Hurricanes

Katrina approaching New Katrina approaching New OrleansOrleans

August 2005August 2005

What is a hurricane?What is a hurricane? A large rotating storm A large rotating storm

– centered around an area of very low pressurecentered around an area of very low pressure– strong winds blowing at an average speed strong winds blowing at an average speed

over 74 miles per hourover 74 miles per hour The whole storm system may be up to 10 The whole storm system may be up to 10

miles high and on average 500 miles widemiles high and on average 500 miles wide It moves forward like an immense It moves forward like an immense

spinning top, at speeds up to 20 mphspinning top, at speeds up to 20 mph

How do hurricanes How do hurricanes form?form?

For a hurricane to form, you need two For a hurricane to form, you need two things:things:

1.1.Warm, moist airWarm, moist air2.2.Just the right wind conditionsJust the right wind conditions

http://www.aoml.noaa.gov/hrd/tcfaq/A15.html

Engineers protecting Engineers protecting peoplepeople

Ways that engineers can protect people Ways that engineers can protect people from hurricanes:from hurricanes:– Early warning systemsEarly warning systems– Strong buildings, bridges and roadsStrong buildings, bridges and roads– Flood prevention Flood prevention

LeveesLevees PumpsPumps FloodwallsFloodwalls

All About LeveesAll About Levees Protect people from the Protect people from the

flooding of a river or lake.flooding of a river or lake.

Made from piled dirt that Made from piled dirt that is wide at the bottom and is wide at the bottom and level at the top. level at the top. Sometimes extra Sometimes extra sandbags are used at the sandbags are used at the top for reinforcement.top for reinforcement.

Some areas that see a lot Some areas that see a lot of flooding may have not of flooding may have not just one, but several just one, but several levees. levees.

LeveeRiver or Lake

Levee

Side View

Top View

What happened in New What happened in New Orleans?Orleans?

Brief New Orleans Brief New Orleans historyhistory

Founded in the 19Founded in the 19thth century century Mississippi River seasonal flooding was always an Mississippi River seasonal flooding was always an

issue, with additional occasional floods from the issue, with additional occasional floods from the lake during severe storms.lake during severe storms.

Levee construction began along the Mississippi Levee construction began along the Mississippi soon after the city was founded.soon after the city was founded.

Small lake levees were built and then expanded in Small lake levees were built and then expanded in the 1920s as the land near the lake was the 1920s as the land near the lake was developed. developed.

A pump and canal system was built to keep water A pump and canal system was built to keep water out.out.

As hurricane Katrina moved over land, the water As hurricane Katrina moved over land, the water it brought poured into the lake.it brought poured into the lake.

The levees could not hold back the water. They The levees could not hold back the water. They broke in three places, letting water pour into the broke in three places, letting water pour into the city.city.

The lake is usually 1 foot above sea level, and it The lake is usually 1 foot above sea level, and it peaked at 8.6 feet above sea level.peaked at 8.6 feet above sea level.

New Orleans New Orleans sits between sits between Lake Lake Pontchartrain Pontchartrain and the and the Mississippi, Mississippi, below sea below sea level.level.

Katrina’s impact..Katrina’s impact.. At first, it seemed that N.O. had At first, it seemed that N.O. had

missed the brunt of the storm.missed the brunt of the storm. Industrial Canal levee breach, Industrial Canal levee breach,

major breaches at 17major breaches at 17thth and and London Street levees.London Street levees.

In a portion of the city's 9In a portion of the city's 9thth Ward, reported 3 pump failures. Ward, reported 3 pump failures.

A 200 ft. breach in the 17A 200 ft. breach in the 17thth Street Canal levee flooded the Street Canal levee flooded the area under 25 ft. of water.area under 25 ft. of water.

Smaller breaches and Smaller breaches and “overtoppings” throughout the “overtoppings” throughout the city.city.

Researching what Researching what happened..happened..

Several groups of engineers and scientists have been Several groups of engineers and scientists have been researching exactly what happened in New Orleansresearching exactly what happened in New Orleans — and why. — and why.

Hurricane Katrina storm surges resulted in numerous Hurricane Katrina storm surges resulted in numerous breaches that flooded approximately 75% of the New breaches that flooded approximately 75% of the New Orleans metropolitan area. Orleans metropolitan area.

Evidence indicates that most of the levee and Evidence indicates that most of the levee and floodwall failures were caused by overtopping, floodwall failures were caused by overtopping, however other factors were the reason for failure in however other factors were the reason for failure in the 17the 17thth Street Canal and London Avenue Canal Street Canal and London Avenue Canal breaches. breaches.

What happened, What happened, cont’d...cont’d...

Data suggests that structural failure due to seepage and Data suggests that structural failure due to seepage and piping and even weak soil layers within or under the piping and even weak soil layers within or under the earthen levees combined to contribute to the levees and earthen levees combined to contribute to the levees and walls to giving way against the shear force. walls to giving way against the shear force.

Additionally, investigators have not ruled out other Additionally, investigators have not ruled out other contributing factors, such as trees growing near the contributing factors, such as trees growing near the levees that may have undermined fills or weak soil levees that may have undermined fills or weak soil layers. layers.

The wider debate still continues on with evidence that The wider debate still continues on with evidence that the sheet piles were not driven to sufficient depth, the sheet piles were not driven to sufficient depth, perhaps allowing entire sections of earthen levees with perhaps allowing entire sections of earthen levees with wall to shift.wall to shift.