Differential distribution regularity of collapse-landslides and debris flows along Palong Zangbu River Valley in Tibet
西藏帕隆藏布河谷崩塌滑坡、泥石流的分布规律

Collapse-landslides and debris flows are main types of mountain disasters in Palong Zangbu river valley of Tibet. These disasters are large in scale and serious in harm-fulness to the valley. Differences of hydro-thermal conditions related to aspect of valley slope lead to differences distribution of the collapse-landslide and debris flows.Differences of the geomorphologic evolution and morphologic processes of the valley lead to distribution differences of the disasters along the river. Differences of growth conditions between collapse-landslides and debris flows lead to distribution differences of the two types of disasters. For control of mountain disasters and site selection of highways and railways along the river, distribution regularities of the collapse-landslides and debris flows with the above-mentioned differences are identified, by quantitative methods including orderly sample optimum cutting method and the variance analysis, method. These regularities are: (1) the whole river section (from Ranwu to Lulang) can be divided into: a) upstream gorge section with concentrateddistribution of debris flows, avalanches and debris cones; b) midstream broad valley section with more concentrated distribution of debris flows and collapse-landslides; and c)downstream gorge section and the tributary of Layue with extremely concentrated distribution of debris flows and collapse-landslides. (2) Quantities and scales of collapse-landslides and debris flows on the northern slope surpass those on the southern slope of the river valley. (3) The collapses and landslides have an increase tendency towards downstream and the debris flows have a decrease tendency in order of the downstream gorge section, the upstream gorge section and the midstream broad valley section. Further, some suggestions on site selection principle of road plane are advanced.