Characteristics and Influencing Factors of River Bed Incision in the Braided Reach of the Lower Yellow River in Recent Years
Dramatical channel erosion has occurred in the braided reach of the Lower Yellow River(LYR)since the Xiaolangdi Reservoir op-eration.Study on characteristics and influencing factors of river bed incision has great significance for the river embankment and flood control in the braided reach of the LYR.The accumulated downcutting depths of river bed and channel bankfull depths were calculated based on the observed post-flood profiles at 28 cross-sections in the braided reach from 1999 to 2020.The annual water level-discharge curves of each hy-drological station were obtained based on the hydrological data,and the annual change of water level at certain discharges was calculated.The results show that:① The cumulative scour volume of the LYR was 2.05 billion m3,and the braided reach experiencing the most channel erosion with a cumulative scour volume of approximately 1.47 billion m3 from 1999 to 2020.② The braided reach of the LYR experienced the most severe river bed downcutting between 2000 and 2007,with an average annual downcutting depth of 0.24 m/a.From 2008 to 2020,the degree of river bed downcutting in the braided reach decreased,with the average annual downcutting depth reducing to 0.05 m/a.③ There have been significant changes in the water level-discharge relationships at three hydrological stations,with a noticeable decrease in water levels at given discharges at the three hydrological stations.There is a certain time lag in the decline of water levels at hydrological stations along the braided reach,with a lag time of approximately three to four years.The magnitude of water level decline at each hydrological station under a discharge of 500 m3/s is greater than that under a discharge of 3 000 m3/s,with the largest decline observed at Gaocun station.④ The bankfull depth in the braided reach increased from 1.6 m to 4.0 m from 1999 to 2018,and then decreased to 3.8 m in 2020.⑤ Influencing factors of river bed cumulative incision were investigated quantitively,including incoming flow and sediment regime and channel boundary conditions.It is found that the previous 6-year average incoming sediment coefficient is the primary factor influencing the accumulated down-cutting depth of river bed in the braided reach of the LYR.In addition,the inhibition of continuous river bed coarsening on river bed incision were quantitively analyzed in the braided reach.
river bed incisionincoming sediment coefficientXiaolangdi Reservoirbraided reachLower Yellow River
万方数据
维普
