Flooded! How one southern city was destined for disaster.

DID YOU KNOW?

* In 1953, U.S. scientists began naming hurricanes using women's names in alphabetical order throughout the season. In 1979, meteorologists began alternating men's and women's names. The letters Q, U, X, Y, and Z are not used because names starting with those letters are scarce. After a particularly severe storm, a name may be retired.

* The city of New Orleans was founded in 1718 by French settlers. The earliest European residents made use of the vast Mississippi River system and the Gulf of Mexico, turning the city into a rich hub for trade.

CRITICAL THINKING:

* Suppose there's an oncoming natural disaster. You're given 30 minutes to plan your evacuation. Come up with an evacuation procedure. Include a list of what you plan to bring with you.

CROSS-CURRICULAR CONNECTIONS:

ART: Research to create a poster that alerts your community on how to prepare for a natural disaster.

RESOURCES

* For basic information about hurricanes, visit the National Hurricane Center: www.nhc.noaa.gov/

* The following articles were written a few years ago. They cover what scientists predict would happen to New Orleans if a storm of Katrina's magnitude struck the city:

"Drowning New Orleans," by Mark Fischetti, Scientific American, October 2001.

"The Furious Storm," by Larry O'Hanlon, Science World, October 18, 2002.

Late last August, Hurricane Katrina whirled toward the U.S. coast in the Gulf of Mexico. With initial weather forecasts reporting that the city of New Orleans, Louisiana, would take a direct hit, many of the city's residents scrambled to evacuate to safer ground. But as the monster storm neared the shoreline, the eye of the storm veered eastward. With pouring rain and winds topping 225 kilometers (140 miles) an hour, Katrina pounded Mississippi. New Orleans and surrounding regions were hit hard too, but it looked like the city nicknamed The Big Easy had dodged the worst of the storm.

Not so. The rising waters left by Katrina were too much for New Orleans' flood-control methods to handle. A day after the hurricane hit land, some barriers built to contain water broke or were washed away. Water from swollen canals and a nearby lake began filling the city. Soon, 80 percent of the town was under up to 6 meters (20 feet) of water. Residents were forced from flooded homes. Some clung to rooftop islands waiting to be plucked to safety by rescue workers in boats and helicopters.

While shocked TV viewers watched the city drown, scientists weren't surprised at all. For years, researchers had warned that New Orleans was a nightmare waiting to happen. "Something like this was pretty much inevitable," says Hugh Willoughby, a hurricane researcher at Florida International University in Miami. Read on to learn how three main factors made New Orleans so vulnerable.

SINKING CITY

The key to New Orleans' flooding catastrophe lay in the fact that nearly 80 percent of the city sits below sea level--more than 2.4 m (8 ft) below it in some areas (see diagram, p. 22). This "bowl" is surrounded by Lake Pontchartrain to the north and the Mississippi River to the south. Residents have long on an extensive system of earthen and concrete barriers, called levees, lining Pontchartrain and the Mississippi to keep high waters front spilling into the low-lying city.

New Orleans didn't always sit so much lower than the surrounding waters: The city has sunk 2.7 m (9 ft) since it was built in 1718. Why the sinkage? New Orleans is situated on the Mississippi Delta, where water flowing front the Mississippi River meets the Gulf of Mexico. There, the river's current slows, allowing sediment, such as mud, to fall to the bottom. Over millions of years, this sediment has built up.

But the resulting land is far from sturdy. "The Mississippi Delta is basically a pile of mud in the Gulf of Mexico," says Willoughby. "If you take a pile of mud and slop it on a tabletop, it's going to spread out. And that's what the Delta does." The spongy ground on which New Orleans was built is slowly spreading and sinking.

If nature were allowed to run its course, New Orleans would be sitting high--though not completely dry. That's because each spring, as snow upriver melts and drains into the Mississippi, the river floods the Delta. Left uncontrolled, these floods can deposit a new layer of mud that builds the ground back up. But in the 18th century, European settlers began building levees to keep floodwater out of the city. No flooding means no new sediment is added. So the land on which the city sits sinks farther below sea level. This bowl shape makes the city prone to flooding.

DISAPPEARING DEFENSES

New Orleans had another strike against it--one that made it especially vulnerable to Katrina's wrath. With each passing year, the sinking city has become doubly defenseless against hurricanes due to the loss of a natural line of protection: The marshes (swamps) and the barrier islands (long narrow islands that run parallel to the mainland) that cradle New Orleans are vanishing. Marshes and offshore islands help absorb storm surges, or rushes of ocean water pushed onshore by storms, before they reach the city. The bad news: These defenses are eroding, or wearing away (see Nuts & Bolts, right).

The marshes rely on sediment from the Mississippi to replenish them. With levees blocking the river's mud, 25 to 30 square miles of Delta marshes vanish every year. "That's about the size of a college football field [lost] every 15 to 30 minutes," says Gregory Stone, a coastal geologist at Louisiana State University in Baton Rouge.

HYPED-UP HURRICANES

New Orleans didn't stand a chance against the final blow: According to scientists, the number and intensity of Atlantic Ocean hurricanes runs in cycles. Their frequency and ferocity increase for a few decades at a stretch.

Researchers believe a new active cycle began in 1995. Translation: More monster storms loom ahead.

ND EASY FIX

As engineers mend the levees and pump water out of New Orleans, everyone is left wondering: Is it possible to rebuild the city and prevent a similar nightmare from occuring again? Suggestions include toting in sediment to rebuild the marshes, raising the height of the levees, and building a second fortress of levees inside the city.

All these proposals have been discussed before, but the money wasn't provided to carry them out. Some people have even suggested quitting the fight against nature and moving the city to a different spot.

There's no easy fix. But experts agree: Something must be done to keep this tragedy from recurring.

THE BIG BOWL

Nearly 80 percent of New Orleans sits below sea level (level of the surface of the ocean). Hurricane Katrina caused Lake Pontchartrain--which is usually .3 m (1 ft) above sea level--to fill to 2.6 m (8.6 ft) above sea level. When levees broke, the city flooded.

Nuts & Bolts

Marshes south and east of New Orleans once shielded the city from hurricanes. But as storm surges tear up marshes and sediment gets swept away, these natural barriers erode. Today's levees and canals prevent them from being replenished.

THEN: MARSHES EXPAND

Mississippi floods spread mud--building protective marshes.

NOW: MARSHES VANISH

Levees and canals reroute the river, funneling mud into the sea. Marshes are eroding.

DIRECTIONS: Circle the correct word(s) in the parentheses. There may be more than one correct answer.

1. Nearly (67, 80, 90) percent of New Orleans sits (above, below, at) sea level.

2. Marshes help absorb (storm surges, the eye of a hurricane, lightning).

3. New Orleans has sunk (5.5, 9, 12) feet since 1718 because (an earthquake shook its foundation, it was built on soft river mud, the multitude of skyscrapers placed too much pressure on the ground).

4. Which of the following contributed to New Orleans' flooding during Hurricane Katrina? (city's location, marsh erosion, population growth, levees, traffic gridlock)

ANSWERS

1. 80, below 2. storm surges 3. 9, it was built on soft river mud 4. city's location, marsh erosion, levees