Environmental Engineering Reference
In-Depth Information
vegetation-erosion analysis the upper Yangtze River basin is divided into three areas according to climate,
topography, soil, morphology, and soil erosion and vegetation: Qinghai-Tibet plateau, hot and dry valleys,
and Yuannan-Guizhou-Sichuan area, as shown in Fig. 2.44.
On the Qinghai-Tibet Plateau, the annual average temperature is only -4.2 ć at the Tuotuohe meteorological
station, which results in low evaporation. Vegetation may slowly develop and mainly is herbaceous. The
Jinsha River valley and many tributary valleys on the Yuannan-Guizhou Plateau are dry and hot valleys,
where the annual average temperature is about 20 ć , and monthly average rainfall from December to April
is less than 10 mm, which results in poor vegetation. In the summer from June to September, the monthly
rainfall is more than 120 mm, which causes high soil erosion. Splash erosion, sheet erosion, and rill erosion
are moderate but gully erosion is extremely intensive. The sediment eroded from the area is composed of
clay, silt, sand, gravel, cobbles, and boulders. More than 50% of the sediment load in the Yangtze River are
from the Jinsha River basin. On the Yunnan-Guizhou Plateau and in the Sichuan basin, it is warm and
wet. The average annual precipitation is about 1,000 mm and annual average temperature is about 18 ć .
Vegetation develops well and soil erosion is low.
Fig. 2.44 Zoning of the upper Yangtze River basin for vegetation-erosion analysis
Using the data of vegetation and erosion rate measured in the Mengzong Watershed on the Qinghai-Tibet
Plateau, the four parameters are determined as follows:
2
2
2
a c b f (2-26)
With the values of the parameters the vegetation-erosion chart for the Qinghai-Tibet Plateau is developed,
as shown in Fig. 2.45(a). The chart has a very small Zone C and a large Zone D. The vegetation is
vulnerable and has no capacity of self-restoration. If the vegetation on the Qinghai-Tibet Plateau is
destroyed, it is very difficult to restore. Therefore, the main management strategy for the area is careful
protection of the vegetation.
In the hot and dry valleys the vegetation is poor and the soil erosion is intense. The four parameters are
determined with data as follows:
0.001(1 / t);
0.0000014(km
/ yr);
0.01(1 / yr);
190(t / km yr )
a
0.017
0.03(1 / yr);
c
0.000002
0.000005(km
2
/ t);
(2.27)
22
b
0.045
0.054(1 / yr);
f
200
350(t / km yr )
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