Short answers, pulled from the story.
The word levee comes from the French verb lever meaning to raise and it first appeared in New Orleans just a few years after the city was founded in 1718. This simple linguistic origin belies the immense engineering challenge that has defined human history with water.
The Mississippi levee system was begun by French settlers in Louisiana in the 18th century and extends some 1,200 miles along the river. By the mid-1980s the system had reached its present extent with an average height of 15 feet and some sections standing as high as 100 feet.
On the 29th of August 2005 the catastrophic failure of levees in Greater New Orleans during Hurricane Katrina exposed the fragility of even the most massive engineering projects. The breach in the 17th Street Canal was caused by the failure of the foundation allowing water to flow through the soil beneath the levee.
The construction of levees has led to a paradoxical situation where the land they protect is slowly sinking beneath sea level due to subsidence. Natural flooding adds a layer of sediment to the floodplain and the added weight of such layers over many centuries makes the crust sink deeper into the mantle.
Levees interrupt floodplain ecosystems that developed under conditions of seasonal flooding and lead to the loss of biodiversity and the degradation of wetlands. The interruption of natural flooding cycles has led to the loss of coastal sediment as the river is prevented from depositing sediment on the delta leading to the erosion of beaches and the loss of land.