What Is a Stream Gradient?

Measurement

• To measure the stream gradient, you first need to select the stretch of stream that you want to examine. You then measure the elevation of the stream at each point, and subtract the lower elevation from the higher elevation. Divide the resulting number by the distance between the two points on the stream that you have selected. Using the standard units of measurement, express the resulting number in feet per mile.

Speed

• Among the important characteristics of a stream that are influenced by its gradient is the velocity of the running water in the stream. The extent of the slope helps determine how fast water will flow in a stream. A stream with a high gradient -- one that slopes sharply -- will tend to have a faster velocity, depending on other characteristics, according to Miriam Helen Hill of Jacksonville State University.

Profile

• Stream gradients tend to vary in part by where they are located along the path or channel of the stream, according to Stephen Nelson of Tulane University. In particular, gradient often depends on how close the section of the stream being measured is to the source of the stream and the stream's mouth where it empties into a larger body of water. The part of the stream located near the source tends to be steeper as the water builds momentum to run over land while the section of the stream near the mouth tends to have a flatter gradient.

Miscellaneous

• The gradient of smaller streams tends to be steeper than the gradient of larger streams. As small streams flow into larger streams, growing into larger flows of water, the gradient decreases. A stream's gradient affects its capabilities for causing erosion because velocity plays a key role in erosion. For this reason, when comparing two streams that contain a similar volume of water, the stream with the higher gradient likely will cause more erosion because its velocity will be higher, according to David Allison of the University of South Alabama.