Geology Reference
In-Depth Information
Table 9.10
Particle information for sediment leaving the watershed.
Particle composition
Diameter (mm)
Specific gravity (g cm
−
3
)
Sand (%)
Silt (%)
Clay (%)
Organic matter (%)
Fraction in flow exiting
0.002
2.60
0
0
100
3.1
0.086
0.010
2.65
0
100
0
0
0.280
0.030
1.80
0
73.8
26.2
0.8
0.509
0.490
1.60
21.0
50.3
28.7
0.9
0.110
0.200
2.65
100.0
0
0
0
0.150
Primary particle type
Fraction
Clay
0.251
Silt
0.711
Sand
0.038
Organic matter
0.008
Index of specific area
=
57.03 m
2
g
−
1
Enrichment ratio of specific area
=
1.02
Table 9.11
Sediment delivery and sediment characteristics predicted by 1000-year long WEPP runs.
Size distribution and organic
matter of eroded soil and
surface soil
Total channel
sediment
detachment(+) or
deposition (t y
−
1
)
Total sediment
delivery from
hillslopes (t y
−
1
)
Total sediment
delivery from
watershed (t y
−
1
)
Organic
matter
(%)
Management
systems
Clay
(%)
Silt
(%)
Sand
(%)
Enrichment
ratio
Surface area
(m
2
g
−
1
)
Moldboard
plough
2672
−
539
2133
25.1
71.1
3.8
0.8
1.03
57.2
Chisel plough
1779
−
229
1550
24.9
70.7
4.4
0.8
1.02
56.6
No-till
158
5
163
25.0
69.1
6.4
0.8
1.00
55.7
Grass
109
4
114
24.6
69.3
6.1
0.8
1.00
56.0
Surface soil
---------------------------------------------------------------------------
24.5
69.0
6.5
0.8
-----------------------------------------
of WEPP. Very similar information can be generated
for individual hillslopes by using the WEPP
Hillslope version; in that case, information for
individual storms can be produced, as well as the
monthly, yearly, and total simulation information.
WEPP. If the return period output is selected,
WEPP will produce return period lengths of up to
100 years for 2, 5, 10, 20, 25, 50 and 100 years.
There is also a provision for the user to set desired
return period outputs, but no lengths can be longer
than half of the run length. The return period anal-
yses in WEPP use the Weibull plotting formula
(Haan, 1977).
The daily precipitation and the published
precipitation amounts (US Weather Bureau,
1961) for the same return periods are shown in
9.5.3 Return period
The output from the return period analysis is
shown in Table 9.12, an output option available in
both the Hillslope and Watershed versions of
