Environmental Engineering Reference
In-Depth Information
(a)
(b)
Fig. 4.9 (a) Lake water flows through the enlarged spillway from the Tangjiashan quake lake and scours the landslide
dam on May 31, 2008; (b) Sedimentation and new channel in the downstream reach of the Tangjiashan quake lake
(Nov. 2009)
The landslide created a small quake lake with a capacity of 75,000 m 3 . Witnesses stated that the
landslide moved down along the ravine and was obstructed at the Calabash Mouth, a very narrow section
of the ravine. Thus, the solid materials piled up and formed a dam. The dam was composed of very fine
and loosely deposited materials. During a rainstorm, the water level in the quake lake rose sharply and
soon caused dam failure on May 13, 2008. Two more rainstorms occurred on May 14 and 17, 2008,
which resulted in floods and scouring of the dam. A “V” shape channel with a depth of more than 50 m
and bank slope angle of 38 ° was scoured through the dam.
Three large scale debris flows carried a huge amount of solid materials to the downstream reaches and
created a 2-30 m thick sedimentation layer in a section of about 7 km of the river. The sediment deposit
was scoured again by flood, and intensive fluvial processes occurred in the section. Figure 4.10 shows
the location of the landslide occurrence, the sliding area, the area of landslide deposits, the quake lake
and the deposits of debris flows.
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