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Homeland Security

New Orleans Hurricane Risk

As a result of its elevation near sea level, the Lake Pontchartrain Basin is quite vulnerable to tropical storms and hurricanes. Hurricanes are categorized by their windspeed in miles per hour (mph). Hurricanes have affected the Louisiana coastline with a frequency that peaks in September. Hurricanes with significant monetary or human loss are memorialized by retiring their name.

In addition to its separation from the coast, the topography of the land in the city of New Orleans is adverse. The city is surrounded by a river levee system 25 feet high along its southern boundary, and by hurricane protection levees about 15 feet high along the remaining boundaries. Most of the land in the city is below sea level, with much of the northern half of the city more than 5 feet below sea level. About one half of the population of the city can't and won't evacuate during a hurricane. Many people, about 200,000, do not have automobiles or access to an automobile. There are an additional 20,000 special needs people that cannot be easily moved. Finally, there several hundred thousand people that will not evacuate because of the difficulty of actually evacuating and finding suitable shelters. The hurricane protection levees surrounding the city are designed to protect the city from a category slow 2 or fast category 3 hurricane. Thus for any slow category 3, or category 4 or 5 hurricanes, the possibility exists for flooding the metropolitan area of New Orleans. The city of New Orleans averages 1.8 m (6 ft) below sea level, resembling a shallow depression surrounded by levees and water.

The levee system in New Orleans is one of the most extensive in the world. Levees are earthen structures, made of clay (sedimentary particles smaller in diameter than sand and silt), in cross section forming a truncated triangle. The base is commonly 10 times as wide as the height. Floodwalls are concrete and steel walls, built atop a levee, or in place of a levee, often where space is insufficient for a levee's broad base.

Orleans Levee District, a quasi-governmental body, is resposponsible for 129 miles of earthen levees, floodwalls, 190 floodgates, 2 flood control structures, and 100 valves. The governor appoints six of the board's eight members, and they serve at his pleasure. When a storm approaches it is responsible for closing the hundreds of hurricane protection floodgates and valves on levees surrounding the city. All residents outside of these levees evacuate.

The District's General Fund accounts for all operating funds for the daily operations of the Administrative Offices, Field Forces, Law Enforcement and support operations necessary to maintain the Board's level of services for flood protection and public safety.

The District's Special Levee Improvement Projects Fund (SLIP) accounts for the capital funds for major maintenance and/or capital improvements of all physical property and plant owned by the Board that is identified as directly related to flood protection.

The District's General Improvement Fund accounts for the capital funds for major maintenance or capital improvement of all physical property and plant owned by the Board that is not identified as directly related to flood protection. These projects relate to land reclamation, commercial buildings, improvements (other than buildings), and infrastructure.

The Orleans Marina currently operates with 355 open slips, 66 boathouses, a Harbor Master Office, as well as related marine amenities. The South Shore Harbor Marina was officially dedicated September 19, 1987. The Marina operates with 447 open slips, 26 cover slips, marina center, fuel dock, and Harbor Master Office as well as related marina amenities. The Belle of Orleans gaming operation is housed at South Shore Harbor and is the principal tenant in the harbor. The annual operations require a subsidy to satisfy the operating shortfall resulting from a substantial debt service requirement on the outstanding Marina Public Improvement bonds.

The New Orleans Lakefront Airport commercially operates with 3 fixed base operators, 13 office tenants, and 10 hangar occupants. A hydrocarbon aviation fuel farm facility is used for on-site sales of all aviation fuels at Lakefront Airport. The annual operations require a subsidy to satisfy the operating short-fall resulting from the labor intensive costs of daily operations of Administration, Fire Safety and Maintenance, as well as the reimbursement to the General Fund for an advance used for the early call of the $4,000,000 Fuel Farm Revenue Bonds.

The Mississippi River, which starts at tiny Lake Itasca in Minnesota, is the third largest drainage basin in the world covering 41% of the 48 continuous United States. The river has always been a threat to the security of the valley through which it flows. Major flooding in 1912, 1913, and 1927 destroyed millions of dollars of property. After the flood of 1927 Congress passed the Flood Control Act of 1928. This legislation authorized the Mississippi River and Tributaries (MR&T) project. This project oversees four major flood control methods: Levees, Floodways, Tributary Basin Improvements, and Channel Improvement and Stabilization.

After periods of high water, the Mississippi River's channel at many places is too shallow, too narrow, or too difficult for navigation. The New Orleans District has maintained continuous efforts to improve and stabilize the channel by constructing dikes, revetments, cutoffs, and dredging. The levee setback, as shown above, affords only temporary protection against the river. Once made, it is just a matter of time before the river threatens the relocated levee. To hold the river in the desired alignment and maintain the levee system, its banks are stabalized with revetments.

Furthermore, storm vulnerability is made worse by ongoing wetland loss and barrier island erosion. The Basin is home to more than one million people and is extremely important to the vitality of the Gulf of Mexico ecosystem. For these and many other reasons, it is important to study past tropical storm events to be better prepared for future events.

Prior to 1965, New Orleans had suffered substantial losses of protective barrier islands and wetlands and developed an elaborate system of flood control measures. After Hurricane Betsy struck in 1965, causing more than $1 billion in damages,i hundreds of millions of dollars were spent to upgrade the flood control system that now includes more than 520 miles of levees, 270 floodgates, 92 pumping stations, and thousands of miles of drainage canals. While the new protections did reduce risks to people and property in developed areas, they also encouraged additional development in flood-prone regions. Jefferson Parish and the adjoining Orleans Parish ranked first and second among communities receiving repeat payments for damage claims under the National Flood Insurance Program between 1978 and 1995. These two communities alone accounted for 20 percent of the properties with repeat losses, at an average of nearly three claims per property, for a total of $308 million in claims.

New Orleans' protective levees are designed to withstand only a moderate (Category 3) hurricane storm surge. The flooding occurs by overtopping of the hurricane protection levees along the lake shore. Were they to fail, according to some estimates the city and surrounding areas could suffer upward of $25 billion in property losses and 25,000-100,000 deaths by drowning.

Four storms represent some of the most devastating, and therefore some of the most studied storms, in the Lake Pontchartrain Basin during the Twentieth Century.

Hurricane of 1947 (September 04-21, 1947)

The 1947 Hurricane made landfall near the Chandeleur Islands, LA on September 19, 1947. Wind gusts of 112 mph and a central pressure of 967 millibars (mb) were measured at Moisant International Airport. A storm surge of 3.0 m (9.8 ft) reached Shell Beach, Lake Borgne. Moisant Airport fields were under 0.6 m (2 ft) of water while Jefferson Parish was flooded to depths of 1.0 m (3.28 ft). New Orleans suffered $100 million in damages. Total loss of life was 51 persons. As a result of this storm, hurricane protection levees were built along the south shore of Lake Pontchartrain to protect Orleans and Jefferson Parishes from future storm surges.

Hurricane Betsy (August 08-27, 1965)

Betsy was a fast moving storm (22 mph forward speed) that made landfall at Grand Isle, LA on September 10, 1965. The central pressure at landfall was 948 mb. Grand Isle experienced 160 mph gusts and a 4.8 m (15.7 ft) storm surge that flooded the entire island. Winds gusted to 125 mph in New Orleans with a 3.0 m (9.8 ft) storm surge that caused the worst flooding in decades. Winds reached 100 mph over most of southeast Louisiana and exceeded 60 mph as far inland as Monroe, LA. Offshore oil rigs, public utilities, and commercial boats all suffered severe damage. Loss of life from Betsy was a total of 81 persons, with 58 in the state of Louisiana. Damage in Southeast Louisiana totaled $1.4 billion. The Orleans Levee Board raised the existing levee to a height of 12 ft in response to the flooding caused by Betsy.

Hurricane Camille (August 14-22, 1969)

Camille intensified rapidly in the Gulf of Mexico, reaching Category 5 status by August 16. The small-diameter hurricane headed NE at 14 mph and made landfall in a sparsely populated section of the Mississippi coast on August 17. Wind estimates during landfall reached 175 mph. Atmospheric pressure at landfall was 901 millibars, second only to the Labor Day Hurricane of 1935 (892 millibars) as the most powerful storm ever to reach the U.S. coast. The storm surge generated by Camille flooded areas from lower Plaquemines Parish, LA to Perdido Pass, AL. The storm surge exceeded 24 ft in Pass Christian, MS. A 4.6 m (15 ft) storm surge inundated Boothville, LA. Storm surge reached 2.7 m (9 ft) in the Rigolets and 1.4 m (4.6 ft) in Mandeville, LA. The confirmed U.S death total was 258. Louisiana damages totalled $350 million. Structural damage at landfall was near complete. Louisiana damage was severe south of Empire, LA. New Orleans would have been flooded if the hurricane had followed a track about 10 miles to the west of its actual track. The storm was a category 5 storm and produced flooding of over 20 feet along the Mississippi coast.

Hurricane Georges (September 15 - October 01, 1998)

Georges did extensive damage to Haiti, the Dominican Republic, Puerto Rico and other Caribbean islands. Georges made final U.S. landfall near Biloxi, MS on September 28. The maximum sustained surface wind at landfall was 104 mph and the minimum central pressure was 964 mb. Maximum storm surge in Louisiana was 2.7 m (8.9 ft) at Point la Hache. Maximum surge along the U.S. Gulf Coast was 3.4 m (11 ft) in Pascagoula, MS. Georges severely eroded the Chandeleur Islands which are the first line of storm surge defense for southeast Louisiana and southern Mississippi. Total loss of life was 460 persons, all outside of Louisiana. Dozens of camps not protected by levees were destroyed along the south shore of Lake Pontchartrain. Hurricane Georges was forecast (advisory 44) to have a speed that was so slow that the storm produced flooding that was a full category higher that its category 2-3 intensity. Actually the storm moved to the east and missed the city. When Georges appeared headed for New Orleans, the Superdome was opened as a shelter and an estimated 14,000 people poured in. But there were problems, including theft and vandalism, and people were cooped up in the Superdome for days. Georges again showed the vulnerability of New Orleans to hurricanes, and efforts resumed the following year to improve the levee system along the canals that connect the city with the Lake.

Hurricane Ivan (September 14 2004)

Although Hurricane Ivan did not cause significant damage in New Orleans, the Class 4 hurricane did expose shortcomings in the city's evacuation plans. More than 1 million people tried to leave the city and surrounding suburbs on Tuesday September 14, 2004, creating a traffic jam as bad as or worse than the evacuation that followed Georges. In the afternoon, state police reversing inbound lanes on southeastern Louisiana interstates to provide more escape routes. But the state police never expected the 60 miles between New Orleans and Baton Rouge would turn into a seven-hour-long crawl. Those too poor to leave the city had to find their own shelter - a policy that was eventually reversed, but only a few hours before the deadly storm struck land.

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Page last modified: 13-07-2011 12:49:48 ZULU