Report of RUSLE 2 Soil Erosion
Calculation
Introduction
With the help of RUSLE 2 program
version 2010, the soil loss could be estimated by investigating the effect of
several factors, including the organic matter, spatial structure, contouring,
barrier type and sediment.
By Wischmeier and Smith’s
explanation in 1978, the USLE mathematical structure is:
A = R*K*L*S*C*P.
A--average
annual erosion
R-- average
annual erosivity factor
K-- average
annual soil erodibility factor
L-- average annual slope length
factor
S-- average
annual slope steepness factor
C-- average
annual cover-management factor
P-- average
annual support practice factor
Basic structure of estimating soil erosion.
Ireland is chosen as the location
with the soil type of silt loam from the Generic Subsoil category. The slope
length is originally 150 feet with 6.0% slope steepness. Other factors are
defined as default or none. With this profile as a control group, it can show
how each factor influence the soil loss with changing only one factor value each
time as a treatment group.
The control group shows a value
of soil loss erodibility portion as 30.
Effect of organic matter in the soil (C)
The high level organic matter can
be chosen as dense grass, with the soil loss 0.063.
The medium level organic matter
can be chosen as ‘smooth bare, no disturbance’. The soil loss is 32.
The low level organic matter can
be chosen as ‘rough base, freshly disturbed’. The soil loss is 75.
It means that a higher level
organic matter causes a smaller soil loss. Because the more organic matter in
the soil can build a stronger cover to prevent soil loss by the overland flow.
Effect of length of profile (L& S)
When the slope length is changed
as 300, soil loss erodibility portion is 40. When the slope length is changed
as 75, soil loss erodibility portion is 25. In this case, steepness is 6.0% as
a constant.
As slope length is positive
relationship with L but not sensitive. Soil loss is also positive relationship
with slope length but not sensitive. Hence, the change of the soil loss is not
following the same changing rate of the slope length.
Effect of contouring (P)
The contouring factors do not
show an influence to the soil loss value. Because the basic soil is without
covering crops. The surface cannot slow down the runoff which takes the soil away.
Effect of permeable barriers (P)
The 3 types of barriers,
including default, full retardance and half retardance, do not show significant
differences with the value as 30, 31 and 31, respectively. Because barriers
will control sediments more directly rather than the soil loss.
Effect of sediment ponds (P)
The first type sediment pond is
chosen in the profile. Then the observation shows that soil loss is 30 with any
grade terrace at the bottom. At the same time, soil loss is 24 with any grade
terrace in the middle.
Sediment at the bottom can rise
the water level at a maximum rate which is larger than sediment appears in the
middle. The more runoff takes the more soil.
Conclusion
All the factors in the USLE
equation shows positive relationship with the soil loss. The combined effect of
contouring, barrier and sediment is complex. The barrier may deside the
sediment ponds performance. But the combined indicator P still show positive
relationship with soil loss.
Reference
Wischmeier, W. and D. Smith. (1978).
‘Predicting rainfall-erosion losses: A guide to conservation planning’. Agriculture
Handbook 537. U.S. Dept. of Agriculture, Washington, DC.
NRCS-USDA State Office of
Michigan. (2002). ‘SUSLE factors’. Institute of Water Research, Michigan State
University.
USDA-Agricultural Research Service. (2013). ‘Science
Documentation: Revised Universal Soil Loss Equation Version 2’. USDA-Agricultural
Research Service.
Available at: http://fargo.nserl.purdue.edu/RUSLE2_ftp/RUSLE2_Program_File/RUSLE2_Science_Doc%202013.pdf
[Accessed date: April 8th, 2016]
