I found this article in National Geographic to be very interesting. Here are a couple of selections:
“On Thursday afternoon, U.S. Army Corps of Engineers officials briefed reporters on the status of that levee system, even as much of the city remained flooded and crews worked to repair breeches along city canals.
The bowl-like shape of New Orleans prevents water from draining away, as broken levees continue to allow water to flow into city streets. No one is sure how long it will take to pump out floodwaters once the levees are repaired.
Lt. Gen. Carl Strock, chief of engineers for the Corps, dismissed suggestions that recent federal funding decreases or delayed contracts had any impact on levee performance in the face of Katrina’s overwhelming force.
Instead he pointed to a danger that many public officials had warned about for years: The system was never designed to withstand a storm of Katrina’s strength.
“It was fully recognized by officials that we had Category Three [hurricane] level of protection,” Strock said. “As projections of Category Four and Five were made, [officials] began plans to evacuate the city.
“We were just caught by a storm whose intensity exceeded the protection that we had in place.”
The current system in New Orleans was designed decades ago and has been shaped over time by past storms.
An unnamed hurricane on September 1947 flooded Jefferson Parish, which includes metropolitan New Orleans, to depths of about three feet (one meter). The storm caused 100 million dollars (U.S.) worth of damage.
After the storm, hurricane protection levees were built along Lake Pontchartrain’s south shore.
Hurricane Camille made landfall some 50 miles east of New Orleans on September 10, 1965. Winds in the city reached 125 miles per hour (200 kilometers an hour) and the storm surge neared 10 feet (3 meters). After extensive flooding, the Orleans Levee Board raised existing levees to a height of 12 feet (4 meters).
In 1998 Hurricane Georges triggered a mandatory evacuation of the Crescent City. The storm devastated much of the Caribbean but largely spared New Orleans.
Still, traffic snarls illustrated the difficulty and danger that would accompany evacuation in the face of a more direct hitâ€”like the one delivered by Hurricane Katrina.
Until the day before Katrina’s arrival, New Orleans’s 350 miles (560 kilometers) of levees were undergoing a feasibility study to examine the possibility of upgrading them to withstand a Category Four or Five storm.
Corps officials say the study, which began in 2000, will take several years to complete.
Upgrading the system would take as long as 20 to 25 years, according to Al Naomi, the Corps’ senior project manager for the New Orleans District.
Martin McCann, a civil and environmental engineering professor at Stanford University in California, warns that long-term planning may not account for changes to the risk equation.
“As further development goes on behind levees, over decades you need to revisit the question and say, Are those levees providing us the protection that we wanted?” he said.
“The answer is probably no, because the exposure is probably greater. The number of people and the [amount of] valuable property [behind the levees] is greater.”