Abstract: The upper reaches of Changjiang River are the most serious regions of debris flow hazards. Nearly 60 counties and cities as well as hundreds of towns are under menaces of 6 800 gullies of debris flow in various kinds and scales claiming annual deaths of tens to hundred and causing annual economic loss amounting to 120~180 million US dollars. Debris flow gullies are scattering in geomorphologic transitional strips with great relief and concentrating in fault zones. Debris flow is a principal cause lagging and limiting the economic development in mountainous areas there. Further studies on theory and control measurements are in imminence. The upper Changjiang is flowing eastwards across two geomorphologic transition zones of the largest relief in China: 1.transition zone from the first terrace, i.e., the Qinghai-Xizang Plateau, down to the second terrace, i.e., the Yunnan-Guizhou Plateau, where rainy and glacial debris flows are developed;2.transition zone from the second terrace descending down to the third terrace, where the dominating agents are rainy debris flows.The great difference of altitude in the transition is in element responsible for the distribution. In particular, the concentration of debris flow in the first zone is mainly dependent upon the more favorable conditions compared to the second: the higher altitude, greater relief, and more concentrated precipitation, etc.

Key words: the upper reaches of Changjiang River, debris-flow, hazards, features