Katrina flooding reasons still being debated
Overtopping, says corps; breaches, says LSU analyst
Wednesday, April 26, 2006
By Robert Travis Scott Capital bureau
BATON ROUGE -- Eight months after Hurricane Katrina, a heated debate continues over whether levee breaches or overtopping caused most of the flooding. Advertisement
While the Corps of Engineers contends that most of the damage from floods in the New Orleans area resulted from water topping levees, an analyst at Louisiana State University says that 87 percent of the flooding in the area was because of levee breaches and only 13 percent was from water flowing over the tops of the levees.
An upcoming report sponsored by the corps will show maps of the inundation of the metro area, including what conditions would have been like if levee walls had not breached, said Dan Hitchings, the civilian head of Task Force Guardian, the corps' effort to rebuild New Orleans area levees to pre-Katrina levels.
"The breaches just made it worse," Hitchings told the House Transportation Committee in a special hearing Monday. Setting the breaches aside, "We will all be surprised at how much water still came into the system."
More of the same?
Parallel to that finding, Hitchings said, if another Katrina-like storm hits close to New Orleans, everyone can expect approximately the same level of flooding. The corps is on track to fix the levees to pre-Katrina levels by June 1, the beginning of hurricane season, Hitchings said. But even at those levels, the same storm would produce about the same results, he said.
Hitchings said the report by the Interagency Performance Evaluation Task Force, the corps-sponsored panel investigating the failures, will be out in June.
His remarks stunned some members of the committee who have attributed much of the flooding, particularly in Lakeview, Gentilly, Old Metairie and many areas in Orleans Parish and downtown, to breaches in the 17th Street and London Avenue outfall canals, which were not overtopped.
The corps is putting gates near the mouth of those canals near Lake Pontchartrain to close them off against storm surges. That would prevent lake waters from pouring into the city through the canals in case of another canal wall breach, but Hitchings said that doesn't necessarily mean New Orleans will be spared deep flooding in another storm.
"A lot of that flooding came from the Industrial Canal as well," he said, adding that overtopping on the west side of the canal contributed to more flooding in the city than people generally know.
As for flooding in the Lower 9th Ward, St. Bernard Parish and eastern New Orleans, those waters were because of a combination of levee overtopping and to breaches caused by the overtopping, Hitchings said.
Ivor van Heerden, assistant director of the LSU Hurricane Center and a member of the Team Louisiana group that has been probing levee failures independent of the corps, said the corps' presentation is wrong.
"The corps seems to have taken a step backward and seems to have taken the approach of denial, once again," van Heerden said.
Breaches caused by overtopping must be counted as breaches and as faulty design by the corps, Van Heerden said.
"It's design, design, design," he said.
Van Heerden said storm surge models show 16 percent of the volume of water in the Orleans metro bowl, basically the area west of the Industrial Canal, was from overtopping, and the rest from breaches. Breaches were responsible for 92 percent of the flood water volume in St. Bernard Parish and 65 percent in eastern New Orleans, he said.
Overtopping would have occurred for up to three hours the day of the storm, totaling nowhere near the amount of sustained water flowing in because of breaches, he said.
J. David Rogers, an engineering professor at the University of Missouri-Rolla who is an expert on levee failures and a member of a National Science Foundation investigation into the disaster, said overtopping led to breaches and flooding in St. Bernard and in the east.
"But for Lakeview and Gentilly, I don't know what he is talking about," Rogers said of Hitchings.
There was overtopping on the western side of the Industrial Canal, but for at most six hours, he said. "It's not what caused everybody to leave their homes," Rogers said. "As a percentage of property damage, it's not significant."
Missing the point?
As for the 9th Ward, overtopping on the east side of the Inner Harbor Canal, which is the lower end of the Industrial Canal, led to a major breach that could have been prevented with inexpensive improvements, Rogers said.
"Had the structures survived the overtopping, you're talking nowhere near the kind of damage that ended up being suffered," Rogers said.
The corps' emphasis on overtopping tends to support the agency's case that Katrina's force exceeded the required heights of the area's hurricane protection system.
Rogers said the corps' focus on overtopping and levee height misses the point.
"When you build something to a certain level, and not the maximum level, then it has to be Category 3 survivable," Rogers said. "It's not just about Category 3 height, it's about Category 3 survivable."
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Robert Travis Scott can be reached at firstname.lastname@example.org or (225) 342-4197.