Hurricane Katrina – August 29, 2005

Hurricane Katrina was both the deadliest and the costliest hurricane in U.S. history.

Hurricane Katrina was the costliest and one of the deadliest hurricanes in the history of the United States. It was the sixth strongest Atlantic hurricane ever recorded and the third strongest land-falling U.S. hurricane ever recorded. Katrina occurred late in August during the 2005 Atlantic hurricane season and devastated much of the north-central Gulf Coast of the United States. Most notable in media coverage were catastrophic effects in the city of New Orleans, Louisiana. Katrina’s sheer size devastated a one hundred-mile stretch of the Gulf Coast. The storm surge that swept over New Orleans was as high as twenty-seven feet but that was not the main cause of the damage. The levees were fundamentally flawed. They had not been given proper foundations. The soil beneath them was washed away opening the city to the water of Lake Pontchartrain, a source of water beyond anything that the storm surges could produce. The city was drowned.

Katrina was the eleventh named storm, fifth hurricane, third major hurricane, and second category 5 hurricane of the 2005 Atlantic season. It formed over the Bahamas on August 23, 2005, and crossed southern Florida as a moderate category 1 hurricane before strengthening rapidly in the Gulf of Mexico and becoming one of the strongest hurricanes ever recorded in the Gulf. The storm weakened considerably before making its landfall near New Orleans as a category 3 storm on the morning of August 29. The storm surge caused major or catastrophic damage all along the coastlines of Alabama, Mississippi, and Louisiana, including the cities of Mobile, Biloxi, Gulfport, and Slidell. Levees separating Lake Pontchartrain from New Orleans were undermined by the surge, ultimately flooding roughly 80 percent of the city and many areas of neighboring parishes.

This hurricane formed in the third week of August 2005 off the coast of the Bahamas. Over the following seven days it grew from a tropical storm into a catastrophic hurricane. It first made landfall in Florida and then hit along the Gulf Coast in Mississippi, Louisiana, and Alabama, leaving a trail of devastation and human suffering. This hurricane caused physical destruction everywhere along its path. It flooded the historic city of New Orleans, ultimately killing over 1,300 people and it became the most destructive natural disaster in U.S. history. Katrina’s winds and the storm surge that reached as high as twenty-seven feet was an extremely severe blow to New Orleans. It overwhelmed levees all around the city of New Orleans and the consequences for a city of this size, which was already standing, for the most part, below sea level, were pretty dire.

Of course the states of Florida, Alabama, Mississippi, and Louisiana all got hit by Katrina, but New Orleans became the focus for more than one reason. To begin with, it was the biggest city in the area, with a population of about a half million people, and after the first levees began to collapse the entire city was really stuck in the middle of an ocean because the water had reached a level where only boats could give access from one part of the city to another. And, of course, power and telephone communications began to collapse in the process of all this. All this flooding and the destruction of the levees by the twenty-seven-foot high storm surge completely overwhelmed the levees, which were never designed to handle that level of water. So the flooding really destroyed New Orleans, much as the fire that burned Chicago in 1871 destroyed that city and the earthquake and fire that finished off San Francisco in 1906, destroying the economic and cultural centers of that entire region. It was a similar story in Galveston in the famous hurricane of 1900. And even beyond New Orleans, the span of destruction cast by Katrina was widespread all over the coastal areas. Towns and cities, small and large, were destroyed or heavily damaged by the hurricane, but the focus remained on New Orleans. It was here that the greatest damage had occurred and it was here that the greatest challenge was presented to all levels of government as to how to secure rescue of the many stranded people.

When we compare the reaction of the authorities in New Orleans to the approaching storm with the experiences of the people in Florida we find a sharp contrast. In Florida, because they are so accustomed to serious hurricanes, there is a highly developed system of preparation and a coordinated set of organizations that ensure predictable and safe action well ahead of the storm’s arrival. New Orleans rarely has had a serious hurricane, yet it is far more vulnerable than any other place in all of the United States so one would expect that given a repeated series of warnings, all of them predictable as it turned out, there should have been much greater action in preparation than there actually was.

As early as the beginning of May, the director of the National Oceanic and Atmospheric Administration, that is the overall organization that predicts and follows the movement of hurricanes, gave a warning for the upcoming season that it was, in all likelihood, going to be much more violent than in previous years. The director’s estimate was that storms for the year 2005 would have a 70 percent higher chance of an exceptional season and after the first two months of the season had passed all events confirmed that earlier prediction.

On Tuesday, August 23, almost a week before Katrina actually hit New Orleans, the National Weather Service identified a tropical depression in the area of the Bahamas and it looked as if it would develop into a serious hurricane. Military authorities and all other agencies responsible began to issue warning alerts and began to follow the path of this storm every moment of every day. Within a day this tropical storm off the Bahamas had been identified, given the name Katrina, and on the following day it had strengthened to a tropical storm. A day later, on August 25, Katrina was a category 1 hurricane. It made landfall in south Florida later that day and winds were up to eighty mph at that time. The volume of rain and destruction was quite severe. Fourteen to fifteen inches of rain were dropped in some parts and the overall death toll during its one-day passage over Florida was more than a dozen. Over a million people lost power and flooding was found in a number of areas. The total damage to Florida amounted to about $2 billion.

As the storm passed into the Gulf of Mexico and traveled northwards, federal authorities arranged for emergency quantities of food and water to be shipped to all of the states along the Gulf, including Georgia, Alabama, Louisiana, Texas, and South Carolina as well. The recognition was made at that stage that, on the evening of August 25, a very serious hurricane was moving towards the coastal area of the northern part of the Gulf of Mexico. On the afternoon of August 26, a forecast was issued by the National Hurricane Center regarding Katrina. This forecast pointed out that Katrina would make its next landfall as a category 4, or even 5, the highest possible, somewhere along the Gulf Coast, just east of New Orleans. As the hurricane moved it seemed more and more certain, to a degree that the National Health Service had not experienced before, that the path it projected was being followed precisely as anticipated. On top of the direction of landfall and location of landfall, the prediction was that flooding to the level of as much as twenty feet above normal tide levels could be anticipated.

This one factor alone should have been sufficient to terrify every person in New Orleans, had it been observed with greater care, because it is well known that a flood tide of twenty feet was beyond what the levees could withstand. This was now well into August 26, three days before the landfall that would cause all the trouble at New Orleans. But at that point, apart from issuing a state of emergency, the governor of Louisiana had not taken any additional direct action and the mayor of New Orleans, who was responsible for the evacuation of half a million people, took no action either on that day, nor indeed on the following day, August 27. It was late on August 27, after the governor of Louisiana was aware of the indifference on the part of large numbers of people, that she decided to enact what is called the counter flow traffic arrangements. That is a system whereby all incoming traffic to New Orleans is cut off and only exit from New Orleans is permitted. That action made a beginning late on August 27. Action had still to be taken by the mayor to get people moving and get them out of the city, especially those who had no transportation of their own and required buses to be made available for them. By this time, because the storm was moving northwards from the Gulf of Mexico and because there was no outlet for the heightened waves that were created ahead of the storm, the water level at Louisiana and at New Orleans was already rising far above the highest tide level.

In fact, this rise in the water level began to leak through one of the levees, not overtopping it, but simply creating a leak by the pressure from outside and so a beginning was made to the destruction of the levees long before the height of the water caused it. So serious did the danger of the hurricane appear to the director of the National Hurricane Center, that he did what he had never previously done in his life—he personally called the mayor of New Orleans, warning him of the extreme danger from the hurricane and urging him to do everything possible. Despite that further warning and another call from the headquarters of the Hurricane Center, the mayor of New Orleans did not begin a mandatory evacuation until the following morning, Sunday, August 28. In fact, it was too late for many of the people who had no cars and no friends who could accommodate them in their cars. From that time; the disaster that happened when the stadium that so many of these stranded people used as a refuge was damaged to the point where it ceased to provide protection.

Like Chicago in its early battles with flooding, New Orleans’ principal concerns center on water but to a far greater extent than Chicago ever experienced. It might even be said that the greatest engineering challenge facing this city at the mouth of the Mississippi is to keep it from drowning. Additionally, the city has very weak conditions in its foundation, so much so that it has been described as the flattest, lowest, and geologically youngest of any major city in the United States. Average elevation is less than two feet above sea level and no surficial deposits are older than 2,500 years. About half of the urbanized area is at or below sea level. Floods on the Mississippi at times reach twenty feet above sea level and hurricane surges on Lake Pontchartrain to the north of the city have exceeded six feet above sea level. Rainfalls of ten inches within a period of twelve hours have been recorded on several occasions!

It is rare to find a city whose unconsolidated foundations date within the period of human history. They belong to the Holocene Epoch and range in depth from fifteen feet to more than forty-five feet. New Orleans is about forty-five miles from the Gulf of Mexico and more than twice that distance from the mouth of the Mississippi. It is part of that river’s delta, a broad region of bayous and wetlands. Nowadays the main built up part of the city is free from marshes as a result of the extensive measures taken to drain or pump away the water. Both natural and built levees run east and west within the city between the Mississippi River and the Lake Pontchartrain that stretches northwards for more than twenty miles.

Levees extend along both sides of the lower Mississippi for a total distance of 1,500 miles. Farther up the valley of the river these levees are quite high, as much as thirty-six feet with base widths of 360 feet, but those around the city area average only fifteen feet above the natural levee ridges on which they were built. Because the differences in elevation between the water level inside the levees and the lowest parts of the city are so big, there is a great need for a thoroughly dependable levee system. Fortunately, the natural levees overlie coarse-grained inorganic deposits and these are the best shallow foundation soils in the New Orleans area. In addition to the levees, there is a floodway through which water can be by passed during a river flood.

As far as the city is concerned, hurricane-induced flooding can be just as catastrophic as a Mississippi flood. Rarely does a hurricane pass over the center of New Orleans but when it happens the devastation is widespread and costs are enormous. Flooding of populated areas is a certainty. The amount of advance warning is usually less than a day because, although its path can be traced for several days before it strikes land, its behavior as it approaches landfall is unpredictable. What can be done when flooding occurs? To move even a small percentage of the city’s population to safe ground out of town cannot be done in a day. The only practicable alternative is to evacuate vertically, that is move people to floors of homes or buildings that are above flood level.

Diversion of water is the usual method of minimizing threats to the city. To the west is a large floodway beginning far upstream and continuing down the Atchafalaya Basin into the Gulf, affectionately named Old River Control Structure. Half of all the water in the Mississippi when it is at flood stage can be bypassed in this way. On the western outskirts of the city, on the main river, is another diversion, the Bonnet Carre Spillway. It can be opened to divert water from the river into Lake Pontchartrain. It is seldom used but is always available. There is a continuing concern about the stability of these protective measures because of the nature of the underlying sediments. During a major flood in 1973, for instance, part of the Atchafalaya was undermined and one wall failed.

Because there is so much unconsolidated material everywhere in and around the city, compaction of these sediments from time to time is the major cause of subsidence. Land sinking, shoreline erosion, and salt water encroachment all are active and add to this problem of maintaining a consistent level of land. At times these forces cause sudden changes to buildings and facilities. Differential settlement, along with bank failures and flooding are the sorts of things that happen. If allowance is made for sea level variations, the general picture of subsidence rates is about seven inches a century. Local groundwater withdrawals further aggravate the situation.

About one in ten homes and the same proportion of commercial buildings, plus one out of every three streets and sidewalks show signs of differential subsidence. Structures on the natural levees rarely are at risk but the large number built on organic swamp and marsh deposits stand on a very unstable base. Typical conditions include buckling of patios and exposure of foundation slabs. Driveways too subside to such an extent that it is impossible to drive into carports. Gas and water leaks occur as underground utility lines sag. The problem worsens with development as new impermeable coverings of streets, parking lots, and buildings lead to dewatering and compaction in the organic soils beneath and hence subsidence.

When the first settlers occupied some high ground on the banks of the Mississippi almost three hundred years ago, there was little thought about the problems of growth but the risks gradually increased as the settlement expanded. Today the city continues to push its frontiers farther and farther into low-lying marshy tracts where building is possible only with the best of modern technology. Structures six hundred feet tall stand where formerly the ground could not support the weight of one person. Water levels, when the river is in flood, can be as high as twenty-seven feet above the lowest areas of the city. There seems to be great faith in the stability of the dikes, but those responsible for them are always on alert, especially when strong winds blow. Early building techniques used the natural levees. Crossed timber supports and masonry footings constituted the foundations. Later, piles were introduced for the bigger structures. These piles were driven down to the first sand stratum at a fairly shallow depth where sufficient resistance was encountered to indicate a safe foundation. In the late 1930s, one twenty-story hospital was constructed in this way, with piles that went down twenty feet, but within a year or two the building began to settle and before long it had to be abandoned.

Unstable layers of deposits beneath the sandy foundation gave way. At that time there was little detailed knowledge of subsurface geology so no one knew about this weakness. Over time, thousands of borings to depths of 180 feet or more identified the nature of the underlying layers, not only the sand strata that seemed to be strong enough to hold up buildings but beyond that into the deeper Pleistocene deposits. When, in the late 1950s, a second hospital was built close to the site of the former failed one, over 2,000 piles were driven seventy-five feet into the ground, deep enough to reach the Pleistocene deposits even though the building had only nine stories. Some settlement of the ground was anticipated and construction plans took account of this. That building has stood well. The Pleistocene deposits are now the bedrock on which buildings need to rest. Where they are close to the surface pile lengths and numbers can be few. Even so there are deeper strata within the Pleistocene where compaction occurs if the load is great enough. The general rule now is this, the higher the building the deeper the piles. Both the number and type of concrete piles are other considerations. A 1968 building of forty-five stories had piles going down 150 feet, and a still more recent one, having fifty stories, used octagonal piles with diameters of twenty inches and depths of two hundred feet.

In summary, the significance of Katrina in the history of the United States may best be seen when it is compared, as in the following list, with the deadliest and costliest U.S. natural disasters since 1900, even when that list is expanded to include the costs of the Nine Eleven Terrorist assaults.

Top Disasters                                                     Estimated Deaths                            Estimated Damage (in $billions)

Galveston Hurricane, 1900                            8,000                                                   1
San Francisco Earthquake, 1906                 5,000                                                     6
Atlantic–Gulf Hurricane 1919                       600                                                       1
Mississippi Floods 1927                                  246                                                       2
Hurricane San Felipe 1928                            2,750                                                     1
New England Hurricane 1938                       600                                                       4
Northeast Hurricane 1944                             390                                                        1
Hurricane Diane 1955                                     184                                                        5
Hurricane Audrey 1957                                  390                                                         1
Hurricane Betsy 1965                                      75                                                           7
Hurricane Camille 1969                                  335                                                         6
Hurricane Agnes 1972                                     122                                                         8
Hurricane Hugo 1989                                      86                                                           11
Hurricane Andrew 1992                                 61                                                           33
East Coast Blizzard 1993                                270                                                         4
Nine-Eleven Terrorist Attacks                     2,981                                                      18

Katrina is estimated to be responsible for $75 billion (2005 U.S. dollars) in damages, making it the costliest hurricane in U.S. history.

The storm killed at least 1,836 people, making it the deadliest U.S. hurricane since the 1928 Okeechobee hurricane. Criticism of the federal, state, and local government’s reaction to the storm was widespread and resulted in an investigation by the United States Congress and the resignation of FEMA head Michael Brown.

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