| The Yellow River is known as the highest sediment concentration river.The average annual sediment of Yellow River into the sea accounts for 8% of the total amount of sediment entering the sea.However,since the 1970 s,especially after 2000,the amount of water discharge and sediment load in the Yellow River has dropped significantly.Many scholars at home and abroad have studied the problem of sediment reduction in the Yellow River in recent years.Different results suggest different mutation time of the Yellow River sediment reduction,including 1970,1960,1979,etc.;The understanding of factors influcing sediment load change is not uniform,but in general it can be concluded that since the 1970 s,the contribution of human activities to the reduction of sediment in the Yellow River has continued to increase.Some scholars have predicted the future sediment transport of the Yellow River.The predicted values range from 0.3 billion t/a to 1.2 billion t/a.There is no uniform and convincing prediction.In this paper,the Yellow River Basin above Tongguan station is taken as the research object.The changes of meteorological sequence and water-sediment sequence in the Yellow River Basin since 1919 are analyzed.The annual average temperature,annual precipitation,annual average natural discharge and sediment load sequence of the study area from 1919 to 2016 are divided into different time periods(3?5 periods)by MannKendall nonparametric test.The measured sediment transport volume at Tongguan has experienced three stepwise declines since 1932.The sediment transport in the three periods from 1932 to 1959,1960 to 1978,and 1979 to 1996 fluctuated around the stable mean values,and the mean values were successively reduced.From 1997 to 2016,the amount of sediment transport decreased linearly,with an average annual reduction of 0.026 billion tons.The analysis of the double-cumulative curve of sediment loadprecipitation shows that the impact of human activities on the sediment transport of the Yellow River has been increasing since 1919.HydroTrend was used to simulate the change process of sediment transport in the Yellow River during the historical period.The average annual sediment transport of the Yellow River in Tongguan during the mid-Holocene warm period was 0.358-0.413 billion tons,which is consistent with the calculation results of the sediment analysis literature.From the Middle Holocene to the Qing Dynasty(except the Western Han Dynasty to the late Eastern Han Dynasty),the enhancement of the Yellow River sediment production by humans gradually increased,and human activities were the main reason for the increase in sediment transport load in the Yellow River.For the simulation of 10 time periods from 1919 to 2016,the anthropogenic factor and sediment transport reached their peaks from 1932 to 1944.After that,both of them continued to decline.During 2006-2016,the sediment transport volume dropped to a historical low of 0.162 billion tons.The anthropogenic factor was less than 1.0 for the first time.The main reason for the decrease in sediment transport load in the Yellow River in the past 100 years is the reduction of anthropogenic factor.Especially after 1978,the impact of human activities dominated the change in sediment transport in the study area.Based on the study of the variation of sediment transport in the Yellow River during the historical period,this paper makes a preliminary prediction of the Yellow River's sediment transport in the next 30-50 years.It is assumed that the anthropogenic factor gradually approch the state of the original period.Under the meteorological conditions in the future,the annual mean sediment transport load will be 0.18-0.34 billion t/a. |
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