The 'Big One' might be a flood

[avaistheone1]

Source: Sacramento Bee

California has more risk of catastrophic storms than any other region in the country – even the Southern hurricane states, according to a new study released Thursday.

The two-year study by the U.S. Geological Survey is the most thorough effort yet to assess the potential effects of a "worst-case" storm in California.

It builds on a new understanding of so-called atmospheric rivers, a focusing of high-powered winds that drag a fire hose of tropical moisture across the Pacific Ocean, pointed directly at California for days on end. The state got a relatively tame taste of the phenomenon in December...

Potential consequences include:

• $1 trillion in damages statewide – five times worse than a massive earthquake, which likely would affect only one region.
• 1.5 million people displaced, about the same number affected by Hurricane Katrina in New Orleans in 2005.
• Potentially hundreds of people killed, based on the inability of some vulnerable groups to evacuate, or for help to reach them.
• Pollution from flooded wastewater treatment plants, refineries and dairies. Some sewer plants might not return to operation for months.





Read more: http://www.sacbee.com/2011/01/14/3323275/the-big-one-might-be-a-flood.html

[dipsydoodle]

1. c. AD500

Peru had it almost non stop for 30 years.

[alfredo]

14. "100 Years of Solitude" by Gabriel Garcia Marquez talks of

such an event in the mythical town of Macondo.

http://www.amazon.com/Hundred-Solitude-Gabriel-Garcia-Marquez/dp/006112009X/ref=sr_1_3?ie=UTF8&qid=1295208999&sr=8-3

If you haven't read this book, why haven't you? It is required reading.

[jwirr]

2. I see that this covers many cities but is there a lot of farm acreage

in this area? I am thinking food shortages for the whole nation could be a real consequence.

[Hell Hath No Fury]

6. Yes, the Valley -

both north and south is filled with primarily agriculture, dotted with some pretty large cities like Sacto and Frenso.

Such flooding would devastate our food production.

[Psephos]

9. It's already being devastated by diversion of irrigation water to protect the delta smelt. n/t

[indimuse]

3. Its flooding in alot of places right now!

People should prepare. ;)

[Uncle Joe]

4. Kicked and recommended.

Thanks for the thread, avaistheone.

[Gamey]

5. FEMA preparing to leverage well known and repeated disaster areas

[necso]

7. As I remember it,

a few years ago there was a multi-day storm (something on the order of 4-6" of rain here, I seem to recall) where the prevailing influence was (said to be, anyway) the jet-stream passing over a warm-spot in the Pacific (PDO related, it was said) roughly to the west of California (ie, not moisture streaming from the Hawaiian Islands or beyond).

And it isn't an uncommon pattern for storms to the north of us (like in the Pacific Northwest) to follow one another in relatively rapid succession ("Rain fell on and off for 45 days."); these storms just generally don't make it this far south with much punch, if they make here at all (although this varies widely by year and storm). (Average rainfall tends to drop as you go south in California, although topographical and microclimate effects complicate the picture.)

So I think there are at least three possible scenarios for such unusual amounts of rain. (Sometimes we get the remnants of hurricanes, and these can produce quite a bit of rain, but these are generally short-term events. And sometimes we get "monsoonal" moisture that's significant. However, both of these potential rain-makers tend to be over with before the winter rains come.)

Perhaps rainfall data from Hawaii and the Northwest, together with snowfall data from the Sierras (etc; and temperature data more widely) might provide supporting data one way or the other. (Satellite and radar data being relatively new.)

And a large earthquake that disrupts water-delivery systems (transportation corridors, etc), combined with wind-driven fires, could produce a disaster on a scale that I'm not convinced the authorities have a good handle on. Residents should maintain disaster-proof stores of water, food, etc -- and predetermine nearby fire-refuges.

[Xithras]

8. Geologically, the entire Central Valley is a flooding "worst case scenario".

The Valley is flanked by three major mountain ranges and one short one. It's one of the flattest spots on the Earth, with only about a 150 foot elevation variance over its entire 450 mile length. It is fed by 13 rivers, and yet only has one outlet.

Before human engineering became involved, the Central Valley used to develop a 250 mile long inland sea nearly every wet winter. We channeled the rivers, built levees, and raised dams to keep that from happening, but we're always just one unlucky roll of the weather dice away from another major flood. This land WANTS to be underwater.

[xchrom]

10. +1 -- indeed.

that valley is in a wet zone and many homes are in fire zones.

in cali there is the problem of living where we really shouldn't.

[Gormy Cuss]

12. It was a shocker for me the first time I went through the Central Valley.

You really are at the bottom of a very large bowl.

I hadn't heard about the natural inland sea, but it makes sense.

[Xithras]

15. There are early photographs of it.

The Valley used to have two major water structures that don't exist anymore. The first was Lake Tulare, which was once the largest freshwater lake west of the Mississippi. Bigger than Tahoe. Bigger than Mono. Only the Great Salt Lake was bigger overall. They used to run steamboats on it, the lake once supplied half the freshwater fish to the markets of San Francisco, and it was written about by Mark Twain during his journeys through California. Like the Great Salt Lake, it was very shallow, and it completely evaporated when the rivers that fed it were diverted for irrigation. The land was converted for agriculture, and there is now almost no sign that a lake EVER existed there. The only evidence is a small section of its old shoreline that is still visible southeast of Kettleman City if you look on Google Maps. From the ground, there's no sign at all.

The second structure was the inland sea, which was really an extension of the SF Bay/Delta. The ground is so flat that the water would back up behind the Delta into one massive flood that would stretch nearly from Yuba City to Fresno, and would last for up to two months at a time. So much water flowed through the Delta that early records show that the salinity of the SF Bay itself dropped measurably during the winter as all that freshwater forced its way through the Carquinez Strait into the SF Bay. Early ships had to adjust their ballasts at different times of the year...a ship that would float in summer might sink during a wet winter because the lower salinity lowered the Bays buoyancy.

[Desperadoe]

11. Worse than the flooding

From what I have read, if the levees give way, it would open up the entire aqua system to saltwater from the Bay. This could destroy the entire farming system, as well as all drinking water. The kicker is that those levees are mostly very old earthen and should have been replaced many years ago.

[Xithras]

13. Temporarily, yes.

The Delta is naturally a freshwater ecosystem, but if ALL of the levees were to fail (major earthquake), the water to fill the land would have to come from somewhere. Physics says it would come from the Bay.

How long the salt would stay is heavily dependent on when that happened. If it occurred at the start of a wet winter, the saltwater would be flushed out within weeks as the higher inflow from the river systems displaced the saltwater back into the Bay. Short term damage to the Delta would be severe, but there would be few long term effects.

If this happened at the beginning of summer, the Delta would remain salty all summer because inflows from the rivers would be very low. The salt water would probably remain in the Delta until the following winter, completely destroying the ecosystem (not that much of the original ecosystem remains anyway).

The real problem is that most of the levees were built by the farmers, and not by actual engineers. They've been extremely resilient and reliable when you consider the fact that they are 100+ years old and were built by amateurs with no experience or training building earthen structures of ANY kind.