Hurricane Katrina roared ashore Aug. 29, 2005, as a Category-3 storm with sustained winds of 205 kilometers per hour (125 miles per hour).
The storm brought heavy rain, 20 to 25 centimeters (8 to 10 inches), and a strong storm surge, 4 to 8 meters high.
The flooding that ensued engulfed more than 80 percent of the city, killed more than 1,800 people in Louisiana and Mississippi, and left hundreds more unaccounted for.
Damages have been estimated at $150 billion.
Many of the levees in the United States were built more than a century ago to protect farmland, and have been negligibly, if at all, maintained. Furthermore, people keep moving into floodplains and into harm’s way.
New Orleans is surrounded by 580 kilometers (360 miles) of levees built at various points over the past 150 years.
Investigations, involving direct observations, as well as numerical and physical modeling, revealed that about 97 kilometers of the levees failed.
After Katrina struck, the Army Corps of Engineers worked furiously to plug the major holes in New Orleans’ levee and floodwall system by June 1, the beginning of the Atlantic hurricane season.
At the end of May, the Corps reported that with few exceptions, it achieved at least a pre-Katrina level of flood and storm protection.
In addition to repairing the levees and floodwalls, it installed floodgates, similar to those the Dutch use.
How fast is New Orleans sinking?
Ever since people altered the course of the Mississippi River, and drained swamps and marshes on the Gulf Coast to create a place to live, New Orleans and the surrounding land have been sinking.
Most of the New Orleans area is sinking at a rate of 6 millimeters per year.
In some areas subsidence rates are much higher, up to 25 millimeters per year.