Garden with Insight v1.0 Help: Soil params erosion group
Channel roughness coefficient for water erosion: Determines the roughness of the channel
through which water flows during rainfall, which helps determine the rate of water flow, which helps determine the amount of runoff and water erosion. Ranges from 0.01 to 0.2; higher values mean a
rougher channel.
CHN - Channel roughness factor (Manning's "n") (1)
The channel roughness factor is Manning's "n" values. Table II.2
contains suggested values of Manning's "n" for various condition.
Channel flow *
A. Excavated or dredged Value chosen Range
1. Earth, straight and uniform [ .0250] 0.016-0.033
2. Earth, winding and sluggish [ .0350] 0.023-0.05
3. Not mantianed, weeds and brush [ .0750] 0.04-0.14
B. Natural streams
1. Few trees,stones, or brush [ .0500] 0.025-0.065
2. Heavy timber and brush [ .1000] 0.05-0.15
* Taken from Chow (1959)
Surface roughness coefficient for water erosion: Determines the roughness of
the soil surface over which water flows during rainfall, which helps determine the rate of water flow,
which helps determine the amount of runoff and water erosion. Ranges
from 0.01 to 0.3; higher values mean a rougher surface.
SN - Surface roughness factor (Manning's "n") (1)
The surface roughness factor is Manning's "n" values. Table II.2
contains suggested values of Manning's "n" for various condition.
Overland flow *
Fallow, no residue [ .0100] 0.008-0.012
Conventional tillage, no residue [ .0900] 0.06-0.12
Conventional tillage, residue [ .1900] 0.16-0.22
Chisel plow, no residue [ .0900] 0.06-0.12
Chisel plow, residue [ .1300] 0.10-0.16
Fall disking, residue [ .4000] 0.30-0.50
No till, no residue [ .0700] 0.04-0.10
No till (0.5-1.0 t/ha) [ .1200] 0.07-0.17
No till (2.0-9.0 t/ha) [ .3000] 0.17-0.47
Rangeland (20% cover) [ .6000]
Short grass prairie [ .1500] 0.10-0.20
Dense grass [ .2400] 0.17-0.30
Bermudagrass [ .4100] 0.30-0.48
* Taken from Engman (1983)
Coefficients for MUSI water erosion equation: Coefficients for the MUSI
version of the modified universal soil loss equation that uses special parameters.
BUS(1) - 1st Param. est. for MUSI erosion equation (1)
YSD(5)=BUS(1)*QD**BUS(2)*QP**BUS(3)*DA**BUS(4)*KCPLS
Erosion control practice factor for water
erosion: A parameter for the effectiveness of erosion-control practices such as terracing. If zero, stops
water erosion entirely. Between zero and one, a greater number means less erosion-control efforts. Above
one, magnifies water erosion to study its effects.
PEC - Erosion control practice factor
The erosion-control-practice factor normally ranges from about 0.1
to 1.0 depending upon the effectiveness of the conservation practice.
However, PEC can be set to 0.0 to eliminate water erosion entirely.
When this is done, the soil profile remains relatively static because
it is reset to initial conditions at the end of each year. This feature
is very convenient for a given soil profile. At the other extreme,
(PEC=10.) erosion rates are increased 10 times to improve log-term
simulation efficiency. This feature is a big time saver in estimating
water ersion effects on soil properties over periods of up to 1000
years. Obviously, the 1000-year period can be approximated with a
100-year simulation using PEC=10. Values of PEC provided by Wischmeier
and Smith (1978) are contined in table VI.1)
Table VI.1.a.
P values and slope-length limits for contouring
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Land slope P value Maximum length *
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1 to 2 [ .60] 400
3 to 5 [ .50] 300
6 to 8 [ .50] 200
9 to 12 [ .60] 120
13 to 16 [ .70] 80
17 to 20 [ .80] 60
21 to 25 [ .90] 50
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* Limit may be increased by 25% if residue cover after crop seedlings
will regularly exceed 50%
Taken from Wischmeier and Smith (1978)
Table VI.1.b.
P values for contour-farmed terraced fields *
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----Farm planning------- --- Computing sediment yield *** ----
Land slope Contour Stripcrop Graded channels Steep backslope
(percent) factor ** factor and outlets underground outlets
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1 to 2 [ .60] [ .30] [ .12] [ .05]
3 to 8 [ .50] [ .25] [ .10] [ .05]
9 to 12 [ .60] [ .30] [ .12] [ .05]
13 to 16 [ .70] [ .35] [ .14] [ .05]
17 to 20 [ .80] [ .40] [ .16] [ .06]
21 to 25 [ .90] [ .45] [ .18] [ .06]
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* Slope length is the horizontal terrace interval. The listed values
are for contour farming. No additinal contouring factor is used in
the computation
** Use these values for control if interterrace erosion within specified
soil loss tolerances.
*** These values include entrapment efficiency and are used for control of
offsite sediment within limits and for estimating the field's contrib-
ution to watershed sediment yield.
Taken from Wischmeier and Smith(1978)
Method for estimating water erosion: The method used to calculate the amount
of soil lost through erosion from water running off the surface of the soil.
Lag coefficient for wind erosion: A parameter to adjust the
amount of lag from one day's wind erosion to the next. The larger this number, the more yesterday's wind
erosion affects today's wind erosion.
Factor for accelerating wind erosion: A parameter to magnify wind erosion to better observe it in
a short time frame. The daily amount of soil lost to wind erosion is multiplied by this number.
ACW - Wind erosion adjustment factor (7)
The wind erosion adjustment factor is used along with PEC values to shut off or accelerate erosion. As
with water erosion, wind erosion can be shut off by setting ACW=[0.00]. A normal level of wind erosion
is obtained with ACW=[1.00]. Also, AWC can be increased to a high level ACW=[10.00]) as a short cut
in estimating wind erosion effects on the soil profile. Since ACW is related linearly to wind erosion, 1000
year' simulation can be approximated by 100 years' simulation using ACW=10.
Maximum wind erosion allowed per day: This parameter places an upper limit
on the amount of wind erosion per day. In a small garden this should not be very important.
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