"Dredging could have contributed to levee failure"
Tags: levees, floodwalls, army corps of engineers, universities, 17th street canalFrom this:
When the New Orleans Sewerage and 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 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 they believe ultimately led to the breach…
Before the project, the canal formed a roughly symmetrical “U” shape common to most canals. In the sections that would later fail during Hurricane Katrina, its average depth was about 12 feet below sea level and, at normal water levels, the Orleans side had about a 20-foot buffer of mud between the water and what was then a bare steel flood wall. That wall of sheet piling ran through the center of the levee to a depth 9.8 feet below sea level.
After the dredging, the bottom was 18.5 feet below sea level, and the canal-side levee had been shaved so narrow, water now touched the wall on the Orleans side. The “U” was now lop-sided and the water in the canal had shorter paths to the outside of the levee.
A review of records maintained by the two levee districts hasn’t yet revealed why more extensive dredging was done on the Orleans side of the canal than on the Jefferson side.
“I’ve never seen a canal profile unbalanced like that, and I can’t account for why it was done that way,” said Bob Bea, a University of California-Berkeley professor and member of the Science Foundation team…
