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A model of soil erosion assessment was
developed, named as RASEAM which stands for
Rough Area Soil Erosion Assessment Model.
RASEAM adopts six factors to
assessment for soil erosion intensity, which are
rainfall, vegetation, slope, soil and parent
material, land use and soil sonservation measures.
All of these six factors were quantitized into
ranks. Land use type was assumed to be the key
factor influencing soil erosion, so RASEAM
conducts assessment in two ways for both
agricultural and non-agricultural land. The
quantitative assessment was based on a discovered
rule of the research which indicates that soil
erosion follows an inverse relationship with
vegetation and slope.
1.3 Results
The research was conducted in the very rough
southwest China mountain area which has
developed many kinds of soil erosion. Thematic
Mapper (TM) and SPOT images, helped by color
airphoto interpretation, were used to generate land
use and vegetation maps. Other maps were used in
analysis, such as soils, topography map etc..
RASEAM was used manually for soil erosion
mapping of 3120 square kilometers.
RASEAM was used in two computer formats: PC
ERDAS 7.3 which produced a soil erosion map in
raster format and PC ARC/INFO which produced
a soil erosion map in vector format. Both maps
presented correct mapping results. Due to data and
hardware limits, the maps produced by computer
covered a 200 km” subarea, in a very rough part
of the study area.
For the purpose of providing easier service,
RASEAM was programmed into independent X-
window software which can be loaded on any
UNIX or LINUX platform, reading ERDAS .lan
file and produce raster format maps.
conduct
817
2. GOALS AND STRATEGY
2.1 Background
The research area is located in the southwest
mountains, N 27 32-28 10', E 101 46—102/31',
where the altitude ranges from 1170 meters to
4182 meters. This big relief, 3012 meters, creates
five vertical climate zones. Average annual
rainfall is 1013.1 mm with annual average
temperature 17.0 C. This sufficiency of rainfall
and solar energy enables various vegetation types
to grow in the five vertical climate zones. The
vegetation development in the low altitude V-
shaped valleys are relatively poor due their hot
and dry climate. Crops are developed according to
the climates with rice, wheat, potato being the
main products.
Due to the strong tectonic movements, the
geological background is very complicated with
the existence of many rock types generated from
Paleogene to Quaternary. The tectonic movements
heavily squeezed and cracked the rock layers, so
the bedrocks are normally instable. Consequently,
many soil types were developed in this changing
environment.
In this rough environment, which has sufficient
rainfall and steep slopes with cracked bedrocks,
soil erosion developed in many forms, including
mud-and-rock-flows and mud-forest, with
varying intensities.
2.2 Soil Erosion Map
2.2.1 Soil Erosion Intensity: The intensity was
classified into six grades which was defined by
Chinese National Hydro-Power Ministry
(CNHDM,, and illustrated in Table 1.
Table 1. Erosion Intensity Definitions
Rank | Intensity | Definition Soil Layer
(T/km?.Yr) Dep. Loss (mm)
1 None < 500 None
2 Slight 500 -- 2,500 <1,9
3 Medium | 2,500--5,000 | 1.9 --2.7
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
