Geology Reference
In-Depth Information
Table 9.1
Topographic data for hillslopes and channels.
Hillslopes (H) or channels (C)
Area (ha)
Drains to
Average slope (%)
Length (m)
Width (m)
H1
12.22
C4
1.7
325
376
H2
13.78
C3
1.7
325
424
H3
4.70
C4
2.8
125
376
H4
5.30
C3
2.8
125
424
H5
5.30
C2
2.8
125
424
H6
6.36
C2
2.8
150
424
H7
5.64
C6
2.8
150
376
H8
4.70
C6
2.8
125
376
H9
3.19
C1
2
75
425
H10
2.81
C8
2
75
375
C1
0.04
C9
2
425
1
C2
0.09
C7
2
425
2
C3
0.09
C5
2
425
2
C4
0.08
C5
2
375
2
C5
0.06
C7
2
275
2
C6
0.08
C7
2
375
2
C7
0.06
C9
2
200
3
C8
0.08
C9
2
375
2
C9
0.02
Outlet
2
81
2
Total watershed area
64.57 ha
that hillslopes and channels discharge into.
No topographic surveys were available, so slopes,
lengths and channel dimensions were estimated.
For this example application, hillslopes and
channels were laid out on a rectangular grid,
making it fairly simple to enter the various
dimensions. In WEPP, a watershed can be con-
structed using an aerial photograph or a contour
map as a background, locating the channels and
hillslopes using the visible features on the back-
ground as a guide to draw in the various features.
There are tools to draw and scale the various fea-
tures. While WEPP internally computes every
hillslope as a rectangle, the watershed can be
constructed using a series of polygons, and WEPP
will convert the polygon to a rectangle, preserv-
ing the hillslope area.
stochastic weather generator which, for a single
point, provides a daily estimate of solar radiation,
wind, dewpoint and temperature, using monthly
parameters derived from historical measurements.
It produces the information needed for the soil ero-
sion model as well as other information to estimate
the status of the land, biomass and water. The
Cligen database was developed to have at least one
Cligen station for most of the approximately 3000
counties in the US. The nearest Cligen station is
Fort Scott, KS, about 25 km west of the area to be
modelled. The Cligen database and the program to
generate a climate is part of the WEPP package.
Additionally, methods and data are available to
develop climate files from international data
(http://www.ars.usda.gov/Research/docs.htm?
docid
18094). WEPP can also use historical data or
breakpoint precipitation data.
The Cligen parameters can be adjusted to com-
pensate for orographic effects and climate change.
WEPPCAT was developed to adjust Cligen data
for climate change (http://typhoon.tucson.ars.
ag.gov/weppcat/index.php). It includes PRISM
=
9.4.2 Climate
The climate data for WEPP was generated using
the software program Cligen. Cligen (http://www.
ars.usda.gov/Research/docs.htm?docid=18094) is a
