黄河下游游荡段断面滩岸崩退过程概化模拟

Conceptual modelling of bank erosion processes at typical sections in braided reach of lower Yellow River

近期黄河下游游荡段河床冲淤变化剧烈,滩岸崩退是该河段河床调整的一个重要方面,研究滩岸崩退过程对揭示黄河下游游荡段河势稳定的主控因素具有重要意义。首先建立了断面尺度的崩岸概化模型,并计算了2004年汛期下游游荡段樊庄与夹河滩两个典型断面的滩岸崩退过程,分析了抗冲强度、抗剪强度、渗透系数、坡脚堆积比例等主要因素对滩岸崩退的影响。结果表明:两断面滩岸累计崩退宽度计算值分别为413 m及733 m,与实测值较为吻合;滩岸崩退与坡脚横向冲刷宽度的变化一致,且坡脚横向冲刷宽度越大越不利于滩岸的稳定。滩岸崩退宽度随土体抗冲强度的增大而减小,当土体起动切应力由0.1 N/m2增加至0.3 N/m2时,樊庄及夹河滩断面滩岸崩退宽度分别减小34%和33%;滩岸崩退宽度随崩塌土体坡脚堆积比例的增大而减小,当坡脚堆积比例由50%增加至100%时,樊庄及夹河滩两断面滩岸崩退宽度分别减小10%和7%,因此坡脚堆积有利于增加滩岸的稳定性。

In recent years,significant channel evolution has occurred in a braided reach of the lower Yellow River(LYR),and a key factor of its channel lateral deformation is bank erosion that has negative influence on the stability of this reach.To investigate the bank erosion,this study develops a cross-sectionscale conceptual model for simulating the time development of bank erosion at the cross-sections of Fanzhuang and Jiahetan observed in the flood season of 2004,and identifies the key factors of bank erosion.The results indicate that the calculated cumulative erosion widths were 413 m and 733 m for these two typical sections,agreeing well with the observations in-situ;the calculated time variations in bank erosion width were consistent with those in lateral bank-toe erosion width,demonstrating the unfavorable effect of large lateral erosion widths on bank stability.By the calculations,erosion width is decreased with an increase in soil erosion strength.The decreases in bank erosion width were 34%and 33%at Fanzhuang and Jiahetan respectively when soil erosion strength increasing from 0.1 to 0.3 N/m2.And at these two sections,the bank erosion widths were decreased by 10%and 7%respectively when the bank-toe deposition ratio of collapsed soil increasing from 50%to 100%,showing a favorable effect of high bank-toe deposition ratios on river bank stability.