Environmental Engineering Reference
In-Depth Information
Figure 2.39(a) shows the vegetation status in Zone A in Wudu County in the upper reaches of the Jialing
River where the vegetation has been destroyed erosion is severe and debris flow occurs often. Figure 2.39(b)
shows the vegetation status in Zone C in Guangyuan City in the upper reaches of the Jialing River, which
is only about 200 km distance from Wudu County. The vegetation has been preserved and erosion is
controlled by the vegetation. The two states in the figure are relatively stable and disturbances by humans
can hardly change them.
(a)
(b)
Fig. 2.39 (a) Vegetation-erosion status in Zone A in Wudu County in the upper reaches of the Jialing River;
(b) Vegetation-erosion status in Zone C in Guangyuan City (about 200 km distance from Wudu County) in the upper
reaches of the Jialing River
Determination of values of the four parameters a , c , b , and f is difficult for areas or watersheds without
long term data of soil erosion and vegetation. Because the four parameters depend mainly on climate, soil,
and topography, Wang and Wang (2007) collected data from 13 small watersheds on the loess plateau.
They applied the vegetation-erosion dynamics equations to the areas and obtained the values of the four
parameters for the Eq. (2.14) for best agreement with the data. The geographical locations of the 13 small
watersheds are shown in Fig. 2.40 and the basic features and the values of the parameters a , c , b , and f
for the 13 watersheds are listed in Table 2.2.
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