A levee is a type of dam or wall, usually a man-made embankment, that acts as a barrier between water and property. It is often a raised berm that runs along a river or canal. Levees reinforce a river's banks and help prevent flooding. By constricting and confining the flow, however, levees can also increase the speed of the water.
Levees can "fail" in at least two ways: (1) the structure is not high enough to stop rising waters, and (2) the structure is not strong enough to hold back rising waters. When a levee breaks at a weakened area, the levee is considered "breached," and water flows through the breach or hole.
A levee system often includes pumping stations as well as embankment. A levee system can fail if one or more of the pumping stations fail.
Definition of Levee
"A man-made structure, usually an earthen embankment or concrete floodwall, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide reasonable assurance of excluding temporary flooding from the leveed area." - U.S. Army Corps of Engineers
Types of Levees
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 (or parallel to any body of water that may rise), to create 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.
Origin of the Word
The word levee (pronounced LEV-ee) is an Americanism - that is, a word used in the United States, but not anywhere else in the world. It should come as no surprise that "levee" originated in the great port city of New Orleans, Louisiana, at the mouth of the flood-prone Mississippi River. Coming from the French word levée and the French verb lever meaning "to raise," handmade embankments to protect farms from seasonal floods became known as levees. A dike serves the same purpose as a levee, but that word comes from the Dutch dijk or German deich.
Levees Around the World
A levee is also known as a floodbank, stopbank, embarkment, and storm barrier.
Although the structure goes by different names, 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, Snake, and Sacramento Rivers.
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.
Levees, New Orleans, and Hurricane Katrina
New Orleans, Louisiana, is largely below sea level. The systematic construction of its levees began in the 19th century and continued into the 20th century as the federal government became more involved with engineering and funding. In August 2005, several levees along waterways of Lake Ponchartrain failed, and water covered 80% of New Orleans. The U.S. Army Corps of Engineers designed the levees to withstand the forces of a fast-blowing "Category 3" storm; they weren't strong enough to survive the "Category 4" Hurricane Katrina. If a chain is as strong as its weakest link, a levee is as functional as its structural weakness.
A full year before Hurricane Katrina slammed into the Gulf Coast, Walter Maestri, the emergency management chief for Jefferson Parish, Louisiana, was quoted in the New Orleans Times-Picayune:
"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." - June 8, 2004 (one year before Hurricane Katrina)
Levees as Infrastructure
Infrastructure is a framework of communal systems. In the 18th and 19th centuries, farmers created their own levees to protect their fertile farmland from inevitable floods. As more and more people became dependent on other people for growing their food, it made sense that flood mitigation was everyone's responsibility and not simply the local farmer. Through legislation, the federal government helps states and localities with engineering and subsidizing the cost of levee systems. Flood insurance has also become a way for people living in high risk areas can help with the cost of levee systems. Some communities have combined flood mitigation with other public works projects, such as highways along riverbanks and hiking paths in recreation areas. Other levees are nothing more than functional. Architecturally, levees can be aesthetically pleasing feats of engineering.
The Future of Levees
Today's levees are being engineered for resilience and built for double duty - protection when needed and recreation in the off-season. Creating a levee system has become a partnership among communities, counties, states, and federal government entities. Risk assessment, construction costs, and insurance liabilities combine in a complex soup of action and inaction for these public works projects. The building of levees to mitigate flooding will continue to be an issue as communities plan and build for extreme weather events, a predictable unpredictability from climate change.
- "USACE Program Levees," US Army Corps of Engineers at www.usace.army.mil/Missions/CivilWorks/LeveeSafetyProgram/USACEProgramLevees.aspx
- "United States of Shame," by Maureen Dowd, The New York Times, September 3, 2005 accessed August 12, 2016
- History of Levees, FEMA, PDF at //www.fema.gov/media-library-data/1463585486484-d22943de4883b61a6ede15aa57a78a7f/History_of_Levees_0512_508.pdf
- Inline photos: Mario Tama/Getty Images; Julie Dermansky/Corbis via Getty Images (cropped)