Developing a GIS-Based Soil Erosion Potential Model
for the Jemez Watershed – Using the Revised
Universal Soil Loss Equation (RUSLE)
Josh Page
CE 547 – GIS in Water Resource Engineering
April 23rd 2012
Revised Universal Soil Loss Equation
(RUSLE)
RUSLE computes average annual erosion from field slopes in
tons/acre/year (Renard, 1997)
A = R*K*(LS)*C*P
A = Computed Average Annual Soil Loss
R = Rainfall-Runoff Erosivity factor
K = Soil Erodibility Factor
L = Slope Length Factor
S = Slope Steepness Factor
C = Land Cover-Management Factor
P = Conservation Practice
RUSLE – R Factor
The R-Factor is the rainfall and
runoff factor spatially
distributed by geographic
location
The greater the intensity and
duration of the rain storm, the
higher the erosion potential.
Isoerodent – Contour lines
representing the R-Factor,
created by the USDA
www.westernexcelsior.com/EEDdocs/Isoerodent_Maps.pdf
(ft-ton-in)/(ac-h-yr)
RUSLE – K Factor
The K-Factor is the average soil loss in
tons/acre per unit area for a particular
soil in cultivated, continuous fallow with
an arbitrarily selected slope length of
72.6 ft. and slope steepness of 9%
( ~ 40 degrees).
It is a measure of the susceptibility of
soil particles to detachment and
transport by rainfall and runoff.
Texture is the principal factor affecting K,
but structure, organic matter and
permeability also contribute.
soils.usda.gov/survey/online_surveys/new_mexico/
(Top Soil: 0-10 inches)
(Soil Depth: 10-30+ inches)
RUSLE – LS Factor
The LS-Factor represents
a ratio of soil loss under
given conditions to that
at a site with the
"standard" slope
steepness of 9% and
slope length of 72.6 feet.
The LS-Factor was
computed from a 10m
DEM using an OpenSource C++ Program
http://www.iamg.org/
RUSLE – C Factor
The C-Factor is used to determine
the relative effectiveness of soil and
crop management systems in terms
of preventing soil loss.
It is a ratio comparing the soil loss
from land under a specific crop and
management system.
Important Note: The C factor
resulting from this calculation is a
generalized C factor value for a
specific crop that does not account
for crop rotations.
(Goldman et al. 1986)
RUSLE – P Factor
The P-Factor is known as the support practice factor.
It reflects the effects of practices that will reduce the amount
and rate of the water runoff and thus reduce the amount of
erosion.
The P factor represents the ratio of soil loss by a support
practice to that of straight-row farming up and down the slope.
For this study the ratio will be kept at 1, indicating strait-row
farming.
Support Practice
P-Factor
Up & Down Slopes
1.0
Cross Slope
0.75
Contour Farming
0.50
Strip Cropping/Cross
0.37
Strip Cropping/Contour
0.25
http://www.omafra.gov.on.ca/english/engineer/facts/00-001.pdf
R-Factor
K-Factor
LS-Factor
C-Factor
P-Factor
For Each 10m x 10m Grid Cell
A = R x K x LS x C x P
Looking into the Future….
Since all of this data is from 6 years ago, it would
be interesting to cross reference my model’s
prediction with actual sediment loss in the
Jemez Watershed.
Although more careful calculations of the P & C
Factors would be necessary.
Questions