Large numbers of field investigation and observation have revealed the distribution regularity of debris flow disaster along the Sichuan-Tibet highway in Sichuan province

which consists of four zones respectively in Longdanxi catchment

in Yajiang catchment

in Bogexi catchment and in Batang-Jinshajiang catchment.Specially

debris flow disasers are deeply serious in both Bogexi and Batang-Jinshajiang catchments

there are 24 giant debris flows with their basin areas over 20 km

2

.From east to west along the highway

debris flows evolve gradually from torrents with various rocks to dilute debris flows.The environment to develop debris flow disasters along the highway is characterized of complex geological tectonic actions

landforms with deep valle

ys and high mountains

active earthquakes

intense precipitation

and abundant thawing water from snow and ice.Four types of mechanisms to trigger debris flows can be classified generally

i.e.

rainfall impact

strength attenuation

erosion cutting and drawing.More than 30 giant debris flow disasters have been harnessed with the technical measures of bank protection works

highspeed drainage structures

anti-impact structures

guiding-flow dams

energy releasing ridges etc.since 2003

which have ensured significantly the communication service of the Sichuan-Tibet highway.