WATER ALL AROUND US: LAKE VIEWS - Along with the river, the 630-square-mile Lake Pontchartrain dominates the landscape of New Orleans. In the event of a hurricane, it also presents the dominant danger. Some hurricane experts fear that even a moderate hurricane could churn up the lake, causing a sloshing effect that would top the levee, leaving much of New Orleans under water, possibly for months. If the levee were topped, houses such as those near Lakeshore Drive between Canal and Wisner boulevards, could be completely underwater.
(PHOTO BY ELLIS LUCIA / The Times-Picayune)

Levees choke delta growth

The problem for south Louisiana is that the natural protections are rapidly deteriorating, and that in turn is weakening man-made defenses, mainly because the entire delta region is sinking into the Gulf of Mexico. The Louisiana coast resembles a bowl placed in a sink full of water. Push it down, or just tip it slightly, and water rushes in.

Inland areas now see deeper flooding more often from storms. Tropical Storm Frances pushed a 4.5-foot storm surge into St. Charles Parish in 1998, putting U.S. 90 under water for a week, for example. The coast's sinking profile has emergency managers fretting that low points will be cut off during an evacuation -- including Interstate 10, which drops 12 feet below sea level at the railroad underpass near the Jefferson Parish line.

"The big thing that has put coastal processes in fast forward here in Louisiana relative to other systems is the rapid sinking of the land, subsidence," Louisiana State University coastal geologist Greg Stone said. "That makes it a fascinating place. What takes centuries to millennia in another place, here is happening in a decade."

Sinking is largely a natural process: The earth deposited by the river crushes the soft soil below it, and abandoned delta areas slowly disappear under water. But humans have accelerated it. Ironically, flood-protection levees are one of the chief man-made causes of subsidence. When the corps started systematically leveeing the river in the 19th century, it cut off the region's main source of silt, the raw material of delta-building. The weight of large buildings and infrastructure and the leaching of water, oil and gas from beneath the surface across the region have also contributed to the problem.

The Mississippi River delta is subsiding faster than any other place in the nation. And while the land is sinking, sea level has been rising. In the past 100 years, land subsidence and sea-level rise have added several feet to all storm surges. That extra height puts affected areas under deeper water; it also means flooding from weaker storms and from the outer edges of powerful storms spreads over wider areas.

The marshes that ring New Orleans have sunk the quickest. "We live on a platform given us by the Mississippi River," Curole said. "But Yscloskey, New Orleans, all the way to western Terrebonne Parish, we're all in the same boat, and it's sinking."

The combination of sinking land and rising sea level has put the Mississippi River delta on average 2 feet lower relative to sea level than it was 60 years ago, according to studies by University of New Orleans geologists. According to data that UNO researchers gathered for The Times-Picayune, the marshes around Bayou Teche are more than 2 feet, 9 inches lower than they were in 1942. At Schooner Bayou to the west, the figure is more than 1 foot, 4 inches. The New Orleans lakefront has been comparatively lucky, sinking 5 inches in that time.

By 2100 the area will be an additional 3.2 feet below sea level, according to a paper analyzing future trends in sea-level rise and subsidence by scientists at the U.S. Geological Survey, the National Geodetic Survey and other agencies.

Most of the region's original settlements were built on a network of ridges that were relatively safe from flooding. Now they're going under.

"Areas near Shell Beach (in St. Bernard Parish) that didn't flood during (Category 5 Hurricane) Camille did flood during (Category 2 Hurricane) Georges," said University of New Orleans geologist Shea Penland. "The ridges had subsided, trees had died because of saltwater intrusion, and the wetlands are converting from a brackish marsh system to a fragmented salt marsh."

The owners of Campo Marina at Shell Beach have raised the dock and marina shed a total of 3 feet since it opened in 1960.

"Water started coming over the steps, so we raised it. Ten years later it came over the steps again and we raised it. And it still comes up," owner Ken Campo said.

Models predict dire floods, erosion

Computer modeling shows how the threat of flooding has spread and deepened across a wide area. Using digitized maps of the delta landscape from the 1800s up to a projected map for 2020, Louisiana State University engineers Joseph Suhayda and Vibhas Aravamuthan showed how flooding from a hypothetical storm got deeper and spread steadily westward and northward as erosion and subsidence took their toll.

Houma, dry in a 1930 simulation of a Category 3 hurricane, would be surrounded by water in the same storm in 2020. At the same time, flood levels are lower along the coast because there is no longer anything to block the water and cause it to build up; it all flows inland.

As the Mississippi delta sinks, the coastline grows ragged. Saltwater flows farther inland and kills sensitive plants that hold the marshes together. Human activities -- such as canal-building, drilling and dredging -- have sped up the fragmentation of marshes and worn down barrier islands.

Erosion has created a distinct set of problems. Unlike subsidence, erosion doesn't make flooding much deeper or worsen direct hits by major storms. But it has amplified the weaker storms and glancing blows by stronger ones because there is less marsh to slow the floodwaters and wind. Storms in turn tear up marshes and islands and accelerate the cycle of decay.

Marshes are a rough surface that produces drag on moving masses of water and wind, causing a storm-surge wave to lose energy and height and the wind to die down as they move inland. As the marsh disappears, so does the benefit.

Scientists working for the state Department of Natural Resources measured some of these effects during Hurricane Andrew in 1992. Andrew's surge height dropped from 9.3 feet at Cocodrie to 3.3 feet at the Houma Navigation Canal 23 miles to the north. For every mile of the marsh-and-water landscape it traversed, it lost 3.1 inches of height, sparing some homes farther north from more flooding.

Barrier islands are low-lying, eroding outcroppings of delta, but their role in storm surges looms large. Every extra mile of barrier beach and each vertical inch keeps some water from flowing inland during a storm. Even small changes in the islands' shape change the speed and height of storm surges, tides and wave action behind them.

LSU scientist Suhayda has done computer modeling that shows that if barrier islands had not been there during Hurricane Andrew, then Cocodrie would have seen an extra foot of water. If island heights were raised and inlet channels between them narrowed, the surge hitting Cocodrie would have been cut by as much as 4 to 5 feet.

The widening areas of open water across south Louisiana may even allow storms to retain more strength as they move inland, said Hugh Willoughby, director of NOAA's Hurricane Research Division in Miami, though scientists have not yet closely examined the issue.

One example of this phenomenon may have been Hurricane Danny, which made landfall at Grand Isle in 1995. "Hurricane Danny was a tropical storm over Grand Isle and then it intensified," said Curole of the Lafourche levee district. "You can't find a record of any storm or hurricane before that that intensified after it crossed a barrier island."

'We're still recovering'

The emerging new landscape of open water and levees ringing cities and towns is in some ways more dangerous than the old.

The risks vary dramatically depending on where you live. Communities outside federally built hurricane levees -- which protect New Orleans, East Jefferson and parts of St. Bernard, the West Bank and Lafourche Parish -- have little protection from storm surges, depending mostly on smaller levees likely to be topped.

Hurricanes have frayed these communities over the years. Many residents -- mainly younger people -- have moved north. In Dulac, every other block contains businesses that never reopened after Hurricane Andrew pushed a 10-foot flood through town in 1992: a shrimper's supply store, a branch office of the energy exploration company Unocal, Dwayne's barber shop.

On Orange Street, damaged homes and trailers sit shuttered, waiting for the next flood to claim them. "We're still recovering," resident Donald Lirette said. "These houses are rotting because of water, abandoned now. They turn them into crackhouses."

Inside levees, the threat is different.

If enough water from Lake Pontchartrain topped the levee system along its south shore, the result would be apocalyptic. Vast areas would be submerged for days or weeks until engineers dynamited the levees to let the water escape. Some places on the east bank of Orleans and Jefferson parishes are as low as 10 feet below sea level. Adding a 20-foot storm surge from a Category 4 or 5 storm would mean 30 feet of standing water.

Whoever remained in the city would be at grave risk. According to the American Red Cross, a likely death toll would be between 25,000 and 100,000 people, dwarfing estimated death tolls for other natural disasters and all but the most nightmarish potential terrorist attacks. Tens of thousands more would be stranded on rooftops and high ground, awaiting rescue that could take days or longer. They would face thirst, hunger and exposure to toxic chemicals.

"We don't know where the pipelines are, and you have the landfills, oil and gas facilities, abandoned brine pits, hardware stores, gas stations, the chemicals in our houses," said Ivor van Heerden, assistant director of the LSU Hurricane Center. "We have no idea what people will be exposed to. You're looking at the proverbial witch's brew of chemicals."

Scientists address the risk

These complex dangers have inspired some to come up with audacious plans to avert disaster. LSU scientist Suhayda, for example, proposes bisecting New Orleans and Jefferson Parish from east to west with a flood wall rising 30 feet above sea level starting at the foot of Esplanade Avenue, running toward Lake Pontchartrain and then across the city along the Interstate 610 corridor into Metairie. That would create a "community haven" on the river side of the wall where those left behind could retreat, and would protect buildings from floodwaters entering from the lake.

Only in the past few years have government agencies and political and community leaders mobilized to address rising storm risks from the sinking coast and the potential catastrophe in the New Orleans area. The Federal Emergency Management Agency is preparing a plan for the unprecedented response that would be needed if the New Orleans bowl were flooded. The corps has begun a study to look at whether the levees surrounding the New Orleans area should be raised high enough to prevent that scenario. Local scientists, politicians and some business leaders have forged a consensus that the region's best shot for long-term survival is a major effort to rebuild lost marshes and barrier islands. But it would cost at least $14 billion.

The region remains on a precipice. The lucky record of near misses could continue -- or run out. Between 1909 to 1926, for example, three major hurricanes and two smaller storms hit south Louisiana. A series of smaller storms over a few seasons could devastate many towns. A single major storm could cripple New Orleans.

"A legitimate question to ask is: Given this kind of catastrophe, given the city is on its knees, many of its historic structures have been destroyed, considering the massive influx of federal dollars that will be required, do you rebuild it" said Walter Maestri, Jefferson Parish emergency services director. "I don't know the answer to that. Especially since we're below sea level and it can happen again the next week.

"That's a question for the elected political leaders I work for," he said, recalling the founding of New Orleans in 1718 by Jean Baptiste le Moyne, sieur de Bienville. "Planners need to think about that: Do we repeat Bienville's mistake?"