小浪底水库运用后黄河下游游荡段主槽摆动特点

Characteristics of main channel migration in the braided reach of the Lower Yellow River after the Xiaolangdi Reservoir operation

天然冲积河流主槽摆动具有复杂的时空变化性,分析其摆动特点对研究黄河下游游荡段河床演变规律具有重要意义。以1999—2016年黄河下游游荡段汛后卫星遥感影像与实测28个淤积断面地形资料为基础,计算了断面及河段尺度的主槽摆动宽度及强度,确定了小浪底水库运用后游荡段的主槽摆动特点,并定量分析了影响游荡段主槽摆动强度的主要因素。计算结果表明:游荡段主槽摆动方向具有往复性,主槽摆动宽度呈现中段大、上下两段小的特点;小浪底水库运行后,游荡段主槽摆动宽度及强度呈逐渐减小趋势,多年平均值分别为188 m/a和0.16;上游来水来沙条件是影响主槽摆动强度的主要因素,河床边界条件(滩槽高差、河床组成等)是次要因素;建立了游荡段主槽摆动强度与前3年平均水流冲刷强度的幂函数关系,相关系数良好。

The response of main channel migration to the altered flow and sediment regime is characterized by complexly temporal and spatial variations in the Lower Yellow River (LYR),and the investigation into the characteristics of main channel migration is crucial to understand the principles of river regime adjustments and fluvial processes in the LYR. In this study,widths and intensities of main channel migration at section- and reach-scales were calculated based on the data of remote sensing images and 28 observed cross-sectional profiles in the braided reach of the LYR during the period from 1999 to 2016,with the characteristics and the key influencing factor to control main channel migration intensity being identified quantitatively. It is found that the main channel processes in the braided reach migrated back and forth towards the left or right direction,and section-scale migration widths in the middle reach were generally larger than the values in the upper and lower reaches. The width and intensity of main channel migration show a gradual decreasing trend,with the average were 188 m/a and 0.16 respectively. It is confirmed that the incoming flow and sediment regime is a dominant factor to influence the main channel migration,although the channel boundary conditions can influence the intensity of main channel migration,covering the influencing factors of the level difference between main channel and floodplain,and composition of bed material. The main channel migration intensity of the braided reach can be expressed as a power function of the previous three-year average fluvial erosion intensity,and the calculated main channel migration intensities in 1999-2016 using the proposed relation generally agree with the observed data.