 Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers.When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load.Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.