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Thu November 20, 2008 - Southeast Edition
NEW ORLEANS (AP) Subterranean termites that have infested New Orleans since World War II may be a much bigger threat to this city’s levees and floodwalls than many experts suppose, a new entomological paper said.
For the past 70 years New Orleans has been battling the voracious wood-eating Formosan termites that arrived on military ships returning from the Pacific. But that battle has mostly taken place at the neighborhood and street level, ridding homes and buildings of the pest.
A new article in the Entomological Society of America’s magazine, American Entomologist, said there is ample evidence termites are infesting the city’s levees and floodwalls and potentially weakening flood defenses.
In his article, “The Termite Menace in New Orleans: Did They Cause the Floodwalls to Tumble?,” Louisiana State University AgCenter termite expert Gregg Henderson said engineers in New Orleans are not taking the termite threat seriously enough.
In March 2006, Henderson presented his concerns to the Interagency Performance Evaluation Task Force, the Army Corps of Engineers’ investigative team looking into Katrina breaches. Henderson’s concerns were not included in the team’s reports.
The corps, which is overseeing levee reconstruction, said it was aware of the termite threat but did not consider it a factor in the 50 major breaches during Hurricane Katrina that contributed to the flooding of 80 percent of New Orleans.
“We did not find any evidence of that as a problem with any of the failure sites right after Katrina, but that doesn’t mean that it’s not a problem in New Orleans,” said Ed Link, a University of Maryland engineer who led the corps investigation. The termite factor is “not something that can be ignored, but it’s something people are aware of,” Link said.
The corps believes a combination of design flaws and the massive storm surge from Katrina stressed and broke the levees.
The danger to levees posed by rodents, insects and other earth-digging creatures such as crawfish is not a new concept. Worldwide levee managers try to keep levees free of wildlife.
In his paper, Henderson argues that engineers need to do more research to understand and attack the termite problem.
Henderson said he has found evidence of termites in many places where floodwalls collapsed with catastrophic effect.
“Everywhere we’ve looked on the 9-mile stretch [of the London Avenue] was infested with Formosan termites,” Henderson said. The canal’s floodwalls breached in two places.
He said material in the floodwall seams — a combination of compacted rubber and sugarcane waste known as bagasse — had been eaten through by termites. And the same has occurred throughout New Orleans’ extensive floodwall system.
Termites eating away at mats in floodwall seams, though, may not be the biggest threat. The paper said damage termites cause underground needs to be understood.
Relying mostly on research from China, Henderson said the insects’ behavior poses a threat to a solid levee.
That’s because termites dig deep into the ground as they nest and pursue food. In the process, they build elaborate colonies with populations in the millions. Termite galleries have been known to span areas as large as football fields and go as deep as 28 ft. below ground.
As they dig, the insects also displace huge amounts of soil, the paper said. Some researchers calculate that termites can move about 4,410 lbs. of soil per hectare — a little less than 2.5 acres — each year.
“The changes in the soil profile caused by termite gallery construction are likely to change such soil properties as stability, infiltration rate, permeability, and water holding capacity,” the paper said.
This digging — known as “piping” — is so bad in China that researchers there said about 1,700 dike failures since the 1950s were caused at least in part by burrowing termites, the paper said.
The termite that’s wreaking havoc in New Orleans is a native of southern China and the South Pacific.
Formosans have spread in Louisiana at an alarming rate. The first intense U.S. survey of Formosans was in New Orleans in 1966. Back then, researchers found about 9 percent of telephone poles were infested. Traps on telephone poles have recorded growing numbers of insects. For example, in 1989 about 500 wings were obtained on catches at light posts and that number grew to 17,374 wings by 1999, the paper said.
Gene Kritsky, a biologist at College of Mount St. Joseph in Cincinnati and editor-in-chief of American Entomologist, said Henderson’s work poses questions that have been ignored.
“He’s not a lone voice out there, but he’s the first one to take the trouble to write something up about termites and levees,” Kritsky said. “We must make sure that corrections to the levees don’t make them susceptible to termites.”