levee

A levee is an elongated embankment built along a river, coastline, or other watercourse to prevent flooding of adjacent land. Levees can be natural, formed by sediment deposition during floods, or artificial, constructed as engineered earthworks.

Natural levees form when rivers overflow and deposit heavier sediments along the banks, creating raised banks parallel to the watercourse. Artificial levees are typically earth structures with a defined crest and slopes, often reinforced with clay cores, rock faces, or other materials. Coastal levees protect inland areas from storm surge and high tides, and some levees rely on concrete walls or gates to manage water flow. In practice, many systems combine elements of earthen embankments with concrete features, floodgates, and drainage infrastructure.

The primary purpose of a levee is to keep water out of inhabited or agriculturally valuable land, protecting homes, roads, and crops and enabling settled riverine activity and navigation. Design variables include crest height and width, slope angles, and the toe of the embankment. A low-permeability core, drainage channels, and seepage-control features such as cutoff walls help reduce internal erosion.

Maintenance and risk are ongoing concerns. Levees require regular inspection, vegetation management, repair of erosion or scour, and sediment management. Failures can result from overtopping, seepage (piping), erosion, or subsidence, potentially leading to catastrophic floods downstream or inland.

Historically, levees have been used for millennia, with prominent systems along the Nile and in delta regions. In the United States, the Mississippi River levee system expanded in the 19th and 20th centuries and has been re-evaluated after major floods, such as those in 1927 and 2005. Modern practice emphasizes integrated flood management, levee setbacks, and restoration of natural floodplains, alongside traditional protection. Related terms include flood control, dike, floodwall, floodplain, and seawall.