Environmental Engineering Reference
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the degree has increased from 0.2-0.8 to 0.8-1.35. Nevertheless, the natural fluvial processes tend to break
the constraint of the spur dykes, and the flow scours the dykes and causes them to collapse.
Fig. 6.28 Distribution of channelization degree (ratio of the length of the spur dykes to the length of the channel)
along the lower Yellow River (Cheng et al., 2007)
Figure 6.29 shows the probability of collapse of each dyke as a function of the channelization degree.
The probability is calculated with the total times of collapse per year over the number of spur dykes. The
probability is low as if the channelization degree is lower than 0.8. For a channelization degree higher
than 0.8, however, the probability of dyke collapse abruptly increases from 10% to 30%. The high
probability of dyke collapse is due to the conflict between the natural fluvial processes and the constraint
of channelization. In fact the strongest conflict occurs for channelization degrees in the range of 0.8-1.0,
and, therefore, there is a corresponding high probability of dyke failure. Nevertheless, if the channelization
degree approaches to 2 (the two sides of the channel are completely controlled with spur dykes), the
channel motion will change from lateral to vertical. The channel will be deepened, resulting in an increase
in the bank-full discharge. Figure 6.30 shows the probability of dyke failure against the bank full discharge.
Following an increase in bank full discharge the probability of dyke failure decreases.
Fig. 6.29
Probability of dyke collapse as a function of the channelization degree
6.4.5 Water Diversion Changes Fluvial Process
The amount of water diversion from the lower Yellow River has been increasing in the past 50 years.
Water diversion inevitably affects the fluvial processes. Water diversion may even change a section of a
perennial stream to an ephemeral river section (Fogg and Muller, 1999). While water diversion projects
have become a popular and important strategy to meet increasing water demand, the stream flow,
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