The following is from today's New York Times. http://nytimes.com/2005/08/31/national/nationalspecial/31levee.html
*** Would this teach the riverlinkers and big dam builders anything? cm Geography Complicates Levee Repair By CORNELIA DEAN and ANDREW C. REVKIN Published: August 31, 2005 Until engineers can repair breaks in the huge levees that separate New Orleans from Lake Pontchartrain, the city will essentially be an arm of the Gulf of Mexico, subject to the ebb and flow of the tides. Enlarge This Image Vincent Laforet/The New York Times Water engulfed much of New Orleans yesterday, and officials feared a steep death toll after breaches in the levees sent the waters of Lake Pontchartrain pouring into the city. And because the tidal pull widens the breaks, experts said yesterday, that will make it all the harder to repair them - the first step in restoring the inundated city to normal. Last night, even as engineers scrambled to figure out ways to plug a levee breach on the 17th Street Canal, Mayor Ray Nagin, in an interview on WWL-TV, said the waters in neighborhoods east of the breach were rising so fast they might cause the nearby pumping station to fail. "We've been living in this bowl," said Shea Penland, a coastal geologist who has studied storm threats to Louisiana for years. "And then Katrina broke channels into the bowl and the bowl filled. And now the bowl is connected to the Gulf of Mexico. We are going to have to close those inlets and then pump it dry." John Hall, a spokesman for the Army Corps of Engineers, said last night that the corps and other agencies were "in a great frenzy" to figure out how to plug the 300-foot gap along the 17th Street Canal. The narrow canal, which is used to drain water pumped out of the eternally soggy city, is not accessible by barge, in part because a newly built low bridge and hurricane barrier sits 700 feet down the canal toward the lake end. "We can't get at it," Mr. Hall said. Mr. Hall said that the levee failed as the surge from the storm swept in through Lake Pontchartrain, actually a broad inlet off the gulf, and began sloshing over the vertical steel and concrete wall and the earthen berm behind it. "Once it got over, it began to scour down at the base of that flood wall on the protected side," he said. The rising waters in the canal pushed in on the high part of the retaining wall while water cascading over the top ate away at the base, Mr. Hall said, adding: "The effect is like a high-low tackle in football. You hit the head and feet at the same time from opposite directions, and it goes down." Another problem is that whatever is done to block the breach must not also block the canal itself, because that would impede the pumping of the floodwaters. Federal officials are seeking help from agencies and private contractors that might be able to supply heavy cranes and other equipment. The levees, which provide a tenuous barrier between the city and the waters that surround most of it, have long had weak spots and were not designed to withstand the full force of a storm like Hurricane Katrina. The other failure occurred along the Industrial Canal, an 80-year-old channel that had been identified as a weak spot in computer simulations of storm surges from hypothetical hurricanes. S. Jeffress Williams, a United States Geological Survey scientist with long experience in Louisiana, said repairing the levees would require "a large volume of as dense, as heavy material as you can get, applied quickly." "Where you get the material and how you get the equipment up there is going to be a real problem," he went on. "If you don't keep it going, it is just going to erode away. You have to have a persistent and constant feed until it is done." Dr. Penland, the director of the Pontchartrain Institute for Environmental Studies at the University of New Orleans, said it was impossible to say how long it would take to repair the levees and pump the city dry. New Orleans has 22 pumping stations that need to work nearly continuously to discharge normal storm runoff and seepage. But they are notoriously fickle. Efforts to add backup power generators to keep them all running during blackouts have been delayed by a lack of federal money. "Pumping the water out - that's a lot of water," Dr. Penland said. "When the pumping systems are in good shape, it can rain an inch an hour for about four to six hours and the pumps can keep pace. More than that, the city floods." Next Article in National (11 of 18) > _______________________________________________ assam mailing list [email protected] http://assamnet.org/mailman/listinfo/assam_assamnet.org
