Geology Reference
In-Depth Information
tilled and planted up-and-down the slope; (2) the
same tillage, but close to the contour; (3) the same
as (2), but with a single terrace in the middle of
the slope; (4) fall chisel ploughing up-and-down
the slope; (5) fall chisel ploughing, but close to the
contour; and (6) fall strip tillage, where in the fall
only a narrow strip is disturbed in knifing in
nitrogen. The results for each line show the plan-
ner not only the erosion and sediment yield asso-
ciated with each alternative, but also the
estimated fuel cost and the SCI value for that
option, with values > 0 indicating a net increase
in soil organic carbon over time. These generally
show the expected results, with the reduced till-
age option resulting in the lowest erosion, fuel
cost, and highest SCI values.
The graphs shown in Plate 4 indicate some of
RUSLE2's capability in graphically representing
results. In this case the graphs are of the percent-
age of soil surface covered by crop residue, with
the graph on the left for the fall moldboard plough
scenario, and that on the right for the strip till
management. In addition, although it is not dis-
played here, the crop yields for each of the man-
agement alternatives can be set by the user, if it is
thought that the management sequence has an
effect on those.
Another difference is the look and feel of the
screen itself, including especially the visible icons
and the text. These can be things as trivial as
using a bulldozer icon instead of a tractor to rep-
resent field operations, or as substantial as com-
pletely different text shown on the screen for the
same parameter, reflecting differences in termi-
nology. For example, in agricultural settings we
generally speak of crops and of crop residues
added to the surface, while in construction set-
tings we would use the more generic vegetation
and surface cover materials, including synthetic
blankets and added mulches as well as residues
from the vegetation grown on the site.
Another difference mentioned above is the
ability of RUSLE2 to aggregate results not only
on an average annual basis, but over a user-
defined accounting period. For example, in the
situation shown here, the accounting period is
defined as beginning from the time of the first
soil disturbance until either the application of
some non-erodible permanent material (e.g. pave-
ment, sod, or landscaping materials) or 60 days of
growth of perennial vegetation, with days whose
average temperature falls below 35°F not counted.
In Plate 6, the two bottommost results in the
lower left-hand corner indicate whether the sys-
tem meets the definition of the accounting
period, and a green or red colour in the rectangle
indicates whether the system did or did not meet
the allowable sediment delivery threshold, in
this case set by the regulatory body as a total of
no more than 5 Mg ha
−1
(2 US t ac
−1
) over the
entire accounting period.
Users indicated that for construction site use -
unlike for agricultural use - there would be little
need for the capability to save and re-use manage-
ment descriptions, as the timing of field opera-
tions would vary tremendously due to many
factors. Because of this, the view in Plate 6 shows
the management scenario description (dates and
descriptions of field operations) directly within
the general RUSLE2 profile view, rather than
named and stored as a separate database record.
These users also indicated a need to define
complex slope topography, as they wanted to be
able to account for the deposition occurring on
(iii) Example 3. Construction site sediment con-
trol
As described above, although the RUSLE2
calculations for estimating erosion and sediment
yield for construction sites are no different from
those for agricultural settings, the RUSLE2 flexi-
bility allows for a substantially different look and
feel, which makes it easier to use in construction
settings. Several of these differences are shown in
Plate 6.
One primary difference seen here is that for
construction sites the primary output of interest
is not the soil erosion on the hillslope, but rather
the sediment delivery to the receiving channel,
representing the off-site impact. In fact, it is often
comparison of this value to some defined stand-
ard rather than comparison of average annual soil
loss with the soil loss tolerance (
T
) (Johnson,
1987) that indicates the success or failure of a
construction plan.
