A levee is a natural or artificial structure, 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.
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 especially noted on the Yellow River in China near the sea where ocean going ships appear to sail high above the plain on the elevated river. Natural levees are also present on the Rio Grande River in Colorado's San Luis Valley.
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.
A levee can also be an event held on New Year's Day by a mayor and council to greet the townspeople.