Environmental Engineering Reference
In-Depth Information
River, flowing on the Qinghai-Tibet Plateau of China. In the picture a new oxbow lake is forming. Its
upstream end which has been cut off from the river and the lower end is still connecting with the river.
Most natural rivers are meandering river.
Fig. 1.13 A typical meandering river with oxbow lake (tributary of the Yellow River) on the Qinghai-Tibet Plateau
Straight rivers —A straight river is often a straight reach of a river. The straight reach is usually not
long. Channelization of rivers and construction of levees make rivers straight. Even where the channel is
straight it is usual for the thalweg, or line of maximum depth, to wander back and forth from near one bank
to the other. Opposite the point of greatest depth there is usually a bar or an accumulation of mud along
the bank, and these bars tend to alternate from one side of the channel to the other. Figure 1.14 shows a
straight section of the lower East River in south of China. Channelization and hardened banks made the
channel straight.
Fig. 1.14 Channelization and hardened banks made the lower East River a straight river
Braided and anabranching rivers —Braided rivers have separated channels divided by bars. Bars,
which divide the stream into separate channels at low flow, are often submerged at high flow. If the bars have
been stabilized by vegetation and the multiple channels are stable, the river is classified in some literatures
into anabranching river. Figure 1.15(a) shows a braided river in the Lhasa River, which is a tributary of
the Yalutsangbu River. Figure 1.15(b) shows an example of anabranching river in the lower reaches of the
Minjiang River, the famous Dujiangyan irrigation project is shown in the picture. Several channels in the
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