An area that has been built up by stream deposition, generally represented by the main drainage channel of a watershed, is called a floodplain. This area, usually relatively flat with respect to the surrounding landscape, is subject to periodic flooding, with
return periods ranging from one year to 100 years. Floodplains vary widely in size, depending on the area of the drainage basin with which they are associated. The soils in floodplains are often dark and fertile, representing material lost the to erosive forces of heavy precipitation and runoff. These soils are often farmed, though subject to the risk of periodic crop losses due to flooding. In some areas, flood-plains are protected by flood control measures such as reservoirs and levees and are used for farming or residential development. In other areas, land-use regulations, encroachment statutes and local building codes often prevent development on floodplains.