520 bridge waves

[gfish]

As those of you familiar with the Seattle area know, there are two bridges crossing Lake Washington, and they're both kind of unusual. They float. Lake WA is surprisingly deep, see, so piers would be difficult and an unsupported span would be much more expensive. They've become something of a local specialty, actually. 4 of the 5 longest floating bridges in the world are in Washington.

For the most part, they're just like any other bridge. An important difference is that occasionally they sink. (I still have trouble saying Evergreen Point Floating Bridge -- the Pentium bug was only a few later, so half the time I find myself saying Evergreen Floating Point Bridge.) The most obvious difference is that they're very low to the water. This means the water choppiness is usually different on either side -- whatever it's like on the windward side, the leeward side is dead calm. Very visually striking.

Now that I'm doing the vanpool to get to work, I'm commuting across 520 regularly for the first time in a decade. This has lead me to think about this effect. I realized that one reason it is so visually striking is that the choppiness of the windward side is artificially inflated. The bridge not only acts as a wave break, after all, it also is a wave reflector. So not only should you get twice the maximum amplitude on the windward side, but the wave pattern will be much more chaotic and irregular. Which, once I thought to look for it, it is. It always looks like the mess you get when the wind direction has changed, disrupting an established wave pattern.

I had idly been thinking about posting this, but wasn't sure it was quite interesting enough. Then there was a windstorm last Thursday which demonstrated the effect so perfectly, I just couldn't resist. As you can see, it was pretty dramatic:

Comments

[technoshaman.livejournal.com]

I-90, Floating Point, Hood, where's the other? Or does I-90 count as 2?

[rollick.livejournal.com]

Wow, that *IS* really striking. I suppose it shows you the age we live in when I say that my first thought it that it looks like bad CGI, like the designers weren't expecting your camera to pan right, so didn't bother to animate in the activity layer.

[gfish.livejournal.com]

That's definitely the worst I've ever seen it, but I'm not a regular 520 commuter. The windshield wipers were definitely needed, and it wasn't raining at all right then. People said they could feel the bridge moving, but the van was being blown around by the gusts so much that I wasn't convinced.

[gustavolacerda.livejournal.com]

I don't know that I've ever seen such choppy water, so that's remarkable by itself! I have, however, experienced windstorms in Amsterdam and saw our narrow canal in the middle of the city with ocean-worthy waves, like half a meter tall.