Abstract: Annual runoff and sediment transportation changes of Jialing River from 1956-2000 are analyzed in this paper by using Mann Kendall method and average difference T method. The results show that the amount of annual runoff in recent 50 years has no evident variety and the annual sediment transportation has appeared obvious descendent trend. Moreover, with the application of sudden change point searching technology, the paper comes to a conclusion that the annual sediment transportation change duration of the Jialing River may be divided into four periods, 1956-1967，1968-1984，1985-1992 and 1993-2000. The average annual sediment transportation of the above four periods is 1.81×108t，1.35×108t，0.71×108t，0.34×108t respectively. The leapdegree of every stage sediment transportation is 0.46×108t，0.64×108t，0.37×108t. The annual average runoff change duration of Jialing River can be divided into two periods, which is 1956-1992 and 1993-2000, with the range of every stage runoff is 184.73×108m3. The result is consistent with the data obtained by the double accumulation curve method. In order to find out the driving forces of the annual runoff and sediment transportation changes, the relationships between precipitation and sediment transportation and between human activities and sediment transportation ?are analyzed by the results of the mathematical model. Through correlation analysis，it is quite clear that the change in annual runoff and sediment transportation depends on the rainfal1 and human activities, in which human activities include mainly water conservancy project constructions and soil and water conservation measures, thus resulting in a contribution ratio 53.8% in the runoff and sediment transportation changes, and the rainfal1 contribution ratio being 46.2% in the runoff and sediment transportation changes. Human activities were the main reason causing the runoff and sediment transportation descent for nearly 50 years.

Key words: Jialing River , runoff , sediment transportation , driving factor , quantitative analysis