Dealing with Tsunamis 1

[medeek]

This topic is a bit off the beaten path for me and may not be appropriate for this particular board of the forum however I do know that the next itteration of the ASCE 7 will have a new chapter dealing with Tsunami Loads and Effects. I will be very interested to see the particulars of this chapter. Based on what I have read so far it will not apply to standard low rise residential structures. Obviously, the cost associated with designing a structure that could resist the loads imposed by even a minor tsunami (5-10 ft) would put these measures outside the range of a typical residential budget.

The recent article in The New Yorker:

http://www.newyorker.com/magazine/2015/07/20/the-really-big-one

has got me seriously thinking about the tsunami threat again here in Ocean Shores, Washington (where I do most of my work). Currently there is one road out of the town (peninsula) with an average elevation of less than 20 feet. The entire town is within the inundation zone of a major tsunami and it appears that we are overdue for one.

Given a recent study by the USGS it is all the more obvious that the only way to save lives in this community and others is with vertical evacuation. I like the idea of large mounds created strategically throughout the city with parks or other public facilities on top of them, however the cost of building up such mounds/structures will probably take some time to push through the system politically and financially.

In the short term I am wondering if a large barge like vessel(s) could provide an acceptable means of escape/evacuation. The vessel(s) could be easily be brought in offshore and then winched up onto dry land. They would need to be large enough to be able to withstand any debris or forces thrown at it by a tsunami and not be punctured or overturned. If they were large enough they would simply be picked up by the tsunami and smash through anything in their path. Think of them as large "tsunami lifeboats". As with any idea there are probably issues I am missing, tell me the flaws in this concept given your engineering judgement and insight.

What really gets me though is the sign posted right as you enter into Ocean Shores: A Tsunami Ready Community. Nothing could be further from the truth.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[MikeHalloran]

In southern Louisiana, in the Mississippi Delta, more than a hundred miles from real dry land, they sell a few 'redneck houseboats', comprising a camper trailer sitting atop a small barge. Connect your hawser to a big tree, or install a giant outboard motor, and you're all set for The Next Big One.

You need a ramp and a bigger barge to also save your Camaro.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

"In the short term I am wondering if a large barge like vessel(s) could provide an acceptable means of escape/evacuation. The vessel(s) could be easily be brought in offshore and then winched up onto dry land. They would need to be large enough to be able to withstand any debris or forces thrown at it by a tsunami and not be punctured or overturned. If they were large enough they would simply be picked up by the tsunami and smash through anything in their path. Think of them as large "tsunami lifeboats". As with any idea there are probably issues I am missing, tell me the flaws in this concept given your engineering judgement and insight."

As you might recall from videos of the tsunami that hit Japan, the tsunami pushed medium sized freighters around like so many Tinker toys. The power of a large tsunami is not something that one can resist. It's unclear whether people riding such vessels could reasonably survive such an experience.

TTFN
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[Mccoy]

Medeek, I searched Ocean Shores on Google earth and I would say it does not at all appear as a safe place if a Tsunami is triggered.

A lot depends on the wave's height. As IRstuff said, with monster tsunamis like the Indian Ocean 2004 or the Japan 2011 I'm afraid vessels would be pretty useless. With more modest tsunamis, the idea may work. Elevations are not accurate in Google earth, I read a 6 meters elevation for most of the town area, which agrees with your 21 feet elevetaion of the main road.

Again, if a large subduction earthquake occurs not far from the coast and a monster tsunami wave is triggered, only fast evacuation oustide the peninsula and onto higher ground would guarantee safety.

People out there should live with the constant awareness of danger, ready to leave everything and run for their life if a large earthquake is perceived. the main road should be widened and a secundary road created.

Disabled and very elderly people should not live in Ocean Shores, also kindergarten and school staff should receive a specific Emergency training. Mothers with children should have a car ready to run away at all times and a clear passage. Many people would probably be doomed nevertheless. In Japan people had 30 minutes to run away but it may bel elss than that if the quake epicentre is close to the coast.

Acoustical and visual alarms should be installed with signals differentiated in relation to the event magnitude. Numerical Simulations should be run. Emergency simulations should become a part of life.
Up to some magnitude treshold the highest part of the town may be safe, although without a contour map I cannot say that.

These are all common sense solutions. After having seen again and again the images from Japan, which hold a sinister fascination, it is all too evident that running to the hills is the only viable solution with a large tsunami. The best obvious prevention: relocate to another area.

http://www.mccoy.it

 

[Mccoy]

I've read the New Yorker article now, it's pretty exhausting.

Also, it cites liquefaction problems in Seattle, but these are likely to happen in all Ocean Shores, as far as I can see it's all sandy sediments in groundwater.

If that happens, evacuation will be impeded by flooded areas and cracks on roads. Lateral spread may occur and chunks of the peninsula drift down to sea. And this while a giant seawave is preparing to sweep the town away.

http://www.mccoy.it

 

[thaidavid40]

Let's face it - much of mankind lives where the conditions can turn potentially deadly - and in a hurry. Nature's power is typically greater that what we can reasonably muster against it - especially when tens or hundreds of millions of people are involved. Living in a danger zone is a part of life for most of the people on earth. Recognizing that, and living in the face of it is sometimes all we can do. I am not trying to be defeatist here, just realistic, and applying that realism to my own particular situation (F5-level tornados). I can have a personal shelter - and there are "community shelters" too. However, there aren't enough shelters around to save every last soul. So vigilance is our best defense.

Thaidavid

 

[3DDave]

The best method is evacuation and for that to work, advanced warning. Once the warning system is in place, then it requires people to believe and act on it.

In Japan they have a warning system that goes back centuries, but not everyone believed it.

http://www.nytimes.com/2011/04/21/world/asia/21stones.html?_r=0

In the tsunami in Indonesia (I think) there was a small tribe that people were worried had been wiped out. The tribe had a story, also going back centuries, that when the sea pulled away they should head out from shore. They did; they did not know why the story said what it did, but they believed it and all jumped into their boats and sailed out where they were safe, instead of being swept inland.

 

[medeek]

If a Cascadia rupture were to occur the residents of Ocean Shores (Pop. 5628) have approximately 15-30 minutes to evacuate. According to this paper:

http://www.wacoastalnetwork.com/upl...ean_shores_westport_liquefaction_pamphlet.pdf

The main road out passes over a peat bog and will probably be impassable, so likelihood of escape is low in my opinion. Even if the road does remain after the initial earthquake the traffic on this narrow road will quickly turn it into a parking lot.

I also like the idea of personal safety systems however the expense to the individual residents and also the proven effectiveness of these systems probably precludes their widespread usage and adoption.

The entire peninsula is beach sand. The largest building is the convention center in the middle of town which is essentially floating on sand (I spoke with the geotech engineer about this structure only a couple of months ago). I recently had a customer try to build a pole frame building but when trying to dig his post holes he found the tide water at 3-4 ft and we had to abandon the idea and go with a conventially framed structure due to the high ground water. Liquefaction will be a major concern and will probably cause significant structural damage and possibly loss of life even before the tsunami comes ashore.

@thaidavid40

I can understand what you are saying and there is only so much that can be done when mother nature is involved, but as structural engineers I think it is our duty to figure out ways to prevent the loss of life or safety with respect to the forces of nature (seismic, wind, snow, rain, gravity etc...) Figuring out how to deal with a tsunami event is simply taking it a step further.

A large percentage of Ocean Shores residents are older retired folks, so that further complicates the matter. There are also two schools in the inundation zone which are at risk. My first thought would be to rebuild both schools on large berms with an elevation of at least 50-60 ft. The high school is on the north end of town and evacuation would be more feasible from this location however the elementary school is too far down the peninsula to consider reasonable evacuation of the students.

There is a 33% chance of a major tsunami in the next 50 years that will completely wipe this peninsula clean, the geologic record over the last 10,000 years (41 tsunamis) shows an almost clock-like re-occurence of this type of mega event, roughly every 250 years apart. We are currently overdue for another major earthquake along the Cascadia fault line. It is not a matter of if just a matter of when. I feel that the calculated risk is at a high enough level that we should not ignore this issue but actively seek appropriate means to deal with it head on.

The appropriate solution for Ocean Shores, and similar at risk communities along the west coast, in my mind involves more than just printing evacuation and preparedness pamphlets, posting evacuation route signs and touting "Tsumani Ready" with misleading public signage.

Unfortunately, a significant portion of my practice is involved with new construction of residential structures in Ocean Shores. In some ways one could argue that I am contributing to the problem by adding further population and development to this already at risk community. If I am to continue my practice with at risk locations such as this community I feel an obligation to also be one of the loudest voices of warning.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[msquared48]

I am one for having muliple escape routes. Been to Ocean Shores and points north many times over the last 60 years. There is only one way out of Ocean Shores and I cringe thinking about the posted "escape route" which I have long deemed a joke. In the 60's this land was used by a farmer to raise cattle, but sold to a developer for a million dollars. In my estimation, it never should have been developed. It is just a disaster waiting to happen. My father had an opportunity to buy land there but turned it down after talking to a few locals. Glad he did. There is one major reason why there are no trees on the spit. Guess what it is... Same with Longview.

Mike McCann, PE, SE (WA)

 

[msquared48]

For this coastal area, years ago I thought of designing a tsunami shelter to resist a 30 foot wave. That was a challenge to say the least. With the probability of a 100 foot wave, now what I have to say is, what is the point?

Mike McCann, PE, SE (WA)

 

[medeek]

The problem with a fixed shelter or berm is that the height of the tsunami can only be estimated. If it does indeed produce a 100ft wave a fixed shelter may be overtopped. Hence my thinking along the lines of a "lifeboat/ark" type of evacuation.

If you look at some of the photos of large vessels washed ashore by the tsunami it would appear to me that they have a much better survival rate than a fixed structure.

It would appear that none of these large boats were capsized, merely washed ashore.

A large barge like vessel would even fare better in my opinion and be less likely to overturn.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[medeek]

The scale of these vessels would put them out of harms way in my opinion:

300' x 90' x 20'

http://www.marnavi.it/public/flotta/Vervece_brochure.pdf

Even a 100' tsunami would not overturn a vessel this size.

Three of these positioned strategically on the Ocean Shores peninsula would be able to handle all 6,000+ residents with ease. The idea is to have any residence within 5 min. walking distance from one of these lifeboats.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[thaidavid40]

Boarding 2,000 residents in a 15-minute period (per above numbers tossed around)? How would one accomplish such a thing? It takes 30 minutes to board 300 passengers on an airplane. Granted, the two operations are not strictly equivalent, but I still see this as an impractical solution, given the large numbers. Subtract the 5 minutes for walking (on average?) and you only have 10 minutes to cram everyone onto the barge before it gets slammed by the wavefront. This might be a good personal scale answer, but I still do not see how the operation would be successful for a large-scale safety maneuver. On a personal scale, maybe a safety "bubble", which would be watertight, and could take wave and impact action, until it settles after the wavefront passes - assuming it didn't get washed out to sea in the backwash.

Thaidavid

 

[medeek]

@thaidavid40

That is why it takes engineers to figure out if this is feasible. I agree a daunting task to board 2000 residents onto one of these barges but not impossible. Just realize boarding a plane is completely different than boarding one of these barges. First of all as a rough estimate I would have two doors at each end and five door per side, these will be latched shut from the inside and watertight of course. Each door would be 48" wide for argument sake. A total of 14 boarding entrances. You are now boarding an average of 150 residents per entrance. You are also not taking time to seat them or stow luggage, just pushing them in the door as quickly as possible. There may be seats for a few passengers but mostly standing room. At 2000 people and with 27,000 sqft of deck space roughly you get about 13.5 sqft per passenger which is pretty packed but not unbearable in my opinion. It would be even better to provides seats with buckles for the 2000+ passengers but this would drive up costs, grab bars would be a more economical route.

It would actually be quite interesting to stage a drill wherein the residents practice boarding one of these vessels. EMTs would need to be on hand since there would possibly be some injuries but it would be a real eye opener as to the feasibility of this concept and also help residents realize how quickly they would need to mobilize in order to board within a 5-10 minute window.

The personal safety device is gaining traction and recently a company displayed one of there models at an event in Ocean Shores at the convention center but I am still not convinced of the survivability of such a small craft. The chances of getting crushed in the debris or drug under by larger chunks of debris riding over top are a major downside. Furthermore, unless the government supplies these personal units free of charge to every resident I do not see many of the residents shelling out the high dollar amounts to ensure their own safety. Many of them simply cannot afford it, and I would include myself and my family in this category.

The other problem I see with the personal safety device is that it will be located at your place of residence which is fine if that is where you are at the moment the big one strikes. However, what if you are at the movie theater, bank, grocery store or restaurant and more than 15 minutes from your house? The idea with the large lifeboat concept is to have them a max. of 5 minutes walking distance from any location on the peninsula.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[dicksewerrat]

We used to have a saying about the Russian A-Bomb going off.
The drill was "put your head between you knees and kiss your A_ _ goodbye". Looks like that what you may have here. No gov't. will spend the money to make everyone safe for all disasters. no one else can afford it. I'd move.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[3DDave]

The sample is possibly skewed as any boats that did sink or were capsized would not be seen in these photos.

Remember the 15 minutes includes getting to the barge/boat. They need to hear the alarm to evacuate, possibly at 2 am during a rainstorm. There may be a blackout. If they drive, the vehicles will have to be parked somewhere and the later the arrival the more vehicles the people will have to get around to get to the barge/boat.

The best part will be the drills so that it doesn't devolve into total chaos.

 

[msquared48]

Hire ET'S to vacuum up the residents before the wave hits - or develop a mass populace transporter, preset to a particular location.

Mike McCann, PE, SE (WA)

 

[3DDave]

msqaured48 - how do you feel about personal trebuchets and Zorbs? Ref

http://www.zorb.com

 

[medeek]

The problem with risk assessment is determining what level is acceptable enough to live with. Practically every location has some type of potential natural disaster that could get you. However, some risks are more predictable and that is why as an engineering community we design for those risks. In California seismic reinforcing is a no brainer. In Oklahoma City underground shelters are becoming more typical with new house construction. Florida has elevated wind loads due to the seasonal hurricanes. Snow loads around Lake Tahoe are a major consideration in roof design.

Some potential natural disasters are outside our ability to measure their risk such as the Yellowstone super volcano, hence we don't attempt to design for them.

Recent studies have now put our understanding of west coast tsunami risks into a much more quantitative and clear picture. Japan should not be the only country that prepares itself for this type of natural disaster. If the government cannot provide better tsunami mitigation then perhaps it is time to move. The addition of chapter 6 to the ASCE 7-16 is a first step in the right direction but is only the tip of the iceberg.

I found this article about Fudai very interesting and helps put things in perspective:

http://www.dailymail.co.uk/news/art...sea-wall--village-left-untouched-tsunami.html

I'm not saying let's spend billions of dollars on a sea wall rather let's explore the options and see if there might be a relatively inexpensive solution that gives us a good bang for our buck. To do nothing and simply accept our fate is not an option in my play book. Trying to get everyone to move out of their seaside resort is also not a realistic option. The best option is to find a inexpensive form of evacuation.

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[JStephen]

I will point out that for the barge idea, it would be simpler to just build the barges in place rather than winching them onto shore. That's assuming you build them specifically for that purpose, as opposed to buying used barges. You'd have some maintenance issues to consider in the long term.