The term levee refers to a natural or artificial barrier, fill or wall alongside a body of water that prevents sea-level rise and flooding from pouring into low-lying or flood plain lands.
This barrier, also referred to as a dike or flood embankment, is a major flood prevention measure and critical to protecting inhabited areas and arable lands from storm surge.
Naturally occurring levees are built over time when mud and dirt form mounds on river flood plains next to the banks after the waterway floods and then the receding water pulls organic matter toward the initial stream. Ridges build up next to waterways after several floods have occurred. Steep banks can form natural levees around rivers, creeks, streams, and other bodies of flowing water, especially in areas where fine sediment and mud are common.
Constructed levees were a private enterprise in the United States until passage of the the Flood Control Acts (FCA), the first version of which was passed in 1917 and thereafter revised numerous times to account for changes in governmental structure, oversight functions, technology, and state-federal relationships. The FCA dedicated resources and land to the creation of levees in response to devastating flooding in the 1800s and early 1900s. After the FCA, levees were constructed by the federal government and seen as a national interest. Although there are construction standards for levees, there are not maintenance standards. Upkeep of levees is widely disregarded, and disrepair has been blamed for deaths and property destruction from flooding disasters following extreme weather events.
In the United States there are 14,000 miles of known levees that are under the jurisdiction of the U.S. Army Corps of Engineers. In the 1990s and early 2000s, the Federal Emergency Management Agency (FEMA) identified almost three times as many miles of levees that are not officially maintained. However, in many cases levees are not constructed by any official or organization. Since levees can be constructed as simply as bulldozing earth into a mound, there are thousands of miles of unofficial levees that are not monitored or maintained except by their owners. For example, many times farmers create levees surrounding the water elements on their farms to protect crops. Similarly, land developers may do the same to prevent residential or commercial flooding.
Many problems can arise when levees are not maintained or are constructed poorly. A levee that is not structurally sound can pose a severe risk to inhabited areas, such as the breached levees in New Orleans in 2005, when Hurricane Katrina caused flooding into lowland areas. The failure in the levees caused over 100,000 families to be displaced due to flooding. Because the main purpose of a levee is to keep water from flowing into an area, once breached, a levee may also act as a barrier for water trying to return to its origination point.
See also Hurricanes ; Katrina .
Palca, J. “Levee Rebuilding Questioned After Sandy Breach.” National Public Radio. November 4, 2012. http://www.npr.org/2012/11/04/164193857/levee-rebuilding-questioned-after-sandy-breach (accessed November 17, 2012).
Alyson C. Heimer, MA