Environmental Engineering Reference
In-Depth Information
The stability of a landslide dam depends directly on the development degree of the step-pool system,
S P , in the spillway channel on the landslide dam. The definition and measurement of the S P value are
given in Chapter 3. Except for the development degree of the step-pool system on the spillway channel,
the stream power of flow is the most important factor. For small streams with a peak flood discharge less
than 30 m 3 /s the preservation ratio of landslide dams, R , is well related with S p , the development degree
of the step-pool system. Eight field investigations were done to the landslide dams in the Wenchuan
Earthquake area in 2008 and 2009. S P and R were measured with the special instrument and GPS receivers
and laser range meters (Wang et al., 2010a or b). Figure 4.27 shows R as a function of S P . The preservation
ratio, R , linearly increases with S P . If S P is larger than 0.45, the preservation ratio R equals 1, i.e. the
landslide dams may be completely preserved. On the other hand, if S P is smaller than 0.27, R is smaller
than 0.5, i.e. the landslide dam may fail.
Fig. 4.27 Preservation ratio of landslide dams, R , as a function of the development degree of step-pool system, S p , for
small streams
Figure 4.28 shows the Yujunmen barrier lake on the Mianyuan River in Sichuan (left) and a step-pool
system on the spillway channel (right). The lake was created by a landslide which was triggered by the
Wenchuan Earthquake on May 12, 2008. The top part of the landslide dam was removed by humans in
order to reduce the lake water level for constructing a highway along the lake. Two floods scoured the
spillway channel and rearranged the stones to form the step-pool system. The S P value was measured at
0.37 and the preservation ratio was about 0.88.
Fig. 4.28 Yujunmen barrier lake on the Mianyuan River in Sichuan (left) and a step-pool system on the spillway
channel on the Yujunmen landslide dam (right) (See color figure at the end of this topic)
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