Repairing a Levee

The Washington Post has a very good article on the efforts to repair the levee. Here are some highlights.

By Tuesday evening, 80 percent of the below-sea-level city was submerged, with some sections flooded to a depth of 20 feet.

A helicopter drop [of sandbags] probably would not have helped anyway. "You've got a great big spillway," said William Marcuson, director emeritus of the Corps' Geotechnical and Structures Laboratory in Vicksburg, Miss. "At some point the lake will subside, but until it stabilizes, you might as well leave the breaches there."

Bob Anderson, a spokesman for the Army Corps of Engineers in Memphis said: Equilibrium came early Wednesday. New Orleans's harried residents noticed that the floodwater had stopped rising, and as the day wore on, the level began to fall. This, was caused by two factors.

First, many of the city's pumps, particularly in higher-ground areas, never stopped operating and were continuously flushing water into the Mississippi River south of the lake and into undamaged canals.

Second, the lake had subsided so much that the water inside the city was able to flow back the way it had come. The 17th Street and London Avenue breaches became drains. By yesterday afternoon, 53 percent of the city was dry.

Anderson said the Corps planned to leave the 250-foot-wide London Avenue break alone so water would continue to flow out, and that "notches" are being cut in the levee protecting eastern New Orleans -- makeshift gutters so water will spill out.

But if the city relied only on gravity, months would elapse and there would still be two feet of water on the ground. Engineers needed to get pumps working in the areas of heavy flooding, and to do that, they needed to close the 17th Street breach.

For three days, Corps officials had lamented the difficulty of gaining access to the canal, but yesterday afternoon a set of steel sheet pilings were placed at the mouth of the canal to isolate the canal from the lake. This allowed them to start driving piles at the actual breach yesterday evening and hopefully finish by tomorrow. Then the pumping can beging.