Study On The Process And Countermeasures Of Reconstructing Bed In The Fengqiu Reach Of The Lower Yellow River Since Xiaolangdi Reservoir Was Put Into Use

The Fengqiu reach in the lower reaches of the Yellow River is located at the last bend of the Yellow River,"lankao bend",connecting the Yuanyang reach on the upper and Changyuan reach on the lower.The left bank of the river is Fengqiu county and the right bank is Kaifeng xiangfu district,which is a typical wandering river.Fengqiu river section has the typical characteristics of the lower reaches of the Yellow River,which is referred to as the "four maximums" : the widest river section,the largest suspension difference near the back,the largest transverse gradient of the river,and the largest population in the intertidal area.Since the Xiaolangdi reservoir was put into use,the water and sediment conditions in the Fengqiu river section have been changed.Under the new water and sediment conditions,some new problems have appeared in the river section,such as: the uplift and downslide of the river,the instability of the project depending on the river,the frequency of river accidents is large,the situation of "secondary suspension river" is still serious,and the ability to draw water from the Yellow River has decreased.Therefore,it is of great significance and urgency to study the Fengqiu reach for the whole lower Yellow River governance and development.In this paper,58 years' annual runoff,annual sediment transport and average sediment concentration data of the Fengqiu reach in the lower Yellow River from 1961 to 2018 were collected to statistically analyze the incoming and incoming sediment over the years,and the change trend of water and sediment in this reach in recent decades was obtained through the m-k rank correlation analysis.On the basis of collecting the change of the main stream line in the past years,this paper makes a comparative analysis of the change of the river regime in the course of the reconstituted bed of the reach,and summarizes the regularity of the river regime evolution in different periods of the reach.At the same time,four typical cross-sectional data of Liuyuankou,Jiahetan and Chanfang in Fengqiu reach from 2000 to2018 were collected and sorted,and the change characteristics of each cross-section over time and the change trend of the main channel were analyzed,so as to explore the change law of scour and deposition of the channel.The variation of the same discharge water level,the flat discharge and the river phase coefficient are also analyzed,and the characteristics of thesection change in the course of the regenerated bed are given.Combined with the actual situation of the current river engineering of sealing hillock,this paper analyzes the new problems facing this section under the condition of new river regime changes and the countermeasures.By sorting out and analyzing a large amount of measured data,the changes of water and sediment,river regime and section in the process of reconstructing bed in the Fengqiu reach of Xiaolangdi reservoir are summarized.On this basis,according to the existing problems of the river,some countermeasures and Suggestions are given.Secondly,the phenomenon of "two-level suspended river" in the closed hillock section can be controlled by reasonably opening sand mining,increasing the flood level of water and sand regulation and learning from the advanced and mature channel silting and dredging methods at home and abroad.The third is to solve the problem of insufficient water supply capacity for Yellow River diversion in Fengqiu reach by means of culvert reconstruction,channel dredging and agricultural water use efficiency improvement.The fourth is to improve the level of flood prevention and rescue by actively carrying out flood control publicity and comprehensive drills of flood control and rescue.