How do the calculation and expression of a stream gradient compare with those of a slope gradient?

• A. They are calculated the same way, but expressed differently
• B. They are calculated differently and expressed the same
• C. They are unrelated
• D. They are identical in both

Answer: (A)

Both stream gradient and slope gradient rely on the same idea: how much vertical change occurs per horizontal distance. To calculate a stream gradient, you measure the drop in elevation along a downstream reach and divide by the distance along the stream. The value is then expressed in convenient units such as meters per kilometer or feet per mile, or as a percent grade. For a slope gradient in general, you do the same rise-over-run calculation, but you typically express the result as a percent grade or as an angle in degrees.

So the calculation is identical in form, but the way you present the result differs: streams are often given as distance-per-drop (e.g., meters per kilometer or feet per mile), while slopes are commonly given as a percent or an angle. For example, a drop of 20 meters over 5 kilometers can be written as 4 meters of drop per kilometer, or as a 0.4% grade (and about 0.23 degrees).