NRC report casts doubt on adequacy of levee protection for New Orleans

in Technical Issues by Admin — April 26, 2009 at 9:18 am | 2 comments

 

An article by Sheila Grissett and Mark Schleifstein in the April 25 Times-Picayune summarizes the conclusions of a newly released technical report by the National Research Council (NRC) challenging the realism of protecting New Orleans from even a 100 year storm, let alone a future Katrina. I strongly recommend reading the T-P article. Click here for a clear and comprehensive graphic look at the planned 100 year flood (1% per year probablilty of failure) levee system. 

If you activate the link to the NRC technical report you will see the following summary description:

April 24, 2009 – Levees and floodwalls cannot provide absolute protection for New Orleans 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 in vulnerable areas should be considered. If relocation is not feasible, the first floor of buildings should be elevated to the 100-year flood level.

According to Grissett and Schleifstein, the NRC report carries the warning that no system is fail-safe and faults the local political leadership for not taking long term risk into account in terms of the pattern of reconstruction of flood damaged neighborhoods. For example, Grissett and Schleifstein include this ominous statement:

“…the report warned that in this fourth year after Katrina, it looks like the New Orleans region has returned to a policy of business and building as usual.”

A related article by Paul Rioux in the same edition of the Times-Picayune once more raises the issue of sources of high quality clay needed to elevate levees around New Orleans by 2011.  The article focuses mostly on a disagreement among the owner of pasture land rich in clay, the corps and neighboring residents over danger posed by a newly-created 25 foot deep borrow pit and the price of land from which the clay will be “borrowed.” It seems that clay purchased as a commodity sells for $8/cubic yard but if purchased as agricultural land on a per acre basis the clay cost would be considerably cheaper ($1.7 million vs. $32 million).

I have an ongoing interest in the issue in terms of  the credibility of corps’ estimates of coastal sediment needs and sources. Rioux writes:

The corps estimates it needs 75 million cubic yards of clay — enough to fill 16 Superdomes — to raise more than 300 miles of levees by 2011 to protect the New Orleans area from a so-called 100-year storm, defined as one that has a 1 percent chance of hitting in any given year.

In a recent conversation with an acquaintance who works with the corps at the New Orleans District office on this isse (obtaining clay for levee enhancement) I was told that, despite repeated assertions from the district that the 2011 deadline will be met, there is considerable doubt among the folks in the trenches that there are enough trucks, highways, days and working hours in the day to transport, let alone put in place, the 75 million cubic yards in two years.

Whether or not this deadline can be met there is enormous interest in the higher level of protection that is the subject of the draft Louisiana Area Coastal Protection/Restoration (LACPR) plan that is currently under outside review, also by the NRC.  This plan was formerly known as the “Cat 5″ study.

In a previous post  I pointed out that raising existing levees follows a quadratic rule, i.e., the volume of sediment needed to construct a traditional earthen levee is proportional to the square of the overall levee height. For example, raising a twenty foot levee by one foot would require twice as much sediment as adding one foot to a ten foot levee. 

On the broad issue of providing coastwide protection beyond the 100 year standard, Amy Wold wrote an article in the April 15 Advocate describing a recent meeting to discuss the draft LACPR plan.  She reported that John Lopez, with the Lake Pontchartrain Basin Foundation criticized the plan for over-emphasizing levee protection at the expense of ecosystem restoration.  

I share this concern.

I would say more but the weather is perfect so I’m off to the Jazz Fest!

Len Bahr

Post jazz fest addendum: The high point for me at the Fairgrounds on April 26 was watching a fascinating interview with Pete Seeger, who celebrated his 90th birthday and shared some philosophical thoughts on the state of the Hudson River cleanup, the New Orleans recovery and the world. He is truly amazing.

The most provocative question from the audience was on Pete’s thoughts about reconciling sponsorship of the New Orleans Jazz and Heritage Festival by Shell Oil, in view of allegations about Shell in terms of the horrific state of human rights in Nigeria. Similar concerns have been raised locally about the long term damage of oil and gas production on the Louisiana coast and the major sponsorship by Shell of the America’s Wetland campaign.

Seeger’s response: we must talk to (and sing to) those with whom we disagree!