小浪底水库的运用改变了坝下游的水沙条件，引起了黄河下游河道的再造床过程，给防洪及滩地利用等带来了一系列影响。利用黄河下游1999—2015年水沙及断面地形等实测资料，分析了近期黄河下游河床的调整过程及特点：①进入下游河道的年均沙量仅为0．88亿t，累计河床冲刷量达18．7亿m3，其中游荡段冲刷量占总冲刷量的72％，在冲刷过程中河道纵比降变化不大，河床粗化较为明显，床沙中值粒径由建库前的0．06 mm增大到水库运用后的0．15 mm；②河床断面形态调整较为显著，下游各河段调整均表现为向窄深方向发展，其中游荡段主槽展宽较为明显，平滩河宽由1999年的943 m增大到2015年的1275 m，过渡段及弯曲段的平滩河宽调整较小，此外各河段平滩流量也显著增大，游荡段、过渡段、弯曲段平滩流量分别由1999年汛后的3229、2339、3080 m3／s增大到2015年汛后的7126、4864、4721 m3／s；③河床平面形态总体保持稳定，各河段深泓摆动幅度均有所下降，其中游荡段的年平均深泓摆动幅度由建库前的234 m降低到水库运用后的123 m；④河段尺度的平滩河槽形态参数（如平滩河宽、平滩水深、平滩面积、平滩流量）及深泓摆动强度与水库运用后前4a平均的水流冲刷强度密切相关。%The operation of the Xiaolangdi Reservoir has changed the flow and sediment regimes downstream of the dam and led to channel re⁃forming process in the Lower Yellow River ( LYR) , which has a great effect on flood control and floodplain land utilization. Based on the observed hydrological data and cross⁃sectional profiles during the period from 1999 to 2015, processes and characteristics of recent channel adjustments in the LYR were investigated, including a) the average annual sediment load entering into the LYR was only 0.88×108 tons/a, and the cumulative volume of channel scour was 1. 87 × 109 m3 , with the value of the braided reach accounting for 72%. There were little change in the longitudinal channel slope during the degradation process, but the bed material in the LYR tended to coarsen significantly, with the mean median diameter of bed material increasing from 0. 06 mm during the pre⁃dam period to 0. 15 mm during the post⁃dam period;b) substantial changes occurred in the adjustments of channel geometry, with the channels of all the downstream reaches in the LYR becoming narrower and deeper. The process of channel widening was prominent in the braided reach, with the bankfull width increasing from 972 m in 1999 to 1275 m in 2015, while there was little variation in the bankfull width in transitional or meandering reach. The bankfull discharges in three reaches increased dramatically from 3229, 2339 and 3080 m3/s in 1999 to 7126, 4864 and 4721 m3/s in 2015 respectively;c) the plane⁃form geometry generally remained stable in the LYR, with a decrease in the rates of thalweg migration in three reaches. The rate of thalweg migration in the braided reach decreased from 243 m/a during the pre⁃dam period to 123 m/a during the post⁃dam period;d) reach⁃scale bankfull channel geometry ( bankfull depth, width, area and discharge) and thalweg migration intensity were closely related to the previous 4⁃year average fluvial erosion intensity entering the corresponding reach.
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