Geology Reference
In-Depth Information
100%
Table 9.9
Average annual detachment and deposition
in the watershed channels for the various management
systems for the base climate.
80%
Sediment detached (
+
) or deposited (
−
) (t y
−
1
)
60%
Channels Moldboard plough Chisel plough No-till Alfalfa
40%
C1
−
5.5
−
2.0
0.3
0.3
C2
−
72.0
−
31.8
0.6
0.5
Plow
No till
C3
−
15 7. 1
−
65.9
0.6
0.5
20%
C4
−
141.5
−
59.6
0.5
0.4
C5
−
43.3
−
18.8
0.7
0.7
C6
−
65.3
−
29.0
0.5
0.5
0%
0%
20% 40% 60% 80% 100%
Sediment yield events (% of total number)
C7
−
35.9
−
15.4
0.6
0.6
C8
−
4.2
−
1.8
0.2
0.3
C9
−
14.1
−
4.9
0.6
0.6
Fig. 9.4
Total sediment yield over a 1000-year
simulation versus the average number of sediment
yield events per year.
Total
−
539.0
−
229.2
4.7
4.4
could be reduced further by constructing wider
channels on lower slopes. Sediment delivery from
the watershed could be reduced further by the use
of impoundments as sedimentation basins. These
too could be modelled in WEPP.
The results shown in Table 9.9 are average
annual results. It is likely that there will be some
storms for the moldboard and chisel plough sys-
tems where detachment occurs in channels, and
there may be deposition for some storms in no-till
and grass systems. These conditions will depend on
storm, surface, subsurface and biomass conditions.
Table 9.8
Average annual sediment yield from
hillslopes for the base climate.
Sediment yield (t ha
−
1
)
Hillslope
Plough
Chisel
No-till
Grass
H1
45.9
30.6
2.3
1.4
H2
45.9
30.6
2.3
1.4
H3
42.6
28.5
2.6
1.9
H4
42.6
28.5
2.6
1.9
H5
42.6
28.5
2.6
1.9
H6
39.0
25.5
2.4
1.8
H7
39.0
25.5
2.4
1.8
9.5.2 Sediment characteristics
H8
42.6
28.5
2.6
1.9
Information about sediment characteristics esti-
mated by WEPP is shown in Table 9.10, which
gives average particle information for all sediment
generated in the 1000-year run for the moldboard
plough management. A summary for all manage-
ments that includes sediment characteristics is
shown in Table 9.11. For this example watershed,
it is apparent that the material discharged from
the watershed is quite similar to the surface soil.
While the information in Tables 9.10 and 9.11 is
for the total period and represents information
about the material exiting the watershed, this
information can also be generated for yearly and
monthly periods when using the Watershed version
H9
26.7
18.0
2.8
2.1
H10
26.7
18.0
2.8
2.1
permanent grass systems as compared to the mold-
board or chisel plough systems. If the hillslopes are
to be farmed with the moldboard or chisel plough
systems, additional practices should be evaluated
that would control erosion on the hillslopes and
sediment delivery to channels. Some of these prac-
tices might include terracing, buffer strips, and
contour farming. These can be evaluated using
WEPP. While channel erosion is predicted to be
low for the no-till and permanent grass systems, it
