| The hydrology of the Yellow River has the characteristics of less water and more sand,different sources of water and sediment,and inconsistent relationship between water and sediment.Since the 1980 s,especially in the 21 st century,the runoff and sediment transport has decreased sharply,and the relationship between water and sediment has changed significantly,causing widespread concern in all walks of life.For a long time,the study of runoff and sediment transport has mostly focused on a certain section of the river,and relatively few studies have been conducted on the entire Yellow River Basin.This paper analyzes the runoff and sediment transport data of 16 hydrological stations such as Tangnaihai Station of the Yellow River in the past 70 years,and uses traditional mathematical statistics to systematically study the evolution process and characteristics of runoff and sediment along the whole river.The new pattern of runoff and sediment has comprehensively analyzed the driving factors of water and sediment changes in different intervals,with a view to providing scientific support for ecological protection and high-quality development.The main conclusions are as follows:1.The evolution law of natural runoff in the Yellow River in the past 550 years is analyzed,and it is concluded that the natural runoff shows a significant downward trend as a whole during random fluctuations and periodic changes,and there is a sudden change.Natural runoff occurred at a maximum value in the middle and late 19 th century and changed greatly.The long-range natural runoff has obvious characteristics of abundance and dryness,and the number of occurrences of continuous flat water years and continuous rich water years is more than that of continuous dry water years.2.The characteristics of the annual and interannual runoff changes of the stations along the Yellow River are revealed.It can be seen that the annual internal runoff of the main stations in the upper,middle and lower reaches is concentrated between June and October and the difference is large,and the spatial difference is significant.Except Tangnaihai and Lanzhou stations,the annual runoff of other hydrological stations has an obvious downward trend,and the decline rate increases along the way.The mutation years of each station are mainly 1985 and 1990.The runoff of each station along the road in different years showed that it first increased to the Huayuankou station to reach the maximum value and then declined.The annual changes of sediment transport and sediment content at major stations along the Yellow River have a clear trend,and there are large differences before and after the mutation.At the same time,the annual sediment transport and sediment content of each hydrological station(except Tangnaihai Station)decreased significantly.On the contrary,the annual median particle size value of most hydrological stations increased significantly.The annual sand content in the upper,middle and lower reaches is the same as the amount of sediment transport,and the overall trend is to decrease year by year in the upper and middle reaches,and increase in the downstream year.The frequency distribution of annual sediment transport and sediment content in each interval is quite different,and the upper and middle reaches of the interval both decrease after the mutation and before the mutation,while the downstream is the opposite.3.The response of rainfall factors and human disturbances to changes in water and sediment was analyzed.The double cumulative curve method was used to analyze the impact of rainfall on representative sites in the upper,middle and lower reaches of the Yellow River and the contribution rate of human disturbance to water and sediment reduction.The contribution rate of runoff reduction is 43% ～ 97% and 3% ～ 57% respectively,while its contribution rate to sediment reduction is 42% ～ 91% and 9% ～ 58% respectively.Human disturbances play a key role in changes in runoff and sediment transport. |
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