The term competence describes the largest particles that a stream can transport under a given set of flow conditions. Transported sediments are usually well sorted by size or density and tend to become finer downstream through breakup during transport. The sinuous bands, or curves in a stream channel are called meanders. The erosion along the outside curves of meanders, with accompanying deposition along inside curves, results in a slow downstream migration of the meanders. As the meanders enlarge and migrate, they eventually form a floodplain that borders the stream channel.
Floods occur when streams overflow their banks.
The severity of a flood is influenced by the quantity of water involved and the rate at which it enters the stream. These factors are, in turn, influenced by climate, soil type, topography, and vegetation. Upstream floods are those affecting localized sections of a stream system and are caused by intense rainstorms and events like dam failures. They are typically short-term events. Downstream floods are those affecting large areas of a stream system and are typically caused by prolonged rain or extensive regional slowmelt.