2020年汛期长江下游镇扬河段水位异变分析

Cause Analysis of Abnormal Water Level in Zhenjiang-Yangzhou Reach of Lower Yangtze River in Flood Season of 2020

2020年汛期,长江发生了新中国成立以来仅次于1954年、1998年的流域性大洪水。镇扬河段的世业洲汊道水位异常增高,泗源沟闸、瓜洲闸站超历史最高水位。为探究汛期间世业洲汊道的水位异常变化原因,对比分析了2020年与1998年的水位、流量变化过程,并从水文条件、河道演变与涉河工程3个方面对世业洲汊道的水位异变原因进行了综合分析。研究结果表明,1998—2020年间的河道冲刷下切是流量较小情况下,2020年水位低于1998年的主要原因。此次洪水过程中强潮流的顶托作用与河段内涉河工程的兴建是造成世业洲汊道水位在流量大于58 000 m^(3)/s时反超同流量下1998年的水位,甚至超过历史最高水位的主要原因。

In the flood season of 2020, the Yangtze River experienced a catastrophic flood that was only second to 1954 and 1998 floods since the founding of the PRC. The Shiyezhou Branch witnessed abnormally high water level, and the water levels at Siyuangou Gate and Guazhou Gate stations exceeded the highest water level in history. We compared the processes of water level and flow in 2020 and 1998, and analyzed the cause of abnormal change of water level in Shiyezhou Branch from aspects of hydrological conditions, river evolution and river-related projects. Results unveiled that the scouring and undercutting of river channel in 1998-2020 was the major cause of lower water level in 2020 than that in 1998 under small discharge. Moreover, when discharge exceeded 58 000 m^(3)/s, the water level at Shiyezhou Branch was higher than that in 1998 under the same discharge or even higher than historical record mainly because of the jacking effect of strong tidal current in flood process and the construction of river related projects in the river reach.