A levee is a type of dam that runs along the banks of a river or canal. Levees reinforce the banks and help prevent flooding. By confining the flow, levees can also increase the speed of the water.
Levees can be natural or man-made. A natural levee is formed when sediment settles on the river bank, raising the level of the land around the river.
To construct a man-made levee, workers pile dirt or concrete along the river banks, creating an embankment. This embankment is flat at the top, and slopes at an angle down to the water. For added strength, sandbags are sometimes placed over dirt embankments.
Levees protect the land in many parts of the world. In Europe, levees prevent flooding along the Po, Vistula, and Danube rivers. In the United States, you will find important levee systems along the Mississippi and Sacramento Rivers.
In New Orleans, the systematic construction of levees began in the 19th century. The current levee system dates to the 1960s. The US Army Corps of Engineers designed the levees to withstand the forces of a fast-blowing "Category 3" storm. Work on the levees was not completed; they weren't strong enough to survive the "Category 4" Hurricane Katrina. In August 2005, several levees along waterways of Lake Ponchartrain failed. Water covered 80% of New Orleans.
In California, an aging levee system is used in Sacramento and the Sacramento-San Joaquin Delta. Poor maintenance of the Sacramento levees have made the area prone to flooding.
Global warming has brought stronger storms and greater risks of flooding. Engineers are seeking alternatives to levees for flood control. The answer may lie in modern flood control technologies used in England, Europe, and Japan.
"It appears that the money has been moved in the president’s budget to handle homeland security and the war in Iraq, and I suppose that’s the price we pay. Nobody locally is happy that the levees can’t be finished, and we are doing everything we can to make the case that this is a security issue for us."