Monday, March 05, 2007

100-year protection is not enough

The Times-Picayune printed an Op-Ed I wrote in the Saturday, March 3 edition. I don't know why but it does not appear to be available online. It was adapted from my column recently published in The Louisiana Civil Engineer, the official journal of the American Society of Civil Engineers Louisiana Section. Here is the original version of what I submitted to the TP.

Update: It is now available online here.


100-year protection is not enough

There is an enormous amount of work being done right now on the hurricane protection system in the New Orleans area. Under orders from congress and the president, the Army Corps of Engineers is designing levees to meet the requirements of the National Flood Insurance Program (NFIP). That is, levees to provide a so-called 100-year level of protection.

This is a mistake for two important reasons.

First, I would argue that a 100-year level of protection is not an appropriate level of safety for densely populated, highly developed areas. Second, the terminology employed is easily subject to misinterpretation, giving a false sense of security to residents that may in fact cause more harm.

The National Flood Insurance Program (NFIP) selected the 100-year event as its benchmark. They use it to establish Base Flood Elevations and as the basis for the insurance they provide for buildings and contents.

The 100-year event might make perfect sense for property insurance, but it is woefully inadequate as a benchmark for life safety. Here’s why:

What the so-called 100-year event really means is there is a 1 percent chance that the design capacity will be exceeded in a given year. Engineers refer to this as the probability of annual exceedence.

A 1 percent chance may sound like good odds to the layperson, but engineers and scientists know better. That’s because as years go by, we know the odds get worse because the probability of exceedence accumulates with each year.

So while there may be a 1 percent chance of seeing a damaging flood in any single year, the probability snowballs over many years. The laws of probability tell us that the risk of experiencing an event exceeding the 100-year level of protection over a 30-year period is a whopping 26 percent.

In the long run then, we can expect more than one out of four homes with the 100-year level of protection to be flooded within the time span of a typical mortgage. And the chances get worse each year.

From the property insurance perspective of the NFIP, we might be able to justify the financial risk of building and maintaining development exposed to such peril. From a life-safety point of view, the risk would certainly be unacceptable to society—if it were properly described.

This leads to my second argument against the 100-year level of protection: the public is misled by the terminology and so does not understand the statistical implications of a 1 percent probability of annual exceedence.

A lot of people misinterpret the “100-year” terminology to mean “once in 100 years,” and you could not fault them if they did so. As just shown, however, that is not at all what it means.

I have no doubt this misunderstanding of the risk of flooding encourages inappropriate development such as slab-on-grade houses. Worse, I suspect it may influence people’s decision to evacuate or not. Anyone who thinks, “It only happens once in a hundred years,” may decide to stay when the next hurricane comes—with potentially deadly results.

As an engineer obligated and dedicated to protecting the public, I am greatly concerned that we have learned little or nothing since 2005.

Policymakers need to understand that the hurricane protection system does not simply protect property—it safeguards lives, too. Levees and other components of the hurricane protection system must be considered life safety features and should be designed, constructed and maintained with appropriate diligence.

Everyone living and building in the New Orleans area must understand that flooding can and will happen, no matter what their NFIP flood zone classification. Elevation to the BFE must be required, and additional elevation above the BFE should be strongly encouraged.

We’re all eager to rebuild New Orleans and revive the entire area. But our leaders must be honest and open about the risks of living here, and work to properly describe those risks.

The hurricane protection system should not be designed simply to satisfy the requirements of an insurance program. It must be designed, built and maintained with full realization that it protects lives—thousands and thousands of lives. To do less would be unconscionable.


Chuck said...


I saw it in the TP and enjoyed the read. Keep up the good work. Many like me still need to be educated in these things that we are ignorant of. Best to you and your family.
Go Big Blue!

pirx said...

Your explantion of terminolgy is admirable but I don't reach the same conclusion. In fact, levees DO primarily, protect property. In the extreme, the failure of levees threatens the lives of those who put their trust in them, so the very existence of levees is a risk factor. The lesson I took from 2005 is that evacuation saves lives. If the resilience of the levee system must be increased beyond the 100 year flood level because the general population is not educated to the risk, would it not be easier and less expensive to downgrade the levees to a 10 year flood level. No one could miss the lesson. Rational property investment would be restricted to a combination of property and structure designed to survive that guaranteed level of inundation. Thus the more resilient the levee, the greater protection for property.

Anonymous said...

Pirx, I disagree with you. My life is not restricted to breathing. My life includes friends, parks, restaurants, festivals, work, school and more. If you build a 10-year levee and I leave, and it floods and destroys all those things, I live, but I have lost my life. I don't disagree that a 10-year levee is cheaper than a 100-year one. But, in terms of an entire city: I think it is far easier and cheaper to add a foot to 200 miles of levees than it is to raise tens of thousands of individual structures one more foot. I think a large city, like New Orleans, should be protected from the maximum probable event (whatever that is) as dams are. Lastly, people are sometimes killed while evacuating.