Geology Reference
In-Depth Information
N
Land use
Cropland
Orchard/cash
Wood/shrub
Wasteland
Vegetables
Fallow
Fig. 12.1
Land use of the
Danagou catchment in 1998.
250
0
250
500
750 Meters
in summer. On average three to four storms each
year are large enough to cause runoff, but the actual
number varies widely from year to year. In the
Danangou catchment, discharge only occurs dur-
ing these heavy storms, when peak discharges of
over 10 m
3
s
−1
can be reached within 15 minutes of
the onset of channel runoff. The catchment is
deeply dissected by gullies, which, according to
the digital elevation model (DEM), have slope
angles of up to 250% (68°). Gullies occupy about
25% of the catchment area.
The main land uses in the Danangou catchment
are wild grassland (wasteland) and cropland. Wild
grassland is mainly located on the steeper parts of
the gully slopes as well as on the gully bottoms,
and was until recently used for grazing goats. This
practice has ceased since grazing was prohibited in
September 1999. Cropland is located mainly on
the hilltops, on slopes that are usually between 25
and 50% (14-27°), but sometimes even steeper,
and on the relatively gentle slopes at lower eleva-
tion. The most common crops in the area are potato,
millet, soybean, buckwheat and maize. Fallow
land is mostly situated along the hilltops and
woodland in the upper parts of some of the valleys.
Figure 12.1 shows land use in 1998.
12.3 LISEM Model
12.3.1
Structure of LISEM
Figure 12.2 shows a simplified flow chart of the
LISEM model. LISEM can be divided into two
parts: a water part and an erosion part. Rainfall is
the basic input of the water part. Interception is
subtracted from the rainfall. The remaining rain-
fall reaches the soil surface, where it can infil-
trate or form a surface storage. Since LISEM is a
storm-based model, the infiltrated water is essen-
tially a loss of water in the sense that infiltrated
water cannot resurface. Infiltration can be simu-
lated using one of several available equations.
Partly empirical equations such as the Green and
Ampt and Holtan equations can be chosen, as
