1986—2018年黄河下游游荡段洲滩演变特点

Characteristics of Channel Bars Evolution in the Braided Reach of the Lower Yellow River in 1986-2018

黄河下游游荡段洲滩密布,研究洲滩的时空演变特点对充分认识游荡段河床演变规律具有重要意义。以1986—2018年黄河下游游荡段遥感影像资料为基础,逐年确定枯水流量下河道内洲滩数目、面积及长度,并计算洲滩的形态指数,分析近33 a游荡段洲滩的时空演变特点。结果表明:游荡段多年平均洲滩数目由小浪底水库运行前的105个增加到小浪底水库运行后的140个,其中小型洲滩数目大大增加,大型和超大型洲滩有所减少;受水库运行后河床持续冲刷的影响,游荡段多年平均洲滩总面积由小浪底水库运行前的81 km2减小到小浪底水库运行后的62 km2,洲滩形态趋于细长;从分河段来看,研究期内花园口以上河段洲滩数目最多、面积最大,夹河滩—高村河段数目最少、面积最小。

The braided reach of the Lower Yellow River is densely covered with channel bars,and it is of great significance to investigate the characteristics of channel bars evolution for better understanding the fluvial processes in the braided reach.The number,area and length of channel bars were identified annually under the low flow based on remote sensing images in the braided reach from 1986 to 2018,and the shape index of channel bars was also calculated.The characteristics of channel bars evolution were analyzed temporally and spatially in recent 33 years.The results show that the average number of channel bars is increased from 105 to 140 after the operation of the Xiaolangdi Reser⁃voir,and the number of small channel bars has been increased greatly,with the number of large and very large channel bars decreasing.The average area of channel bars is decreased from 81 km2 to 62 km2 owing to channel scour,and the shape of channel bars is prone to slender.The above HYK reach has the maximum number and area of channel bars,and the JHT⁃GC reach has the minimum number and area of chan⁃nel bars during the study period.