Changes In Flow And Sediment Regimes In The Yellow River

The paper is intended to summarize the changes in flow and sediment regimes in the Yellow River before and after the mid - 1980s and analyze the reasons for them. By the analysis of the measured data in the basin, we have come to realize striking features of the hydrologic regime changes. The river has been in low flow and sediment regimes since the mid - 1980s. Water volume and sediment load have become 40% less each since the mid 1980s than the average values over the long term at the hydrometrical stations in the stem river. Besides, distributions of flow and sediment in a year have changed significantly. The ratio of flow volume in the flood season to the total annual volume decreased from 60% to 40%. Frequencies of discharges more than 1, 000 m(3)/s have decreased so much that the problem of no flow has not been solved fundamentally. Frequencies of large floods occurring have decreased a lot while frequencies of small and middle floods with high concentrations have increased a lot. There will be still chances for large floods to happen in the Yellow River. Mean sediment particle size in the flood season has become smaller since the mid 1980s than before but the composition remains the same as before. If heavy rainfall comes, the mean particle size will become big just similar to that before the mid - 1980s. Reasons for the changes in flow and sediment regimes are investigated. The research results indicate that 23% of the change in flow regime and 39% of the change in sediment regime are caused by the changes in natural factors while the rests, 77% and 61%, are caused by human. activities, respectively