III. Predicting Soil Loss

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