levee

levee (lĕv`ē) [Fr.,=raised], embankment built along a river to prevent flooding by high water. Levees are the oldest and the most extensively used method of flood control. They are constructed by piling earth on a surface that has been cleared of vegetation and leveled. From a broad base the levee narrows to a flat crown, on which sandbags or some other temporary protection may be placed to contain unusually high waters. Levee surfaces are commonly protected from erosion by vegetation, notably Bermuda grass. A banquette, or low terrace of earth, is usually added on the land side of high levees to prevent loss of material from the slope through rain erosion. On the river side, plantings of willows, weighted brush matting, or concrete revetments protect those sections of levee that are exposed to strong waves or currents, while ditches or drainage tiles keep the foundation from becoming waterlogged. Levee systems require careful planning, with sections set back from the river to form a wider channel and with flood valley basins divided by cross levees to prevent inundation of large areas by a single break. The most extensive levee systems in the United States are along the Mississippi and Sacramento rivers and their tributaries. The dikes of Holland are a form of levee, and levee-type embankments are used along the Danube, Vistula, Po, and other European rivers.