California Megaflood: Lessons from a Forgotten Catastrophe | Hacker News Reader

California Megaflood: Lessons from a Forgotten Catastrophe

scientificamerican.com

70 pointsyoungerdryas19 comments

If you're curious where these rivers are, take a look at a Map of California Rivers that I made a few years ago[1]. Note that nearly the entire Sierra Nevada range drains through the San Francisco Bay. Also note the small blue globs along the rivers (e.g. Yuba) - these are reservoirs, which provide some degree of flood protection, though probably not enough for the size of event described.

  1. https://sites.google.com/site/calirivermap/

I had never heard of these "atmospheric rivers" prior to this article and started doing a little reading.

"Atmospheric rivers are typically several thousand kilometers long and only a few hundred kilometers wide, and a single one can carry a greater flux of water than the Earth's largest river, the Amazon River." [1]

That's really impressive. I'm curious about their density and whether airplanes have to avoid them, or if they're able to fly through.

[1] http://en.wikipedia.org/wiki/Atmospheric_river

Just to fill out the first four pages a little more:

[Edit] In the US [/Edit] your home and office are most likely already set outside the floodwaters of the 100-year storm. New roads are typically designed to convey floodwaters at no more than 1 foot deep for the same event.

Protecting a building that has a lifespan of less than 100 years against an event with a probability of occurring between .005 to .002 (the 200-year to 500-year event) is a hard sell.

> Protecting a building that has a lifespan of less than 100 years against an event with a probability of occurring between .005 to .002 (the 200-year to 500-year event) is a hard sell.

Only in America. The Delta Works in the Netherlands are designed for the 2000-year flood. This is the minimum - there are areas that are protected against the 10000-year flood.

This makes sense. It is not normal that densely settled areas are flooded at least once during the human lifespan.

Noted, thanks.

In the context of a 10000-year flood, it's interesting to consider what the southern North Sea looked like until ~6200 BCE:

http://en.wikipedia.org/wiki/Doggerland

>Only in America.

You don't seriously claim all of Europe is prepared for a 2000 year flood. I doubt a lot of nations can afford it.

South Holland is, and it has 4 million people living in it.

I was thinking more of Italy and its notorious construction fiascos.

"Protecting a building that has a lifespan of less than 100 years against an event with a probability of occurring between .005 to .002 (the 200-year to 500-year event) is a hard sell."

It is not only protecting the building; it also protects those living in them.

Also, you should use 'expected damage done', not 'life expectancy of hardware' as your metric. Rebuilding your house may cost you a year of productivity. Rebuilding a hospital or factory will easily take more.

Wild, I've lived here nearly 30 years and had not heard about this flood. I also found the concept of a concentrated stream of moist air (the the "atmospheric river") to be an interesting, if somewhat sensationalized, phenomena. Given the relative density of water vapor in these things they should be pretty easy to spot by satellite.

Spotting it isn't really the problem - there's still nothing you can do about it. Anything we could try to do would be like trying to stop a blizzard in Chicago with hair dryers.

Even if you can't spot it you do have time to get out (it's not like all of the rain happens in 24 hours), but the consequences of something like this happening now in California would be enormous for the whole country just on the basis of food. In the 1860's most food was (relatively) local, but these days California actually produces something more than a quarter of the US food supply (quick googling gives widely varying numbers without any attribution, research is up to you), particularly fresh fruits and vegetables. Imagine the Central Valley losing an entire year or more of growing season, probably with the loss of a significant percentage of fruit & nut trees that take years to replace. The ripple effect through the rest of the economy would be ugly.

Well if someone could tell me that the big storm today was likely to last for a month and by the end of it much of California would be a federal disaster area, I'd consider driving over to Reno to spend some quality time on much higher ground :-)

California supplies a lot of Canada's food too.

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