Dynamic Changes of Sediment Discharge and the Influencing Factors in the Yellow River, China, for the Recent 90 Years

The dynamic changes in the sediment discharge over 90 years from 1919 to 2008 in the Yellow River in China were assessed on the basis of annual rainfall series and annual sediment series in Shan County hydrological station. The key factors affecting sediment discharge, such as rainfall, and human activities were studied. Anomaly accumulation method and double mass curve were employed to test the stage changes of sediment discharge, and to determine the main factors of sediment decline. Results showed that the annual average sediment discharge under natural conditions was about 16 x 10(8) t, but the measured annual average sediment during 1919-2008 was 12.71 x 10(8) t. The highest annual average during the study period was 39.10 x 10(8) t in 1933 while the lowest was 1.77 x 10(8) t in 2008. Sediment discharge in the Yellow River experienced two low sediment stages (1924-1931 and 1979-2008) and a high sediment stage (1932-1971), respectively. Since 1979, there was a significant decreasing trend in the sediment discharge, and the main influencing factor was fierce human activities. Annual average sediment discharge in the post-development period (1979-2008) was 69.7% lower than that in the pre-development period (1919-1978), with average reduction of 81 and 19% caused by human activities and rainfall, respectively. These results provide important evidence for making protecting policy for water resources quality and environmental safety of the Yellow River.