A natural or artificial embankment along a river channel that confines floodwaters and prevents inundation of adjacent land. Levees are fundamental flood control structures but can increase flood risk if they fail.
A levee is an elongated ridge or embankment that runs parallel to a river channel and serves to contain floodwaters within the channel and prevent inundation of adjacent floodplain areas. Natural levees form through repeated overbank flooding, when sediment-laden floodwaters decelerate as they leave the channel and deposit the coarsest fraction immediately adjacent to the bank. Artificial levees, constructed from compacted earth, concrete, or sheet piling, are among the oldest and most widespread flood control structures worldwide, with the Mississippi River levee system extending over 5,600 km. While levees protect land behind them during floods up to their design capacity, they also eliminate natural floodplain storage, increase peak flows and stages downstream, and disconnect rivers from their floodplains, reducing ecological functions. Levee failures (breaches or overtopping) can produce catastrophic flooding, as exemplified by the 2005 failures in New Orleans during Hurricane Katrina. The U.S. Army Corps of Engineers maintains a National Levee Database inventorying over 48,000 km of levees. Levee certification, required for recognition on FEMA flood maps, involves evaluating structural integrity, freeboard, erosion protection, and maintaining performance standards. Modern approaches to flood management increasingly emphasize levee setbacks and managed retreat to restore floodplain connectivity.