This is a bit longer than anticipated, but......
Gibson,
It appears I was a bit off in parts of my guesstimate.
The highest levee in N.O. that I could find is 18.5 ft.according to the Corps of Engineers (the average seems to be between 6 to 12 ft) and instead of 30 to 40 miles of levees, there are 350 miles :
http://www.mvn.usace.army.mil/pao/response/amaps.asp
I found little on the actual dimensions needed to withstand a Cat 5 but the dimensions I quoted in the previous post appear fairly accurate. I found a forum where a group of engineers were discussing the issue:
http://www.eng-tips.com/viewthread.cfm?qid=133257&page=1
http://www.eng-tips.com/viewthread.cfm?qid=133153&page=1
A little bit about the levees history from National Geographic:
http://news.nationalgeographic.com/news/2005/09/0902_050902_katrina_levees.html
A few interesting articles on funding problems and subsidence.
http://alternet.org/story/24871/
http://news.yahoo.com/news?tmpl=story&u=/ap/20050905/ap_on_re_us/katrina_corps_spending
http://www.pbs.org/newshour/bb/weather/july-dec05/levees_8-31.html
Found this and had to include it in its entirety. From:
http://blogs.chron.com/sciguy/
My colleague, Ed Hegstrom, shared an excerpt from Mark Twain's "Life on the Mississippi" with me this afternoon. The book's discussion of the Army Corps of Engineers, published in 1883, only affirm's Twain's brilliance:
"The military engineers of the Commission have taken upon their shoulders the job of making the Mississippi over again -- a job transcended in size by only the original job of creating it.
They are building wing-dams here and there, to deflect the current; and dikes to confine it in narrower bounds; and other dikes to make it stay there; and for unnumbered miles along the Mississippi, they are felling the timber-front for fifty yards back, with the purpose of shaving the bank down to low-water mark with the slant of a house roof, and ballasting it with stones; and in many places they have protected the wasting shores with rows of piles.
One who knows the Mississippi will promptly aver -- not aloud, but to himself -- that ten thousand River Commissions, with the mines of the world at their back, cannot tame that lawless stream, cannot curb it or confine it, cannot say to it, Go here, or Go there, and make it obey; cannot save a shore which it has sentenced; cannot bar its path with an obstruction which it will not tear down, dance over, and laugh at.
But a discreet man will not put these things into spoken words; for the West Point engineers have not their superiors anywhere; they know all that can be known of their abstruse science; and so, since they conceive that they can fetter and handcuff that river and boss him, it is but wisdom for the unscientific man to keep still, lie low, and wait till they do it.
Captain Eads, with his jetties, has done a work at the mouth of the Mississippi which seemed clearly impossible; so we do not feel full confidence now to prophesy against like impossibilities.
Otherwise one would pipe out and say the Commission might as well bully the comets in their courses and undertake to make them behave, as try to bully the Mississippi into right and reasonable conduct."
Of course Twain was talking about levees along the Mississippi, not those protecting the city from Lake Pontchartrain.
But the analysis is eerie all the same.