Levees can't save New Orleans from floods: report

Chris Baltimore, Reuters 24 Apr 09;

HOUSTON (Reuters) - Bigger, higher and stronger levees cannot save New Orleans from the worst floods and the city remains vulnerable to a repeat of Hurricane Katrina, the National Academy of Sciences said on Friday.

New Orleans had the flood protection of a 350-mile network of levees, I-walls and T-walls ringing the city when Hurricane Katrina slammed ashore on August 29, 2005. The levees broke, flooding 80 percent of the city.

The hurricane killed about 1,500 people along the U.S. Gulf Coast and caused $80 billion in damages, making it the costliest U.S. natural disaster.

As Katrina demonstrated, "the risks of inundation and flooding never can be fully eliminated by protective structures no matter how large or sturdy those structures may be," said the report by the National Academy of Engineering and the National Research Council.

"Substantial risks" of living in flood-prone areas were never clearly communicated to residents before Katrina, it said, and simply rebuilding New Orleans and its hurricane-protection system back to pre-Katrina levels would leave the city vulnerable to another flooding disaster.

The first floor of buildings in flood-prone parts of the city should be raised at least to the 100-year flood level, which the report called a "crucial flood insurance standard." But for heavily populated cities like New Orleans, that standard is inadequate, said the report, part of a five-part study by the academies in the wake of Katrina.

The 100-year standard basically stipulates protection based on the assumed worst damage of the worst flood in the last 100 years. It determines insurance rates for the National Flood Insurance Program administered by the federal government.

But structures in New Orleans' most flood-prone areas have a 26 percent chance of flooding over the term of a 30-year mortgage, and the 100-year standard is "far too risky" to rely on, the report said.

Authorities should discourage settlement in flood-prone areas and encourage voluntary relocation away from them, the report said. They should also shore up electricity supplies that are key to running giant pumps that route floodwaters away from the city, the report said.

Large portions of New Orleans are below sea level, which makes it vulnerable to floods and storm surges from hurricanes. Located at the mouth of the Mississippi River delta, New Orleans is in close proximity to Lake Pontchartrain and Lake Borgne.

The city's levee system was tested again in September 2008, when a surge from Hurricane Gustav nearly overtopped a protective T-wall along New Orleans' Inner Navigation Canal.

(Editing by Doina Chiacu)