Meandering channels cause this type of flow. Helical flow has an important role in sediment transport and deposition , and in the creation of point bars . Finally, flow is not always contained within the stream channel. During periods of high stream discharge overbank flow may occur. Overbank flow or flooding involves the spilling of water over the stream's banks and onto the floodplain .
All streams carry sediment .
Most of the sediment found in a stream has been washed into the channel from surface runoff . Sediment is also added from the erosion of the stream channel bed and banks . The quantity of sediment in a stream varies temporally due to changes in discharge. Normally, as discharge and velocity increase, the amount of sediment being carried by the stream rises correspondingly. For many discharge stations, scientists have determined the quantitative relationship between stream discharge and concentration of sediment transported by the stream.