Corps: Lessons from Katrina are being put to work

Published 12:00 am Sunday, August 30, 2015

The U.S. Army Corps of Engineers learned the hard way about the consequences of trying to contain Mother Nature.

Michael Sharp, technical director of the Corps’ Engineering Research and Development Center Geotechnical and Structures Laboratory, and research geologist Joseph Dunbar said the lessons from Hurricane Katrina have resulted in changes made since to improve the levee and floodwall systems’ abilities to survive future storms.

“We typically learn for our mistakes,” Dunbar said.

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“It an eye-opening experience for the Corps,” Sharp said.

When Katrina made landfall Aug. 29, 2005, a combination of erosion caused by water topping levees and the geology of the area around New Orleans contributed to the failure of the flood walls and levees and led to the widespread flooding that hit the city as the storm made its way inland, according to research by ERDC’s Geotechnical & Structures Laboratory.

As it moved inland, Katrina’s storm surge pushed excessive amounts of water into the waterways that crossed and surround New Orleans, overwhelming the pumps and the levee and floodwall systems protecting the city.

In many areas, water topped levees and I-wall barriers — concrete sheets driven in the ground — collapsed causing breaches in other levees.

“What the Corps needed to understand was the magnitude and the nature of the failures that occurred,” said Dunbar, who was part of a Corps team that included people from the National Science Foundation and the American Society of Civil Engineers that went to New Orleans to study the problems. “You had levees that washed away that were in the Mississippi Gulf Outlet. You had major construction components of the I-wall system overwhelmed — they failed.”

The ERDC study looked at two things: the structures, and the effect of the area’s geology on the protection systems.

“It’s all about understanding the structure and how it will perform,” Sharp said. “We have lab testing going on, which is small scale stuff. We also do some larger-scale testing where we actually build a model of the structure itself and subjected to loading and see how it will perform. The things we look for are will that structure stay intact once it’s subjected to the storm, or will it fail?”

Some of the tests look at phenomena like subsurface erosion, where water is placed in part of a small tank of soil to see how the soil responds and whether it is porous enough to allow the water to form a channel through the layer.

“They’ve (engineers) looked at ways to harden the levees; to put different material on the levee, either natural materials or synthetic materials, to try to make the levee as resistant to erosion as possible should it be topped again,” he said.

Part of the problem affecting the structures, Dunbar said, is New Orleans’ location in a delta region formed years ago by the Mississippi River.

“We did a forensic investigation of the various failures,” he said. “Many years earlier, I mapped the delta, and the geology was a big part of what caused some of the failures. There’s a major beach ridge that goes under New Orleans. Before land was there, there was this extensive barrier island under some of those walls, and some of the deposits were causing uplift of the soils which undermined the foundation of the walls.”

Because the area is in a delta, Dunbar said, there is natural subsistence, or reduction in the ground level, “so there were parts of the system that may not have been to the grade or the elevation it was designed for.” That, coupled with the increased development in the New Orleans area, he said, reduced the elevation of some of the levees in the city.

“The level of protection, which is the height of the levee, has to be authorized by Congress, because building it bigger takes more money,” Sharp said.

“It’s multi-year process to construct all those levees, so they were not all at the level they should have been. Because of the time to construction, the soil subsidence was at varied levels.”

“When a lot of the flood walls were built, they were built to a designed flood event,” Dunbar said. “Especially in the Ninth Ward, where the Inner Harbor Navigation Canal passed, the water got so high in there, it just overtopped. It was not built to withstand that level of storm.”

“New Orleans has just about rebuilt its entire levee system that was damaged,” Dunbar said. “They’ve done a number of things. They’ve moved their pumps out to the front of the canals, they’ve rebuilt the walls that were damaged (and) they’ve changed the design of those walls as a result.”


About John Surratt

John Surratt is a graduate of Louisiana State University with a degree in general studies. He has worked as an editor, reporter and photographer for newspapers in Louisiana, Mississippi and Alabama. He has been a member of The Vicksburg Post staff since 2011 and covers city government. He and his wife attend St. Paul Catholic Church and he is a member of the Port City Kiwanis Club.

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