Geography Reference
In-Depth Information
LISS III, represents 44 classes of land use with a 150 m of positional accuracy resolution,
with a minimum mapping unit of 25 ha.
The soil protection map was obtained by crossing the land use map with the vegetation
coverage map. According to the classification proposed by Zavala (2001) the soil protection
was classified into the following classes: 1-Very High, 2- High, 3- Moderate, 4- Low , 5- Very
Low 6- Unprotected.
A DEM was obtained by ordinary kriging of 32,000 points, which were retrieved from a set
of 526,770 points obtained from discretization of 10 m equidistant contour lines (military
1:25,000 map).
The hillslopes map was obtained from the DEM (see Eq.(3)). The slopes were classified into
ranges: 0-3%, 3-16%, 16-21%, 21-31% and over 31%.
The lithofacies map was created from a 1:50,000 scale Portuguese Geological Map (DGM,
1984). Five lithofacies classes were defined based on the PAP/RAC, (1997) classification.
The erodibility map was obtained by crossing the slope and lithofaceis maps. Accordingly to
Zavala (2001) five levels of erodibility were set: 1- Very Low, 2- Low, 3- Moderate, 4- High
and 5- Very High.
The erosive status map was obtained by crossing erodibility and soil protection maps.
According to Zavala (2001) five levels of erosive status were set: 1- Very Low, 2- Low, 3-
Moderate, 4- High and 5- Very High. Soil erosive states are expressed in terms of protection
and erodibility (Table 5).
Protection
Erodibility
Classes
1
2
3
4
5
1
1
1
1
2
2
2
1
1
2
3
4
3
1
2
3
4
4
4
2
3
3
5
5
5
2
3
4
5
5
Unprotect
3
4
5
5
5
Table 5.
Classification of soil erosive status.
3.3.2. Modified Fournier Index model
The Modified Fournier Index (
MFI
), an improved version of the Fournier Index (
FI
);
Fournier (1960), is used to estimate the rainfall aggressivity for all months as in this area it
occurs along the year, since the
FI
is only used in regions characterized by dry seasons. The
MFI
is calculated by Eq. (7) (
e.g.
, Arnouldus, 1978).
n
P
i
MFI
.
(7)
P
i
1
t
