长江感潮河段潮波传播变化特征及影响因素分析

径潮相互作用是感潮河段水动力变化的典型特征,受其影响潮波传播具有明显的洪枯季及沿程变化。本文基于长江感潮河段天生港、江阴、镇江、南京、马鞍山及芜湖6个潮位站2002-2014年连续高低潮位资料及大通站月均流量数据,统计分析长江感潮河段潮波振幅衰减率、潮波传播速度及余水位坡度等传播特征值的洪枯季及沿程变化特征,并探讨这些潮波传播特征的变化规律及其主要影响因素。结果表明,潮波传播特征的洪枯季差异自上游至下游逐渐减小,其分界点位于天生港与江阴之间(其中,天生港和江阴站的多年平均洪枯季潮差差值约为0.01 m和-0.04 m);径流动力对潮波衰减的影响主要位于江阴以上河段,江阴以下河段主要受潮汐动力控制;径流驱动下余水位坡度引起的余水位及水深增加,导致潮波传播的有效摩擦减小,当流量超过某个阈值时潮波振幅衰减反而减弱,特别是上游马鞍山-芜湖段最为明显,统计结果表明该河段流量阈值约为33 000 m3/s。本文分析结果作为前人研究的重要补充,可为长江河口感潮河段径潮相互作用机制研究及河口治理等提供基础参考。

Investigation into the spatial and temporal tide-river dynamics and the underlying controlled factors along the tidal reach of the Changjiang River

As tidal waves propagate into the estuary, they are featured by significant longitudinal variation in seasonal scale due to the nonlinear interactions between tide and river discharge. In this study, the variations of tide-river dynamics in terms of tidal damping rate, wave celerity and residual water level slope were explored based on long-term time series of tidal water levels from 2002 to 2014 along the tidal reach of the Changjiang River (including the Tianshenggang, Jiangyin, Zhenjiang, Nanjing, Maanshan and Wuhu stations) in together with the monthly averaged river discharge observed at Datong hydrological stations. Subsequently, the underlying controlled factors that influence the tidal wave propagation were discussed. It was shown that the seasonal difference in tide-river dynamics was gradually reduced in the seaward direction. We identified a transitional zone located between the Tianshenggang and Jiangyin stations, where the seasonal differences in tidal range are 0.01 m and -0.04 m, respectively. Generally, upstream from Jiangyin Station the dynamics character was river-dominated, while in the lower reaches it was mainly controlled by the tidal forcing. In addition, we show that there exists a threshold in river discharge in the upper reaches of the tidal reach of the Changjiang River due to the increase of residual water level and hence water depth caused by the residual water level slope. This phenomenon was particularly true in the upstream reach between Maanshan to Wuhu stations, where the threshold of river discharge was approximately 33 000 m³/s. The results obtained from this study can enhance our understanding of tide-river interaction, and will, hopefully, provide guidelines for water resources management in the tidal reach of the Changjiang River.