Wednesday, April 29, 2009

Change the odds

A new report from the National Academy of Sciences generated sensational headlines recently. Unfortunately those attention-grabbing headlines and the ill-informed commenters that responded all seem to have missed the major point.

The report, The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness, was most widely quoted as declaring that New Orleans can never be made safe. The most popular quote appears to be this one: “Levees and floodwalls surrounding New Orleans -- no matter how large or sturdy -- cannot provide absolute protection against overtopping or failure in extreme events.”

Many seemed to have stopped reading right there and joined one of two opposing camps: those who say it’s hopeless and we should quit wasting time and money trying to do the impossible in New Orleans, and, those who say scientists, engineers and politicians who would surrender the city to nature are either idiots or cowards.

They're both wrong.

A more careful reading of the report, available online, reveals that the true intent of the engineer and scientist authors is to fully alert the public to the stark reality of residual risks. That is to say, no matter what science concocts or what government provides, it is neither possible nor realistic to expect all danger to be removed.

Is this surrender to the whims of nature? No. It is a plainly stated view of reality. The world is dangerous. We can do many things to reduce danger, but there’s always a risk. There’s always a risk.

Is this a cry of hopelessness? Again, no. Scientists and engineers accept the challenge head-on. Humans are naturally proud, stubborn and intelligent enough to figure things out. Some may crumble and compare the struggle for survival to the punishment of Sisyphus, but most of us are stout-hearted and bold with resolve.

And here’s what the NAS report recommends: don’t rely entirely on levees and floodwalls. Build smart. Choose wisely. Be proactive.

A levee is no guarantee. New Orleanians have had water in their homes many times when there was not a hurricane in sight. One example is May 3, 1978, a date many of us remember. Torrential rain filled the streets and flooded cars and houses in Orleans, Jefferson and St. Bernard Parishes.

A floodwall is no guarantee. Even if the new floodwalls are rock solid and bulletproof, there is always the possibility of a storm surge taller than the wall. The current goal is to build a system to stop a 1% per year chance exceedence flood. But as I've blogged before and as the NAS report points out, that so-called 100-year level of protection is really pretty small when you think about it.

The odds might be 1 in 100 if you live here for 1 year, but each successive year the odds get worse and worse. If you live a full 72 years in New Orleans, there’s a 52% chance you will experience that big flood that will overtop the floodwalls.

The major point the NAS wanted to make is that levees and floodwalls are just part of the answer. The rest is up to us.

So what can we do?

First, understand that the levees and floodwalls form the perimeter defense. Once water overtops or falls as rain inside the system, water is going to pool in the lowest parts of the city. Even when the pumps are going full bore—and we have the best pumping system in the world—we know we can still be flooded. If at all possible, we should build on naturally high ground.

After Katrina, I lived for a while in the “Sliver by the River.” That part of the city remained dry not because of better floodwalls or pumps—it was purely natural elevation that spared the homes and businesses there.

Secondly, we have to elevate our homes. Slab-on-grade houses are modern, less expensive and dangerous. I speak from experience here. My Gentilly home was just too darn low. Houses like that are just tempting fate. Every foot above the ground adds safety from flooding.

Thirdly, we have to build above the inadequate and dangerous 100-year level of protection. Not just levees and floodwalls—I’m talking about houses here. When the city issues a building permit, they will give the 100-year elevation required to qualify for the National Flood Insurance Program. That’s the MINIMUM elevation for construction. Why stop there? Add a foot. Add two or three.

Remember that the 1% per year exceedence flood will occur sooner or later. There’s a 26% chance it will happen in 30 years, and a 39% chance in 50 years. Those are not good odds.

We can change the odds by building higher.

Finally, buy insurance. All of the things I discuss above can and will reduce your exposure to the risk of flooding, but nothing is going to totally eliminate the danger. If all else fails, your final safety net is flood insurance to lessen the financial blow.

Just as seatbelts, airbags, and all the safety systems of a modern highway will not guarantee survival in the event of a car accident, the NAS wants everyone to understand that levees and floodwalls, no matter how high or sturdy, cannot guarantee safety from flooding. There is always some residual risk. And just as safe driving habits will bring us safely home, smart building and planning will go a long way to keeping our homes safe.


Clay said...

Yeah, the writeups of the report were awful. Can't trust English Majors to get it write.

I came away with the same conclusion you did: 100-year storm protection is the problem. Good to see scientific recognition of what the locals have figured out the hard way.

mominem said...

The New Scientist has horrible.article entitled "Levees won't save New Orleans from another Katrina" They don't even link to the study, so you can follow up.

Jeff said...

The low parts of New Orleans should be restored as floodplain, in order to provide buffer to the naturally higher elevated parts of the City.