【作者】 胡日军；

【导师】 李广雪； 吴建政；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2009， 博士

【摘要】 海洋泥沙在河口及邻近海域环境中具有重要的作用,因为它们既是营养盐和有机物的载体,又对污染物的迁移和循环产生显著影响;同时,由于人类活动和泥沙运移的相互作用,使得泥沙运移对港口开发、航道维护、海洋构筑物建设以及海底光缆的铺设等人类活动产生明显影响。因此,充分了解河口及邻近海域的泥沙运移和动力机制,一方面,对于港口开发等人类活动具有重要的实际意义,另一方面,对于探讨现代沉积过程和分析污染物扩散则具理论意义。舟山群岛海域北临长江口,西接杭州湾,既是长江水体南下的必经之路,也是杭州湾水体与东海水体交换的主要通道;同时,舟山群岛海域岛屿众多、水深地形多变、水动力条件复杂。因此,舟山群岛的泥沙分布及输运必然存在特殊性质。本文以实测资料为基础,利用不同的研究方法和计算公式,系统地分析了舟山群岛海域泥沙的分布和运移特性,揭示了泥沙运移的动力机制,探讨了群岛对泥沙分布和运移的影响。以实测资料为基础,对研究区的海流、悬浮泥沙和表层沉积物的分布特征进行了系统地分析。结果表明,研究区悬沙浓度自杭州湾向外海迅速降低;落潮平均含沙量一般高于涨潮平均含沙量;水位波动对潮周期内悬沙浓度的变化影响显著,由水位变化引起的泥沙运移掩盖了流速变化对悬沙浓度的影响;粉砂是研究区内分布最广的沉积物类型,主要分布受群岛影响较小的海域,局部分布有砂质粉砂、砂和砾,主要出现在岛屿周围;群岛对表层沉积物类型、粒度参数以及不同粒级组分的分布影响显著。利用通量机制分解方法和悬沙沉降公式,并结合前人的研究成果,分析了舟山群岛海域悬浮泥沙的输运通量、运移方向和动力机制,研究了悬浮泥沙的沉降特性。结果表明,研究区净悬沙通量自杭州湾内向外海迅速变小,悬沙总体由杭州湾向外海输运,但同时存在向杭州湾方向的净输沙;研究区基本处于水动力平衡带,悬沙输运具有往复搬运、净输沙量小的特点;平均流输运、Stokes漂移输运和垂向净环流输运是引起悬沙泥沙净输运的主要作用机制,自口门至外海,平流输运作用逐渐减弱,垂向净环流输沙在悬沙净输运中所占比例逐渐增加;舟山群岛海域既是杭州湾向东海输运泥沙的重要通道,也是东海沿岸流携带泥沙向南输运的过渡地带;研究区单颗粒泥沙沉降速度很小,远小于絮凝沉降速度,在研究本区悬沙沉降时必须考虑絮凝的影响。利用泥沙起动流速公式、沉积物输运通量公式以及粒度趋势分析方法,结合东海表层沉积物分布和东海流系,分析了表层沉积物的起动流速和输运通量,讨论了表层沉积物的运移趋势和影响因素。结果表明,研究区总体上从杭州湾向外海,泥沙起动流速越来越大,也就是说,越往外海泥沙越难以再悬浮;表层沉积物整体由湾口向外海运移,平均日单宽输沙通量总体由杭州湾内向外海减小;在群岛内,由于受到岛屿的限制,泥沙基本沿水道走向运移,在外海区,沉积物净运移存两个明显的运移趋势,分别对应长江口泥质区和闽浙沿岸泥质区;潮流是控制泥沙运移的主要动力因子,同时,潮汐、东海沿岸流、风浪、台湾暖流、群岛以及地形等因素对泥沙输运的影响亦不可忽视。在上述研究结果的基础上,借鉴河流的边滩理论,探讨和分析了群岛对泥沙分布和运移的影响。结果表明,舟山群岛的存在对研究区海流变化、泥沙分布和泥沙运移影响显著,具有明显的“群岛效应”;所谓“群岛效应”主要是指受群岛分布制约和水动力条件变化影响下的泥沙运移、沉降、再悬浮以及分布的过程;群岛的存在,使水道内产生涨落潮流控制下的“双向环流”,该环流控制着泥沙的横向分布和运移,而涨落潮流则控制泥沙的纵向分布和运移;舟山群岛海域对来自长江口和杭州湾的泥沙具有“过滤器”和“扩散器”的双重作用,即对粗颗粒物质具有过滤作用,而对细颗粒物质则有扩散作用。更多还原

【Abstract】 Sediment transport processes play an important role in the estuarine and nearshore environment, because the sediments are not only important carriers of various nutrients and pollutants, but also have a stong impact on the transfer and recycling of pollutants. At the same time, sediment transport will significantly influence changes of landform and physiognomy; meanwhile, such changes will correspondingly have great effect on human activity such as port development, seaway maintenance, marine structures construction and laying of submarine cable and so on. Therefore, it is vital to understand the sediment transport and dynamic mechanism in the river mouth and adjacent areas. For one thing, it has important practical significance for human activities such as the development of the port; for another, it has theoretical significance for discussing modern sedimentary processes and spread of pollutants.Zhoushan Archipelago sea area is located in the southeast waters offshore the Changjiang River Mouth and outer edge of the Hangzhou Bay. The study area is not only the only way to the south for Changjiang Diluted Water, but also the main channel for the water exchange between Hangzhou Bay and the East China Sea. It is characteristic of numerous islands, changeful water depth and topography and complicated hydrodynamic conditions. Therefore, the distribution and transport of sediments in the study area must have special properties. Based on the measured data, using different research methods and formulas, sediment distribution and transport characteristics are systematically analyzed, sediment transport mechanisms are revealed, and impacts of Archipelago on the sediment distribution and transport are discussed.Characteristics of ocean current, distribution of suspended sediment and surface sediment are systematically analyzed on the basis of measured data. Results show that the suspended sediment concentration sharply decreases from the Hangzhou Bay to the offshore area. Average suspended sediment concentration of ebb tide is generally higher than that of flood tide. Changes of suspended sediment concentration are significantly affected by fluctuations of water level in a tidal cycle. Impact on the suspended sediment concentration caused by changes of flow velocity is covered up sediment transport induced by fluctuations of water level. Silt is the dominant sediment type which is primarily distributed in the open sea area where it is less affected by Zhoushan Archipelago. Sandy silt, sand and gravel are locally distributed around the islands. Distribution of surface sediment type, grain size parameters and the different components of surface sediments grain size are greatly affected by the Archipelago.Flux, transport direction and mechanism of suspended sediments are analyzed using flux decomposition method. Settlement characteristics are studied based on formula of suspended sediment settling velocity and previous research results. Results show that the suspended sediment flux quickly decreases from the Hangzhou Bay to the offshore area. Although the suspended sediments are primarily transported towards the offshore area, net transport towards the Hangzhou Bay is also found in the study area. The study area is basically located in hydrodynamic balance belt, and the suspended sediment transport is characteristics of reciprocating movement and small amount of net sediment discharge. The net suspended sediment transport is mainly controlled by average current transport, Stokes drift-induced transport and gravitational circulation transport. The advection transport effect gradually weakens and gravitational circulation transport evidently intensifies from Hangzhou Bay to the offshore area. Settling velocity of single particles is far smaller than that of floccules, so, influence of flocculation of suspended sediments must be taken into the consideration.Incipient velocity and transport flux of surface sediments are analyzed using formulas of incipient velocity and transport flux. Transport trend and controlling factors of surface sediments are studied by the method of grain size trend analysis. Results show that surface sediments become more and more difficult to be resuspended from the Hangzhou Bay to the offshore area. The surface sediments are mainly transported from the Hangzhou Bay to the offshore area; meanwhile, the net transport fluxes per day rapidly decrease towards the offshore area. In the area of archipelago, the surface sediments are mainly transported along the trend of channel because of the restriction of archipelago. In the offshore area, there are two obvious sediments transport trends that correspond to the Changjiang Estuary mud area and Zhejiang Fujian coastal mud area. Tidal current is the major dynamic factor dominating in the sediment transport. Meanwhile, the East China Sea Coastal Current, Taiwan Warm Current, wind waves and topography also play important roles in the sediment transport.The impact on the sediment distribution and transport of the archipelago is discussed according to the research results of this article and the reference of theory about point bar of river. Results show that the changes of ocean currents, distribution and transport of sediments are significantly affected by the archipelago that has obvious“archipelago effect”. The“archipelago effect”means processes of transport, deposition, resuspension and distribution of sediments controlled by the restriction of the archipelago and changes of hydrodynamic conditions. "Two-way circulation" is dominated by flood/ebb tide because of the existence of the archipelago. It controls the transverse distribution and transport of sediments, meanwhile, the flood/ebb tide masters the lengthways distribution and transport of sediments. The Zhoushan Archipelago has a dual role in the sediments derived from the Changjiang Estuary and the Hangzhou Bay that is“filter”process and“diffuser”process. Coarse particulate matter is filered and fine particulate matter is diffused by the archipelago.更多还原