er 
1n 
ME 
eir 
ity 
ng 
1g. 
Table 3. Soil and Parent Material 
Table 4. Slope Grades 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
8 recent mixure mass movement 
  
In Table 3, the red soil, which is the zonal soil, 
was ranked into three grades according to the 
parent material. Because red soils developed from 
different parent materials, they have different 
textures which lead to different resistabilities. 
This ranking system, consisting of eight grades, is 
fixed in RASEAM. The authors think that a 
ranking system of eight grades can support the 
complicated soils ranking required GIS in 
modeling. The thematic map of this factor was 
made by manually editing a soil map a the 
geological map, then a part of it was digitized into 
ARC/INFO format and converted into ERDAS 
format as illustrated in Figure 1. 
3.3 Slope Factor 
Slope ranking is crucial to RASEAM. The 
ranking, in five grades, was established based on 
the soil erosion characteristics and topographic 
map. If the grade difference were too small, it 
would be hard to detect small difference in the 
fields and even on maps in a rough area. Since 
the mapping output is soil erosion intensity, rather 
than soil erosion quantity, it is unnecessary to set 
up slope length factor. The Table 4 illustrated the 
ranking system. 
819 
Rank | Soil P. Material Rank | Slope Descrip. Erosion 
l mountain meadow soil, | metamorphic rocks, (degree) Feature 
mountain brown soil granites <=5 gentle sheet erosion only 
2 mountain yellow brown | metamorphic rocks, 2 6 -- 12 medium major in sheet 
soil, yellow soil granites erosion 
3 red soil, limestonic soil | granite, limestone 3 13 -- 25 steep gully erosion in 
etc. major, sheet 
4 red soil Quaternary red soil erosion minor 
red soil Triassic ^ carbonic 4 26 -- 35 v. steep gully erosion 
shale major 
red soil New Ternary clay 5 > 35 dangerous gully erosion 
purple soil shale & sandstone mar 
  
  
  
  
  
  
  
  
  
The thematic map of this factor was produced by 
manually editing a topographic map, and then part 
of it was digitized into ARC/INFO format because 
commercial Digitized Elevation Models (DEM) 
are not available in China. The ERDAS formatted 
data are shown in Figure 2. 
3.4 Vegetation Factor 
There are two sub-factors, vegetation types and 
vegetation coverage which determines the ranking 
of the vegetation factor. This research, used a 
concept of "the equivalent resistibility to soil 
erosion", to make the ranking for vegetation. In 
Table 5, the coverage stands for the total 
vegetation coverage of arbor, bush and grass. 
Table 5. Vegetation Cover 
  
  
  
  
  
  
  
  
  
  
Rank | Vege. Type Coverage(%) 
1 forest, bush, meadow, >= 90 
tall grass 
2 forest, bush, meadow 60 -- 90 
2 sparse forest, bush & grass | 70 -- 90 
tall grass 
3 forest, bush, meadow 40 -- 60 
3 sparse forest, bush & grass | 50 -- 70 
short grass 
4 sparse forest, bush & grass | 15 -- 40 
meadow 
4 short grass 25 -- 50 
sparse forest, bush & grass | « 15 
5 short grass, bare soil SS 
  
  
  
  
  
Just like slope factor ranking, the grade difference 
was set relatively high for the purpose of easy use 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996