Dredging led to deep trouble, experts say

The Times-Picayune ^ | Friday, December 09, 2005 | Bob Marshall and Sheila Grissett

[UpTurn]

When the New Orleans Sewerage & Water Board developed a plan in 1981 to improve street drainage by dredging the 17th Street Canal to increase capacity for Pump Station No. 6, residents across the city applauded. Increasingly heavy rains were not only flooding streets, but also pushing water into homes. Action was needed. It seemed like a no-brainer.

Today, forensic engineers investigating the levee breach that flooded much of city during Hurricane Katrina aren't so sure. The search for the cause of the failure keeps returning to that dredging project as the probable starting point for a series of mistakes engineers think ultimately led to the breach.

[rellimpank]

--"You can't do only one thing" --

[Rumplemeyer]

This explains a sketch I saw in Engineering News-Record showing the cross section of the canal at the failure locations, it showed the existing steel sheetpile wall toe above the invert of the canal.

This explains why the sheets rotated and failed, there was not sufficent force to prevent the water from pushing the top of the sheets away from the canal, what brain trust allowed them to dredge below the toe depth?

These sheets probably needed to be 10 to 12 feet BELOW the dredge line.

[Capt. Tom]

Ear witnesses know what caused the leevee to fail.

And they so testified before congress.-Tom