul 24 2005

       Good to see that this is causing some interest.   

       Ling, thats certainly another interesting way to signal an alarm, although it may have issues with electrodes quickly becoming damaged or less than reliable due to saltwater corrosion and fouling. Maybe stainless steel or gold could get around this problem. Your suggestion of an alarm based upon a rapid activation of two or more of the switches at descending levels on the pylon is excellent and possibly an even more accurate method, but yes you would need to allow for regular waves hitting/filling the exposed sensors at low tide. My only worry would be the reliability of exposed sensors in an unforgiving ocean environment and as you say it would need at least two of the systems in place on the same pylon to crosscheck and possibly give an audible signal when there was a problem with one of the sensors. You would just have to ensure that the malfunction sound was very different to the actual warning siren. The pylon should probably also have a low voltage LED light or similar on it to show that the battery is still charged... no flashing would mean battery level low (although people are less likely to noticed something that no longer flashes so might take some time for people to realise).   

       Baconbrain: Ive also been aware of drainout indicating approaching Tsunami for some time.. but this is probably as I live in western society and movies such as Deep Impact have given me at least some useful tidbits of information. A laser based wave detector is also a good idea, however it may be beyond the reach of poorer countries and I see a standalone system as being particulary useful in poorer countries.   

       Yes, poor education as to the danger signs is heavily to blame for deaths in recent Tsunami's, take for example the videoclip of the lone person (child?) sitting on the beach in a drainout area, it is not until the wave is almost on top of them that they decide to stand up and run, they probably take 3 steps before being engulfed, horrific images indeed. And this is with a wave coming at them at probably >30mph and a sound like a freight train.
gjupp, Jul 25 2005


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