What Factors Affect the Velocity of a Stream?

Grade

• The angle at which the stream flows from higher elevations to lower ones affects the velocity at which the water flows. The steeper the grade is, the faster the stream will flow. Because this grade changes at various points along the stream's path, the velocity of the water changes in accordance to the grade. For instance, a stream that begins high up on a steep mountain will flow quickly down the side of the mountain until it reaches ground that is more level. At this point, the stream slows down.

Friction

• Like all other aspects of movement, friction and resistance play roles in the velocity of the stream. A stream bed that consists of rocky, uneven ground has a lower rate of velocity than a stream that has a smooth bottom and sides. Streams that contain larger amounts of vegetation also experience slowing. In addition, a stream that flows in a somewhat straight line is more likely to be a faster-flowing stream than one which contains many twists and turns.

Dams

• Humans may place a dam along a stream to slow down the flow. This can help reduce the risk of flooding in areas below the dam as well as serve as a source of energy if the velocity above the dam is high enough. The use of the dam can change the velocity of the water by controlling how much water can spill over or through the dam at any given time.

Debris

• As a stream runs its course, it picks up dirt and other debris from the bottom and the banks of the stream. In addition, streams that flow past or through farms can pick up soil-laden runoff from the farm fields. The more sediment picked up by the water, the slower the flow becomes. Therefore, the flow of a stream is often much higher at its beginning when the water is still clear than it is near the end of the stream.

Tides

• While a stream is not susceptible to the impact of tides directly, the tides of the ocean can have an impact on the velocity of streams that enter the ocean. When the tide comes in, the water from the ocean backflows into the stream, greatly decreasing and sometimes reversing the flow of the stream at its base. This change is temporary and reverts back to the stream's normal velocity once the tide goes back out.