National Geographic : 2007 Aug
POTENTIAL LEVEE AN PROBLEM FLOODWAY DUNCAN CANAL ID ALL Lake Pontchartrain ORLEANS AVE. LONDON AVE. CANAL CANAL SIN 17THSTREET CANAL 6 New Orleans issi's DUSTRIAL ANAL 7)'f MISSISSIPI VER GULF OUTLET (MRGO) 0km 5 SOURCE:ROBERTG. BEA,UNIVERSITYOFCALIFORNIA,BERKELEY Weakened Levees Last year the U.S. Army Corps of Engineers said it had restored New Orleans' levees and floodwalls to pre Katrina strength. But this spring engi neer Bob Bea of the University of California, Berkeley, identified poten tial weak spots. They include levees along the Mississippi River Gulf Outlet, which Katrina's storm surge breached. Rebuilt of soft soil, the levees are already eroding. Bea also pointed to Katrina-damaged floodwalls, still not repaired, and gaps in the barriers that could admit flooding. Bea is an expert witness in a law suit against the corps. But others share his concerns. One expert notes that the new floodgates guarding the city's three main drainage canals have no mechanism to clear debris that might keep them from closing. He also doubts the reliability of pumps installed to expel rainwater from the city when the gates close. The corps says the city's defenses are a work in progress. "After Katrina we achieved a massive accomplish ment, repairing the damage," says John Meador, deputy director of the Army Corps group rebuilding the lev ees. "We believe we are putting the system back better than it was before, but we're not at an end point yet." 52 NATIONAL GEOGRAPHIC * AUGUST 2007 POINTS OF CONCERN 1 DUNCAN CANAL FLOODWALL Built on soft soil, it is sinking and buckling; repairs with steel pilings may be inadequate. 2 17TH STREET CANAL Levee work constricts water flow and could lead to flooding. 3 ORLEANS AVENUE CANAL During Katrina, water spilled through a floodwall gap that still has not been closed. 4 LONDON AVENUE CANAL New pumps and floodgates are designed to keep out storm surge, but some experts are skeptical. 5 LONDON AVENUE CANAL The floodwall still includes sections damaged and weakened by Katrina. 6 LONDON AVENUE CANAL A gap in the wall makes way for a bridge across the canal-but could admit floodwater. 7 BAYOU BIENVENUE Concrete and rock armor could channel water onto the adjacent earthen levee, eroding it. 8 MRGO LEVEES Rainwater has carved furrows into the newly reconstructed levees along the channel. More on Levees For additional details on this story and more photographs of the levee prob lems, go to ngm.com/0708.