The furious storm: one wild hurricane could drown a major American City. Can scientist prevent the disaster in time?

Larry O'Hanlon

Here's a tip from the experts: If you're in New Orleans when the "Big One" hits, have a lifeboat handy. Some scientist warn that the right hurricane--a tropical cyclone with at least 74-mile-per-hour winds--could strike the Gulf Coast in a way that would hurl millions of gallons of water to turn the city known as the Big Easy into the Big Soup Bowl (see map, next page).

A major flood could submerge much of central New Orleans beneath 20 feet of water, leaving many of the metropolitan area's 1.3 million residents clinging to rooftops--a prospect that has engineers and city planners scrambling for defensive strategies. "It's the luck of the draw," says hurricane expect Hugh Willoughby at the National Oceanic and Atmospheric Administration (NDAA). He thinks it's a matter of when--not if--the Big One will pound New Orleans During some annual hurricane season between June and November.

Why is New Orleans so vulnerable? Try these three main reasons:

* Sandwiched between Lake Pontchartrain and the Mississippi River, most of the city lies below sea level. A flood that gushes over shielding levees (earthen walls built in the late 1800s to protect against river overflow) would submerge New Orleans underwater.

* Marshes, fresh and saltwater swamps of mud and diverse plant life, divide New Orleans from the Gulf of Mexico. They once acted as barriers from storm surges--high water accompanying storms. Now marshes are quickly eroding, or wearing away. This is partly because levees block and reroute the Mississippi's periodic flooding cycles, which spread mud and sediment (rock particles) that shore up marshes. In some places, the gulf has receded 32 to 48 kilometers (20 to 30 miles) closer to New Orleans.

* The number and intensity of Atlantic Ocean hurricanes tend to increase in cycles every few decades, experts say. "We've just entered a more active phase," says Willoughby (see "How Hurricanes Form," p. 24).

New Orleans hasn't always faced such danger. When first built in 1718, the city sat on higher land beside the Mississippi. But it was erected on soft river mud--a mix of silt (loose rock particles) and clay minerals--deposited over millions of years by flowing water at the delta, or mouth where the Mississippi meets the gulf. Trouble is, the soft ground beneath central New Orleans has sunk nine feet in nearly 300 years. (Most New Orleans skyscrapers are supported by deep piles, so they don't rely on the soft ground for support)

PERFECT STORM

Not just any hurricane could engulf New Orleans, Willoughby explains; otherwise, the city would have drowned long ago. New Orleans' nightmare will be a "perfect" storm--one that strikes in just the right way.

Every year, an average of five or six hurricanes that form in the Atlantic Ocean churn toward Central and North America--often with Florida and the Caribbean islands dead in their paths. But changes in wind direction and Earth's air currents cause most hurricanes to sweep around and roll up the U.S. East Coast, weakening as they move over colder seawater. About once a year, however, a hurricane stomps right over Florida, where warm water in the Gulf of Mexico can reenergize it as a monster storm, thrusting it westward.

The perfect storm could either strike New Orleans east of the city, with gale-force winds blowing south, shoveling water from Lake Pontchartrain over the lake levees; or the storm could strike west of the city, causing winds to heave Gulf of Mexico seawater up the Mississippi River and crash over its levees.

Joseph Suhayda, former director of the Louisiana Water Resources Research Institute at Louisiana State University, uses computer models to study potential hurricane hits. His surprising finding: A severe but not catastrophic Category 3 storm (see next page) would be enough to swamp New Orleans if it slowed down and hovered east of the city. "A slow storm has more time to build up the wind effect over the lake," says Suhayda. Waves can add four to five feet to surging lake waters, he adds.

RIVER WALLS

Engineers and city planners are racing to soften a hurricane's blow to New Orleans. In addition to hashing out elaborate evacuation plans, one strategy calls for slowing the loss of marshlands by building control gates. These would let the Mississippi overflow once again, spreading sediment-rich water to rebuild marshes. Another idea: shoring up barrier islands in the gulf. But no plan would remove the hurricane threat immediately, and public officials say costs for all schemes are prohibitive.

With early storm detection, most of New Orleans can be safely evacuated, Suhayda says. For those who can't get out, Suhayda offers his own controversial scheme: Engineers would construct a 20-foot-high east/west wall along the north edge of the French Quarter, which would seal off a downtown section. The existing Mississippi River levees would surround the "haven" on three sides and are high enough now for Category 5 hurricane protection. The sealed off "bowl" could provide safety for several hundred thousand people.

But even with a walled-off safe haven, it could take months to pump the rest of New Orleans dry. What's more, water damage and toxic chemical leaks from flooded industrial facilities in the area would probably make much of New Orleans impossible to live in, says Willoughby: "We may need a new New Orleans."

A HURRICANE'S DIRECT HIT could plunge New Orleans' fabled French Quarter (far left) underwater. Fast-eroding coastal marshes (center) make the city more vulnerable to hurricane damage. Experts worry the city could suffer similar devastation to the Galveston storm of 1900 (left), which killed around 8,000. (big picture) Florida Keys residents flee 1998's Hurricane Georges.

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NEW ORLEANS city under siege?

HOW A CITY CAN DROWN

This elevation map shows a large part of New Orleans lies below sea level (in red). If hurricane winds blew from north to south, surging water from Lake Pontchartrain could flood--and become trapped--in these below-sea-level areas.

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COASTAL DEFENSES

Going, going, gone?

Marshes south and east of New Orleans once shielded the city from storms. But they're eroding quickly.

THEN: NATURAL FLOW

The Mississippi's periodic floods once spread sediment and mud--building up protective marshes.

NOW: VANISHING MARSHES

Levees (earthen walls) and canals reroute the river. Sediment washes away into the sea.

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ESCAPING THE STORM

City planners worry that evacuating New Orleans' residents during a hurricane could be deadly: (1) Interstate 10 can easily flood from Lake Pontchartrain. (2) When winds exceed 50 mph, the 24-mile Lake Pontchartrain Causeway is shut. (3) Traffic gridlock would clog Interstates 10 and 59.

If you had to come up with an evacuation plan for this endangered city, what would it be?

IT'S YOUR CHOICE

Choose the correct answer(s) to these questions:

1 Which factor(s) would make New Orleans
less vulnerable to hurricane damage?

A eroding marshlands    C inner-city wall
B rising sea levels     D pumping groundwater

2 Which of the following have rerouted
the Mississippi River?

A levees                         C canals
B Lake Pontchartrain Causeway    D Interstate ID

3 In the map above, which section of
New Orleans lies six feet below sea level?

A Algiers        C Downtown
B Matairie       D French Duarter

4 How many feet above sea level would
Lake Pontchartrain's average crest be
in a moderate hurricane?

A 6      C 10
B 12     D 24

ANSWERS IN TEACHER'S EDITION

HOW HURRICANES FORM

A hurricane is a tropical cyclone with fierce winds of at least 74 miles per hour. It can stretch out to 600 miles in diameter. Here's how a typical hurricane forms.

1 Warm water meets moving air

An Atlantic Ocean hurricane is born when sun-heated seawater evaporates into warm, moist air, or water vapor. The humid air collides with westward-moving airwaves from Africa.

2 A tropical storm forms

As the humid air rises, it cools and condenses to form thunderclouds.

3 The storm become a hurricane

Fierce winds and Earth's rotating axis swirl the thunderclouds like a pinwheel. When winds reach 74 miles per hour, the storm officially becomes a hurricane.

4 The hurricane spins

North of the equator, a hurricane swirls counterclockwise. As it spins, it sucks up about 200,000 tons of humid ocean water vapor daily.

5 Hurricane strike

The storm hits the continent at around 1 2 mph. If it reaches the Gulf of Mexico, a few deep eddies (water running against the currents) in otherwise shallow water can turn it into a monster.

6 Storm death

Once a hurricane is cut off from a supply of warm, moist ocean air, the storm quickly loses power and dies out in two to three days.

Hurricane hunters

Research planes fly directly into hurricanes to gather scientific data. A new unpiloted robotic plane called the Aerosonde will skim into dangerous storms close to the sea surface.

The "engine"

As a hurricane keeps absorbing humid, hot air, the cool, dry air on top creates an area of low pressure that sucks more warm air toward it.

Wind zone

Winds of up to 185 mph blow here. On land, they can uproot trees and flatten vehicles.

Outer edge

It can be as far as 300 miles from the eye, or center, and produces strong rains.

Flooding

Coastal cities like New Orleans could suffer severe floods if hit by a hurricane.

HANDS-ON SCIENCE

WILD WINDS

How could one hurricane flood New Orleans? See for yourself!

You Need

9 in. x 13 in. baking dish * flexible straw * ruler * duct tape * water

To Do

1 Pour a .5 in. (1.3 cm)-thick layer of water into the dish. Bend the straw into an L shape. Tape the short-end of the straw (facing upward) inside the middle of one 9-in. pan edge. The long-end of the straw should rest horizontally above the water, and point toward the opposite pan edge. Tape a ruler vertically to the other g-in. side of the pan.

2 Blow gently into the straw to create "wind." Look at the ruler to measure the height of the resulting "wave."

3 Repeat Step 2 twice, blowing harder each time.

4 Repeat Steps 2 to 3 twice, first with 1 in. of water in the pan, then with 1.5 in. of water.

Think About It

Do you think hurricanes cause higher waves on the open sea or near land? Why?

Hurricane category levels The Saffir-Simpson scale categorizes hurricane strength by air pressure, storm surges, and wind speed.

1

MINIMAL

Wind:
74-65 mph
Waves:
4 to 5 ft

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2

MODERATE

Wind:
96-110 mph
Waves:
6 to 8 ft

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3

SEVERE

Wind:
111-130 mph
Waves:
9 to 12 ft

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4

VERY SEVERE

Wind:
131-155 mph
Waves:
13 to 18 ft

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5

CATASTROPHIC

Wind:
Over 155 mph
Waves:
Over 18 ft

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Satellite image of 1992's Hurricane Andrew

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Did You Know?

* The term hurricane originated in ancient civilizations. The Mayan storm god was named Hunraken. And Huracan was an evil god of the Caribbean Taino people.

* "Tropical cyclone" is the generic term for hurricanes, tropical storms, and tropical depressions. A hurricane has winds over 74 miles per hour, a tropical storm has winds between 39 to 74 mph, and a tropical depression has winds below 38 mph.

* In 1953 U.S. scientists began naming hurricanes using women's names in alphabetical order throughout the season from June to November. In 1979, meteorologists began alternating between men's and women's names. And after a particularly severe storm, a name may be retired.

Cross-Curricular Connection

Language Arts: Write a short story about a city under siege by a hurricane. Students must include real science in the story.

Resources

The NOAA/National Weather Service has two excellent Web sites:

National Hurricane Center: www.nhc.noaa.gov/

Hurricane Awareness: www.nws.noaa.gov/om/hurricane/index.shml

To learn about the U.S. Army Corps of Engineers' hurricane-protection efforts in New Orleans: www.mvn.usace.army.mil/pao/response/index.asp

CHECK FOR UNDERSTANDING

Directions: Circle the correct word(s) in the parentheses.

1. A hurricane is a tropical cyclone with winds of at least (48, 74, 131,155) miles per hour.

2. North of (the equator, New Orleans, Gulf of Mexico), a hurricane swirls (clockwise, counterclockwise).

3. New Orleans has sunk nine feet in almost 300 years because (an earthquake shook its foundation, it was erected on soft river mud, the multitude of skyscrapers placed too much pressure on the earth).

4. Which of the following contributes to New Orleans' vulnerability to flooding during a hurricane: (city's location, marsh erosion, population growth, levees, traffic gridlock)?

ANSWERS

1. 74

2. the equator, counterclockwise

3. it was erected on soft river mud

4. city's location, marsh erosion, levees

1. C, D 2. A, C 3. B 4. B

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