Factors Affecting a River's Velocity

Channel Shape

• The shape of the channel affects the velocity of a river. Around the perimeter of the river -- that is, at the sides and along the river bed -- friction is created as water flows against the edges. Water flowing through a wide, deep river channel encounters less resistance than water flowing in a narrow, shallow channel, since a smaller proportion of the total water molecules will be slowed by the river's edges. The center of the river experiences the greatest velocity.

Volume of Water

• The volume of water that flows through a river within a given amount of time -- known as the discharge -- also affects its velocity. As the volume of water in a river increases, through smaller streams flowing into it, for example, the velocity of the river increases. An increase in water volume can also affect a river̵7;s velocity in the long term; this is because the increasing mass of water is capable of causing more erosion, resulting in a wider, deeper river channel that allows water to flow more freely.

Smooth and Rough Channels

• Rough river channels contain a large quantity of rocks, pebbles and boulders, either at the bottom of the river or embedded within its sides. A great deal of friction is created between water molecules and these stones as the river flows past them; in rough channels, the resistance caused by this friction reduces the river's velocity. In a smooth river channel, with fewer pebbles and rocks, velocity is higher because there is less friction causing energy to be expended as it flows.

Riverbed's Gradient

• The gradient of a river refers to how steep its slope is; this also has a significant effect on the velocity of a river. When a river flows down a steep slope, the gravitational force that pulls the water downward is stronger than it would be on water flowing down a gentle slope, resulting in the river having a greater level of velocity.