Engineer cites soil, design flaws in levee damage in New Orleans|[2/24/06]

Published 12:00 am Friday, February 24, 2006

Improving the design of levees and protecting against fast-rising storm surges using armor are two of the engineering lessons learned from Hurricane Katrina, said a co-author of an independent report studying levee failures in New Orleans.

Dr. Gordon Boutwell, president of Soil Testing Engineers Inc. of Baton Rouge and member of a Levee Assessment Team set up by the American Society of Civil Engineers to document and investigate levee failures, addressed about 100 fellow engineers at an annual luncheon for National Engineers Week at Vicksburg Auditorium on Thursday.

Boutwell presented photographs and statistical information from four areas of New Orleans taken by members of the ASCE’s team, which reviewed the work of a larger group set up by the Army Corps of Engineers, the Interagency Performance Evaluation Task Force.

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Additionally, Boutwell pointed out differences in the way Orleans Parish and Jefferson Parish pump out storm water to Lake Pontchartrain from small outfall canals.

In Jefferson Parish, pumping stations are atop levees to pump the water away from the canals. In Orleans, there was no such system in place.

Design of the I-wall system at the 17th Street Canal, the parish line between the east bank of Jefferson and Orleans, needs to be modified to fit better estimations of soil slope strength, Boutwell said.

&#8220That was classic soil slide,” Boutwell said.

The soil strength was averaged using too broad of an area along the levee, Boutwell said, leaving the overall safety of the floodwalls compromised.

Levees were breached at London Avenue, in the eastern side of the city, causing a scope of destruction in the Ninth Ward neighborhood that Boutwell compared to the bombing of Hiroshima during World War II.

Boutwell illustrated how water quickly seeped into a level of sand 12 feet underneath the levee at London Avenue and created a &#8220bottom heave” effect, where water burst through the clay layer above it to breach the structure.

Armoring the inland side of levee structures is a critical method of protecting against &#8220scour,” or the steady peeling away of earth due to rushing water that causes overtops.

The lack of armoring along the city’s 350 miles of levees and floodwalls was listed in a joint report by the ASCE and the National Science Foundation as a principal weakness in the system’s pre-Katrina condition.

Blocking drainage canals to ensure that water levels in them remain constant if Lake Pontchartrain rises is a necessity, Boutwell said, adding that previous efforts to do that was blocked by environmental groups and the levee board in Orleans Parish.

Ten analysis teams comprise IPET, primarily from inside the government.

The first of three IPET investigative reports on the levee failures was issued in January and is available on the IPET Web site,

The second and third reports, dealing with structural analysis, are slated for public release March 10 and May 1 respectively.

IPET’s final report is due June 1.

The ASCE/NSF joint report on the levee failures in New Orleans was released within the past week. It recommended the Army Corps armor all levees in the area as soon as possible and update models used to establish storm threats to the region.

Streamlining organizational control within the Corps and on the local government level, especially with local levee control authorities, was also recommended.

The ASCE/NSF report is available at the ASCE Web site,