Do the 500 year flood plain designations need to be revisited?

Factual Questions
1

I realize that it’s statistically possible to have 500 year floods spaced anywhere along a 500 year timeline, because in the long run that’s how it shakes out, historically. But is it?

We’ve had 3 of them in the midwest in the last 15 years. I don’t want to bring up the term that rhymes with noble norming, but my layman’s brain is thinking that we might need to have another look at whether these designations remain accurate. Again, I understand that these events occurring in that space of time are quite statistically possible; that’s not what I’m getting at, though I know you can’t ignore statistics.

I’m thinking that insurance companies, etc. might start to bring pressure to bear on FEMA/USGS, etc., because they base rates on those designations and I’ll bet they’re taking a bath (heh) right now.

Any dopers with more expert knowledge than myself (ain’t saying much) have any thoughts on this?

(If this is IMHO, my apologies…the hampsters are screwing the pooch right now and I don’t want to lose this…)

2

[QUOTE=An Arky]
I’m thinking that insurance companies, etc. might start to bring pressure to bear on FEMA/USGS, etc., because they base rates on those designations and I’ll bet they’re taking a bath (heh) right now.
[/QUOTE]

Most insurance companies exclude flood damage so I’m not sure they’re an influence on FEMA/USGS as suggested.

That said, I’m curious about the responses to this. My house is in a little trickle of flood zone on a FEMA map. The house next door and one across the street are not on the mapped zone. It’s rather annoying really.

We have to buy separate flood insurance to make our mortgage holder happy.

3

Yeah, I was a little non-specific on that. Sorry…

But still there are Powers That Be (like mortgage holders) that base things on those maps that represent mucho dinero…seems like some formerly 500 year flood plains might be more prudently labelled 100 year flood plains. The economic ramifications could be quite significant, I would think.

4

[QUOTE=An Arky]
I realize that it’s statistically possible to have 500 year floods spaced anywhere along a 500 year timeline, because in the long run that’s how it shakes out, historically. But is it?

We’ve had 3 of them in the midwest in the last 15 years. I don’t want to bring up the term that rhymes with noble norming, but my layman’s brain is thinking that we might need to have another look at whether these designations remain accurate. Again, I understand that these events occurring in that space of time are quite statistically possible; that’s not what I’m getting at, though I know you can’t ignore statistics.

I’m thinking that insurance companies, etc. might start to bring pressure to bear on FEMA/USGS, etc., because they base rates on those designations and I’ll bet they’re taking a bath (heh) right now.

Any dopers with more expert knowledge than myself (ain’t saying much) have any thoughts on this?

(If this is IMHO, my apologies…the hampsters are screwing the pooch right now and I don’t want to lose this…)
[/QUOTE]

Well you will be happy to know that the 500 year flood for your area is being updated. In fact, it is updated (sooner or later, takes times to crunch the numbers) every time there is a flood in a floodplain. The problem isn’t that the folks doing the calculations are bad at math and picked an unreasonably low flood level for a 500 yr flood, it is just that is what the data supports. The USGS and the Corps of Engineers (depends on what floodplain you are in) takes all the recorded information and plugs it into a model. Out pops the 500 yr flood level. More data=new level. Garbage in = Garbage out.

As for the Insurance companies, they don’t care-they don’t offer insurance for flooding. FEMA cares, but they are under tremendous pressure to keep the flood zones small and the rates low and the payouts high and… Well you get the idea.

One piece of advice: there is NO place in the US where flood insurance isn’t a good idea. I would buy flood insurance (if available) in the middle of death valley or the top of Pikes Peak. If flooding is extremely unlikely, the rates will be silly cheap. If the flooding is unlikely, the insurance is a vital, well insurance, to have. And remember, buy early. You lock in the zone when you buy a house. Even if new maps come out, you are in the zone that covered your house when your house was built and when you bought your insurance. If they discover later on that you are 4 ft below sea level (I live in Louisiana so I have friends who are) but at one time you were in flood zone C and bought insurance-your rates will be favorable. It is to encourage people to buy insurance.

5

If we can pump oil from Alaska to the Lower 48, why can’t we pump water to places that need it from places that have too much? Just wait – next year there’ll be a drought and we’ll wish we had a way to store some of this excess water.

6

[QUOTE=rbroome]
Well you will be happy to know that the 500 year flood for your area is being updated. In fact, it is updated (sooner or later, takes times to crunch the numbers) every time there is a flood in a floodplain. The problem isn’t that the folks doing the calculations are bad at math and picked an unreasonably low flood level for a 500 yr flood, it is just that is what the data supports. The USGS and the Corps of Engineers (depends on what floodplain you are in) takes all the recorded information and plugs it into a model. Out pops the 500 yr flood level. More data=new level. Garbage in = Garbage out.
[/quote]
Couldn’t have said it better myself.

Nitpick: Its the NFIP (National Flood Insurance Program), a part of FEMA.

Absolutely correct. HOWEVER, if the community you live in does not participate in the NFIP then you cannot buy flood insurance from the NFIP. Private flood insurance is nonexistant.

An Arky, this is a brief run-down of how the NFIP does the mapping:

The different flows are calculated (as mentioned above) by either USGS or COE. They use regional equations which are based on measured data. These equations are updated about every 10 to 20 years.

Then computer modeling is used to model these flows down the river channel & floodplain. This predicts the water levels. These models are updated more rarely- in some places we are using models which are 30 years old.

So, in answer to your question, hydrologists are anxious to include new data from flood every time one occurs. It just takes time for that data to be processed and the maps redone.

You may find this thread to be of interest: Ask the Certified Floodplain Manager.

Auntie Pam: That will happen when water becomes as expensive as oil. The enormous cost of those pipelines would have to be justified.

7

When you finance a property, either purchase, refi or equity your lender is required by federal lending laws to have a report sent that determines using the available FEMA maps as to if your home is in a flood zone. If your house is in a flood zone, your lender will force you to purchase and maintain flood insurance. FEMA isn’t out anything if your house floods and it’s not in a flood zone, they’re just trying to make things a decent risk on a standard 30 year mortgage. They’re not a guarantee that the house won’t flood, just an indication of your risk level.

I’ve worked with these things for years, they’re mostly automated these days and based off of your zip code. If you don’t like the findings on the FEMA maps for your area you can obtain either an elevation certificate that establishes that your home sits high enough above flood levels that you’re off the hook, or FEMA occaisonally issues LOMR (letters of map revision) that you have to keep forever to prove that you’re not in the flood zone. Still tough titty if your house floods.

8

[QUOTE=Cluricaun]
If you don’t like the findings on the FEMA maps for your area you can obtain either an elevation certificate that establishes that your home sits high enough above flood levels that you’re off the hook, or FEMA occaisonally issues LOMR (letters of map revision) that you have to keep forever to prove that you’re not in the flood zone.
[/QUOTE]
Right. You have to show that your lowest habitable finished floor elevation is above the Base Flood Elevation. That includes the under-floor beams for some types of structures.

The smart way to do that is: get your LOMR-F (Letter of Map Revision Based on Fill), so that your home is removed from the zone; then get your flood insurance re-issued. The cost will be very low, but you’re still protected from the peril of flood.

Note that the NFIP is funded solely by premiums.

9

[QUOTE=AuntiePam]
If we can pump oil from Alaska to the Lower 48, why can’t we pump water to places that need it from places that have too much? Just wait – next year there’ll be a drought and we’ll wish we had a way to store some of this excess water.
[/QUOTE]
At the risk this is a whoosh, we must take into account the price of oil compared to the price of water, with consideration given to how much an average person uses each day of each.

10

[QUOTE=NinetyWt]
Note that the NFIP is funded solely by premiums.
[/QUOTE]

Of all the times I’ve waited with my meager fistfull of Things I Know A Lot About on these boards I have to run into a flooder on this one. :smiley:

The NFIP is an example of good government at work. It costs nothing to taxpayers and actually does some good. Pay attention to these things. The poor folk in Lake Delton Wisconsin were dropped from the NFIP because…well, they’re not too sure yet which means that none of those homeowners were even able to have flood insurance. I have my own opinions as to why I think that it happened, but this is GQ so I’ll save those for some other time.

11

[QUOTE=Cluricaun]
Of all the times I’ve waited with my meager fistfull of Things I Know A Lot About on these boards I have to run into a flooder on this one.
[/QUOTE]
At least you were vindicated, that you are right. :wink:

As to Lake Delton, check out that thread I linked. Harmonious Discord mentions that very thing:

[QUOTE=Harmonious Discord]
What can people who are in a community that doesn’t have the option of federal flood insurance do to change it. Last year it was announced that a certain town that has residents that really wanted it, couldn’t get the insurance. How do they make the community one that participates.
[/QUOTE]
Perhaps now the idea will gain some traction.

Also from that thread, Wisconsin just got re-mapped - I had forgotten that.

12

Thanks for the very informative answers!

Just one point of clarification, if I may…I don’t have any sort of problem with how it’s done; I simply was wondering if they indeed remapped when significant events occur. The answer appears to be yes, and I think that’s a good thing.

13

[QUOTE=Santo Rugger]
At the risk this is a whoosh, we must take into account the price of oil compared to the price of water, with consideration given to how much an average person uses each day of each.
[/QUOTE]

Not a whoosh. This one flood has already cost billions. Why can’t we do more to manage our water resources? Canals, levees, pumps, reservoirs, artificial lakes, underground storage – it’d be an engineering and environmental and aesthetic challenge, but we need to figure it out.

14

[QUOTE=AuntiePam]
Why can’t we do more to manage our water resources?
[/QUOTE]
Costs and environmental reasons, mostly. Otherwise we’d be doing it. We already have canals, levees, pumps, reservoirs, artificial lakes, and underground storage; it’s not a matter of engineering but of scale.

Then there is the issue of water rights. Here is an interesting article about the ‘water war’ in the western U.S.

[QUOTE=An Arky]
I simply was wondering
[/QUOTE]
Darn. Here I was thinking I’d given you a fascinating glimpe of the scintillating world of floodplain mapping.

15

Actually, you did. Thanks, NinetyWt!

My floodplain mapping story:

Back in the early 90s, I worked for a Emergency Management software company, and I was given a project to take a paper floodplain map and digitize it to make an overlay for a county in WV along the Ohio River (their Emergency Management Dept. was our customer). By digitize it, I mean lay it on a table and trace my mouse along the outlines of the 100 and 500 year floodplains. It was a PITA, but somewhat interesting.

16

I’m a bit surprised that I’m the first to state the obvious: in America, engineers simply don’t (yet) have 500 years of data to work from, so the 500-year flood plains have always been no more than educated guesses. (At least they’re honest enough to rework their estimates when new data shows the old estimates to be wrong.)

17

[QUOTE=BJMoose]
I’m a bit surprised that I’m the first to state the obvious: in America, engineers simply don’t (yet) have 500 years of data to work from, so the 500-year flood plains have always been no more than educated guesses.
[/quote]

Sure, if you want to call using a generalized least squares regression analysis to crunch all the numbers to predict the 0.2%-chance flow an “educated guess”. :wink:

I agree with you about the years of record for the data. There are also other factors in the accuracy of flood-frequency estimates. These include measurement or computational errors, use of unrepresentative probability distributions, and time-sampling errors. In regards to the mapping, error is introduced at every level - surveying, modeling, drafting. That’s why the map zones are properly referred to as “zones of risk” as mentioned above by Cluricaun.

The bottom line is that streamflow characteristics and floodplain delineation can only be estimated - nobody will really ever know what the “real” 1%-chance flood is. The best we can do is use the data and methods we have to try to predict these zones of risk.

Thanks for the compliment, but this is misrepresentative; sounds like the hydrologist grudgingly picks the study back up and revises it. In actuality, we are very interested in any results which new data will bring - it’s like solving a puzzle. We actively seek out new data and methods to try to increase the accuracy of streamflow estimation. We call our colleagues after a big rain and want to know “what did your raingage read??” The hitch in our get-along is getting funding for studies.

18

[QUOTE=NinetyWt]
Right. You have to show that your lowest habitable finished floor elevation is above the Base Flood Elevation. That includes the under-floor beams for some types of structures.

The smart way to do that is: get your LOMR-F (Letter of Map Revision Based on Fill), so that your home is removed from the zone; then get your flood insurance re-issued. The cost will be very low, but you’re still protected from the peril of flood.

Note that the NFIP is funded solely by premiums.
[/QUOTE]

It’s not just finished floors. It’s any structure on the property. A structure being defined as a building that has walls (generally agreed to be three walls) and a roof. So a garden shed, for instance, which is located on your property, and is in the flood zone, would trigger the lender to require flood insurance on your property.

The fines for lenders can be large, and in fact, are about to be increased as soon as the president signs the newest revision to the law.

I say this knowing that my institution will be paying fines of approximately $125,000 this year due to problems with our processes last year. And even if we find the problems now, and fix them, and no loss resulted because of our poor procedures… we still pay.

19

[QUOTE=whatami]
So a garden shed, for instance, which is located on your property, and is in the flood zone, would trigger the lender to require flood insurance on your property.
[/QUOTE]

An important distinction is that this depends upon the lender. Just as the lender can require you to have earthquake insurance or PMI, they can require you to have flood insurance. The NFIP does not require it (they do encourage it).

The finished floor elevation I am referring to lets the insurance actuaries set the premium rate for the structure. I’m not familiar with trying to get outbuildings removed from the floodplain - I wonder, would that also remove the insurance requirement? After all, the structure is what’s insured, not the land. (Crop insurance is different).

Is this legislation you refer to pertaining to banking or the NFIP? I don’t see it on my ASFPM Legislation list (and I’m curious).

20

Out of curiosity, I looked into the insurance side of the NFIP and learned a bit about lenders and insurance. Here is the link to the FAQ page.

Of interest are answers to questions 27, 28, 29, 32, 34, 36, and 38.

#32 says that flood insurance is mandatory as a conditon of federal or federally related loans. I’m glad I looked that up, I was a little hazy on that - I apologize for my above statement which is incorrect (concerning the NFIP not requiring flood insurance).

#34 says “if the lender determines that the structure is within the SFHA” then flood insurance will be required. I would take that to mean the insurable building - not the entire property, although I have heard many times of banks which consider the entire property “in” if even a corner touches the floodplain. Are lenders interpreting this more broadly? I know that after the Midwest floods of the 90’s , many lenders became stricter on flood policies.

#38 says that normally one building and its contents can be insured, but a separate policy can be written for other buildings. (From 2 to 10 buildings).