Debris flow disaster in the upper reaches of the changjiang river, China

Abstract

The upper reaches of Changjiang River are the most serious regions of debris flow disasters. Nearly 50 counties and cities as well as hundreds of towns are under menaces of 6 800 gullies of debris ow. Every year debris flow claims deaths of tens to hundred and causes economic loss amounting to 120-180 million US dollars, which has lagged and limited the development in the areas. Debris flow gullies are widely distributed in the Upper Changjiang, which stretches eastwards across two geomorphologic transition zones in China: 1) the transition zone from the Qinghai-Xizang Plateau, down to the Yunnan-Guizhou Plateau, where develop rainy and glacial debris flows; and 2) the transition zone from the Yunnan-Guizhou Plateau to the area of middle mountains and hills, where dominate the rainy debris flows. The concentration in the rst zone mainly depends on the more favorable conditions compared to the second: such as the higher altitude, greater relief, and more concentrated precipitation. Hundreds or thousands of debris flows occur here each year. Coarse grains are playing the dominating roles, e.g. pebbles of more than 20 mm in diameter counts for 49.8% (weight percent) in average.