Velocity is highest in the zone overlying the deepest part of the stream. In these areas, sediment is transported readily resulting in pools. Where the velocity of the stream is low, sediment is deposited to form bars . The bank closest to the zone of highest velocity is usually eroded and results in a cutbank . The natural velocity structure of a running water on Earth's surface is a meandering one, especially in streams flowing over low gradients with easily eroded banks - straight channels will eventually erode into meandering channels.
Erosion takes place on the outer parts of meander bends where stream velocity is highest.
Sediment deposition occurs along the inner meander bends where the velocity is low. Because meandering streams are continually eroding on the outer meander bends and depositing sediment along the inner meander bends, meandering stream channels tend to migrate back and forth across their flood plain. In streams having highly variable discharge and easily eroded banks, sediment gets deposited to form bars and islands that are exposed during periods of low discharge. In such a stream the water flows in a braided pattern around the islands and bars, dividing and reuniting as it flows downstream. Such a channel is termed a braided channel.