New Orleans sits between (and below) the Mississippi River and Lake Pontchartrain.
Vertical cross-section of New Orleans, showing maximum levee height of 23 feet.
Hurricane and flood preparedness in New Orleans has been an issue since the city's early settlement, as the city was built on a delta marsh, many parts of New Orleans are below the level of neighboring water bodies.
There were many predictions of hurricane risk in New Orleans before the strike of Hurricane Katrina in August 2005. Due to the city's unique geography as well as its levee system and the decrease of surrounding marshland, there have been various plans to mitigate or prevent such an event from being catastrophic, but none were carried out at the time of Katrina. Ongoing strengthening and raising of levees in the area, such as along the outer Mississippi, is primarily intended to contain river flooding.
A category 5 hurricane directly striking New Orleans was calculated to be a one in 500 year event by the Army Corps of Engineers. The Corps of Engineers, along with Louisiana State University (LSU), and the authorities in Jefferson Parish have modeled the effects and aftermath of a Category 5 strike on New Orleans. The outcome was an unprecedented disaster, with extensive loss of life and property. The key problem is an effect called "filling the bowl", when the hurricane drives water into Lake Pontchartrain, which overwhelms weaker levees bordering Pontchartrain and canals leading to it and flows into the below-sea-level city accompanied by water overtopping the levees along the Mississippi on the south side of the city center.
In September 2002, the American RadioWorks aired a documentary, Hurricane Risk for New Orleans, describing the modeling efforts at LSU, the Army Corps of Engineers and the Jefferson Parish Emergency Management Center, the results, and possible long-term solutions. The official budget was highlighted as being far below requirements and is already being considered for increase. There has been criticism of the funding for hurricane preparedness of New Orleans.
"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 category
5 - were to hit the city, much of New
Orleans could find itself under more than 20 ft (6 m) of water"
The January 25, 2005 Louisiana Sea Grant forum (part of an LSU college program) discussed the results of several simulations of strong hurricanes hitting New Orleans. The presentations and animations from the forum are accessible to the public at the forum's website.
In early 2001, FEMA, the Federal Emergency Management Agency of the US Federal Government, listed a hurricane hitting New Orleans as one of the three most serious threats to the nation. The other two were a terrorist attack in New York City and a large earthquake hitting San Francisco.
In-depth media reports
In 2002, the New Orleans Times-Picayune published an award-winning five-part series called Washing Away  that covered various scenarios (including a Category 5 hurricane hitting the city from the south) and explored the various environmental changes that have increased the area's vulnerability. One article in the series concluded, "Hundreds of thousands would be left homeless, and it would take months to dry out the area and begin to make it livable. But there wouldn't be much for residents to come home to. The local economy would be in ruins."
The American Prospect carried "Thinking Big About Hurricanes" on May 23, 2005. That article described the likely aftermath of a major storm surge. "Soon the geographical "bowl" of the Crescent City would fill up with the waters of the lake, leaving those unable to evacuate with little option but to cluster on rooftops - terrain they would have to share with hungry rats, fire ants, nutria, snakes, and perhaps alligators. The water itself would become a festering stew of sewage, gasoline, refinery chemicals, and debris."
Popular Mechanics ran a story in September of 2001 called New Orleans Is Sinking discussing what might happen if a hurricane of this size landed on New Orleans.
Scientific American published an
article by Mark Fischetti in October of 2001 called Drowning New
Orleans. This article begins,
New Orleans is a disaster waiting to happen."
The National Geographic Magazine published a feature in its October 2004 issue titled Gone With the Water. The article's primary focus is on the destruction of the Mississippi delta's wetlands and the effects that this has on the region's ability to withstand a hurricane, in addition to ecological and social impacts. The article begins with a haunting hypothetical worst-case scenario.
The PBS science show Nova aired an episode on the hurricane threat to New Orleans in January 2005, including interviews with New Orleans officials and scientists involved in the LSU study.
The June 2005 FX docudrama Oil Storm depicted a category 4 hurricane hitting New Orleans that forced residents to evacuate and hide out in the Superdome. It went on to speculate about a national economic meltdown caused by the decreased oil supply.
In 2001, The Houston Chronicle published a story, Keeping its head above water: New Orleans faces doomsday scenario which predicted that a severe hurricane striking New Orleans "would strand 250,000 people or more, and probably kill one of 10 left behind as the city drowned under 20 feet of water. Thousands of refugees could land in Houston."
The November 2004 edition of Natural Hazards Observer carried an article entitled What if Hurricane Ivan Had Not Missed New Orleans?, which suggested "The potential for such extensive flooding and the resulting damage is the result of a levee system that is unable to keep up with the increasing flood threats from a rapidly eroding coastline and thus unable to protect the ever-subsiding landscape."
Louisiana's sinking coast
When the Army Corps of Engineers 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. Following the great floods of 1927, the Mississippi River was surrounded by a series of levees meant to protect the city from such floods. In 1965, New Orleans was hit by Hurricane Betsy. This storm caused tremendous amount of flooding in the New Orleans area. The federal government began a levee-building program to protect New Orleans from a Category 3 hurricane (which was the same strength as Betsy.) These series of levees were only completed recently.
However, an unintended consequence of the levees was that natural silt deposits from the Mississippi River were unable to replenish the delta, causing the costal wetlands of Louisiana to wash away and the city of New Orleans to sink even deeper. 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.
The problem with the wetlands was further worsened by salt water intrusion caused by the canals dug by the oil companies and private individuals in this marshland. This erosion of the wetlands not only caused Louisiana to lose 24 square miles per year of land annually and 1,900 square miles of land since the 1930s, but it also destroyed Louisiana's first line of defense against hurricanes.
Hurricanes draw their strength from the sea, so they quickly weaken and begin to dissipate when they make landfall. Hurricanes moving over fragmenting marshes toward the New Orleans area can retain more strength, and their winds and large waves pack more speed and destructive power. 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. Currently Louisiana has 30% of the total coastal marsh and accounts for 90% of the coastal marsh loss in the lower 48 states. The engineering of the river has basically brought the Gulf of Mexico right to the doorstep of New Orleans, making it more vulnerable to hurricanes.
The combination of sinking land and rising seas has put the Mississippi River delta as much as 3 feet lower relative to sea level than it was a century ago, and the process continues. That means hurricane floods driven inland from the Gulf have risen by corresponding amounts. Storms that once would not have had much impact can now be devastating events, and flooding penetrates to places where it rarely occurred before. The problem also is slowly eroding levee protection, cutting off evacuation routes sooner and putting dozens of communities and valuable infrastructure at risk of being wiped off the map.
Disastrous predictions have come true. Katrina, a category 4 storm at landfall, brushed by New Orleans but breached the levees of Lake Ponchartrain, which was several meters above the elevation of New Orleans - which itself was mostly lower than sea level.
As of August 31, 2005, 80% of the city was flooded up to the level of the lake. The only element missing from this scenario is that the Mississippi River was not also overpouring its banks and flooding the city.
The US Corps of Engineers starting in 1920 built the levees (aka dikes) to withstand category 3 hurricanes, and Katrina was a strong category 4. Scientific and engineering studies have long predicted that New Orleans would be eventually washed away by hurricanes and the Mississippi River, although the likelihood of this event happening in the near future was low.
In the wake of Hurricane Katrina
The adequacy of funding for
hurricane preparedness of New Orleans has been questioned in the
aftermath of Hurricane Katrina. Since 2001, many U.S. Army Corps of
Engineers requests for hurricane protection projects have been cut
back or delayed. Critics charge that these cutbacks were a direct
result of funding for the Iraq war and the Bush Administration's tax
cuts. Others argue that it is common for projects like these to be
underfunded and even had the remaining 25% of funding requests been filled,
Southeast Louisiana Project funding:
An international perspective
The Dutch have long had experience of coping with flooding and below sea level cities. As U.S. military engineers struggled to shore up breached levees, experts in the Netherlands expressed surprise that New Orleans' flood systems failed to restrain the raging waters. With half of the country's population of 16 million living below sea level, the Netherlands has been preparing since floods in 1953 that killed 2,000 people. The nation installed massive hydraulic sea walls known as the Delta Works.
"I don't want to sound overly critical, but it's hard to imagine that (the damage caused by Katrina) could happen in a Western country," Ted Sluijter, press spokesman for Neeltje Jans, the public park where the Delta Works are exhibited. "It seemed like plans for protection and evacuation weren't really in place, and once it happened, the coordination" was poor.
After heavy rains several times in the 1990s nearly caused Dutch rivers to overflow their banks, the Netherlands instituted a new policy of "room for the rivers", involving the maintenance of flood plains and nomination of a few smaller settlements on these plains which if necessary would be sacrificed to protect major cities. It also created financial incentives and regulations to encourage the depopulation of these flood plains over time. This environmental-based flood plain approach is directly opposed to the longstanding engineering-based approach, common throughout the Western world, of creating ever higher and stronger artificial flood defenses, concreting river banks, straightening river courses and reclaiming flood plains for development. In the US, the importance of wetlands as natural flood defenses had been increasingly recognized, but there were other priorities.
The Chicago Tribune wrote "Despite continuous warnings that a catastrophic hurricane could hit New Orleans, the Bush administration and Congress in recent years have repeatedly cut funding for hurricane preparation and flood control. The cuts have delayed construction of levees around the city and stymied an ambitious project to improve drainage in New Orleans' neighborhoods."
Editor and Publisher reported that "after 2003, the flow of federal dollars toward SELA dropped to a trickle. The Corps never tried to hide the fact that the spending pressures of the war in Iraq, as well as homeland security -- coming at the same time as federal tax cuts -- was the reason for the strain. At least nine articles in the Times-Picayune from 2004 and 2005 specifically cite the cost of Iraq as a reason for the lack of hurricane- and flood-control dollars." He also wrote "In early 2004, as the cost of the conflict in Iraq soared, President Bush proposed spending less than 20 percent of what the Corps said was needed for Lake Pontchartrain, according to a 16 February 2004, article, in New Orleans CityBusiness."
The Newhouse News Service said "In its budget, the Bush administration had also proposed a significant reduction in funding for southeast Louisiana's chief hurricane protection project. Bush proposed $10.4 million, a sixth of what local officials say they need."
However, the levee failures appear to have occurred on areas of levee that had already been funded, but not hardened or reinforced. The main breach, on the 17th St. Canal was of a concrete wall levee constructed in the last two years.
"Levees would have been higher, levees would have been bigger, there would have been other pumps put in, I'm not saying it would have been totally alleviated but it would have been less than the damage that we have got now." Mike Parker, former Mississippi congressman who headed the Corps from 2001 to 2002
Sidney Blumenthal, from the Clinton Administration, appeared as a guest on BBC's The World 2005/09/01. Blumenthal claimed that the Bush Administration had specifically diverted approved money at the U.S. Army Corps of Engineers from water and storm protection efforts to be used instead by the Corps in Iraq. As a result, the Corps had performed only last-minute and substandard reinforcement of levees some of which subsequently failed. It is unclear that better construction would have held, but was clear that inferior construction had failed.
Until recently, the threat that the loss of the wetlands posed Louisiana was not taken seriously. Thanks to the Breaux Act, and awareness campaigns undertaken by the Louisiana State Government, state and federal officials have pushed a $14 billion plan to rebuild wetlands over the next 30 years, to be funded by oil and gas royalties. But budget constraints in Washington have stymied the plan, though Louisiana will receive $540 million under the energy bill enacted in August 2005. More money for this program is likely to come with aid from Hurricane Katrina.