April 26, 2009
New Orleans Not Protectible From Extreme Flooding?

A report from the National Academy of Engineering and the National Research Council argues that either people should be moved out of part of New Orleans or their houses should be elevated against flooding.

WASHINGTON -- Levees and floodwalls surrounding New Orleans -- no matter how large or sturdy -- cannot provide absolute protection against overtopping or failure in extreme events, says a new report by the National Academy of Engineering and the National Research Council. The voluntary relocation of people and neighborhoods from areas that are vulnerable to flooding should be considered as a viable public policy option, the report says. If relocation is not feasible, an alternative would be to elevate the first floor of buildings to at least the 100-year flood level.

This report looks at lessons learned in the aftermath of Hurricane Katrina.

The report is the fifth and final one to provide recommendations to the Interagency Performance Evaluation Task Force (IPET), formed by the U.S. Army Corps of Engineers to examine why New Orleans' hurricane-protection system failed during Hurricane Katrina and how it can be strengthened. The previous four reports by the NAE and Research Council examined various draft volumes of the IPET. This report reviews the 7,500-page IPET draft final report, reflects upon the lessons learned from Katrina, and offers advice for how to improve the hurricane-protection system in the New Orleans area.

Since New Orleans continues to sink while the coast continues to erode the situation there is going to become more precarious with time. Efforts to divert more of the silt in the Mississippi into flood plains could slow (reverse?) the erosion. That would lessen the demands on the levees. But this report argues that levees and floodwalls can't guarantee safety.

Although some of the report's recommendations to enhance hurricane preparedness have been widely acknowledged for years, many have not been adequately implemented, said the committee that wrote the report. For instance, levees and floodwalls should be viewed as a way to reduce risks from hurricanes and storm surges, not as measures that completely eliminate risk. As with any structure built to protect against flooding, the New Orleans hurricane-protection system promoted a false sense of security that areas behind the structures were absolutely safe for habitation and development, the report says. Unfortunately, there are substantial risks that never were adequately communicated to the public and undue optimism that the 350-mile structure network could provide reliable flood protection, the committee noted.

The Dutch decided to create barriers that can be extended to hold back the sea during severe storm conditions. This greatly shortens the length of water-land interface that they have to defend against worst case sea levels. I'd like to know why the authors of this report do not think this strategy will work for New Orleans. Is the cost too high? Or does the geology of the area make that approach unworkable?

Comprehensive flood planning and risk management should be based on a combination of structural and nonstructural measures, including the option of voluntary relocations, floodproofing and elevation of structures, and evacuation, the committee urged. Rebuilding the New Orleans area and its hurricane-protection system to its pre-Katrina state would leave the city and its inhabitants vulnerable to similar disasters. Instead, settlement in areas most vulnerable to flooding should be discouraged, and some consideration should be given to new designs of the New Orleans metro hurricane-protection system. As part of the future design, relocation of some structures and residents would help improve public safety and reduce flood damages.

The Netherlands takes a far more aggressive approach toward flood protection because it is a small country and doesn't have the choice of abandoning a substantial fraction of its territory. Whereas America is much larger and the people of New Orleans could live elsewhere. Rather than design for 100 year events the Dutch design for 1250 to 10,000 year events.

Urbanized areas of the country - such as the region surrounding Ter Heijde, which includes The Hague and Rotterdam - are engineered to withstand the kind of storm surge that comes only once in 10,000 years. More sparsely populated areas, such as those protected by the Delta Works, are safe against a 1-in-4,000-year flood. The lowest level of protection, found in rural areas, is for a 1-in-1,250-year flood. All are many times safer than New Orleans ever was.

If the land values of southern Louisiana are not high enough to pay for the most extreme flood protection then the most aggressive flood prevention approach does not seem justified to me. Obviously we can expect many denizens of New Orleans to disagree.

Share |      Randall Parker, 2009 April 26 10:26 PM  Engineering Large Scale


Comments
Mthson said at April 27, 2009 3:13 AM:

Climate models that are "generally accepted as conservative" predict all of New Orleans will be underwater by 2050 or 2100 (New Scientist 2009). That prediction assumes no climate-engineering.

Some Micronesian islands are already having to relocate to Australia and New Zealand (ibid.).

Anonymous said at April 27, 2009 7:21 AM:

s/silk/silt/, I presume.

"If the land values of southern Louisiana are not high enough to pay for the most extreme flood protection then the most aggressive flood prevention approach does not seem justified to me."

As long as voluntary economic transactions are ignored and outlawed by feudal lords in the capitol, the value of the land to the people using it isn't going to make much of a direct difference. There's always indirect, though (rent-seeking).

In the coastal areas of Texas, houses are usually elevated. I know sinking puts a different spin on it, but do they really not do it in New Orleans?

bbartlog said at April 27, 2009 8:35 AM:

Unless the erosion of the barrier islands can be stopped, the ocean will eventually take New Orleans down. Assuming that the Mississippi River doesn't take it out first via delta switching. The city simply isn't in a stable position.

crescentCityRay said at April 27, 2009 9:19 AM:

You left out some of the report's findings and recommendations.

The Science Panel's report agreed with IPET findings that the outfall canal floodwalls fell down long before even being overtopped because of engineering mistakes made by the US Army Corps of Engineers. Although the cause is still disputed for some of the other 48 breaches, the Science Panel kind of agreed with IPET that most of the rest of the breaches were caused by erosion from storm surge water overtopping those structures.

The report said New Orleans should get a storm surge protection system to protect from a higher storm surge than what is expected during a storm with a 1 in a 100 chance of hitting in any given year, as is the current plan.

The most important recommendation was that the US Army Corps of Engineers reform to the extent that they would at least accept some small form of oversight from local government engineers, like the ability to review Corp designs of our flood control structures.

Regarding the report's elevation recommendations and smaller footprint idea. Isn't it irrelevant for them to say what we should have done? Families that were flood victims only had one shot at recovery. The Road Home Program is almost finished. Moronically, RHP is giving out elevation money last. Who could afford to wait this long? We already rebuilt. We did the best we could with what we had and built smaller, stronger and above the flood line.

If civil engineers cannot design a levee or floodwall to remain upright against a storm surge then they should have their PE taken away. The article serves to give the Corps a pass on their mistakes that destroyed so much. The whole american society of civil engineers has been campaigning to convince everyone that the levee failures were not their fault. They would prefer you blame us stupid no good for nothing locals for our losses.

Allan said at April 27, 2009 9:34 AM:

It all comes down to cost benefit analyses.

Should the US fund the levees to protect New Orleans to such a high level of protection? Should the US continue to control the path of the Mississippi which as resulted in the erosion of the delta that once protected New Orleans?

My reply is no, the US shouldn't unless there is a resulting economic benefit to the US that is more than the cost of the levees.

If Louisiana and New Orleans want to fund the levees, then let them but expect the US to fund levee construction above that needed to keep commerce moving up and down the Mississippi.

Shannon Love said at April 27, 2009 10:38 AM:

Given that pre-Katrina, New Orleans had a poverty rate of 30% it appears that the city cannot economically support big parts of its population. Does it really make sense to spend billions of dollars to build dykes just to trap tens of thousands of poor people down in a hole below sea level? The poor parts of the city are the ones in the lowest areas while the economically self-sustaining areas are already largely above sea level. It would be cheaper and more human to pay poor people to relocate to safer areas. Then we could fill in the low areas over a period of years thus turing New Orleans into an island as the French Quarter is now then rebuild on top of it. Or we could just turn the areas into parks or build elevated housing.

It makes more sense to turn New Orleans into a low-population, high cost, upper income domain like San Francisco. That way it will be easier to protect the city and if that fails, the people who stay there will at least be able to afford their own funerals.

Blastula said at April 27, 2009 1:40 PM:

Poor people beget poor people. Since they typically have low IQs, they cannot fend for themselves and must be taken care of by the state, the feds, and the Army Corps of Engineers. The least that should be done is to move the most helpless and incompetent persons out of harms way, so that their children's children's children will not be drowned by the next Katrina in 60 years.

Randall Parker said at April 27, 2009 7:40 PM:

crescentCityRay,

Who should pay for the system needed to protect New Orleans from a really big storm? The people of New Orleans or the rest of us? If the rest of us then why the rest of us?

People who already rebuilt: Gotta say, doing that before sufficient protection is in place seems very imprudent to me.

I do not see the irrelevance of the recommendations since not everyone has rebuilt.

Blame: Well, the locals should certainly have the power to look at designs regardless of the funding sounce. But I'd say they'd have originally had the power to look at designs if they were paying for them with locally raised money spent by local agencies.

John Mooree said at April 27, 2009 8:25 PM:

New Orleans has a huge interface to protect, because it has large canals running throughout the city. Furthermore, it is subject to flooding from the E (the bay) and N (Lake Pontchartrain ). Many of these canals have thin floodwalls, rather than levees. However, even the levees to the E were overtopped by Katrina's all time record storm surge.

Long before Katrina, I attended a talk by Dr. Bob Sheets, then head of the National Hurricane Center. He said his greatest nightmare was a Cat 3 hurricane headed for New Orleans. Katrina was a Cat 5.

Houses in NO are not built elevated (except some of the replacements post-Katrina). A very large part of the city is below the normal water level, much less the flood levels.

Given the large length of perimeter to be protected, and the limited real estate in which much of that protection must sit (without major eminent domain actions)A probabilistic failure analysis would show there is zero room for error, material failure, or other adverse events. Hence it is not really practical, and certainly not wise, to try to protect N.O.

Had Katrina not changed course at the last moment and suddenly dropped in intensity (which didn't reduce the surge), wind damage would have leveled the residential areas of the city even if the floods didn't.

The good news is that downtown and the French Quarter - the historic heart of N.O. were mostly untouched by the flooding. This is not a coincidence - the site for the French Quarter (built by the Spanish) was chosen because the Indians said it had the least flooding. It is the residential sprawl where the main problem lies.

If the locals want to pay to try and protect NO, fine. I don't think the rest of us should.

crescentCityRay said at April 28, 2009 5:49 AM:

The Science Panel's report ALSO agreed with IPET findings that the outfall canal floodwalls fell down long before even being overtopped because of engineering mistakes made by the US Army Corps of Engineers. Although the cause is still disputed for some of the other 48 breaches, the Science Panel kind of agreed with IPET that most of the rest of the breaches were caused by erosion from storm surge water overtopping those structures - which civil engineers think is forgivable.

We paid our local cost share and waited forty years for the Corps to design and build the levees that fell down.

In New Orleans, we all knew there would be LIMITED flooding if the levees were overtopped by storm surge waters during a hurricane. No one but the Corps knew our outfall canal floodwalls would fall down like movie props before water even rose half way up the wall.

The most important recommendation was that the US Army Corps of Engineers reform to the extent that they would at least accept some small form of oversight from local government engineers, like the ability to review Corp designs of our flood control structures. You left that out.

Regarding the report's elevation recommendations and smaller footprint idea. Isn't it irrelevant for them to say what we should have done? Families that were flood victims only had one shot at recovery. The Road Home Program is almost finished. Moronically, RHP is giving out elevation money last. Who could afford to wait this long? We already rebuilt. We did the best we could with what we had and built smaller, stronger and above the flood line.

As you reported, the report said New Orleans should get a storm surge protection system to protect from a higher storm surge than what is expected during a storm with a 1 in a 100 chance of hitting in any given year, as is the current plan. Hopefully, we will never know if the structures they are rebuilding are reliable structures designed by competent engineers.

New Orleans requires reliable engineering structures that won't fall down when they encounter water, regardless of their height. Engineers are capable of building such structures. It is negligence to build knowingly unreliable engineering structures.

Randall Parker said at April 28, 2009 6:32 PM:

I read "our local cost share" as "a small portion of the total cost".

Rebuilding before the needed level of protection was known - let alone built: That seems very irresponsible. Shouldn't people be responsible for their own choices?

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