Debris Flows and Landslides - River Dynamics and Integrated River Management - page 199

Slid e area

2

Cha nnel before slide

X i aoyuanbao

New channel

Xiaojiazicao

Quake lake

Calabash Mouth

P P

Xieziping

Fig. 4.10 Huoshigou Gully landslide and the initiated disaster chain

Figure 4.11 shows the longitudinal profiles of the river pre-, post-, and one year after the earthquake.
The longitudinal profile and cross-sections before the earthquake were obtained from a 1960s topographic
map with a scale of 1:50,000. By using the map and the measured cross sections, the volumes of the
landslide deposits and debris flows deposits were calculated. The volume of the landslide deposit was
7.21 million m 3 , and the volume of the debris flow deposit was 1.25 million m 3 . The debris flow caused
an intensive fluvial process, which in turn caused habitat loss and dramatic reduction of biodiversity in
the downstream reaches. Two samples of benthic invertebrates were taken in the river reaches affected
and unaffected by the debris flows about ten months after the earthquake. The sampling area, flow
velocity, and substrates were similar at the two sites. The species were identified under a microscope. In
the unaffected reach sixteen families or genus were found including several very intolerant species, such
as Corydalidae, Rhyacophilidae, and Goeridae. In the affected reach, however, only seven families or
genus were found. The biodiversity was much lower due to the intensive fluvial process.

Fig. 4.11 Longitudinal profiles of the Huoshigou Ravine channel pre-and postf-earthquake, and one year after the
earthquake