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Last Updated: Wednesday September 07 2005 16:55 GMT

Fact file: Katrina hits New Orleans

Flooding in New Orleans

Here's some more detailed information if you want to use what happened for projects and case studies.

The location
  • New Orleans, Louisiana, USA. 30N, 90W

  • On the Mississippi River 180 km upstream from its mouth in the Gulf of Mexico. At the southern shore of Lake Pontchartrain.

  • Altitude: Ranges between 3m above and 3m below sea level. About 80% of the city is below sea level

The city

Population: 469,032 (Estimated in 2003)

History: The city was founded by the French in 1718 and was sold to the United States by Napoleon Bonaparte in 1803. It developed as a port serving ships using the Mississippi and more recently has benefited from the oil extraction and refining industry in the Gulf of Mexico.

Economy: New Orleans is poor by American standards. Median household income is $27,133 compared to a national figure for the USA of $41,994 . Source: 2000 census, U.S. Census Bureau.

Causes

Location: New Orleans' location near the Gulf of Mexico means it is hit by a hurricane every 13 years on average. The hurricane season runs from June 1 to November 30 and September 10 is considered the peak.

Strength of the hurricane: Measured by central air pressure alone Katrina is the fourth most intense storm ever to be recorded in the Atlantic. It is the third most intense ever to hit land in the USA. (Lowest central pressure was 90.2 kPa = 902.00 mbar).

Tropical Storm Katrina formed over the Caribbean on August 23. Two days later it had gathered enough power to be reclassified as a hurricane. Its maximum sustained wind power was 280 km per hour and its strongest gust was 346 km per hour.

Hurricane season 2005: The strength and number of storms that form in any year is affected by water temperatures in the Atlantic and the speed of high level winds.

In 2005 the water was warm which meant lots of powerful storms were likely. The high level winds were weak so it was easier for storms to turn into hurricanes.

Big storms started appearing earlier than normal and a total of seven named storms had already formed by the end of July.

Nature of the evacuation: The city had been evacuated but it's possible that up to 100,000 people stayed behind. They stayed for a variety of reasons but most were unable to leave because they did not have cars or enough money to organise travel. Many residents were too elderly or infirm to travel. Among those left behind in the path of the category four hurricane were the city's weakest and most vulnerable inhabitants.

The effects

Wind: On August 29 Katrina, a category four storm, was producing winds of up to 225 km per hour. Its eyewall passed over the eastern edge of New Orleans hitting the city's buildings and remaining residents with 160 km per hour winds.

Levee failure: The most important damage that the hurricane caused was to the city's flood defences. The levees protecting New Orleans from Lake Pontchartrain failed in three places; London Avenue, Industrial Canal and at one point in the Main Lake Levee.

It's thought that the levees were high enough but not strong enough. They did not overflow but instead collapsed due to the increased water pressure.

Flooding: Since 80% of New Orleans is below sea level the water flowed from the lake into the city and most of the buildings were flooded. The power, water and sewage systems were knocked out and the city was rendered uninhabitable. The number of casualties is not yet known.



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