But Dr. Bea, an author of a blistering 2006 report on the levee failures paid for by the National Science Foundation, said erosion furrows, or rills, suggest that “the risks are still high.” Heavy storms, he said, may cause “tear-on-the-dotted-line levees.”

Dr. Bea examined the hurricane protection system at the request of National Geographic magazine, which is publishing photographs of the levee and an article on his concerns about the levee and other spots on its Web site at ngm.com/levees.

Corps officials argue that Dr. Bea is overstating the risk and say that they will reinspect elements of the levee system he has identified and fix problems they find. The disagreement underscores the difficulty of evaluating risk in hurricane protection here, where even dirt is a contentious issue. And discussing safety in a region still struggling with a 2005 disaster requires delicacy.

Hurricane season begins again next month.

The most revealing of the photographs, taken from a helicopter, looks out from the levee across the navigation canal and a skinny strip of land to the expanses of Lake Borgne. From the grassy crown of the levee, small, wormy patterns of rills carved by rain make their way down the landward side, widening at the base into broad fissures that extend beyond the border of the grass.

Dr. Bea, who was recently appointed to an expert committee for plaintiffs’ lawyers in federal suits against the government and private contractors over Hurricane Katrina losses, said that he could not be certain the situation was dangerous without further inspection and that he wanted to avoid what he called “cry wolf syndrome.” But, he added, he does not want to ignore “potentially important early warning signs.”