Big Waves

[johan]

If a 50 foot wave hits the east coast and I live 35 feet above sea level, am I toast? What about a 10 foot wave if I live 5 feet above sea level? That must happen all the time. Does it have to do with how far inland I live? If so, how much of a difference does that make?

Want to figure out where to build my house to be safe if the Canaries cave in.

[moes lotion]

The short answer to your question is "It depends." A wave, travelling across the ocean, can be thought of as a travelling bundle of energy that causes the water on and near the surface to rise and fall, but not to move significantly horizontally. The reason waves can travel very long distances is that water is, well, a liquid and so fairly easy to push around. Now, when a wave hits the shore, part of the energy is reflected and part, if the wave is large enough, forces a portion of the wave onto land. The land however, not being liquid, is not so easy to push around and so the energy of the wave dissipates, meaning the height of the wave falls very rapidly as it moves inland. Another way to think of this is that, even for your 50-footers, the total volume of water in the portion of the wave that makes it on shore is very rapidly spread out as the wave moves inland. Exactly how far inland is "safe" will depend a lot on the lay of the land, it would be worse to live at the base of a deep bay with cliffs on both sides leading to the river delta where you've built your dreamhouse than to be a little way inland from a straight shoreline with a gently rising elevation.

[AskNott]

It does have to do with how far inland you are. I was told recently of a friend of my brother (FOMB) who built a house just past the place in Florida where the law requires you to put projectile-proof windows in a new house. He gambled, and didn't buy the terribly expensive windows for his new house. None of this year's slew of Florida hurricanes heaved a tree through his ordinary windows, so he won the bet.

New houses in the storm zone near the coast must be, essentially, on stilts. You can use the ground floor for storage or garage space, but all ground floor walls must be flimsy enough to blow through if a ground swell hits. That way, you might lose your car, but the house will still be standing.

No matter where you choose to live, you have to allow for the local hazards. I could list them, but you know what they are. "Life here is great, except for ..."

[NinetyWt]

If you live in a coastal area of the U.S., chances are that there are flood zone maps depicting the area. You can use these maps to determine if you are at risk from "storm surge". These maps can tell you the depth of flooding from storm surge.

BTW if you live inland, you can also be suceptible from river flooding. Go down to the county or city office and look at the maps.

[johan]

Thought I'd bump this thread in light of recent events.

[Hail Ants]

You shouldn't think in terms of height, i.e. a '50-foot wave'. Tsunamis don't really work like this. Check out some of these videos. You can see that although the waves aren't very tall, there is a tremendous volume of water pushing inland with great force, flooding and knocking down everything in its path.