- A major hurricane could swamp New Orleans under 20 feet
of water, killing thousands. Human activities along the Mississippi River
have dramatically increased the risk, and now only massive reengineering
of southeastern Louisiana can save the city
-
- The boxes are stacked eight feet high and line the walls
of the large, windowless room. Inside them are new body bags, 10,000 in
all. If a big, slow-moving hurricane crossed the Gulf of Mexico on the
right track, it would drive a sea surge that would drown New Orleans under
20 feet of water. "As the water recedes," says Walter Maestri,
a local emergency management director, "we expect to find a lot of
dead bodies."
-
- New Orleans is a disaster waiting to happen. The city
lies below sea level, in a bowl bordered by levees that fend off Lake Pontchartrain
to the north and the Mississippi River to the south and west. And because
of a damning confluence of factors, the city is sinking further, putting
it at increasing flood risk after even minor storms. The low-lying Mississippi
Delta, which buffers the city from the gulf, is also rapidly disappearing.
A year from now another 25 to 30 square miles of delta marsh--an area the
size of Manhattan--will have vanished. An acre disappears every 24 minutes.
Each loss gives a storm surge a clearer path to wash over the delta and
pour into the bowl, trapping one million people inside and another million
in surrounding communities. Extensive evacuation would be impossible because
the surging water would cut off the few escape routes. Scientists at Louisiana
State University (L.S.U.), who have modeled hundreds of possible storm
tracks on advanced computers, predict that more than 100,000 people could
die. The body bags wouldn't go very far.
-
- A direct hit is inevitable. Large hurricanes come close
every year. In 1965 Hurricane Betsy put parts of the city under eight feet
of water. In 1992 monstrous Hurricane Andrew missed the city by only 100
miles. In 1998 Hurricane Georges veered east at the last moment but still
caused billions of dollars of damage. At fault are natural processes that
have been artificially accelerated by human tinkering--levying rivers,
draining wetlands, dredging channels and cutting canals through marshes.
Ironically, scientists and engineers say the only hope is more manipulation,
although they don't necessarily agree on which proposed projects to pursue.
Without intervention, experts at L.S.U. warn, the protective delta will
be gone by 2090. The sunken city would sit directly on the sea--at best
a troubled Venice, at worst a modern-day Atlantis.
-
- As if the risk to human lives weren't enough, the potential
drowning of New Orleans has serious economic and environmental consequences
as well. Louisiana's coast produces one third of the country's seafood,
one fifth of its oil and one quarter of its natural gas. It harbors 40
percent of the nation's coastal wetlands and provides wintering grounds
for 70 percent of its migratory waterfowl. Facilities on the Mississippi
River from New Orleans to Baton Rouge constitute the nation's largest port.
And the delta fuels a unique element of America's psyche; it is the wellspring
of jazz and blues, the source of everything Cajun and Creole, and the home
of Mardi Gras. Thus far, however, Washington has turned down appeals for
substantial aid.
-
- Fixing the delta would serve as a valuable test case
for the country and the world. Coastal marshes are disappearing along the
eastern seaboard, the other Gulf Coast states, San Francisco Bay and the
Columbia River estuary for many of the same reasons besetting Louisiana.
Parts of Houston are sinking faster than New Orleans. Major deltas around
the globe--from the Orinoco in Venezuela, to the Nile in Egypt, to the
Mekong in Vietnam--are in the same delicate state today that the Mississippi
Delta was in 100 to 200 years ago. Lessons from New Orleans could help
establish guidelines for safer development in these areas, and the state
could export restoration technology worldwide. In Europe, the Rhine, Rhône
and Po deltas are losing land. And if sea level rises substantially because
of global warming in the next 100 years or so, numerous low-lying coastal
cities such as New York would need to take protective measures similar
to those proposed for Louisiana.
-
-
- Seeing Is Believing
-
- Shea Penland is among those best suited to explain the
delta's blues. Now a geologist at the University of New Orleans, he spent
16 years at L.S.U.; does contract work for the U.S. Army Corps of Engineers,
which builds the levees; sits on federal and state working groups implementing
coastal restoration projects; and consults for the oil and gas industry.
His greatest credential, however, is that he knows the local folk in every
little bayou town, clump of swamp and spit of marsh up and down the disintegrating
coast--the people who experience its degradation every day.
-
- Penland, dressed in jeans and a polo shirt on a mid-May
morning, is eager to get me into his worn red Ford F150 pickup truck so
we can explore what's eating the 50 miles of wet landscape south of New
Orleans. The Mississippi River built the delta plain that forms southeastern
Louisiana over centuries by depositing vast quantities of sediment every
year during spring floods. Although the drying sands and silts would compress
under their own weight and sink some, the next flood would rebuild them.
Since 1879, however, the Corps of Engineers, at Congress's behest, has
progressively lined the river with levees to prevent floods from damaging
towns and industry. The river is now shackled from northern Louisiana to
the gulf, cutting off the sediment supply. As a result, the plain just
subsides below the encroaching ocean. As the wetlands vanish, so does New
Orleans's protection from the sea. A hurricane's storm surge can reach
heights of more than 20 feet, but every four miles of marsh can absorb
enough water to knock it down by one foot.
-
- The flat marsh right outside New Orleans is still a vibrant
sponge, an ever changing mix of shallow freshwater, green marsh grasses
and cypress swamp hung with Spanish moss. But as Penland and I reach the
halfway point en route to the gulf, the sponge becomes seriously torn and
waterlogged. Isolated roads on raised stone beds pass rusted trailer homes
and former brothels along now flooded bayous; stands of naked, dead trees;
and browned grasses and reaches of empty water.
-
- Down in Port Fourchon, where the tattered marsh finally
gives way to open gulf, the subsidence and erosion are aggressive. The
lone road exists only to service a collection of desolate corrugated buildings
where oil and natural-gas pipelines converge from hundreds of offshore
wellheads. Countless platforms form a gloomy steel forest rising from the
sea. To bring in the goods, the fossil fuel companies have dredged hundreds
of miles of navigation channels and pipeline canals throughout the coastal
and interior marshes. Each cut removes land, and boat traffic and tides
steadily erode the banks. The average U.S. beach erodes about two feet
a year, Penland says, but Port Fourchon loses 40 to 50 feet a year--the
fastest rate in the country. The network of canals also gives saltwater
easy access to interior marshes, raising their salinity and killing the
grasses and bottomwood forests from the roots up. No vegetation is left
to prevent wind and water from wearing the marshes away. In a study funded
by the oil and gas industry, Penland documented that the industry has caused
one third of the delta's land loss.
-
- Alligator Science
-
- The Duet brothers know firsthand how various factors
accelerate land loss beyond natural subsidence. Toby and Danny, two of
Penland's local pals along our route, live on a 50-foot beige barge complex
anchored in the middle of 15 square miles of broken marsh, some 20 miles
northwest of Port Fourchon. Their family leased the land from oil companies,
for fishing and hunting, 16 years ago when it was merely wet. Now it lies
under five to eight feet of water. They filter rain for drinking water,
process their own sewage, catch the food they eat and make money hosting
overnight fishing parties for sportsmen. A dozen wellheads dot the marsh
where Toby picks us up by boat. Heading out to the barge through one canal,
he says, "I used to be able to spit to the mud on either side. Now
they run big oil containers through here."
-
- Inside the barge's wide-open room, Danny offers other
measures: "Two years ago we drove a wooden two-by-four into the mud
on the edge of a canal, to stake our alligator trap. I went past it the
other day; the edge has receded 18 feet from the stake. Doesn't much matter,
though. The gators are gone. Water's too salty."
-
- With the marsh disappearing, the delta's only remaining
defense is some crumbling barrier islands that a century ago were part
of the region's shoreline. The next morning Penland and I travel an hour
down the coast to the Louisiana Universities Marine Consortium, a scientific
outpost in Cocodrie, an encampment of scientists and fishermen on the coast's
edge. From there we head out in one of the consortium's gray research boats.
-
- The boat pounds across what appears to be choppy sea
for 50 minutes before we reach Isles Dernieres ("last islands"
in French). But the open surf is never more than seven feet deep. The vast
reach of shallow water was once thick with swaying grasses, parted occasionally
by narrow, serpentine waterways full of shrimp, oysters, redfish and trout.
Penland beaches us in the bayside mud. We walk across a mere 80 yards of
barren sand before we toe the ocean. A similarly diminutive outcrop is
visible in the distance to either side. They are what remains of a once
very long, staunch island lush with black mangroves. "It broke up
ocean waves, cut down storm surges and held back saltwater so the marsh
behind it could thrive," Penland says in mourning. Now the ocean rushes
right by.
-
- Louisiana's barrier islands are eroding faster than any
around the country. Millions of tons of sediment used to exit the Mississippi
River's mouth every year and be dragged by longshore currents to the islands,
building up what tides had worn away. But in part because levees and dredging
prevent the river's last miles from meandering naturally, the mouth has
telescoped out to the continental shelf. The sediment just drops over the
edge of the underwater cliff into the deep ocean.
-
- Back in New Orleans the next day it becomes apparent
that other human activities have made matters worse. Cliff Mugnier, an
L.S.U. geodesist who also works part-time for the Corps of Engineers, explains
why from the third floor of the rectangular, cement Corps headquarters,
which squats atop the Mississippi River levee the Corps has built and rebuilt
for 122 years.
-
- Mugnier says that the earth beneath the delta consists
of layers of muck--a wet peat several hundred feet deep--formed by centuries
of flooding. As the Corps leveed the river, the city and industry drained
large marshes, which in decades past were considered wasteland. Stopping
the floods and draining surface water lowered the water table, allowing
the top mucks to dry, consolidate and subside, hastening the city's drop
below sea level--a process already under way as the underlying mucks consolidated
naturally.
-
- That's not all. As the bowl became deeper, it would flood
during routine rainstorms. So the Corps, in cooperation with the city's
Sewerage and Water Board, began digging a maze of canals to collect rainwater.
The only place to send it was Lake Pontchartrain. But because the lake's
mean elevation is one foot, the partners had to build pumping stations
at the canal heads to push the collected runoff uphill into the lake.
-
- The pumps serve another critical function. Because the
canals are basically ditches, groundwater seeps into them from the wet
soils. But if they are full, they can't take on water during a storm. So
the city runs the pumps regularly to expel seepage from the canals, which
draws even more water from the ground, leading to further drying and subsidence.
"We are aggravating our own problem," Mugnier says. Indeed, the
Corps is building more canals and enlarging pumping stations, because the
lower the city sinks, the more it floods. In the meantime, streets, driveways
and backyards cave in, and houses blow up when natural-gas lines rupture.
Mugnier is also worried about the parishes (counties) bordering the city,
which are digging drainage canals as they become more populated. In St.
Charles Parish to the west, he says, "the surface could subside by
as much as 14 feet."
-
- The Scare
- Humankind can't stop the delta's subsidence, and it can't
knock down the levees to allow natural river flooding and meandering, because
the region is developed. The only realistic solutions, most scientists
and engineers agree, are to rebuild the vast marshes so they can absorb
high waters and reconnect the barrier islands to cut down surges and protect
the renewed marshes from the sea.
-
- Since the late 1980s Louisiana's senators have made various
pleas to Congress to fund massive remedial work. But they were not backed
by a unified voice. L.S.U. had its surge models, and the Corps had others.
Despite agreement on general solutions, competition abounded as to whose
specific projects would be most effective. The Corps sometimes painted
academics' cries about disaster as veiled pitches for research money. Academia
occasionally retorted that the Corps's solution to everything was to bulldoze
more dirt and pour more concrete, without scientific rationale. Meanwhile
oystermen and shrimpers complained that the proposals from both the scientists
and the engineers would ruin their fishing grounds.
-
- Len Bahr, head of the governor's Coastal Activities Office
in Baton Rouge, tried to bring everyone together. Passionate about southern
Louisiana, Bahr has survived three governors, each with different sympathies.
"This is the realm in which science has to operate," Bahr says.
"There are five federal agencies and six state agencies with jurisdiction
over what happens in the wetlands." Throughout the 1990s, Bahr says
with frustration, "we only received $40 million a year" from
Congress, a drop compared with the bucket of need. Even with the small
projects made possible by these dollars, Louisiana scientists predicted
that by 2050 coastal Louisiana would lose another 1,000 square miles of
marsh and swamp, an area the size of Rhode Island.
-
- Then Hurricane Georges arrived in September 1998. Its
fiercely circulating winds built a wall of water 17 feet high topped with
driven waves, which threatened to surge into Lake Pontchartrain and wash
into New Orleans. This was the very beast that L.S.U.'s early models had
warned about, and it was headed right for the city. Luckily, just before
Georges made landfall, it slowed and turned a scant two degrees to the
east. The surge collapsed under suddenly chaotic winds.
-
- A Grand Plan
-
- The scientists, engineers and politicians who had been
squabbling realized how close the entire delta had come to disaster, and
Bahr says that it scared them into reaching a consensus. Late in 1998 the
governor's office, the state's Department of Natural Resources, the U.S.
Army Corps of Engineers, the Environmental Protection Agency, the Fish
and Wildlife Service and all 20 of the state's coastal parishes published
Coast 2050--a blueprint for restoring coastal Louisiana.
-
- No group is bound by the plan, however, and if all the
projects were pursued, the price tag would be $14 billion. "So,"
I ask in the ninth-floor conference room adjacent to the governor's office
in Baton Rouge, "give me the short list" of Coast 2050 projects
that would make the most difference. Before me are Joe Suhayda, director
of L.S.U.'s Louisiana Water Resources Research Institute, who has modeled
numerous storm tracks and knows the key scientists, Corps engineers, and
city emergency planners; Vibhas Aravamuthan, who programs L.S.U.'s computer
models; Len Bahr; and Bahr's second-in-command, Paul Kemp. All were involved
in designing Coast 2050.
-
- First and foremost, they decide, build a river diversion
at several critical spots along the Mississippi, to restore disappearing
marshland. At each location the Corps would cut a channel through the river
levee on its south side and build control gates that would allow freshwater
and suspended sediment to wash down through select marshes toward the gulf.
The water could disrupt oyster beds, but if the sites were carefully selected,
deals could be made with landowners.
-
- Every 24 minutes Louisiana loses one acre of land.
-
- The second step: rebuild the southern barrier islands
using more than 500 million cubic yards of sand from nearby Ship Shoal.
Next, the Corps would cut a channel in the narrow neck of the river delta
at about halfway down. Ships could enter the river there, shortening their
trip to interior ports and saving them money. The Corps could then stop
dredging the southern end of the river. The mouth would fill with sediment
and begin overflowing to the west, sending sand and silt back into those
longshore currents that could sustain the barrier islands.
-
- The channel plan might be integrated into a larger state
proposal to build an entire new Millennium Port. It would provide deeper
draft for modern container ships than the Port of New Orleans and its main
channel, the Mississippi River Gulf Outlet (MRGO, pronounced Mr. Go), which
the Corps dredged in the early 1960s. The outlet has eroded terribly--from
500 feet across, originally, to 2,000 feet in places--and let in a relentless
stream of saltwater that has killed much of the marsh that once protected
eastern New Orleans against gulf storms. If the channel or the Millennium
Port were built, the Corps could close MrGo.
-
- A remaining chink in the delta's armor is the pair of
narrow straits on Lake Pontchartrain's eastern edge where it connects to
the gulf. The obvious solution would be to gate them, just as the Netherlands
does to regulate the North Sea's flow inland. But it would be a tough sell.
"We've proposed that in the past, and it's been shot down," Bahr
says. The project's costs would be extremely high.
-
- This list of the most promising Coast 2050 projects is
only one small group's vision, of course, yet other established experts
concur with its fundamentals. Ivor van Heerden, a geologist who is deputy
director of L.S.U.'s Hurricane Center, concurs that "if we're going
to succeed, we've got to mimic nature. Building diversions and reestablishing
barrier-island sediment flows are the closest we can come." Shea Penland
pretty much agrees, although he warns that the Mississippi River may not
carry enough sediment to feed multiple diversions. U.S. Geological Survey
studies by Robert Meade show that the supply of suspended sediment is less
than half of what it was prior to 1953, diverted mostly by dams along the
river's course through middle America.
-
- With no action, one million people could be trapped.
-
- As far as the Corps is concerned, all of the Coast 2050
projects should be implemented. The first to become a reality is the Davis
Pond diversion, due to begin operating by the end of this year. Project
manager Al Naomi, a 30-year Corps civil engineer, and Bruce Baird, a biological
oceanographer, brought me to the construction site on the Mississippi's
southern levee, 20 miles west of New Orleans. The structure looks like
a modest dam, in line with the levee. Steel gates in its midsection, each
large enough to drive a bus through, will open and close to control water
flowing through it. The water will exit into a wide swath of cleared swamp
that extends south for a mile, forming a shallow riverbed that will gradually
disperse into boundary-less marsh. The structure will divert up to 10,650
cubic feet per second (cfs) of water from the Mississippi, whose total
flow past New Orleans ranges from less than 200,000 cfs during droughts
to more than one million cfs during floods. The outflow should help preserve
33,000 acres of wetlands, oysterbeds and fishing grounds.
-
- The Corps is bullish on Davis Pond because of its success
at Caernarvon, a smaller, experimental diversion it opened in 1991 near
MrGo. By 1995 Caernarvon had restored 406 acres by increasing the marsh's
sediment and reducing its salinity with freshwater.
-
- Who Should Pay?
-
- The corps of engineers is hiring more scientists for
projects such as Davis Pond, a signal that the fragmented parties are beginning
to work better together. Bahr would like to integrate science and engineering
further by requiring independent scientific review of proposed Corps projects
before the state signed on--which Louisiana would need to do because Congress
would require the state to share the cost of such work.
-
- If Congress and President George W. Bush hear a unified
call for action, authorizing it would seem prudent. Restoring coastal Louisiana
would protect the country's seafood and shipping industries and its oil
and natural-gas supply. It would also save America's largest wetlands,
a bold environmental stroke. And without action, the million people outside
New Orleans would have to relocate. The other million inside the bowl would
live at the bottom of a sinking crater, surrounded by ever higher walls,
trapped in a terminally ill city dependent on nonstop pumping to keep it
alive.
-
- Funding the needed science and engineering would also
unearth better ways to save the country's vanishing wetlands and the world's
collapsing deltas. It would improve humankind's understanding of nature's
long-term processes--and the stakes of interfering, even with good intentions.
And it could help governments learn how to minimize damage from rising
seas, as well as from violent weather, at a time when the U.S. National
Oceanic and Atmospheric Administration predicts more storms of greater
intensity as a result of climate change.
-
- Walter Maestri doesn't welcome that prospect. When Allison,
the first tropical storm of the 2001 hurricane season, dumped five inches
of rain a day on New Orleans for a week in June, it nearly maxed out the
pumping system. Maestri spent his nights in a flood-proof command bunker
built underground to evade storm winds; from there he dispatched police,
EMTs, firefighters and National Guardsmen. It was only rain, yet it stressed
the response teams. "Any significant water that comes into this city
is a dangerous threat," he says. "Even though I have to plan
for it, I don't even want to think about the loss of life a huge hurricane
would cause."
-
- © 1996-2005 Scientific American, Inc. All rights
reserved.
- Reproduction in whole or in part without permission is
prohibited.
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