Environmental Engineering Reference
In-Depth Information
N
0
100
200
Km
Beijing
A
Tianjin
A
Bohai Sea
d
Taiyuan
A
A
Jinan
Lunan hilly land
A
Zhen gz hou
Weihe River
A
Xi'a n
Fig. 8.7 The Yellow River and its parasitizing rivers
Small male rivers have their parasitizing rivers in their delta, which mostly developed from abandoned
distributaries. Figure 8.8 shows the Luanhe River delta and its parasitizing rivers. The Luanhe River rises
on the Mongolia Plateau, it travels through the Yanshan Mountains, and finally flows into the Bohai Gulf.
The average annual runoff of the river is 4.56 billion m 3 , but 70%-80% of it occurs in the flood season
from June to September, and the flood season also transports 93% of the sediment load of 20.1 million
tons. In 1915, the Luanhe River changed course to its present position, and has since developed its modern
delta (Feng and Zhang, 1998). The delta land is 1-2 m above sea level. The sediment consists of mainly silt,
fine sand and a small amount of clay. There are eight distributary courses. There is only one main drainage
course for every period of development, the others tend to be abandoned gradually (Feng and Zhang, 1998).
A few of them have developed into parasitizing rivers.
The parasitizing rivers on the Luanhe Delta become 300-500 m wide during a flood. The deposits in
these channel beds are fine sand and sand. The upper reach is mainly composed of sand, but in the lower
reach, there are many water pools, in which clays and silts are deposited. The dam construction and water
and sediment diversion have caused the sediment load of the Luanhe River to decrease sharply to less than
1 million tons since 1980. The delta channel of the Luanhe River has become deep. As a consequence,
the gender of river will change from male to female. The parasitizing rivers may finally link with their
father-mother river and combine into a channel web like other female rivers.
Parasitizing rivers have no tributaries or mountainous watersheds. All runoff water comes from rain.
Therefore, flow occurs only during rain season and the hydrograph of flow has only peaks and there is no
flow between the peaks. Figure 8.9 shows the discharge hydrographs of the Majia River. The Majia River
is a parasitizing river of the Yellow River, which is 425 km long and has a drainage area of 8,830 km 2 .
The river originates from the Beijindi Levee of the Yellow River. The river was once a channel dug by
humans to drain the rainwater. Runoff is closely related to rainfall. In the past 20 years, discharge has
increased faster than that of the period from 1956-1979 because urbanization and highway construction
Search WWH ::




Custom Search