Mountain Rivers and Incised Channels - River Dynamics and Integrated River Management - page 170

Fig. 3.52 Satellite image of the anabranching channels upstream of the Dari knickpoint

Several or even hundreds of landslide dams often occurred simultaneously on a reach of an incised
mountain river, which were triggered by one great earthquake. The potential energy of bank failure and
the slope erosion were greatly reduced and sediment yield from the watershed was reduced nearly to zero.
In this case the quake lakes may be preserved for long term and become beautiful landscapes. The Tiger
Leaping Gorge lake on the Jinsha River is an examples.
Figure 3.53 shows the bed profile of the Jiuzhai Creek in Sichuan. The creek was an incised mountain
stream with average slope of about 4% where intensive landslide activities occurred. More than 100
landslides have created 118 quake lakes and 12 water falls 20,000 years ago. The slope of the spillway
channels on the landslide dams is as high as 20% and the deepest lake has an average water depth of
more than 80 m. All the landslide dams and quake lakes have been preserved. The preservation of the
dams and lakes stopped stream bed incision and stabilized the stream. These landslide dams have
become knickpoints controlling the bed incision of the stream. Such system has super-stability and
remains stable under extra-ordinary stresses. No more landslides occurred on the Jiuzhai Creek during the
Songpan Earthquake in 1976 (Ms 7.2, i.e., magnitude 7.2 in Richter scale), which was only 70 km from
Jiuzhai. The Wenchuan earthquake in 2008 (Ms 8.0) had no influence on the Jiuzhai Creek.

Fig. 3.53 Profile of the Jiuzhai Creek and locations of the landslide dams and lakes