The diagram below shows stream gradient. If a stream has a horizontal distance of 20 km and begins at an elevation 100 m higher than where it ends, what is its stream gradient?
A. 20 km + 100 m = 120 km/m
B. 100 m / 20 km = 5 m/km
C. 100 m × 20 km = 2000 m/km
D. 20 km / 100 m = 0.20 km/m
