河床边界条件改变对强约束型分汊河道冲刷调整的影响

Influence of riverbed boundary condition on erosion adjustment of strong-restriction braided reach

通过实测资料分析的方法,以宜都河道为例,研究了水库蓄水后强约束型分汊河道的冲刷调整规律。在此基础上,进而通过概化模型试验,研究强约束性分汊河道中,河床边界条件的变化对分汊河道水流运动和冲刷调整规律的影响。研究表明:1)由于水库蓄水后河床发生剧烈的冲刷调整,将导致河道河床边界条件特别是两汊高程差的变化,分流格局随之改变;2)河道边界条件发生变化,水流动力轴线可以由稳定于一汊转化为两汊交替,其冲刷调整形式也从一汊冲刷占优转化为两汊冲刷交替占优;3)分汊河道在水库蓄水初期的剧烈调整过程及其河床边界条件的变化一定程度上影响着分汊河道的发展趋势,要充分认识分汊河道在水库蓄水初期剧烈调整过程中所可能出现的问题,引导其朝好的方向发展。

Based on the analysis of the observation data and taking Yidu reach as an example, we studied the erosion adjustment rule of strong-restriction braided reach. Furthermore, through the generalized model test, we analyzed the influence of the change of riverbed boundary condition on the flow movement and erosion adjustment. The result indicates that： （1） The drastic bed erosion after reservoir impoundment will bring the changes of riverbed boundary, especially the changes of elevation contrast between two branches, and the follow-up change of diversion pattern; （2） The decrease of the riverbed elevation of one branch makes the flow dynamic axis change from swinging in only main branch to alternately swinging between the main and branch channel; And the erosion changes alternates between the two branches following the alternation of flow dynamic axis; （3） The changes of riverbed boundary condition caused by drastic erosion after reservoir impoundment may influence the evolution trend of the braided reach to some extent.