Geology Reference
In-Depth Information
could be improved. Work began to address these
issues in 1996, culminating in the release of a
first RUSLE2 version in 2001 and the beginning
of a US-wide NRCS implementation with actual
distribution of the program to the field offices
beginning in 2004. Based on some of the lessons
learned in RUSLE1 implementation, this included
a much earlier push to begin establishing the
required databases, as well as to begin the itera-
tive process of developing and modifying the pro-
gram based on user feedback.
A primary change in the RUSLE2 implemen-
tation of the USLE relationships could be
described as downplaying the importance of the
individual factors. In the original USLE concept,
these factors (except perhaps for
C
and
P
) were
generally considered to be independent. This
was clearly no longer the case in RUSLE1, as
exemplified by the dependence of the
b
term in
the
LS
relationship (Equation (8.3) ) on various
soil and management factors, which also impact
the
K
and
LS
values. The factor-based RUSLE1
implementation caused both science and user
problems. Inconsistent values could be entered
in the various factors (a science error) and the
program required the user to jump back and forth
between factors in order to enter relevant and
related data.
Implementation of RUSLE1 also made clear
many places where the science was not specifi-
cally in error, but could be greatly enhanced. The
most obvious of these was in full implementation
within RUSLE2 of the CREAMS (Foster
et al
.,
1980) sediment transport and deposition approach,
allowing the definition of the RUSLE2 hillslope
to include depositional zones all the way down
to the concentrated flow channel, and making
RUSLE2 much more applicable to water quality
problems. Other places where it was thought that
the science could be enhanced by smaller
improvements were many, especially in reducing
the need for user selection of values by develop-
ing ways for the program to calculate needed
values from information already available in
databases. For example, in RUSLE1 the user
needed to describe in several places the suscepti-
bility of the soil to rilling; but this would vary
with time, and can be estimated using parameters
such as the soil texture, slope steepness, and
management parameters already calculated
within RUSLE2.
As with RUSLE1, many scientists and engi-
neers were involved in producing and delivering
the RUSLE2 technology, including those involved
in data collection and preparation for analysis.
Most of these individuals are acknowledged in
the references for the corresponding documents.
8.3.1
General approach to RUSLE2
science problems
The following summary brings up to date ear-
lier and more extensive summaries of science
improvements in RUSLE2 (Foster
et al
. 2000,
2003; USDA-ARS, 2008a,b). In this treatment,
distinctions are drawn between RUSLE2 and
RUSLE1 version 1.04, as documented in AH703.
Some of the science enhancements in RUSLE2
exist in later versions of RUSLE1, specifically
in RUSLE1.05 and RUSLE1.06, which were
developed with the support of the US
Department of Interior Office of Surface Mining
(Foster
et al
., 2003).
RUSLE2 retains the conceptual use of the
USLE factors, makes computations that are based
on soil loss estimates referenced to unit plot con-
ditions, and uses ratios to adjust predictions to
other conditions. However, RUSLE2 goes beyond
the USLE. It uses process-based equations derived
from fundamental erosion science and profes-
sional judgment to make RUSLE2 applicable to
situations beyond the scope of USLE or RUSLE1.
As scientific approaches improved, RUSLE2 was
calibrated to reproduce the core SLRs for different
cropping systems and crop growth stages listed in
Table 5 of Agriculture Handbook 537 (Wischmeier
& Smith, 1978). This calibration ensured that
RUSLE2 erosion estimates for common situations
would be similar to the established and accepted
values that have been used for decades in the US
for conservation compliance assessment.
A major change in RUSLE2 was the de-emphasis
of the USLE factors, and the organization of
information into 'objects'. This object-oriented
