New Orleans floodwalls should have stood up to Katrina’s storm surge

Why did the floodwalls on Lake Pontchartrain fail to protect New Orleans? The official explanation from the U.S. Army Corps of Engineers has been that the key 17th Street and London Avenue floodwalls were built to protect against a Category 3 hurricane — a Category 4 like Katrina wasn’t in the plan. But some Louisiana hurricane experts are rejecting that exculpatory storyline. They point out that Katrina didn’t hit New Orleans directly; data shows that sustained winds over the lake reached only 95 mph, lower than typical for a Cat 3 hurricane. Engineers at Louisiana State University’s Hurricane Center have now found that the resulting storm surges never sent water over Pontchartrain’s floodwalls. That makes flawed design and/or poor construction — i.e., Corps of Engineers’ screw-ups — the more likely culprits. “The event exceeded the design,” insists a Corps spokesflack. Did not, says Ivor van Heerden, the Hurricane Center’s deputy director: “We are absolutely convinced that those floodwalls were never overtopped.”