Stream channel is the physical confine of a stream (river) consisting of a bed and stream banks. Stream channels exist in a variety of geometries. The stream channel development is controlled by both water and sediment movement. There is a difference between low gradient streams (less than a couple of percent in gradient) and high gradient streams. Wide variety of stream channel types can be distinguished (e.g. Braided rivers, Wandering rivers, Single Thread Sinuous rivers etc.). During floods may water exceed the capacity of the channel and floodwaters spill out of the channel and across the valley bottom or floodplain. A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill (occasionally ghyll), kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or runnel. Streams are important as conduits in the water cycle, instruments in groundwater recharge, and corridors for fish and wildlife migration.