Abstract: The lower reach of the Jinsha River, the study area of this paper, lie in the Hengduan Mountains in the transitional zone between the Qinghai Tibetan Plateau and the Yuannan Guizhou Plateau. Stretching for 786 km from Panzhihua to Yibin, the topography of the area rises and falls sharply. The area’s geology is complex and tectonic movements new and active. The area has rich water resources. The Ministry of Electric Power has planned 4 large scale hydroelectric stations with an installed capacity of 36.9 million kW. The area has experienced repeated landslides and rock mud debris flows that have seriously affected its engineering work and economic development. Remote sensing interpretation and site verification reveal that the area has 400 landslides with volumes >10 8 m³. These landslides are distributed mainly along the middle section of channel bank and in the river’s tributaries where the elevations range between 400 m～ 3 200 m. The forms of the landslides are various and complex. Those with high rushing speeds and large scale clastics are the most damaging to engineering work and the environment. At present, about 70% of the landslides are partially active. The study area’s drainage basin is >0.2 km² in size. In the first grade tributaries of the river, there are 438 large scale debris flows whose deposit fans are 0.01 km²～3.1 km². These debris flows are distributed mainly in the study area’s middle section where the elevation is 500 m～4 000 m. The areal size of 80% of the debris flows’ drainage basins is 1 km²～50 km². The study area has 299 viscid debris flows, accounting for 68% of the total, with only 11% of the total being dilutive. The numbers of gullies where debris flows of extra large, medium and small scales may occur are, respectively, 6, 136, 183 and 103. Numerous new debris flows are being developed in the area. Landslides and debris flows have caused serious damages to the area and strongly impacted the environment. The massive volume of silt the river carries from the area posses a major problem to the Three Gorges Dam downstream.

Key words: landslides, debris flows, disasters, influence on environment, the lower reach of the Jinsha River