Flash Flood Alley Segements

Assessing Your Flood Risk

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Your chances of being flooded are much greater than some other risks you face daily. If you live in a 100-year floodplain, there is more than a 1 in 4 chance that you will be flooded during your 30-year mortgage. During a 30-year mortgage period you are 27 times more likely to experience a flood than having a fire.

Event % chance of happening during the next year
25-year flood 4 chances in 100
Involved in a
car accident
3 chances in 100
Some form of cancer 3 chances in 100
Victim of larceny 2 chances in 100
50-year flood 2 chances in 100
Victim of burglary 1 chance in 100
Injured in a car accident 1 chance in 100
100-year flood 1 chance in 100
Victim of auto theft 1 chance in 300
Victim of
aggravated assault
1 chance in 500
Victim of robbery 1 chance in 1,000
Residential fire 4 chances in 10,000
Killed in car accident 3 chances in 10,000

Source:
Floods and Your Family brochure,
U.S. Army Corps of Engineers

Understanding the "100-year floodplain"

The first thing you need to know about the concept of a 100-year floodplain is that it is based on a statistical probability needed by the insurance industry as a standard upon which to base policies. Both the federal government and the private sector assist the insurance industry in gathering scientific measurements that are then used to generate a "*best guess" of stream flow peaks over a time. All this information goes into a formula/statistical model that generates elevations on tracts of land throughout a watershed that have "one-in-one hundred chance (1 percent) of occurrence of flooding in any given year, or a "return period" of once every 100 years."


100-year floodplains are not arbitrary but they are:
1. Limited to the "best information at the time"
2. Not a determination of where and how frequently actual flood damage will occur.
3. Subject to change


*We say "best guess" for several reasons, chiefly that streamflow data has only been collected for a maximum period of 150 years (much less in many areas) which is a small sampling in the context of regional weather patterns and actual flood events.


Read more

The "100-Year Flood" USGS Fact Sheet: http://water.usgs.gov/pubs/FS/FS-229-96/

 
  • Properties can also be at higher or lower risk within a floodplain depending where in the floodplain they are located. For example, one house in the 25-year floodplain may flood 2 feet deep during a storm, but their neighbor deeper in the floodplain may flood 6 feet deep.
  • If you are a typical homeowner, living in a single-story $100,000 home, without a basement, you can expect to suffer the following damages to your house and contents:
    1 foot of water = $14,000
    3 feet of water = $27,000
    Also add the cost of cleanup of mud and residue.

    Source: Floods and Your Family brochure, U.S. Army Corps of Engineers.

  • Myths:
    • Floods only happen to other people.
    • It has never flooded here, so it never will.
    • There was a flood problem, but it has been fixed.
    • If flooding were a problem, someone would have told us. That's why we pay taxes.
    • It's only water. It's no big deal to be flooded.
    • The government will bail me out.
    • My homeowner's policy will cover any flood damage.
    • We just had a "100-year flood", so my family will be safe from future floods for the rest of their lives.
  • Facts:
    • We can't predict when floods will occur, but we can usually tell where they will occur.
    • Just because it hasn't flooded in the past doesn't mean it won't in the future.
    • Just because you had a flood does not mean it won't happen again soon.
    • FLoods are caused by weather conditions and are unpredictable. If the conditions are right, floods will occur again.
    • It is almost impossible to "fix" a flood problem.
    • Real estate agents usually don't know whether flooding has ever occurred on the property.
    • Government assistance after a flood is usually limited to loans which have to be repaid. Who needs a second mortgage?
    • Figuring out how to cope with a flood is your responsibility.

    Source: Floods and Your Family brochure, U.S. Army Corps of Engineers.