Xt 
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i 
n 
id 
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pe 
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ng 
Y=R CAW Xi + WX + WX): lore a. (1) 
Where 
Y is score for soil erosion intensity; 
R is rainfall coefficient; 
C, is land use coefficient; 
X; is soil and parent material; 
X» 1s slope; 
X5 Is vegetation; 
and 
Wi, Wa, W; are weights for Xi, X, X5 
respectively, and 
W,+W,+W.=1.0 
W, and is a constant as Wi-0.1, but W», Ws 
change inversely against each other. This inverse 
changing priority is determined by the land use 
factor, as 
a) When vegetation is high, X, will be small. If X: 
<= X,, the weights will be 
W, = 1 = 0.04 X, X4 
{ dia (2) 
W, = 0.9 = W, 
b) When vegetation coverage is low, and slope is 
gentle. If X; > X,, the weights will be 
W, = 0.04 X, X, 
ç ouh (3) 
W, = 0.9 - W, 
In (1), C, is a land use coefficient defined by 
CAE MX, - 2y)].... (4) 
The dynamic inverse change of weights in (4) and 
(5), truly simulate the dominant factor shift in the 
soil erosion process. In this way, the complicated 
soil erosion mechanism was greatly simplified. 
The Y score in (1) was graded into soil erosion 
intensity by Table 7. 
Table 7. Erosion Intensity 
  
Intensity Non-Agri. Agri. Y Value 
  
  
  
  
Y Value 
  
821 
  
  
  
  
  
  
  
  
  
  
None « 0.84 « 0.82 
Slight 0.84 -- 1.63 0.83 -- 1.36 
Medium 1.64 -- 3.05 1.37 -- 2.40 
Strong 3.06 -- 3.45 2.41 -- 3.10 
Very Strong | 3.46 - 4.14 3.11 -- 3.60 
Severe > 4.14 > 3.60 
  
4.2 Agriculture Land Use 
Cultivated land is the land use which has been 
impact by human activity, so it was regarded by 
the authors as the original soil erosion mechanism 
has been changed. We did not succeed at 
observing any evidence of an inverse relationship 
existing in cultivated land soil erosion, therefore 
a new formula is needed for cultivated land soil 
erosion assessment. 
High intensity soil erosion normally occurrs in 
uplands which have steep slopes. Cultivated land 
usually possesses certain conservation measures, 
such as terraces, drain ditches, contour planting, 
but these conservation measures vary from one 
land type to another. Permanent cultivated upland, 
with a better draining system and higher crop 
density, has stronger resistibility to soil erosion: 
whereas fallow land, with poorer conservation 
measures, is less resisting to soil erosion. 
Nevertheless, conservation measures, except 
terraced fields, greatly lose efficiency as the slope 
increases. For permanent cultivated land the 
threshold is 25 degrees, and for fallow land is 15 
degrees. Obviously, conservation measures are not 
only important but they also can effect soil 
erosion quickly after the measures implemented in 
agriculture land use, so the conservation factor 
was considered in assessment formula: 
YSROC(OIXiT0GX;-05X:) — 7 (5) 
where 
Y is score for erosion intensity; 
R is rainfall factor; 
C; is conservation coefficient; 
X, is soil and parent material; 
X, is slope factor; 
X; is vegetation coverage. 
In (5), C; is defined by 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996