Agriculture Reference
In-Depth Information
For instance, with two contours that are spaced 20 feet apart where
the vertical difference between the contours (the contour interval) is one
foot, the resulting percent of slope created is 5 percent.
S = V / H
S = 1 foot / 20 feet
S = .05 = 5 percent
Notice while looking at the contour lines in Figure 9.10 that they are
not uniformly drawn the same distance between contours. The spaces
between various portions of contours vary, with some contours having
a narrower space between them, while other sets of contour lines are
farther apart. Each set of variations can be measured with an engineer's
scale. The distance measured is the horizontal distance, or H in the
slope formula: S = V / H. The percent of slope can be calculated using
the S = V / H formula between two contours or sets of multiple contours
such as C and E in Figure 9.10. The two contour lines indicated by the let-
ter E are closer together and therefore the degree of slope is steeper than
for the two contour lines labelled C, which are a further distance apart. The
calculation for determining the slope between contour lines 23 and 24 for
the space E is shown in Figure 9.11.
24
G
S
V
F
23
H
A
S = V/H
S = 1/8
S = .125 or 12.5%
C
E
H
D
27
B
2
6
2
5
20 Scale
Figure 9.10
Contour map with three sets of contours to use
in determining their percent of slope
Figure 9.11
How to calculate the percent
of slope between two contours
