BASIC DETAILS ABOUT NEW ORLEANS’ FLOOD CONTROL SYSTEM:

Sarah,

As I’m sure you remember, the levee system in New Orleans failed in 2005 and catastrophic flooding resulted.  After the disaster, the government rebuilt the flood control system.  Last month the new system faced a test against Hurricane Isaac and passed.  Here is a description of the system currently in place:

Levees:

The easiest way to think of levees is to think of city walls.  Just like a fortified ancient city, New Orleans is surrounded by 130 miles of walls.  The newer walls are 30 feet high.  Instead of repelling invaders, these walls protect against rising water levels.  During a storm, the water level on the outside of the walls may be higher than the water level inside the walls.  When one of the walls fails or the water level exceeds the height of the wall, water flows into the city.  New Orleans has walls on all sides because it is completely surrounded by water and it is below sea level.  On one side of the city is the Mississippi River.  On the other side of the city is an enormous lake called Lake Pontchartain.

 

 

 

 

 

 

 

Pumps, Canals, and Floodgates:

Walls are useless if the enemy is already inside.  In a hurricane, enough rain can fall on New Orleans itself to cause flooding.  Accordingly, a system is in place to pump water out of the city as well. 

The system relies on a series of canals that run through the city.  At the end of each canal is a floodgate that moves up and down to control water from coming in and out of the city.  In a storm, water collects in these canals and is then pumped outside the city.  The new pumps installed after Katrina can fill an Olympic size swimming pool in four seconds.

These canals are also bordered by levees.  In a storm, the water level in the canals is higher than the water level in the rest of the city.  During Katrina, these canal levees broke.  This failure was particular upsetting because the water level was not above capacity; the walls simply failed.  The water locked inside the canal that cut through the city rushed through the breach in the wall and flooded New Orleans.  You could argue that the city was flooded from within.

Bottom line: I did not know that much of the water flooding New Orleans came from a canal inside the city.  I was picturing a huge wave going over an outside wall and entering the city like an invading army.  The canal breach is much more terrifying.  It’s like having a huge shark tank in your living room that could break at any second.