| 摘要: |
| 在径潮流相互作用及河口拦门沙综合影响下,长江口潮波传播过程及内在机制十分复杂。目前,仍缺乏基于长序列实测资料开展上述因素影响下长江口各主要分潮振幅的时空变化特征及成因探讨。本文以长江口“下游口门~北槽拦门沙~上游徐六泾”河段为例,基于沿程6个潮位站多年逐时潮位、北槽洪、枯季水文以及上游大通流量资料,采用t-tide分析工具与河道阻力系数公式,重点分析了长江口主要分潮振幅受径、潮流及河口拦门沙影响下的时空变化特征及成因。研究表明,长江口潮波主要由半日分潮(M2、S2、N2)、全日分潮(K1)及四分之一日浅水分潮(M4)组成。空间上,自长江口至徐六泾,长江口各主要天文分潮振幅呈现先增加后减小的特征,而浅水分潮(M4)振幅呈现逐渐增大的特征。时间上,长江口各站点分潮振幅年内呈现单峰或双峰的周期性波动。径潮流相互作用下,振幅较弱的天文分潮(N2、K1)受径流影响小,而振幅较强的天文分潮(M2、S2)则相反。径流对长江口各分潮振幅影响取决于其正、反作用的相互占比。径流的正向作用表现为平均水位的抬高,底摩擦的减少及天文分潮振幅的增加；反向作用表现为径、潮流相互顶冲,天文潮能量的耗散及分潮振幅的减少。越靠近上游(徐六泾站点),径流对潮流反向作用越明显,分潮振幅随径流量增加而呈减少趋势。相反,在下游口门区水域,M2分潮振幅随着径流量的增加而增加。在两者之间的北槽拦门沙水域,M2分潮振幅随径流增加而呈现“先增后减”的变化趋势,其临界径流量约为45000 m3/s。长江口北槽水域的潮波能量耗散不仅与径流影响下洪枯季水位差异有关,也与拦门沙近底高含沙有关,且后者对能量耗散的影响占比更高。拦门沙近底高含沙量减阻效应对长江口潮波传播的影响不可忽略。 |
| 关键词: 长江口 分潮振幅 时空变化 调和分析 河道阻力 |
| DOI： |
| 分类号:P731.2??? ???? ??? |
| 基金项目: |
|
| Characteristics and causes of the propagation of main tidal waves in the Changjiang Estuary |
|
Wang Youming1, Shen Qi2, Li Junhua3, Gu Fengfeng2, Jia Yushao4, Ying ming4
|
|
1.Shanghai Estuarine ＆ Coastal Engineering Consultants LTD Shanghai;2.Key Laboratory of Estuarine ＆ Coastal Engineering,Ministry of Transport,Shanghai Estuarine ＆ Coastal Science Research Center;3.College of Ocean Science and Engineering,Shanghai Maritime University;4.CCCC Shanghai Waterway Engineering Design and Consulting Co,Ltd,Shanghai
|
| Abstract: |
| The propagation of main tidal waves in the Changjiang Estuary is complicate when facing the impacts of runoff current interaction and mouth bar. Up to now, there still lacks a long-term observational analysis on the characteristics and causes of the propagation of main tidal waves in the Changjiang Estuary affected by aforementioned elements. This paper takes the reach from the downstream estuarine mouth to the upstreasm Xuliujing station which is by the way of the North Channel barrier sand as an example. A multi-years water level data of six tidal gauge stations as well as the corresponding runoff of Datong gauge station were collected and the suspended sediment concentration (SSC) in the North Passage during the flood and dry season was also used. With the help of the T-tide tool and the channel resistance formula, an investigation on the characteistics and causes of the propagation of main tidal amplitude in the Changjiang Estuary affected by the interaction of the runoff, the tidal current, the mouth bar and the human intervention was carried out. The results show that the main tidal components of the Changjiang Estuary include three semi-diurnal tides (M2,S2,N2), one diurnal tide(K1) and one shallow water constituent(M4). Spatially, the amplitude of each astronomical tidal constituent along from the Changjiangkou station to the Xuliujin station was increased initially and decreased afterwards. Meanwhile, the amplitude of shallow water constituent was increased from the Changjiangkou station to the Xuliujin station. Temporally, the tidal amplitude of each main tidal component was periodically fluctuated with the single or double peak throughout the year. The amplitude of astronomical tidal constituent with weak tidal dynamics such as N2, K1 was hardly influenced by the interaction of runoff and tidal current, on the contrary, the amplitude of astronomical tidal constituent with stronger tidal dynamics such as M2, S2 was sensitive to the impact of runoff. The variations of tidal amplitude under the interaction of runoff and tidal current are determined by the mutual proportion between the positive and negative effect .The positive effect refers to the enhanced tidal amplitude due to the runoff-induced rising of water level and the reducing of channel resistance. The negative effect refers to the reduced tidal amplitude and the dissipated energy owing to the runoff colliding head-on with the tidal current. The further upstream the reach is (eg. Xuliujing station), the more significently the negative effect becomes, which shows the amplitude of each tidal component decreases with the increasing runoff. On the contrary, near to the estuary mouth (eg. the Changjiangkou station), the amplitude of M2 tide was increased in keeping with the increasing of the runoff. In the North Passage of the Changjiang Estuary which was lied between the upstream reach and the estuary mouth, the amplitude of M2 tide was increased at first when the runoff beggan to increase. And when the runoff was increased up to 45000m3/s, the amplitude of M2 tide reached maximum and started to decrease with the runoff keeping increasing. The dissipation of tidal energy near the North Passage of the Changjiang Estuary was not only related to the different water level during the flood and dry season but also was associated with the variation of near bottom high SSC. The SSC-induced reduced friction had more significant impact on the dissipation of tidal energy than that by the bottom high SSC in the sandbar area. The impact of bottom high SSC in the sandbar area shouldn’t be ignored in studying the propagation of tidal waves in the Changjiang Estuary. |
| Key words: the Changjiang Estuary tidal amplitude spatial and temporal variation harmonic analysis the channel resistance |
