三峡工程运用后长江中游河床调整及崩岸特点

Bank collapse and river bed adjustment in middle Yangtze River after operation of Three Gorges Project

三峡工程运用后,因入库沙量减少及上游水库群的拦沙作用,坝下游河段沙量急剧减小,长江中游河道发生沿程冲刷,2002~2015年该河段累计冲刷量已达16亿m^3,同时平滩河槽形态也发生了显著调整。为更好地掌握长江中游的河床调整特点,分析了近期长江中游水沙过程及河床冲淤情况,采用基于河段尺度的平滩河槽形态参数的统计方法,计算了长江中游各河段平均的平滩河槽形态参数;建立了这些参数与前5 a平均汛期水流冲刷强度之间的经验关系,用于反演各河段平滩河槽形态随水沙条件变化的调整过程。此外,三峡工程运用后长江中游局部河段崩岸险情频发,不仅影响河势稳定,同时危及防洪安全,因此还总结了长江中游河道崩岸的时空分布及其特点,提出了水流冲刷强度增加是导致崩岸发生的主要因素。

Due to sediment retention effects of reservoirs group in upper Yangtze River and reduction of sediment entering the Three Gorges Reservoir after operation of Three Gorges Project,significant decay of sediment discharge and severe river channel erosion are developing at the downstream of Three Gorges Project,reaching a accumulative 1.6 billion m^3 erosion quantity from 2002 to 2015.At the same time,the bankfull river geometry also changed.For better mastering the river adjustment condition in the middle Yangtze River reach,we calculate the mean bankfull river geometric parameters in reach scale by statistics.We establish an empirical relation between these parameters and mean erosion intensity in flood season of previous 5 years,and based on this we carry out back analysis on the bankfull river adjustment process along with the water-sediment change.Aiming at the high frequency bank collapse in the middle reach after the operation of TGP,we summarize the temporal and spatial characteristics of river bank collapse,and confirm that the increase of erosion intensity is the main reason that induces river bank collapse.