A levee (from the French for "raised") is a natural or artificial embankment, usually earthen, which parallels the course of a river. It functions to prevent flooding of the adjoining countryside. However it also confines the flow of the river resulting in higher and faster water flow.
Levees are usually built by piling earth on a cleared, level surface. Broad at the base, they taper to a level top, where temporary embankments or sandbags can be placed. Because flood discharge intensity increases in in levees on both banks, and because silt deposits raise the level of riverbeds, planning, as well as auxiliary measures are vital.
A natural levee results from the deposit of material by a river during flood stage resulting in the land near a river being raised in elevation. When the river is not in flood state it cuts a channel in the elevated material. Natural levees are formed as sediment of larger grain size settle out on the banks of channels due to the drop in flow velocity on the edge of the channel.