长江口南槽近期动力地貌演变研究

发布时间：2018-04-26 12:40

本文选题：长江口 + 南槽　；参考：《华东师范大学》2014年硕士论文

【摘要】：河口处于陆地河流与海洋交接的地带,是河海相互耦合作用的关键区。作为陆地、海洋、大气和生物之间各种过程相互作用最为活跃的区域,河口往往受潮汐、潮流、波浪和入海径流等一系列自然营力的建造与破坏,人类的各类活动如大型水利工程也对其产生巨大影响,这些影响更为直观地体现在河口的地貌变化。因此,河口的时空变化过程尤其是动力地貌演变一直是陆海相互作用研究的核心和焦点内容。南槽作为长江口第三级分汉口,是长江输水输沙的主要通道。在北槽深水航道整治工程之前,一直作为长江口出海主航槽。然而,近年来受长江入海水沙变化和长江口大型涉水工程的影响,南槽的动力地貌过程发生了巨大改变,南槽正不断进行自我调节以适应这些变化。显然,分析和揭示近年来南槽的动力地貌变化过程对理解长江河口响应人类活动和自然驱动作用的变化具有重要意义。本文基于长江河口南槽2012～2013年水文观测数据、悬沙样品资料,大面积走航所采集表层沉积物样品和多年来水下实测地形数据分析南槽的悬沙输移扩散机制及其动力成因、区域内动力沉积特征,探讨沉积物的输运过程与输运方式,进而研究该区域河槽冲淤演变的基本规律。主要结论包括：南槽内以往复流为主,涨落潮流流向与河槽走向基本一致,落潮平均流速大于涨潮平均流速,落潮历时大于涨潮历时,流速和悬沙浓度都随着小潮到大潮潮汐潮流作用不断增强而变大。观测期间的欧拉余流UE方向均指向口外,斯托克斯余流Us方向均指向陆,二者流速均从小潮到大潮呈现明显的增加趋势。南槽沉积物总体较粗,其中沉积物以砂质粉砂为主,次要类型为粉砂、粉砂质砂、泥和砂。从沉积物的分布来看,南槽自上而下河槽呈现为粗～细～粗的分布格局,相应沉积环境的水动力表现为强～弱～强的递变过程,体现出径流、潮流以及其他水动力之间的博弈作用。同时,沉积物的分形计算表明南槽内沉积物粒度组成具有分形结构,分维值的大小能够反映沉积物的演化过程。此外,南槽上段沉积物自上向下沿河槽方向运动；南槽下段(出海口位置和九段沙以下)呈现从深水区向浅水区域输运的明显趋势,沉积物向九段沙尾和南汇东滩部位运动,九段沙沙尾呈现淤积态势。长江口南北槽分流口以1998年为界,呈现不同的地貌状态。1998年以前,分流口地貌经历了由不稳定-相对稳定-动态平衡的阶段,其中分流口沙洲洲头出现下挫-上提-下挫、主泓线则经历分流口南侧-北侧-南侧的周期变化,河槽断面由U型发展为W型。长江大洪水是导致分流口地貌格局出现变化的动力因素。在洪水发生的间歇期,分流口地貌则处于由不稳定向相对稳定发展的调整阶段。1998年修建沙洲洲头潜堤工程后,沙洲洲头出现上提-下挫-上提的微弱变化,但总体上沙洲头向北偏移,这导致进入北槽的分水分沙比有所减小。自2002年以来,沙洲洲头因分流口的淤积而缓慢上提,潜堤北侧北槽上段淤积加重,潜堤南侧尤其紧贴潜堤部位侵蚀加剧,南槽分水分沙增大,分流口落潮冲刷槽进一步向南槽发展。南槽河段在1989年江亚南沙并滩前后呈现两种不同的地貌演化阶段。江亚南沙并滩前,南槽普遍发生淤积,两侧浅滩不断淤涨,河槽总体上呈缩小态势；江亚南沙并滩后,南槽南岸普遍性冲刷,上段江亚南沙和下段九段沙不断淤涨。南槽呈现出“上段冲刷加深,中段微冲、两侧边滩淤积”的状态。同时,河流和海洋作用二者此强彼弱间的变化,使得南槽整体呈现出季节性的洪枯冲淤变化规律：上段在洪、枯季均受径流和落潮流影响,呈冲刷态势；中段尤其是沿九段沙区域呈现明显洪冲枯淤特点,下段则具有洪淤枯冲的特点。此外,近期南槽地貌的冲淤演变过程与南北两侧工程的实施进度密切相关。基于此,受人类活动影响的南槽动力地貌过程需要进一步深入研究。
[Abstract]:Estuaries are the key areas of the interaction of rivers and seas. As the most active regions of land, sea, atmosphere and biology, the estuaries are often built and destroyed by a series of spontaneous forces, such as tides, tidal currents, waves, and sea runoff, and human activities such as large scale. Water conservancy projects also have a great impact on them, which are more intuitively reflected in the geomorphic changes in the estuary. Therefore, the temporal and spatial changes in the estuaries, especially the evolution of the dynamic landforms, have been the core and focus of the study of land sea interaction.
The South trough, as the third grade Hankou in the Yangtze Estuary, is the main channel for water transport and sediment transport in the Yangtze River. Before the regulation of the north channel deepwater channel, it has always been the main channel of the Yangtze Estuary. However, in recent years, the dynamic and geomorphic process of the South trough has changed greatly by the change of the water and sand in the Yangtze River and the large water project of the Yangtze Estuary in recent years. It is obvious that the analysis and Revelation of the dynamic and geomorphic process of the South trough in recent years is of great significance to the understanding of the changes in the human activity and the natural driving effect of the Yangtze Estuary.
Based on the hydrological observation data of the South trough of the Changjiang River estuary for 2012~2013 years, the sediment sample data, the surface sediment samples collected from the large area and the measured topographic data under the inflow of the river for many years are used to analyze the mechanism of suspended sediment transport and diffusion in the South trough and its dynamic causes, the characteristics of the dynamic deposition in the region, and the transport process and transport mode of the sediment. The basic law of scouring and silting evolution in the area is studied.
In the South trough, the past reflow is the main flow. The flow trend is basically the same as the channel direction. The average flow velocity of the ebb tide is greater than the average velocity of the tide, and the ebb tide is greater than the ebb period. The velocity and the suspended sediment concentration increase with the effect of the tide to the tide tidal current. The UE direction of the Euler residual current in the observation period is all pointing out of the mouth, Stokes's surplus. The flow direction of Us is all directed toward land, and the velocity of the two directions presents an obvious increasing trend from neap tide to spring tide.
The sediments in the South trough are generally coarser, and the sediments are mainly sandy silt sand, and the secondary types are silt, silty sand, mud and sand. From the distribution of sediments, the bottom trough of the South trough shows a coarse to coarse distribution pattern, and the hydrodynamic force of the corresponding sedimentary environment is strong to weak to strong progressive process, reflecting runoff and tidal current. At the same time, the fractal calculation of sediment shows that the size composition of sediment in the South trough has a fractal structure, and the size of the fractal dimension can reflect the evolution process of the sediments. In addition, the sediments in the upper part of the South trough are moving upward and downward along the river trough direction, and the lower section of the South trough (the outlet position and the nine section sand) is presented. The obvious trend of transport from deep water area to shallow water area is the movement of sediment to nine segments of sand tail and the east beach of Nanhui, and the nine segments of sand tail are silting.
The diversion port of the north and South trough of the Yangtze River estuary is bounded by the 1998 as the boundary, presenting different geomorphic state.1998 years ago, the distributary mouth geomorphology experienced the stage of instability relative stability dynamic balance, in which the diverting estuary sandbank head fell down - up - up and down, the main branch line experienced the periodic change of the southern side of the distributary mouth - the north to the south side, and the channel section from the U type. The large flood of the Yangtze River is the dynamic factor that causes the change of the distributary geomorphic pattern. In the intermittent period of the flood, the distributary geomorphology is in the stage of the adjustment from the unstable to relatively stable development. After the construction of the Sha Chau Chau head dike project in the.1998 year, the head of the Chau Chau Island is slightly changed, but on the whole the sand continent is in the sand continent. From the north to the north, the ratio of water and sand to the North trough has been reduced. Since 2002, the head of the Chau Island has been slowly raised because of the siltation of the distributary mouth, and the siltation in the upper part of the North trough on the north side of the dike is aggravated, and the south side of the dike is especially closely attached to the submerged dike, and the water separation and erosion in the South trough will increase, and the tidal flushing trough of the diversion outlet is further developed to the South trough.
There are two different geomorphic evolution stages in the south channel of the south channel of Nansha in 1989. Before the Nansha and shoal of Jiangya, the silt in the South trough is generally silted up in front of Jiangya and the beach in the south of Jiangya. The river trough is constantly silting up, the river trough generally shows a shrinking trend; after the Nansha and the beach in Jiangya, the South Bank of the South trough is generally scoured, the upper reaches of Nansha and the lower section of the upper section of the Yangtze River are constantly rising. The South trough presents. At the same time, the change of the strong and weak between the two sides of the river and the ocean, and the change of the strong and weak between the river and the ocean, makes the whole of the South trough show the seasonal variation of the flood and scouring and siltation: the upper section is affected by the flow and the ebb flow in the flood and the dry season, and the middle section is especially along the nine section of the sand area. In addition, the evolution of the erosion and siltation in the southern trough is closely related to the progress of the north and South bilateral projects. Based on this, the dynamic geomorphic process of the South trough affected by human activities needs further study.

【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV148;P737.121

【参考文献】