Levee tests gnaw at termite expert
Corps says insects didn't contribute to wall failure
A termite expert is questioning whether tiny, voracious Formosan termites played a role in the failure of levee walls in New Orleans during Hurricane Katrina.
Louisiana State University entomologist Gregg Henderson said there are clear signs that the destructive insects were present, and he wants the opportunity to dig into the levees beneath the walls to find out if termite nests contributed to their weakening. Army Corps of Engineers officials, however, say no evidence has been found to indicate that termites undermined the integrity of the levees. Henderson, a world-renowned expert on termites, found evidence of insects -- both Formosan termites and fire ants -- in the joints between wall panels on both the London Avenue and 17th Street canals. Fire ants, an enemy of termites, tend to invade the channels created by the wood-destroying insects. The termites are apparently attracted to a paperlike material made of bagasse, the remains of cane stalks after the sugar is removed, that is used in making the concrete form for the wall joints. The material remained in the joints, along with plastic spacers, as the wall was built. Bagasse contains ascorbic acid, which also is used in commercial termite baits containing pesticides, Henderson said.
'A bunch of them in there' At the London Avenue Canal, where several engineering teams believe the pressure of water in the canal undermined a weak layer of sand beneath levee walls and caused them to slide and fail, Henderson found insects in 73 percent of the joints, he said. At the 17th Street Canal, where a thick layer of peaty material was below the section of wall that failed, only 21 percent of the joints Henderson has tested outside the failure area had insects. "We saw little orange things when we pulled some of the bagasse material out, and it started blowing away," Henderson said. "I brought some of it home and looked at it with a magnifying glass and later with a microscope, and found it was termite soldier heads. And there were a bunch of them in there." He also found the remains of Formosan termite nests in fallen trees about 30 feet from one London Avenue Canal wall failure site, and in several houses along the wall. Termites eating out the interiors of large trees have resulted in many being easily downed during hurricanes and high winds. Some engineers say a fallen tree may have played a significant role in the 17th Street Canal failure. Robert Bea, a civil engineering professor at the University of California, Berkeley said computer modeling has indicated that if a tree with a large root ball toppled near the bottom of the levee beneath the wall on the canal, much less water would have been required in the canal to cause the wall to move and fail.
Search request Henderson wants the Army Corps of Engineers to let him search for nests in the earthen mounds on which the concrete levee walls are built. He said Formosan termites, which are an invasive species brought from Asia to New Orleans with shipping material after World War II, are known to nest in higher locations near water. Mature colonies contain between 5 million and 10 million insects that forage through underground tunnels that can stretch over an area as large as a football field, and can live in a main nest and several satellites. The termites build nests of paperlike frass, the name given to the digested cellulose left over from their wood meals that resembles crushed cardboard. The nests can be as large as a dining chair in underground areas, and can cover the interior of an entire wall in a house. Henderson said one of his graduate students conducting research in China has found that such nests have been blamed for a large percentage of earthen levee failures in that country since 1970. It's not the first time that Henderson has expressed concern about Formosan termites and levee walls. In 2000, he investigated complaints from French Quarter residents that water was leaking through Mississippi River floodwalls where termites were living. He found that termites had infested about 80 percent of the joints in walls stretching from the French Quarter to Audubon Park.
Deemed no danger Jerry Colletti, corps manager for completed public works, said engineers determined that the pinholes created by termites in the plastic joint spacers and in some cases in concrete were not dangerous. "From our standpoint, the joint material was sacrificial anyway," Colletti said. But the corps asked all levee districts in the New Orleans area to inspect joints for termites and to stop using bagasse-based material or wood. That was after the construction of the New Orleans levee walls, however. "The corps did an evaluation to determine how much water would come through those little pinholes," he said. "The decision was made not to take any action on the joints. We looked into sealing the joints, and it was going to be expensive and we didn't see a purpose to it; the pinholes didn't cause a structural integrity problem." Colletti said that the only interest in looking into the termite question has been raised by Henderson and others at the LSU Agricultural Center. "We don't have anybody at the corps who's a termite expert," he said. Bea also said that in inspections by him and other engineers financed by the National Science Foundation, no evidence was found of termites playing a direct role in the failure of any wall joints. . . . . . . .
Mark Schleifstein can be reached at firstname.lastname@example.org or (504) 826-3327.