III. Predicting Soil Loss
Predicting Soil Loss
Why?
Erosion & Sedimentation
Putting the Pieces Together
Understanding what makes soil vulnerable
Texture differences (silts vs clays vs organic matter)
Climatic conditions (high wind, intense rainfall)
Lack of cover
Steep slopes
Erosion & Sedimentation
Putting the Pieces Together
Understanding what can minimize erosion
We’
ll spend the rest of the semester talking about
management practices (
structural
and
non
-
structural
) that
help minimize erosion for different land uses
Erosion & Sedimentation
Models
Have you worked with models?
Erosion & Sedimentation
Prediction Models
Help in communication of levels of soil erosion
vulnerability
Helps identify practices to protect soil and water
resources
Create a menu for the land owner
Erosion & Sedimentation
How Much is Too Much?
Tolerable Soil Loss
Erosion & Sedimentation
How Much is Too Much?
Tolerable Soil Loss
–
maximum level of soil
erosion that will permit a high level of crop
productivity to be sustained economically and
indefinitely
‘
T
’
Erosion & Sedimentation
Tolerable Rates
T ranges from 1
–
5 tons / acre
–
year
T values are assigned for each soil series
As it turns out > 5 tons / acre
–
year is the
‘
how
much is too much
’
For fragile soils, sometimes 1 ton / acre
–
year is
too much
Erosion & Sedimentation
Tolerable Rates
Recall the 4 factors affect T:
1.
Depth of soil
2.
Type of parent material
3.
Productivity of surface soil and subsoil
4.
Amount of previous erosion
Erosion & Sedimentation
Soil Loss Models
Wind and Water
Where would you use each?
Erosion & Sedimentation
References
Soil and Water Conservation. Troeh. Chapter 6.
Predicting Rainfall Erosion Losses
-
A Guide to
Conservation Planning. Agricultural Handbook 537.
Predicting Soil Erosion by Water. A Guide to Conservation
Planning With The Revised Universal Soil Loss Equation
(RUSLE). Agricultural Handbook 703.
Revised Universal Soil Loss Equation Version 2. USDA
Universal Soil
-
Loss Prediction Equation for Planning
Resource Use and Management Systems. USDA
-
SCS
Alabama, All Field Offices Technical Guide Section I
-
C
-
1,
revised March 1985.
Erosion & Sedimentation
Wind Erosion
Prediction Models
Wind Erosion Prediction Equation
WEQ
Predicting Soil Loss
Wind Erosion Prediction Equation
Original equation based upon wind tunnel research
Modified as new information developed and new
factors could be included
Erosion & Sedimentation
Wind Erosion Prediction Equation
WEQ is an
empirical
equation
Based upon observed results obtained over a range
of test conditions
Mathematical formulas developed based upon
these results
Erosion & Sedimentation
Question
If you were to develop a model to predict
wind erosion, what factors would you enter
into the model?
What factors would contribute to increased or
decreased wind erosion?
Erosion & Sedimentation
Wind Erosion Prediction Equation
E = ƒ(I K C L V)
E = predicted annual soil loss in tons/acre/yr
ƒ is a notation that a relationship exists
between erosion and the factors in parenthesis
Erosion & Sedimentation
Wind Erosion Prediction Equation
E = ƒ(
I
K C L V)
I = Soil Erodibility Factor
Potential annual soil loss
Wide, Unsheltered, Isolated field
Bare, smooth, noncrusted surface
Erosion & Sedimentation
Wind Erosion Prediction Equation
E = ƒ(I
K
C L V)
K = soil ridge roughness factor
Surface roughness from:
Cloddiness of surface
Ridges
Vegetative cover
Clods or ridged surfaces are less erosive
Erosion & Sedimentation
Wind Erosion Prediction Equation
E = ƒ(I K
C
L V)
C = climatic erosiveness factor
Related to
Wind speed
Surface soil moisture
Temperature
Affects detachment and transport directly
Influences plant growth and residue cover indirectly
Erosion & Sedimentation
Wind Erosion
Prediction Equation
E = ƒ(I K C
L
V)
L = width of field factor
the
unsheltered distance
along the
prevailing wind direction
across the area evaluated
multiply the height of a barrier by 10 to determine shelter
effect
subtract this from the distance of the area traversed by
the wind
Erosion & Sedimentation
1 Mile
½ Mile
Prevailing
Winds
in March
Wind Erosion
Prediction Equation
E = ƒ(I K C
L
V)
Which way is the wind blowing?
Preponderance
describes the proportion of wind parallel to
prevailing wind direction as opposed to forces perpendicular
to prevailing wind direction
1 = no prevailing direction
2 = twice as much erosive force in prevailing
direction as in perpendicular to prevailing wind
direction
Erosion & Sedimentation
1 Mile
½ Mile
Prevailing
Winds
in March
Wind Erosion Prediction Equation
E = ƒ(I K C L
V
)
V = vegetative cover factor
Depends on
Amount of dry matter
Texture
Living or dead
Standing or flat
flattened wheat straw is standard
term normally used is
small grain equivalent
Erosion & Sedimentation
Is there a quicker way?
A
‘
shortcut
’
was proposed by Soil
Conservation Service specialists
Wind Erodibility Groups (WEG) (Table 6
-
15,
167)
No sieving necessary
Erosion & Sedimentation
Erosion & Sedimentation
Wind Erosion Prediction Equation
Changes in management can be applied to
bring down the estimated soil erosion by wind.
What changes would you make to reduce
estimated soil loss?
Erosion & Sedimentation
Wind Erosion Prediction Equation
Limitations of WEQ
Estimates are in soil loss per year
Soil erosion and the values of I, K, C, L and
V change over the year
WEQ was developed for the Great Plains
Some of estimates not valid for other areas
Has been modified some other locations
Erosion & Sedimentation
Wind Erosion
Prediction Models
Wind Erosion Prediction System
WEPS
Predicting Soil Loss
Wind Erosion Prediction System
(WEPS)
In process of refinement
Designed to replace WEQ
Being field tested by NRCS
Predicts soil erosion based upon
simulation
of
fundamental
processes
controlling wind erosion
Continuous, daily time
-
step wind erosion model
Erosion & Sedimentation
Wind Erosion Prediction System
(WEPS)
Provides more information than WEQ
Abrasive damage to crops
Soil productivity changes
Off
-
site deposition
Erosion calculations made upon grid
Two dimensional
WEQ calculates based upon line transect
Erosion & Sedimentation
Wind Erosion Prediction System
(WEPS)
Requires lots of data
4 databases
Climate
Soils
Management
Crops and Decomposition
Erosion & Sedimentation
Wind Erosion Prediction System
(WEPS)
More information is available at
http://www.weru.ksu.edu/weps/
The software may be downloaded from this site
Erosion & Sedimentation
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