New Orleans Levees Not Built for Worst Case Events
for National Geographic News
|September 2, 2005|
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New Orleans is surrounded by waterLake Pontchartrain, the Mississippi River, and the nearby Gulf of Mexico. Resting an average of six feet (two meters) below sea level, the city's safety has long depended on one of the world's most extensive levee systems.
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."
What Price Protection?
The U.S. Army Corps of Engineers has been building levees along the Mississippi River since the late 1800s. The artificial, reenforced soil embankments are designed to curb periodic and destructive floods.
But determining the level of protection needed versus what Congress and the public are willing to pay for isn't often easy.
Acceptable risks must be weighed, including the statistical likelihood of catastrophic events and the possible consequences if they do occur, according to U.S. Army Corps of Engineers officials.
The costs of protection against extreme natural disasters are juggled with other public priorities. Environmental considerations are debated. Stakeholders from all levels of government and the private sector weigh in.
Ultimately, congressional funding levels largely determine just how high the embankments will reach and what levels of risk will be accepted.
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 Betsy 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 hitlike 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."
While New Orleans's levee system is rather unique, such embankments are also critically important to other U.S. cities.
Throughout the Midwest along the upper Mississippi River, communities are protected from destructive floods by levee systems of varying extent and strength.
Another large and possibly vulnerable levee system is housed in the California Delta. The delta provides a vital freshwater conduit from Northern California to the state's Central Valley and on to Southern California.
The area includes a system of islands, some as much as 20 feet (6 meters) below sea level, that are individually protected by more than 1,100 miles (1,770 kilometers) of levees.
"[The islands] house communities, infrastructure, pipelines, road, rail, and agriculture," McCann said. "Because they are below sea level, if even one levee breaks, it fills up an island and sucks salt water in from San Francisco Bay," McCann said.
"The salinty levels get so high that you can't deliver fresh water to the south [parts of the state]," he said.
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