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Saturday September 17, 2005 6:31 PM

AP Photo NY120

By MATT CRENSON

AP National Writer

All it takes is cash and time.

Given enough money, engineers agree that they could eventually build a system of levees and other flood control structures sufficient to protect New Orleans from another Katrina or even a stronger hurricane. But it would cost billions, and the work might not be completed for up to 30 years.

The question is, and always has been, how much the federal government is willing to pay for that protection.

``New Orleans is what it is because the federal government made it that way,'' said Robert Hartwig, chief economist at the Insurance Information Institute. ``And what it is today - underwater.''

Much of New Orleans, especially the neighborhoods that were most severely flooded by Hurricane Katrina, would not be inhabitable at all without the ramparts that have been constructed around the city over the past 40 years. After Hurricane Betsy destroyed much of New Orleans in 1965, Congress authorized a massive construction project to ensure that such a storm would never threaten the city again.

The project began by raising the levees along Lake Pontchartrain on the city's north side, and linking them to the Mississippi River levees to form the ``bowl'' that encloses New Orleans. Over the years, Congress also approved levees to protect suburbs south and east of the city.

At 13 to 18 feet high those levees are high enough to handle another Betsy, but not a Katrina, a Category 4 hurricane.

``We tend to build for the last storm,'' said Craig Colten, a professor of geography and anthropology at Louisiana State University.

It isn't that nobody thought a storm more powerful than Betsy would ever strike New Orleans. The Army Corps of Engineers had looked into the prospect of building the city's levees up to Category 5 protection. But levee construction projects proceed over decades, and the last one isn't even close to finished. Some of the follow-up projects to the original 1965 effort, added during the 1980s and '90s, aren't scheduled for completion until 2018.

``The whole thing takes a long, long time,'' Colten said.

Now that Katrina has supplanted Betsy as the Crescent City's most recent catastrophic storm, the government is likely to embark on a new round of flood control construction. This time, experts say, the goal is likely to be Category 5 protection, achieved through a diversified approach that includes not just higher levees but storm gates and the abandonment of some low-lying areas.

``City and parish officials in New Orleans and state officials in Louisiana will have a large part in the engineering decisions to come, and the Army Corps of Engineers will work at their side to make the flood protection system stronger than it has ever been,'' President Bush said Thursday evening.

Bringing just the area of New Orleans along the Lake Pontchartrain shoreline up to Category 4 or 5 protection would cost $2.5 billion to $3 billion, according to the Army Corps of Engineers' latest estimates.

For comparison, the National Flood Insurance Program received approval this week to borrow $3.5 billion for the settlement of Hurricane Katrina claims. And the losses to the program could go higher than that, said Ed Pasterick, a senior adviser in the Federal Emergency Management Agency's mitigation division.

Bringing the whole city up to Category 5 protection would take about 30 years, Army Corps of Engineers project manager Al Naomi estimated before Hurricane Katrina. Parts of the project could be expedited, but it will be years before all of New Orleans is protected against the strongest storms.

Katrina may also generate the support needed to go ahead with Coast 2050, a plan to restore some of the marshes and swamps along the Louisiana coast that have disappeared since the 1930s. Those coastal wetlands help decrease the destructiveness of an incoming hurricane by slowing down, and thus spreading out, the storm surge it pushes ashore.

The cost of the Coast 2050 Project would be more than improving the levees - about $14 billion over 30 years, depending on how much of it was implemented.

``There are lots of ways of protecting the city,'' said Joannes Westerink, a civil engineer at the University of Notre Dame who builds computer simulations of hurricane storm surges for New Orleans and other parts of the U.S. coast.

Some experts recommend putting flood gates in the channels that funnel water toward the city, specifically in the Mississippi River itself and in the Rigolets, a narrow passage that connects Lake Pontchartrain and the Gulf of Mexico.

The gates would be left open under normal conditions, allowing water and ship traffic to pass unhindered. In the event of an approaching hurricane they would be closed to keep the storm surge from getting into Lake Pontchartrain or moving up the river.

London has a system of such gates in the Thames River. In the Netherlands, an extensive system of dams and gates protects the population from storm surges.

Within New Orleans itself, experts recommend improving the pumps that are used to remove rainwater from the city. Because the levees around New Orleans create a below-sea level bowl, every drop of rain that falls inside the barrier has to either evaporate or be pumped out.

There's no way that pumps could keep New Orleans dry in a Katrina-scale flood. But if they were elevated and had their own power generation, Colten said, the pumps might be able to pump the city dry in days rather than weeks.

It might also be possible to elevate some neighborhoods above flood level. Civil engineer Henry Petroski of Duke University has even suggested raising the entire city. The city of Galveston, Texas, used that approach after a hurricane washed over it in 1900, killing as many as 8,000 people.

Individual houses could be elevated as well. Many homes in New Orleans are already jacked up off the ground for flood protection, but since the 1950s the majority of them have been built directly on concrete slabs.

And it would be just as helpful to go down as up. New Orleans could create drainage basins inside the levee walls to collect floodwater that would otherwise flow into the lowest-lying neighborhoods.

Finally, some have suggested restoring some of the city's most vulnerable areas to the marshlands they once were. Neighborhoods that are up to 13 feet below sea level today got that way in part because they were built on marsh soils that compacted after being drained. The longer those areas are kept dry, the lower they will sink and the more flood-prone they will become.

Generally, the lowest parts of New Orleans lie in a belt just behind the high ground of the Lake Pontchartrain shoreline that stretches from the Ninth Ward in the east to Jefferson Parish north of Louis Armstrong International Airport.

``The lowest of the low areas probably shouldn't be redeveloped,'' Colten said.

There is plenty of time for the vocal debate that is bound to accompany such proposals. The Army Corps of Engineers estimates it will be next year before the Big Easy's flood protection is back up even to where it was before the storm hit.

``Certainly we're not going to be able to restore the levees back to their original protection before the end of hurricane season,'' said Col. Duane Gapinski, the commander of the U.S. Army Corps of Engineers task force responsible for pumping New Orleans dry.

That leaves vast swaths of the city vulnerable to even a relatively weak tropical storm. But as long as 80 percent of New Orleans remains damaged or destroyed by Katrina, another hurricane would add more insult than injury.

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JUNE 2003    CIVIL ENGINEERING  MAGAZINE

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THE  CREEPING  STORM

J.J. Westerink and R.A. Luettich, all

n the late summer of 1965 a disorganized storm system formed over the warm, tropical waters of the mid Atlantic. Soon the storm grew into a high-powered cyclone—a twisting mass of wind and water that would torment the Gulf Coast in the coming days. The National Hurricane Center gave it a hauntingly innocuous name: Hurricane Betsy.

J.J. Westerink and R.A. Luettich, all

Storm prediction was still in its infancy then and researchers could not get a read on Betsy’s erratic path. She zigzagged north from Puerto Rico and first seemed to be heading straight toward the Carolinas. At the last moment, however, Betsy swerved toward the Bahamas, then again toward Florida, finally veering west of the peninsula and straight toward Louisiana.

On September 9 Betsy hit the southern tip of the state. Almost every building in the small coastal town of Grand Isle was quickly destroyed. With 150 mph (240 km/h) winds, Betsy barreled up the Barataria Basin toward New Orleans. Lake Pontchartrain—which is just north of the city and is connected to the Gulf of Mexico—swelled with raging waters. Easterly winds pounded the high waters, in some areas easily topping the levees meant to protect the city. In streets in the eastern part of town water reached the eaves of houses.

Betsy finally calmed near Little Rock, Arkansas. She had dropped only 4 in. (100 mm) of rain on New Orleans and had claimed 81 lives and caused more than $1 billion in damage. Unlike any storm before it, Betsy made clear that the city was all too vulnerable to hurricanes. Cradled in a wide southern meander of the Mississippi River just north of the Gulf of Mexico, New Orleans is surrounded by Lake Pontchartrain to the north, Lake Borgne to the east, and lakes Cataouatche and Salvador to the south. This ring of freshwater is also surrounded by hundreds of square miles of wetlands and the Gulf of Mexico. To make matters worse, most of the city is below sea level.

Soon after the damage from Betsy was assessed, Congress made a historic decision to appropriate federal funds to build a system of levees to protect the city from a similar storm in the future. Its cultural significance aside, New Orleans was fast becoming the most important port in the nation—feeding commodities up the Mississippi to all of the Midwest and serving as an important base for the burgeoning oil and gas industry. Congress was not about to let it wash away.

Today New Orleans rests within a bowl formed by 16 ft (4.9 m) tall levees, locks, floodgates, and seawalls, the edge of the bowl extending for hundreds of miles. It is bisected from west to east by the Mississippi River, which is also contained within massive engineered embankments. Water flows through and all around the city while its residents go about their daily routines. A system of levees forming a ring around the northern half of the city to protect it from surging waters in Lake Pontchartrain is set to be completed within the next decade. Construction of a similar system around the southern half of the city will probably take several years longer than that.

But almost 40 years after beginning these projects, the U.S. Army Corps of Engineers is in the midst of reassessing them on the basis of an ominous question: Are the protective barriers high enough?

The design of the original levees, which dates to the 1960s, was based on rudimentary storm modeling that, it is now realized, might underestimate the threat of a potential hurricane. Even if the modeling was adequate, however, the levees were designed to withstand only forces associated with a fast-moving hurricane that, according to the National Weather Service’s Saffir-Simpson scale, would be placed in category 3. If a lingering category 3 storm—or a stronger storm, say, category 4 or 5—were to hit the city, much of New Orleans could find itself under more than 20 ft (6 m) of water.

The location of New Orleans was ideal for portage because traders could access the Mississippi from the gulf via Lake Pontchartrain, avoiding the treacherous lower 100 mi (160 km) of the river. In the late 1800s Corps engineers began constructing levees of a more permanent type along the river’s channel and cleared sunken ships, dead trees, and other detritus from its outlet to the gulf. With the levees in place, the lowlands beyond the river did not flood as often, and people began building homes in areas once reserved for alligators, mosquitoes, and yellow fever.

In the spring of 1927, the Mississippi River flooded in a way that had never been recorded before. Raging waters tore through levees in Arkansas, Mississippi, and Louisiana, killing at least 1,000 people and inundating 1 million homes. It was the mighty river’s last hurrah. Soon thereafter, Congress directed Corps engineers to straighten the river in places, add floodgates in others, and increase the height of its levees all the way from Vicksburg, Mississippi, to the gulf. At the same time, New Orleans began developing what has become the most sophisticated drainage network in the United States. Today almost 200 mi (320 km) of canals lead to 22 pumping stations located in the low points of the city. The stations are able to pump 35 billion gal (132.5 million m³) of water per day from the city into the surrounding lakes. They could fill the Superdome stadium, the home of the New Orleans Saints football team, to capacity in 35 minutes.

The city is now well protected from floodwaters from the Mississippi. Storm surge from hurricanes, however, is another matter.

Since variations in the storm’s profile occur more rapidly on land, the AdCirc nodes there become more refined. In the open ocean the nodes are spaced every 15.5 mi (25 km), but in New Orleans they are as close as 330 ft (100 m). A snaking line of highly refined nodes represents the Mississippi River, above. In a bathymetric representation of the same area, top, New Orleans surrounds the 109th flood gauge.

In the Flood Control Act of 1965, passed shortly after Hurricane Betsy pummeled New Orleans, Congress appropriated funds to increase the height of the levees around the northern side of the city, where Lake Pontchartrain ominously abuts what used to be swampland but today is suburbia. With help from a meteorologist from the National Weather Service, Corps engineers determined a wind speed and pressure that they felt closely characterized Hurricane Betsy. The work was done before the development of the Saffir-Simpson scale, which today is used to categorize hurricanes. At the time Corps engineers called their approximation a standard project hurricane (SPH), equivalent to what today would be called a fast-moving category 3 storm.

Engineers determined that the levees bordering the Mississippi River as it passes through the city were sufficient to withstand any surge produced by an SPH. So the idea was to create a rough semicircle of hurricane levees along the boundary of the lake that would start at the Mississippi River levee west of New Orleans and end at a point to the east of the city. Additionally, levees, floodwalls, or both would have to be constructed around each of the area’s drainage canals, as well as around bridges crossing those canals and around the pump stations emptying into the lake.

As the program continued, one project spiraled into another. In 1986 Congress authorized the Corps to build a system of levees around the southern half of the city, also forming a rough semicircle extending to and from the Mississippi River levees. In the mid-1990s Congress continued to expand the southern protection zone, requiring a total of about 65 mi (105 km) of levees and thereby protecting tens of thousands of homes.

“People live their entire lives in an area that is below sea level and it just becomes a fact of life,” says Al Naomi, the project manager for all of the Corps’s hurricane protection levees in southeastern Louisiana. “They just keep taxing themselves for drainage and levee improvements to make sure they can stay here. Staying dry is very important in this city. People will vote for improving drainage before they’ll vote for improving schools.”

Naomi was in high school when the Corps began constructing the levees bordering Lake Pontchartrain. And he will probably retire long before the barriers around the southern part of the city are completed—in 2018 if all goes as expected. In the next few years he will also oversee the beginnings of three Corps levees that are now being constructed around less populated areas outside of New Orleans: Venice, Grand Isle, and Larose. About $900 million has already been spent on Louisiana’s hurricane protection program, and before the current projects are complete more than $1.4 billion will be required.

The basic framing system consists of continuous girder trusses spanning the 90 ft (27 m) distances between columns. These large spans and floor-to-floor heights ruled out the use of conventional steel building framing. The building’s gravity-load-carrying system contains more than 40,000 tons (36,000 Mg) of high-strength steel.

Congress is also currently spending millions of dollars on several Corps studies to assess the feasibility of creating hundreds of miles of levees throughout the marshland of southern Louisiana. Those projects—which would be particularly difficult to construct owing to the scarcity of levee borrow material in wetlands—would cost an additional $1 billion.

ven as the Corps approaches the long-awaited conclusion of some of its first levee projects—with many more on deck—it finds itself in the midst of a major reassessment to determine if any of the levees surrounding the city will actually provide the level of protection for which they were designed.

In the mid-1960s, Corps engineers who were asked to model the storm surge associated with an SPH did not have many tools at their disposal, at least not by today’s standards. With wind speeds developed by the U.S. Weather Bureau, they used variations of Newton’s second law to predict a storm’s conservation of mass and momentum. The engineers created a hypothetical storm in one-dimensional slices, eliminating the geometrical complexity of the real world, then drove it on a straight line from the Atlantic perpendicular to selected locations near the shore of the gulf.

Assuming a constant wind velocity over Lake Pontchartrain, the engineers computed the buildup of water at the levees along the lake’s south shore on an hourly basis. They ran simulations mimicking the characteristics of hurricanes that hit New Orleans in 1915 and 1947 and then used the ratio between the actual storm surge recorded during those hurricanes and their computed value to create a factor of safety for the new levees.

“It was a very coarse approximation,” says Joannes Westerink, a professor of civil engineering at the University of Notre Dame who specializes in computational fluid dynamics. “But it’s what they could do at the time.”

Westerink and a colleague—Rick Luettich, a professor at the University of North Carolina’s Institute of Marine Sciences—have developed a modern hydrodynamic circulation model that seems magical by comparison. Their Advanced Circulation Model for Coastal Ocean Hydrodynamics, or AdCirc, is a two-dimensional numerical model that predicts long-term periods of circulation along coastal shelves, coasts, and estuaries. It is used to predict a wide variety of flows, but during the past decade the Corps has devoted millions of dollars to improve its ability to model hurricanes. For the past four years Corps engineers have been calibrating a model expressly designed to represent the New Orleans area.

Red lines in the AdCirc grid, below, represent levees and other structures that might slow or stop hurricane surge. Researchers are most worried about surge buildup in Lake Pontchartrain, which surrounds the 164th flood gauge north of the city, opposite. Some models indicate that surge in the lake from a strong storm could flood the city to a depth of 25 ft (7.6 m).

The numerical equations that underlie AdCirc are similar to the ones used by Corps engineers back in the 1960s—each a variation on Newton’s second law. But the solutions produced by AdCirc are sufficiently complex to create a two-dimensional storm that actually moves within a defined geographic boundary. The boundary—which includes the Atlantic coast all the way from Nova Scotia to Argentina—is divided into a grid of nodes containing depth of water, land structures, and any other real-world characteristics that would affect the storm’s profile.

As recently as the 1980s, hurricane models were run on single processors, vastly limiting the number of nodes that could be solved efficiently. Today, AdCirc is run on parallel processors—as many as 256—and is capable of continuously solving as many as 1 million geographic nodes. This processing power is what enables AdCirc to solve such a large set of equations. In turn, AdCirc enables modelers to initiate a hurricane simulation on the open sea, where a storm’s path is more predictable and its characteristics can be closely defined.

Because less information is required to accurately simulate a hurricane on the open sea, the nodes in that area are not as rigorously defined as those near the coastal shelf. In the areas of a boundary where more variation of depth exists—on the coastal shelf and on land—the nodes contain highly refined information so that they more effectively define variations in the storm. In a visual representation, this boundary takes the shape of a finite-element grid.

The nodes in the middle of the ocean contain information based on a 15.5 mi (25 km) grid, but they become increasingly refined as they approach the shoreline. In the case of a boundary surrounding New Orleans, where the grid extends inland all the way to Baton Rouge, the nodes over land are spaced every 330 ft (100 m) and include information about topography, canals, levees, and any other land masses that might affect storm surge.

On a supercomputer at the Corps’s Waterways Experiment Station, in Vicksburg, Mississippi, engineers run AdCirc simulations of Hurricane Betsy and of Hurricane Andrew, a category 3 storm when it hit Louisiana in 1992. It takes roughly an hour to run the calculations representing 24 hours in the life of the storm. Eventually a trace of storm surge levels is produced at about 200 locations around New Orleans; Corps engineers then compare those results with the actual surge levels recorded in those areas.

Jay Combe, a Corps engineer in charge of the modeling effort, meets every six months with an advisory panel composed of several of the world’s premier modeling experts to review the results. Once AdCirc has been refined to the point where it satisfies Combe and the review committee, it will be used to conduct a comprehensive reassessment of New Orleans’s existing and planned hurricane levees.

Combe says that point should be reached this summer. “I think we’re getting close to the right answer,” he says. “But I want to feel totally confident. And I want our outside review team to feel that this is the best we can do with the state of the art right now.”

Combe is cautious with his work because he knows how much is riding on it. In the coming months Corps engineers will use AdCirc to determine if the levees that have been going up around New Orleans for the past 40 years are tall enough to resist storm surge from an SPH. Perhaps even more important, when the model is ready Naomi will use it to determine what it would take to protect New Orleans from a category 4 or 5 hurricane.

In 1999 the Corps was authorized by Congress to study the feasibility of various proposals for protecting the city against such devastating storms. An obvious possibility would be to raise the current levees to a height deemed acceptable by an AdCirc analysis. That, however, would also require widening the levees, which may not be possible in many areas because of the proximity of homes. Among other alternatives, Naomi will investigate the possibility of creating an immense wall between Lake Pontchartrain and the gulf to keep water out of the lake during a severe storm. Such a project would involve constructing massive floodgates at the Rigolets and Chef Menteur passes, where storm surge would enter the lake.

According to Naomi, any concerted effort to protect the city from a storm of category 4 or 5 will probably take 30 years to complete. And the feasibility study alone for such an effort will cost as much as $8 million. Even though Congress has authorized the feasibility study, funding has not yet been appropriated. When funds are made available, the study will take about six years to complete. “That’s a lot of time to get the study before Congress,” Naomi admits. “Hopefully we won’t have a major storm before then.”

A time-lapse simulation of Hurricane Betsy—with integrated wind speed and direction—replicates the storm’s movement through Louisiana in 1965. Several hurricane models are calibrated by the surge associated with Betsy, which did not hit New Orleans directly but flooded much of the city.

f a storm of category 4 or 5 were to hit New Orleans before the city was adequately prepared, what toll would it exact?

In the 1980s Joseph Suhayda, then a coastal oceanographer in the civil engineering department at Louisiana State University (LSU), began to seek an answer to this question by simulating storms with a modified version of a hurricane model used by the Federal Emergency Management Agency (FEMA). Suhayda first began modeling the storms to help parishes in southeastern Louisiana determine appropriate flood elevations for FEMA’s National Flood Insurance Program. As his modeling capabilities improved, he began to more closely investigate the level of protection provided by the levees encircling New Orleans.

Suhayda’s model contains a geographic information system overlay that divides a fairly large boundary, from Alabama to Texas, into 0.6 mi (1 km) grids containing information about ground elevations, land masses, and waterways. The FEMA hurricane model does not draw on the same processing power as AdCirc and in general produces more liberal projections of flooding from storm surges. But by solving numerical equations representing a storm’s pressure, wind forces, and forward velocity, Suhayda was able to use the model to predict the storm surge associated with an actual hurricane dozens of hours before it hit land. By subtracting the elevations on a topographical map of coastal Louisiana from those surge values, he was able to approximate the flood risk of a given storm.

In the 1990s, Suhayda began modeling category 4 and 5 storms hitting New Orleans from a variety of directions. His results were frightening enough that he shared them with emergency preparedness officials throughout Louisiana. If such a severe storm were to hit the city from the southwest, for instance, Suhayda’s data indicate that the water level of Lake Pontchartrain would rise by as much as 12 ft (3.7 m). As the storm’s counterclockwise winds battered the levees on the northern shore of the city, the water would easily top the embankments and fill the streets to a depth of 25 ft (7.6 m) or more.

Suhayda’s model is not the only one that describes such a catastrophe. A model called SLOSH (Sea, Lake, and Overland Surges from Hurricanes), which is used by the National Weather Service and local agencies concerned with emergency preparedness, portrays an equally grim outcome should a storm of category 5 hit New Orleans. The SLOSH model does not contain nearly as many computational nodes as does AdCirc, it does not use a finite-element grid to increase the resolution of the nodes on shore, and its boundary is much smaller. Even so, its results are disheartening.

“Suppose it’s wrong,” says Combe, the Corps modeler. “Suppose twenty-five feet is only fifteen feet. Fifteen feet still floods the whole city up to the height of the levees.”

Experts say a flood of this magnitude would probably shut down the city’s power plants and water and sewage treatment plants and might even take out its drainage system. The workhorse pumps would be clogged with debris, and the levees would suddenly be working to keep water in the city. Survivors of the storm—humans and animals alike—would be sharing space on the crests of levees until the Corps could dynamite holes in the structures to drain the area. In such a scenario, the American Red Cross estimates that between 25,000 and 100,000 people would die.

That prospect—and the amount of time it would take the Corps to construct adequate levee protection against a storm of category 4—have inspired Suhayda to push for what he calls a community haven project. His idea is for the city to construct a 30 ft (9 m) tall wall equipped with floodgates through the center of town to protect the heart of New Orleans and such culturally important areas as the French Quarter. That portion of the city lies between two bends in the Mississippi River and is therefore already protected by adequate levees on three sides. With its gates closed, the wall would complete a waterproof ring around the area.

Suhayda says the wall would be cheaper and faster to build than the larger projects under consideration by the Corps. It could be constructed along an existing right-of-way and act as a sound wall most of time. “We’re going to build sound barriers along most of these roads anyway,” Suhayda says. “So for a small added cost, go ahead and make them capable of withstanding wind loads and hydrostatic heads.”

The Corps would not necessarily be involved in the construction of such a wall because the latter would be land based. Even so, Naomi is adamantly opposed to the idea. “How do you protect people from two-hundred-mile-per-hour winds?” he asks. “Where do they go? What buildings are designed to withstand that? Where do they get their power and their food, and where do they rest their heads at night? Just keeping the water out isn’t enough. You don’t want to give people a false sense of security by saying that this is a refuge unless you have a place for them to go.”

For the most part, New Orleans does not have places for people to go. The American Red Cross no longer provides emergency shelters in the city because its officials cannot guarantee the structural integrity of the locations. There simply are not enough buildings in the area that could withstand the forces of a category 4 or 5 storm.

During the past 10 years Marc Levitan, a wind and structural engineer and the director of LSU’s Hurricane Center, has been involved in hundreds of building investigations throughout New Orleans to determine if certain structures could be used as so-called refuges of last resort. “With the vast majority of them, if you really do an analysis, you really wouldn’t want to use them,” he says. “They all have some sort of deficiency.”

Most people would not wish to remain in the city if a category 4 or 5 storm were in prospect, but evacuating could be difficult. Experts say close to 400,000 people could be stranded in the city. There are an estimated 100,000 people without easy access to automobiles, and those who can drive may not be able to do so. During Hurricane Andrew, interstates throughout the South were brought to a standstill because simultaneous evacuations were taking place in several states. The only major planning improvement since then has been the decision to keep traffic away from the coast on both sides of evacuation routes.

Complicating the difficulty in New Orleans is the fact that each of the city’s three major evacuation routes is over or near water. Suhayda’s model indicates that during a storm of category 5 Interstate 10, which is constructed on piers for a distance of almost 20 mi (32 km) west of the city, could be covered by more than 5 ft (1.5 m) of water.

ater has literally made New Orleans what it is today. Some locals call southern Louisiana the re–United States because in essence the ground is made up of sediment from throughout North America that has made its way down the basin of the Mississippi. The decision to live in this place, however, has also made water the enemy.

“We’re trying to enforce human decisions on a natural process,” says Naomi. “What we’re trying to do is take a snapshot of geologic time and say, ‘This is what we want; this is where we want to live.’ The question is, Is it going to be feasible in the long term?”

Naomi says this question will not be answered with levee feasibility studies alone. It will also require a more complete understanding of the natural processes at work in and around New Orleans. For example, the wetlands of coastal Louisiana, which would act as a buffer and slow any storm during its approach to the city, are dying because the freshwater and nutrients that historically flooded into them from the Mississippi can no longer escape the river. At the same time, the sediment deposited here by the river long ago is subsiding, and no new sediment is overflowing to replenish it.

The Corps estimates that in southeastern Louisiana a football field worth of wetlands sinks into the sea every 30 minutes, leaving the residents of the area more vulnerable to hurricanes every inch of the way.

In an attempt to curb this growing threat, or, as some refer to it, creeping catastrophe, the Corps is developing a plan—in collaboration with the U.S. Environmental Protection Agency, the Louisiana Department of Natural Resources, and other state and federal agencies—to rehabilitate coastal wetlands throughout Louisiana. Known as the Coast 2050 Plan, it would require $14 billion over the next 30 years to restore natural drainage along the coast and direct the movement of sediment from the Mississippi to rebuild marshes. It also calls for the installation of sediment traps at key locations in the river, from which the material would be pumped through 100 mi (160 km) long slurry pipelines to rebuild wetlands and barrier islands.

Research conducted in the 1970s indicates that Louisiana’s coast has seen no physical growth since the 1880s. By 1913 it was subsiding at a rate of about 7 sq mi (18 km²) per year. Since 1990 various groups have attempted to stave off the effects of coastal erosion under the auspices of the Coastal Wetlands Planning, Protection, and Restoration Act, but until now there has been no large-scale collaboration.

Naomi says he will be keeping a close eye on the Coast 2050 Plan in the future because he is certain it will affect his assessment of New Orleans’s hurricane protection program. But does the question of subsidence raise a more troubling issue?

“Everyone here sees different symptoms,” says Roy Dokka, a geology professor at LSU and the head of the Louisiana Spatial Reference Center. “If you’re a biologist you see the forest dying. If you’re running an oil field down on the coast you see that the roads you used to drive down are now under water during certain periods of time. If you’re an emergency preparedness person you notice that the evacuation roads tend to flood earlier than they did ten years ago.”

The true situation, however, is almost too grave to consider. “Coastal Louisiana is sinking under its own weight,” Dokka says. “The ground in Louisiana is ultimately going to go under.”

Indeed, the state is subsiding so quickly that the National Oceanic and Atmospheric Administration’s National Geodetic Survey (NGS) considers the orthometric markers in Louisiana surveyed every decade for the North American Vertical Datum (NAVD) to be “obsolete.” Dokka and his colleagues, together with experts from the NGS, are now using high-powered transponders and numerous Global Positioning System satellites to develop “true” elevation points in the state on the basis of their relation to the center of the earth.

Using a rate of subsidence measured at a tidal gauge off the coast of Grand Isle adjacent to an original NAVD marker, Dokka was able to calibrate rates of subsidence at hundreds of other markers around the state. His results indicate that the elevations of some areas have dropped as much as 2 ft (0.6 m) since they were last surveyed for the NAVD. Based on Dokka’s “true” elevations, some of the Corps’s levees in New Orleans may be more than 1 ft lower than their posted elevation.

And the sinking continues. In the next 70 years, Dokka and his colleagues estimate that about 15,000 sq mi (39,000 km²) of land in southern Louisiana will be at or below sea level. In the same amount of time, some of the areas in and around New Orleans will have subsided by 3 ft (0.9 m).

“New Orleans is right there,” Dokka says, pointing to a graphic illustration of his research on a computer screen. “But I guarantee you that won’t last, because the ocean is right there on both sides, and any kind of storm is going to take out that area.”

Such dire predictions would seem to favor a drastic solution, such as the Coast 2050 Plan. But Dokka is not easily convinced. “They’re not going to dump freshwater on the areas where people live,” he says. “Even if they haul up the flag of victory and save the wetlands, these areas where people live will not be saved.”

Instead, Dokka proposes an even more ambitious alternative. In 100 years, he says, subsidence will have made Lake Pontchartrain and Lake Borgne one large lake bordering New Orleans to the north and east and opening into the Gulf of Mexico. By diverting the Mississippi into the lake and using sediment from the river like “a big cement truck” to build up a protective boundary along its north shore, engineers could create “the world’s greatest harbor.”

“It’s all going to be artificial in the end anyway,” Dokka says. “People are just beginning to discover what is happening here. But nature wins. Nature always wins in the end. It doesn’t give up. It just keeps on going.”

ut the Coast 2050 Plan currently has widespread support among environmentalists, the oil and gas industry, and hurricane protection specialists.

People such as Windell Curole consider it the last, best chance to save southeastern Louisiana. Curole (pronounced “cure-all”) is the general manager of the South Lafourche levee district, which maintains hurricane protection levees around Bayou Lafourche, a rural area west of New Orleans and the place where he was raised. Decades ago Curole’s grandfather paddled through the wetlands there in a hollowed-out cypress tree collecting oysters. Today much of the same area is completely submerged in salt water.

On a recent sunny morning, Curole visited a freshwater diversion project near New Orleans called Davis Pond, one of only two such diversions from the Mississippi River. The project involves a canal west of the city that releases about 1,000 cfs (28 m³/s) of freshwater from the top of the river into a 9,300 acre (3,700 ha) pond that eventually feeds into Lake Cataouatche. By filling the marsh with freshwater, the idea is to decrease its salinity while feeding it valuable nutrients, in this way mimicking the marsh environment that would have existed before the sides of the Mississippi were dammed.

First authorized by Congress in the late 1960s, Davis Pond was completed by the Corps in March 2002. In the 1960s it was seen as a fairly aggressive step toward addressing the issue of coastal erosion. Today, in Curole’s words, it is seen more as a “Band-Aid.” The project—which does not divert sediment into the marsh in any measurable quantity—is meant to alleviate a total of about 1 sq mi (2.6 km²) of land loss. By most estimates, coastal Louisiana is losing as much as 35 sq mi (90.6 km²) of land per year to subsidence. Despite this grim reality, Curole refuses to see anything in Davis Pond except signs of hope. “It’s a little leak for the river,” he says, looking over the water, “but a giant leak for mankind.”

This is Curole’s first trip to Davis Pond, a place that he and other supporters of the Coast 2050 Plan hope will be viewed as a sort of pilot project for future diversion efforts. Traveling by airboat over thick, floating marshes and rounded levees, he enthusiastically points at countless alligators, scurrying nutrias, and several bald eagle nests. He snaps pictures of waterfowl as if he has never seen them before, or, more likely, as if he might never see them again.

The boat stops at the end of the pond near a rock weir separating it from Lake Cataouatche, the New Orleans skyline in the distance. “It’s just so nice to see the growth here, the green growth,” Curole says. Smiling large, eternally optimistic, he continues: “If we run this thing harder, up to six thousand cfs, or even more, I think we’ll start seeing white shrimp up in here again. That is a major hurdle. If we can start running this at six thousand cfs, who knows what we can do.”

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Geo Engineering:  Mississippi Delta