Are your flood plans adequate?

[subgard]

Check this out
https://en.wikipedia.org/wiki/ARkStorm
https://en.wikipedia.org/wiki/Great_Flood_of_1862

Native Americans knew that the Sacramento Valley could become an inland sea when the rains came. Their storytellers described water filling the valley from the Coast Range to the Sierra.

A Harvey-like flooding can happen without a hurricane, apparently.

Not wanting to start the whole climate change debate (please don't), but it seems like these kind of events will occur more frequently from now on.

https://www.washingtonpost.com/news/won ... dfcf12b348
If you own a house anywhere in a 1000 year floodplain it seems to make sense to purchase flood insurance, or get out.

Also, just physical safety plans. An event like the 1862 flood would cause serious problems across much of the West. I know I'm not currently prepared for something like that.

[George the original one]

Harvey caused me to review my stay-or-flee decision matrix. The common theme you find for significant floods along the Oregon coast (and Willamette Valley) is heavy snowpack melted by a "pineapple express", which are warm tropical rains powered by a fast jetstream from the direction of Hawaii.

A "pineapple express", on its own, will usually push the coast range rivers just over flood stage and some of the Willamette Valley streams. This is the typical seasonal flooding that we'll see 1-5 times per year and you're an idiot for living in any affected floodplain. Floods of this size are routine, minor annoyances, that can temporarily block transportation routes, so one has to be prepared to sit them out. Depending on the wind strength and soil saturation, falling trees can become a significant hazard (another reason to stay put).

So my re-analysis focuses on deciding whether to wait out the flooding elsewhere rather than at home. If there has been significant snowpack AND a sizeable pineapple express is on the way, then evacuation is probably more prudent. For us the risk is traveling on what could still be an ice-covered highway over the coast range, yet if we're going to go, then we need to do it before landslides or treefalls block the highway which can often happen during a pineapple express. The risk of staying put is lack of electricity (routine, fine for a week or longer -- but annoyed -- and a generator would extend that) and the chance of having our well overrun by floodwaters (not good, major bummer).

By neighbor accounts, the Oregon flood of 1996 might have barely overrun the well (1964 was the next prior large Oregon flood and this well did not yet exist nor have I found anyone with memory of the neighborhood conditions then).

***
I don't intend to diminish the ugliness that is a flood, but flood insurance is really for replacing a home after a rare flood. Most of the homes affected by the Harvey rains are flood-damaged rather than needing replacement. Most homeowners will go through the process of ripping out carpeting, soggy insulation, saturated wallboard, and treating for mold while getting on with life. Flood insurance is also rather limited in how much is paid out; I seem to recall the payout is only about 50% of the replacement cost, which is one reason why few people bother carrying any unless the lender requires it.

[Ego]

Tyler Cowen has been talking about the moral hazards of our current mispriced flood insurance schemes as well as the perverse incentives that come up when the government bails out those who plan to rebuild in the same flood zone.

https://www.bloomberg.com/view/articles ... -the-storm

One of the great things about not owning property is that I don't lose much sleep about this kind of stuff. If our place flooded, I'd probably salvage and secure what I could, then help get friends and family secure before grabbing the bug-out-bag and buying a one-way ticket somewhere fun. I got a new water filter a few months ago and forgot to put it in the bug out bag. The images from Harvey reminded me why I needed to do so immediately.

Our biggest risk is an earthquake. We live on the first floor of a hundred-year-old apartment building, built just a few hundred feet from one of the two major faults of Southern California. So.... splat.

[Jean]

I live in an unfloodable place. There are many of them. But why not build on pillars?

[Chris]

But why not build on pillars?

Raising a house is expensive, so people will generally only do it if there is a high likelihood of flooding (some beach houses) or if the economics make sense (insurance cost). More property owners have been doing this since Katrina and Sandy.

[bryan]

https://geography.wr.usgs.gov/science/mhdp/index.html (has other risks in CA), you can find links to the actual report for ARkStorm.

Interestingly, in the report they mention that most dams are designed to withstand such a storm. However, it is assumed that the dams are in good condition (i.e. regular inspections and maintenance and (fully?) operational). I would assume dam failures would exacerbate the damage/risks from an ARkStorm.

"According to this study, total flood-induced building damage is estimated at $200 billion." (2010 or 2007...) (Business interruption at $590 billion).

"Only perhaps 12 percent of California property is insured, so millions of building owners may have limited or no ability to pay for repairs."

"6 megastorms that were more severe than 1861-1862 have occurred in California during the last 1800 years, and there is no reason to believe similar storms won’t occur again."

"Unlike earthquakes, for the ARkStorm there exists a capability to partially predict key aspects of the geophysical phenomena that would create damages in the days before the storm strikes."

A disaster on this scale (Central Valley, Silicon Valley, LA) would spread recovery efforts incredibly thin for a long time (whereas they are more prepared for short recoveries for small areas).

I'm not sure how safe it is to filter/boil flood waters (which may have picked up some really nasty stuff)?

[subgard]

The ARkstorm planners seem to be just focused on California, but the 1862 flood affected the entire West, from Mexico to British Columbia.

A disaster on this scale (Central Valley, Silicon Valley, LA) would spread recovery efforts incredibly thin for a long time (whereas they are more prepared for short recoveries for small areas).

That would probably be the worst consequence. Be prepared for being without some utilities for months, possibly. (I can hear the preppers saying "Well, duh!")

[7Wannabe5]

In many areas it is not as easy to estimate risk due to complexity increase caused by human infrastructure. This article discusses the problem of buried urban streams in my region.

http://greatlakesecho.org/2016/04/11/gr ... w-streams/

[George the original one]

Buried streams are less of a problem than paved-over swamps. Houston, New Orleans, Miami, D.C. are all paved-over swamps with limited high-ground. They are just big bathtubs waiting to be filled up.

[jacob]

We also live on a paved-over swamp (With clay soil) but at least we're not at sea-level.

Paving and building increases run off in maximally built metro areas that haven't prioritized water absorbing green space (because it doesn't bring in as much tax revenue). So the more people and buildings, the worse the problem. Old housing stock and infrastructure did not plan for the massive increase of humans the following decades saw.

We live in an area that regularly gets minor flooding. Standpipes are practically synonymous with the neighboring burbs. Most of the housing stock was built when there was less housing stock (I know that sounds contradictory). So standpipes were added later.

What a standpipe does is to keep the water out of your basement while sending it into other people's basements. Same as what elevating the land on your property. In our area, plumbing had grease traps because the cooking habits were different in the 1940s. The grease trap is a few inches higher than the drain, so the standpipe doesn't provide much protection (given the number of people who now have the $20-400 standpipe installation).

So the city has promoted flood valves on the main sewer line by subsidizing $1500 of the $3000-6000 cost. Like before, this increases the problem on those who don't have them or can't afford them.

Recently the city has been handing out two free rain barrels to whoever wants them. This decreases the pressure on the sewer system (Chicago has a shared system for both sewage and rainwater so getting that shit (literally) backed into your basement is not nice) because rain that originally ended up on the roof and then on the ground now ends up the barrels.

Most houses around here used to direct their downspouts directly into the sewer. I'm not sure whether this is illegal now, but I haven't seen houses where the downspouts haven't been disconnected.

So clearly this is a retreating battle.

PS: When we were out looking for houses in a few years ago, most of the cheap ones we looked at have minor amounts of mold issue in the basement. People had been building extra rooms w/o taking care to install any flood control ... perhaps because it wasn't needed 10-20 years ago.

PPS: While building/raising a house on stilts seems like a good idea in case of flooding, it's a rather terrible idea in case of a tornado.

[Laura Ingalls]

@Jacob

We also live in an area where the existing infrastructure is old we have flood valve and a sumo pump that runs without electricity.

We have also had water two inches deep in the entire basement I think a whole French drain system would help but it would probably double the capital we have in this house

Anyway we tend to get anxious when we have hard rain.

[Kriegsspiel]

My apartment is like, 120 feet above the ground. As long as nobody above me blows a pipe, I do not fear water.

[Riggerjack]

On a ridge, on an island. I'm good until sea level rises more than 300 feet.

But, this is earthquake country, earthquakes cause avalanches, which can in turn cause tsunami, waves that can wipe out up to 400 up an opposing slope. In Washington, nobody is ever really safe.

[enigmaT120]

I'm on a ridge at about 600 feet. The Willamette Valley would be an inland sea before it got up to me. But yeah, earthquake. Or forest fire.

[George the original one]

Florida's hurricane Irma evacuations seem like deja vu as far as reminding everyone that getting out at the last minute is usually a poor decision. It's not quite the last minute yet, but the systemic stress is building now: gas lines, store shelves emptying, confrontations escalating, soon to be accompanied by traffic jams at the exits.

I wonder what first responders choose to do? And how do the non-car owners proceed with their own evacuation?

[jacob]

There are a bunch of livestreaming channels on youtube that switches to whatever cable news station is currently covering it. Enjoy!

Images I've seen:

• Home Depot lumber shelves (you know those floor to ceiling orange ones) with absolutely nothing left on them all the way down to the end wall.
• Ditto random supermarket.
• Cars lining up around the block to pick up 10 (TEN!) free sandbags.
• Interstate moving north at around 20-30mph.
• People going to and being interviewed on the beach because they didn't want to join the fray yet (Yes, seriously!)
• Gas tankers (trucks) are being escorted around by the cops to keep the gas stations pumping. People are instructed NOT to fill up in case they only evacuate to the next county.
• SpaceX launched the military's reusable vehicle before they packed up.

So that was today ... well in advance.

In terms of windspeed Irma (which is the strongest/biggest ever recorded hurricane---it's wider than the state) compares to having a strong F2 tornado hanging over your roof for 45 minutes. Also storm surges around 10ft. Keep in mind that FL is quite flat and almost at sea level if not under (parts of Miami). Ten sandbags per house is not really gonna cut that.

According to the authorities, first responders will eventually evacuate and not be available. (You're on your own.) Some places have mandatory evacs. For those without vehicles: School buses and the likes IIRC. Keep in mind that one doesn't having to evacuate all the way out of the state ... just the several dozen miles out of the highest windspeed regions (which aren't known yet).

PS: Jose is projected to double-tap some of the Caribbean islands that got razed yesterday.

[Riggerjack]

So, if we are talking 10 foot storm surge, how do you make it a few dozen miles from the highest winds, as a safe zone? Is there a 10 foot hill anywhere in Florida?

I was just kicking this around in my head. People have live in Florida forever, there have been storms forever. So how do you survive one of these in older times with less warning? My first thought was dig a hole, tornado shelter style, but 10 foot storm surge makes that not work at all. So if you get high enough to keep your head above water, you get high enough to experience the full wind effects. I'm a pretty good swimmer, but those winds make the surface of the water pretty much unswimmable, as you couldn't get a breath of air without a lot of water in it.

Can't go high, can't go low, can't stay, can't go, what was the pre-auto age solution? Repopulate afterwards?

[George the original one]

Spanish forts made from big stones with 20'-30' high walls.

Isn't Jacksonville about 25' above sea level?

[George the original one]

"Making the decision to stay is often made by people who feel they have a strong social support system who will help them through the hardship, a study published by the American Meteorological Society earlier this year found. The study was based on data gathered during 2016's Hurricane Matthew, which flooded northeast Florida, destroying homes in St. Augustine and the surrounding area with floodwaters.

"We got the opposite results from what I expected because those who stayed and who were under mandatory evacuation, they had more dependable social networks than those who evacuated," said Jennifer Collins, one of the University of South Florida researchers who conducted the study. "Their neighborhoods and local communities — they felt very comfortable to hunker down with them."

From https://www.yahoo.com/news/despite-thre ... 45059.html

[jacob]

This is an example of the "anti-surge". Or rather this missing water (not literally, but figuratively) is currently sitting under and around the eye making the bulge that is locally seen as a surge as the hurricane moves over an area. Since it is finite in volume, it will not cover all of Florida even if the surge is higher than the "highest mountain" in FL.

https://www.youtube.com/watch?v=cOw_i61lads

(Sea level is often thought of a fixed distance from the Earth's center that is everywhere the same (when waves are subtracted) but that is not the case. Pressure and currents change local/regional/continental conditions by several feet.)