Dominant Mechanism For Annual Maximum Flood And Sediment Events Generation In The Upper And Middle Yellow River Basin

Flood and sediment disasters occur frequently in recent years.The Yellow River is known for its devastating floods and extremely high sediment load,and the problem of water and sediment disasters is more obvious than that of other watersheds.Therefore,it is of great significance to understand the seasonal characteristics of runoff and sediment in the Yellow River Basin and to study the formation mechanism and prediction of flood and sediment disasters in the Yellow River Basin.In this paper,the middle and upper reaches of the Yellow River Basin are selected as the research object to analyze the temporal and spatial variation of extreme flood and sediment events and the leading predictors of extreme floods and sediment events in each hydrological station.The main contents are summarized as follows:(1)The spatial and temporal distribution of the maximum precipitation,runoff and sediment events in the middle and upper reaches of the Yellow River is analyzed by the circular statistical approach.The results show that extreme events have a strong seasonal feature,and the date of occurrence is mainly in the period from July to August.Morvover,the inter-annual variability is also small.In the propagation process of rainfall-runoff-sediment events,the inter-annual variability of three extreme hydrological and sediment events was gradually reduced,while the spatial difference increased.(2)Three metrics(daily precipitation,weekly precipitation and daily water storage in channel)are are assumed to be the predictors of flood causes,and the leading predictors causing extreme flood events are analyzed by Spelman rank correlation method.The results show that the mechanism of extreme flood events in the middle and upper reaches of the Yellow River is mainly the immediate hydrological response of Horton runoff generation,and the daily water storage predictors does not play a leading role in the occurrence of extreme flood events.Compared with the daily precipitation predictors,the weekly precipitation predictors is more closely related to the annual maximum runoff event.(3)Three metrics(daily precipitation,daily runoff and sediment storage in channel)are are assumed to be the predictors of sediment events causes,and the leading predictors causing extreme sediment events are analyzed by Spelman rank correlation method.The results indicate that extreme sediment events are generally dominated by precipitation or runoff predictors in areas with small runoff and sufficient sediment supply,while sediment dynamics is controlled by sediment storage predictors at the outlet of tributaries with large runoff and low sediment concentration.In addition,vegetation cover has a certain influence on the dominant mechanisms of sediment events.(4)The sediment transport has a "storage-release" cycle process in the channel on a seasonal scale,and its effect on sediment transport is particularly significant in areas where extreme sediment events are dominated by sediment storage predictors,exacerbating the phenomenon of "small water with large amount of sediment" and "large water with small amount of sediment".