[StBernard] don't gamble

[Westley Annis]

I just read a very well-written article by the president of the LA section
of the American Society of Civil Engrs. that explains very simply what your
risk is of being flooded. To those of you still weighing future flood
insurance issues, to those of you in positions that interact with FEMA's
base flood elevations, perhaps this will put it in perspective.

After Katrina, the Corps of Engrs was authroized to repair and rebuild
levees to "levels of protection necessary to achieve the certification
required for participation in the National Flood Insurance Program under the
base flood elevations"

Now what does that mean, you ask.

That means that levees need to provide for "a 100 year level of protection".
Doesn't that sound impressive?

Well, it's impressive if you mistakenly believe that this means a levee that
will be overtopped once in 100 years.

If you're in this business as an engr, insurance underwriter, or scientist,
you know what it means. It means that the risk every year is determined by
an equation and in that equation each year that the event doesn't happen
merely increases the probability that it will happen. In plain English, if
you live in a place for 30 years, during that time you would have a 1 in 4
chance of the levee being overtopped. These are not acceptable odds to many
of us. If you live 73 years behind a flood levee system, then you have a 1
in 2 chance of the levee being topped during your lifetime. 

This holds true when FEMA says its maps are based on the 100 year rainfall
event. It does not mean a rain that happens once in 100 years. It means the
a .01 percent probability of annual exceedence. Same odds as stated above
for levee overtopping.

Bottom line-if you consider the probability of a levee being topped, PLUS
flooding due to rains heavier than the canals and pumping stations can keep
up, PLUS the risk of a pump station having a mechanical or electrical
failure, PLUS the risk of levee or floodwall being split open by a runaway
barge or faulty design or construction, YOU WOULD NEVER BE WITHOUT FLOOD
INSURANCE AND YOU WOULD WANT TO BE RAISED AS HIGH AS YOU COULD AFFORD TO
BUILD and STILL GET HOMEOWNER'S INSURANCE.  

All this back and forth about base flood elevations should not lure those in
B zones to think they will not be flooded.  If you want to lower the risk,
then don't live behind a levee system with a pumped drainage system and if
you do, have enough insurance.  If you live outside of a levee system, you
still have the same odds that the rain will overwhelm your creeks and
streams if you live close to them.

The American Society of Civil Engrs has called for clear communication to
decision makers and the public about risk.  And now, you clearly know what
the 100 year event means in terms of risk. Deborah Keller