Natural Disaster

From The_Velvet_Rut, a link to the online Pic:

17th Street Canal levee was doomed
Report blames corps: Soil could never hold

The floodwall on the 17th Street Canal levee was destined to fail long before it reached its maximum design load of 14 feet of water because the Army Corps of Engineers underestimated the weak soil layers 10 to 25 feet below the levee, the state's forensic levee investigation team concluded in a report to be released this week.

That miscalculation was so obvious and fundamental, investigators said, they "could not fathom" how the design team of engineers from the corps, local firm Eustis Engineering and the national firm Modjeski and Masters could have missed what is being termed the costliest engineering mistake in American history.

The failure of the wall and other breaches in the city's levee system flooded much of New Orleans when Hurricane Katrina slammed ashore Aug. 29, prompting investigations that have raised questions about the basic design and construction of the floodwalls.

"It's simply beyond me," said Billy Prochaska, a consulting engineer in the forensic group known as Team Louisiana. "This wasn't a complicated problem. This is something the corps, Eustis, and Modjeski and Masters do all the time. Yet everyone missed it -- everyone from the local offices all the way up to Washington."

Team Louisiana, which consists of six LSU professors and three independent engineers, reached its conclusions by plugging soil strength data available to the corps into the engineering equations used to determine whether a wall is strong enough to withstand the force of rising water caused by a hurricane.

"Using the data we have available from the corps, we did our own calculations on how much water that design could take in these soils before failure," said LSU professor Ivor van Heerden, a team member. "Our research shows it would fail at water levels between 11 and 12 feet -- which is just what happened" in Katrina.

Not deep enough

Several high-level academic and professional investigations have found that the sheet piling used in the design to support the floodwalls was too short for the 18.5-foot depth of the canal. In addition to holding up the concrete "cap" on the walls, the sheet piling is supposed to serve as a barrier preventing the migration of water from the canal through the porous soils to the land side of the levee, an event that rapidly weakens the soils supporting a wall and can cause it to shift substantially.

The corps has long claimed the sheet piling was driven to 17.5 feet deep, but Team Louisiana recently used sophisticated ground sonar to prove it was only 10 feet deep.

Van Heerden said Team Louisiana's latest calculations prove investigators' claims that a depth of 17 feet would have made little difference. He said the team ran the calculations for sheet piles at 17 feet and 16 feet deep, and the wall still would have failed at a load of 11 to 12 feet of water.

To the east, the MRGO, if I remember right, contributed heavily to the flooding in St. Bernard Parish. And while I haven't seen any reports re: either the Industrial or London Avenue canals, I wonder if breaches on each might also be due to faulty design/construction. In other words, the disaster wasn't all that natural after all.

I can't think of a single place on earth that's NOT vulnerable to a disaster of some kind--fire, flood, blizzard, drought, earthquake, tornado--you name it. But saying NOLA--and the Gulf Coast--ought to be written off is wrong on so many levels...and it's now becoming clear that the biggest problem facing the city was not the storm itself, but reliance on assurances of protection that turned out to be false.

If this was only a matter between private concerns, it'd be the tort case of all time...

It's certainly proper to identify the faults--and who's responsible--but right now I think the real lesson is achingly clear: as Schroeder and others continue to point out, the City needs GENUINE protection from serious storms like Katrina--but, just as important, MUST also have systems in place that can be counted on for normal, mundane, everyday flood protection too. And I guess we can't rely on mere assurances from the Corps, or their contractors: someone with training needs to watch over them, double check the work, and ensure they're doing what they claim to be doing. Maybe university researchers can be tapped for this oversight position...at any rate, it needs to be done.

I just wish the problems had been noticed BEFORE the fact.