Environmental Engineering Reference
In-Depth Information
coarse particles deposit, the concentration reduces and more particles will deposit because their fall
velocity increases. A chain reaction may be triggered and serious deposition will occur (Wan and Wang,
1994). Maintaining a hyperconcentrated flow through the 800 km long channel without serious deposition
is an arduous task for sediment engineers. (4) Hyperconcentrated flow transports 2.4 billion tons of
sediment to the sea per year. A huge amount of sediment would accumulate in the mouth area and new
retrogressive siltation will occur. How can the sediment at the river mouth be disposed of to avoid
retrogressive siltation? 5) Zhou and Chen (1997) indicated that the sediment deposit in the Sanmenxia
Reservoir is composed of fine material (
d
50
0.005 mm) near the dam but of coarse sediment (
d
50
0.091 mm)
at 9 km or longer distance from the dam. It will be similar for the Xiaolangdi Dam in future. Fine sediment
composes the matrix of the hyperconcentrated flow. Therefore, if the reservoir is successively drawn-down
the fine material will be used up and the hyperconcentrated flow can not sustain for long time.
6.6.4
Interbasin Water Transfer Projects
The water shortage in the Yellow River basin was estimated to be around 7 billion m
3
in 2010 and 15
billion m
3
in 2030 (Chen, 1991). The main strategies to solve or ease the water shortage and save the
river from dying out are reallocation of water resources and interbasin water transfer projects. Three
routes of South-to-North Water Transfer Projects have been proposed and will be implemented. The
West Route will transfer water from the Qinghai-Tibet plateau to the upper reaches of the Yellow River.
The west route of water transfer project will transfer water from the Jinsha River (the Yangtze River),
Yalong River, and the Dadu River to the upper Yellow River. About 1.95 billion m
3
water can flow to the
Yellow River by building dams and tunnels. The water shortage problem of the Yellow River basin can
be solved and the clear water may carry sediment into the sea, thence the siltation of the river channel
can be stopped. Nevertheless, the ambitious project needs a lot of investment. The Jinsha, Yalong and
Dadu Rivers are only 100-200 km from the upper Yellow River. The total annual runoff of three rivers is
120 billion m
3
. The project can divert 19.5 billion m
3
water from the three rivers to the Yellow River.
Nevertheless, the water diversion dams will constructed on tributaries of the three rivers, for instance, the
Ake River, Duke River, Make River and Sequ River are tributaries of the Dadu River. The runoff of these
tributaries are much less than the Dadu River. Water diversion will reduce the runoff by about 50%,
which will impact the local ecology. It is necessary to study the impacts of water diversion on the local
ecology and take measures to mitigate the impacts as the water diversion is implemented.
6.6.5
Liberate Flood Detention Basins
The pressure on land due to population growth and urbanization is increasing. It is proposed to use flood
diversion channels to replace flood detention basins in order to liberate the basins for economic
development and human habilitation (Li, 1999). The impoundment of the Xiaolangdi Reservoir has
enhanced the flood defense capacity of the lower Yellow River from 100-years floods to 1000-years
floods. It was suggested liberate the Beizhan flood diversion basins (Fig. 13) for construction of a water
supply reservoir and an ecological park (Li, 2000)
Review Questions
1. What are the main theories for Yellow River training proposed in history?
2. What are the modern training strategies applied to the Yellow River?
3. What are the main factors that must be considered in the water resources development planning?
4. Why is the rate of the lower Yellow River channel siltation still so high although the total sediment
load has reduced greatly in the past decades?
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