Study On Variation Of Water And Sediment And Evolution Of Erosion And Deposition In Lower Yellow River

The characteristics of less water and more sand in the lower reaches of the Yellow River seriously threaten the life and property of people on both sides.In order to study the relationship between the variation of water and sediment and the erosion-deposition evolution,this thesis first adopted the Mann-Kendall test method,sequential cluster method and cumulative departure method to test the change trend and abrupt time point of water-sediment variation based on the measured data of water-sediment at the Huayuankou and Gaocun stations in the lower reaches of the Yellow River from 1960 to2016.And also,the cumulative curve slope change rate method was adopted to quantitatively analyze the mutation factors of water and sediment.Secondly,based on the Makayev method,the dominant discharge at the two stations was calculated,and the beach altitude was determined to calculate the bankfull discharge.The change process of dominant discharge and bankfull discharge was analyzed,so as to explore the influence of water-sediment variation on dominant discharge and bankfull discharge;Finally,the cross section method was adopted to calculate the amount of erosion and deposition in the river reach from Huayuankou to Gaocun,and the change process of erosion and deposition was analyzed,thus exploring the necessary conditions for the balance state of riverway erosion and deposition.The results are as follows:1.The abrupt time of the annual runoff at the two stations was in 1986 and 1985,and the abrupt time of the annual sediment discharge were in 1999 and 1996,and the water-sediment variation showed a significant downward trend;The contribution rates of rainfall and human activities to the annual runoff reduction are 4.57% and 95.43%,9.24% and 90.76%,respectively.The main driving force of the runoff reduction at the two stations is human activities.2.The analysis showed that the change process of dominant discharge and bankfull discharge at the two stations over the years is similar.The dominant discharge at the two stations increases with the increase of runoff or sediment discharge.The bankfull discharge is affected by the accumulation of runoff,and the cumulative impact of runoff in the previous three years is significant.3.When meeting conditions that the average sediment concentration at Huayuankou Station in the whole year and flood season is 13.43kg/m3 and 26.18kg/m3 respectively,the average incoming sediment coefficient in the whole year and flood season is 0.0093kg·s/m6 and 0.011kg·s/m6 respectively,and the critical ranges of dominant discharge at the two stations are 3700-4200m3/s and 2400-2700m3/s respectively,the river reach of Huayuankou to Gaocun is easy to be in a state of erosion-deposition balance.From 1960 to 2000,beach altitude at the two stations varies greatly,river beach is unstable,and the rivers reach deposits as a whole.After 2000,the change of beach altitude decreased,the beach was relatively stable,and the continuous scouring of the river reach causes the bankfull discharge to show an upward trend.