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$4 billion construction bonanza: a big hole for the Big Easy?

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The good news is that many flood risk reduction projects for SE Louisiana are on schedule for construction in the near term, as described by Mark Schleifstein in today’s New Orleans Times Picayune.  The New Orleans district office of the Corps of Engineers has obviously been scrambling to build the engineering capacity to bolster levees and install pumps and water control structures at an unprecedented pace.  

The $4 billion program described includes a number of the major components of the plan to provide protection from a so-called 100 year storm for the New Orleans region by the year 2011.  This will obviously provide lots of work and help the Louisiana economy – assuming that some of the folks employed live and pay taxes in Louisiana!

On a more sobering note I call your attention to a very critical element of the story, the volume of clay required to complete this construction program: 

Corps officials also believe they’ve identified enough sources of quality clay to raise levees throughout the system to the 100-year protection level.

“The total we need is about 75 million cubic yards,” (Col. Gregory Gunter, operations officer for Task Force Hope) said. “We’ve already identified 60 million cubic yards as suitable material and we still have 65 million cubic yards under investigation.”

The volume of clay required for a levee is approximately proportional to the square of the elevation of the levee.  In other words a levee thirty feet high requires about nine times as much clay as a ten foot levee. 

Seventy five million cubic yards of clay represents a square hole 3 feet deep and 1.64 miles on a side.  It is important to keep in mind that Katrina is estimated to have been a 300-400 year storm.  If 75 million cubic yards of clay will be required to protect against a storm with a 1% annual likelihood of occurrence and each foot of additional levee height requires considerably more clay, protection against a 500 year storm sounds extremely challenging, just from the standpoint of clay availability – not to mention the size of the remaining hole!

Len Bahr

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  2. Mark Schleifstein says:

    Re: the clay cubed scenario. That’s one reason the corps is using T-walls on the St. Bernard levees, to reduce the width, and thus the amount of clay, though they’re phrasing the reason in terms of cheaper land acquisition costs for the smaller footprint. Expect to see similar adjustments as the 100-year projects go forward. And more “innovative” methods, such as hollow concrete shells for larger levees or multiple lines of levees with “water storage” wetland areas between (a version of your artificial chenieres), IF LACPR era levees are attempted. Of course, that requires vigilence on the part of the public to assure all the structures are designed, engineered, built properly. And a recognition of the remaining risk to the public.

    Thanks for linking to the story.

    Mark

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