RESEARCH· ·1970·

B234
EROSION AND SEDIMENTATION
siderable variation of precipitation among the pairs
of watersheds has been observed, but differences between
watersheds of each pair have been rather slight.
The yearly difference in sumrrier rainfall between
grazed and ungrazed watersheds averaged 3 percent,
but the total rainfall for 13 years on each pair of
watersheds did not differ by more than 1.8 percent. No
definite pattern of rainfall was observed over the
basins.
Figure 2 shows the average summer precipitation for
grazed versus ungrazed watersheds and indicates that
precipitation amounts have been quite similar for
paired watersheds.
Runoff
Runoff at Badger Wash -occurs almost wholly in
response to summer rains. Very infrequently, rain-.
storms may occur during the winter that produce some
runoff. Snow generally does not accumulate enough to
cause runoff in the spring.
For the purpose of this pape-r, the comparison of
·average runoff from the four grazed basins with that
from the four ungrazed basins is used to define the
effoot of basin use:. Figure 3A shows a mass- diagram,
by years, of such a comparison. No runoff occurred in
1956, 1958, and 1966. The average slope of the line after
1956 is about 1.3, indicating that the grazed watershed
was producing 30 percent more runoff than the
ungrazed watershed. This change apparently started
almost immediately after livestock were excluded in
the. winter of 1953, but the greatest difference did not
occur until about 3 years later. The individual pairs
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PRECIPITATION ON UNGRAZED BASINS, IN INCHES
1957 0 /
/o1965
1961
FIGURE 2.-Compar.ison of summer rainfall on grazed
and ungrazed waterSheds at Badger Wash.
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RUNOFF FROM UNGRAZED BASINS. IN INCHES
ACRE-FEET PER SQUARE MILE, UNGRAZED
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9,10
EXPLANATION
1-Apr. 1954 to July 1955
2-July 1955 to Nov. 1957
3-Nov. 1957 to Nov. 1958
4-Nov. 1958 to Nov: 1959
5-Nov. 1959 to Nov. 1961
6-Nov. 1961 to Nov. 1962
7-Nov. 1962 to Nov. 1963
8-Nov. 1963 to Nov. 1964
9-Nov. t964 to Nov. 1965
10-Nov. 1965 to Nov. 1966
FIGURE .3.-Mass diagrams. A, •runoff in grazed ·and ung-razed
basins at Badger Wash, by year; B, sediment
yield and runoff at Badger Wash, by periods.
of watersheds all show the same pattern as the average
except for one pair that is complicated by the presence
of an upstream reservoir sediment deposit. The slope
of. the m•ass lrine fur three pairs of watersheds ranges
from 1.40 to 1.45 during the latter part of the study
period.
A . plot of runoff in a grazed basin versus that in arr
ungrazed basin, by storms, (not shown here) indicates
a different relation before and after the break in the