Some of the challenges of building levees in N.O.

"The outflow at the break is filled with old cypress stump and cypress logs, because that was what this area used to be, that was the geology of it," he said. "You probably have cypress stumps and logs under the surface here every 5 meters or so. You can imagine driving a sheet piling into one of those, and the metal could bend or split. That could cause leakage later on."