Annual Evolving Laws Of The Sediment In Jialing River Runoff During Past 50 Years And Its Driving Factors

Annual runoff of discharge and sediment loads of hydrological gauging station of the Jialing River from 1956 to 2006 were analyzed in this paper by using Mann - Kendall trend analysis and average difference T test method. The result indicates that the annual runoff of discharge does not show significant trend at >95% confidence level while the annual sediment load appears significant decrease trend in recent 50 years (this decreasing trend is significant at >95% confidence level). Moreover, with the method of Value Difference t - test, it was concluded that the history of annual discharge change in the Jialing River could be divided into two periods, 1956 similar to 1992 and 1993 similar to 2006, with a decrement of 184.73 x 10(8) m(3); the history of annual sediment load change could be divided into four periods, 1956 similar to 1967, 1968 similar to 1984, 1985 similar to 1988, 1989 similar to 1993, and 1993 similar to 2000; the average annual sediment loads during four periods above are 1.81 x 10(8) t, 1.35 x 10(8) t, 0.71 x 10(8) t, 0.34 x 10(8) t, respectively; and the decrements of each stage sediment load are 0.46 x 10(8) t, 0.64 x 10(8) t, 0.37 x 10(8) t, respectively. This result is consistent with the results of the double cumulative curve. The driving factors that cause the sediment load variation was analyzed from two aspects of nature factors and human activities. Results show that water reservoirs exerted more influences on changes of sediment loads than on runoff, which is the main reason for the decreasing trend of sediment loads.