Geology Reference
In-Depth Information
10
Predicting Soil Loss and Runoff
from Forest Roads and Seasonal
Cropping Systems in Brazil
using WEPP
A.J.T. GUERRA
1
AND A. SOARES DA SILVA
2
1
Department of Geography, Institute of Geosciences, Federal University
of Rio de Janeiro, Rio de Janeiro, Brazil
2
Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
10.1 Introduction
predicts erosion well on the studied Oxisols
where
D
i
is the inter-rill soil loss (kg m
−2
s
−1
),
R
is
the rate of runoff (m s
−1
),
I
is the rainfall intensity
(m s
−1
),
K
i
is the inter-rill soil erodibility (kg s m
−4
)
and
S
fa
is the modified slope factor.
Martins Filho
et al
. (2004) studied the cover-
management subfactor (
C
i
II
) and concluded that
the equations
C
i
II
There have been many papers, MSc dissertations
and PhD theses authored on WEPP applications
in Brazil in the last two decades (Table 10.1).
Favis-Mortlock and Guerra (1999) used WEPP in
Mato Grosso State and noted that simulated aver-
age annual sediment yield increased in one of the
scenarios tested and decreased in the other two,
reflecting the range of uncertainty in predictions
of future rainfall. In another study in Mato Grosso
State, Favis-Morlock and Guerra (2000) found
that WEPP-CO
2
underestimated current-climate
mean annual sediment yield. The model calcu-
lated a value of 6.86 t ha
−1
y
−1
, while the value
measured during four years of monitoring was
12 t ha
−1
y
−1
.
Martins Filho
et al
. (2003) validated the model
to predict inter-rill erosion for three Oxisols. The
initial proposed model for the dimensionless
slope factor (
S
f
) did not provide a good relation-
ship between the actual and predicted soil loss.
The slope factor was better expressed using
the equation
S
fa
e
−2.238
CS
/100
allow good estimates for the cover-management
subfactor, for slopes between 5.3% and 15.3%,
where
CS
is the percentage ground cover on the
soil surface. For slopes
=
e
−2.50
CS
/100
and
C
i
II
=
e
−0.795
CS
/100
is recommended. Nevertheless, the
authors suggested that more research is needed to
improve the calibration for steep slopes.
Many of the dissertations and theses in Brazil
using WEPP have been completed in Agricultural
Engineering departments, reflecting the consider-
able concern over soil loss due to agricultural
activities in Brazil. We have selected examples
from two PhD theses (Garcia, 2001; Gonçalves,
2007) where the authors have applied WEPP in
real situations and considered the associated lim-
itations and potential. We describe in detail how
the model was established and run, and the nec-
essary data obtained for each application. Through
their methodology and results, it is expected that
WEPP users, in different parts of the world, will
be able to use these two case studies as examples
for subsequent model use, development and
∼
36.3% the equation
C
i
II
=
=
1.061
−
1.037 e
−4 sin
q
, than by the
equation
S
f
0.850 e
−4 sin
q
where
q
is the
slope angle (degrees). The model
D
i
=
1.050
−
=
R I K
i
S
fa
