黄河中游小北干流段持续淤积期的主槽摆动特点

黄河中游小北干流河段为典型的游荡型河段,主槽经常发生摆动,揭示主槽摆动特点对研究该河段的河床演变规律具有重要意义.以1986-2001年小北干流段汛后卫星遥感资料与实测29个淤积大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与强度,定量分析了持续淤积期小北干流段的主槽摆动特点及其主要影响因素.计算结果表明:主槽摆动方向具有往复性,断面主槽摆动宽度沿程变化表现为上段大、中下两段小的特点,其中禹门口-庙前段多年平均主槽摆动宽度和强度分别为1151 m/a和0.70,是小北干流段中主槽摆动最为剧烈的河段;建立了小北干流段主槽摆动强度与上游水沙条件(来沙系数)与下游侵蚀基准面(潼关高程)之间的单因素及多因素响应关系,并对综合关系式进行了率定与验证.在综合关系式中,主槽摆动强度随来沙系数和潼关高程的增大而增大,且两者在该关系式中的占比平均值分别为89.3%和10.7%,说明水沙条件是影响黄河中游小北干流段主槽摆动强度的主要因素,潼关高程是次要因素.采用该经验公式得到的计算值与实测值总体符合较好,可用于计算和预测小北干流段持续淤积期的主槽摆动过程.

Characteristics of main-channel migration in the Xiaobeiganliu reach of the middle Yellow River during the continuous siltation period

The Xiaobeiganliu reach of the middle Yellow River is a braided reach,and the main-channel of this reach often migrates,so investigating the characteristics of main-channel migration is crucial to understand the river regime adjustments and fluvial processes of the Xiaobeiganliu reach.In this study,main-channel migration widths and intensities at section-and reach-scales were calculated based on post-flood remote sensing images and 29 observed cross-sectional profiles in the Xiaobeiganliu reach during the period from 1986 to 2001,in order to investigate the characteristics of main-channel migration and to analyze the influencing factors of main-channel migration intensities quantitatively.Calculated results indicate that:(ⅰ)the main-channel migration processes were reciprocating,and section-scale main-channel migration widths in the upper reach were larger than those in the middle and lower reaches;(ⅱ)the width and intensity of main-channel migration of the Yumenkou-Miaoqian reach were 1151 m/a and 0.70,respectively,and it was the most dramatic reach in terms of the main-channel migration in the Xiaobeiganliu reach;(ⅲ)the main-channel migration intensity can be represented by empirical functions of two key hydrodynamic parameters,covering the upstream boundary condition(the previous three-year average incoming sediment coefficient),and the downstream boundary condition(the variation in Tongguan elevation);(ⅳ)higher values of incoming sediment coefficient and Tongguan elevation caused a larger main-channel migration intensity,which contribute about 89.3%and 10.7%,respectively,and it indicates that the incoming flow and sediment regime is the dominant factor affecting the main-channel migration in the Xiaobeiganliu reach,and the Tongguan elevation is the secondary factor;and(v)it is verified that the calculated main-channel migration by using the empirical equation agreed well with the observed data,so the empirical equation can be used to calculate and predict the processes of the main-channel migration in the Xiaobeiganliu reach during the continuous siltation period.