河床横向摆动计算方法及其在黄河下游游荡段的应用

Method to Calculate Channel Migration and Its Application in the Braided Reach of the Lower Yellow River

深泓摆动、主槽摆动等河床横向变形过程容易引起游荡段河床形态的剧烈调整,从而对河道防洪及滩区土地利用等产生重大影响,因此提出河床横向摆动的定量计算方法并用于黄河下游游荡段,对深入研究该河段的河床演变规律具有重要意义。提出利用遥感影像资料、实测断面地形资料以及河段平均的方法来定量计算河床横向摆动宽度及强度,并通过1986—2016年黄河下游游荡段实测资料加以检验。结果表明:小浪底水库运用后,游荡段深泓及主槽摆动的宽度和强度均显著降低,深泓及主槽摆动宽度分别由1986—1999年的234、410m/a减小到1999—2016年的119、185m/a,分别减小49%、55%;来水来沙条件是影响深泓及主槽摆动强度的主要因素,年均水流冲刷强度则是影响摆动强度的关键水沙因子;深泓及主槽摆动是河床横向摆动的不同表现方式,但二者存在本质上的差异,通常大尺度的主槽摆动会引起深泓摆动,但深泓摆动不一定会引起主槽摆动。

Lateral channel deformation including thalweg migration and main-channel migration can lead to remarkable channel adjustments,which has an important influence to the flood control and riparian land use.To propose a method to calculate channel migration is of crucial importance to investigate the lateral channel deformation and full riverbed evolution.In this study,a method to calculate quantitatively the magnitude and rate of channel migration was proposed by using the data of remote sensing images,observed cross-sectional profiles and a reach-average approach,and then the proposed method was applied to calculate the channel migration in the braided reach of the lower Yellow River from 1986 to 2016.It is found that the widths and intensities of thalweg migration and main-channel migration are decreased dramatically after the operation of the Xiaolangdi Reservoir,and it is also discovered that the average widths of thalweg migration and mainchannel migration are reduced from 234 and 410 m/a during the pre-dam period(1986-1999)to 119 and 185 m/a during the post-dam period(1999-2016),with a reduction of 49%and 55%respectively.The incoming flow and sediment regime is a dominant factor to influence both thalweg migration and main-channel migration,with the average fluvial erosion intensity being regarded as the key flow and sediment factor.Thalweg migration and main-channel migration are two different aspects in channel migration,but there exists an essential difference between them.The large-scale main-channel migration will certainly cause thalweg migration,whereas thalweg migration will not necessarily cause the migration of main-channel.