【作者】 季有俊；

【导师】 杨作升；

【作者基本信息】 中国海洋大学 ， 海洋地质学， 2010， 博士

【摘要】 渤海作为中国典型的内陆半封闭浅海,每年接收大量的陆源物质,同时由于气候受季风影响显著,大部分的海域海洋动力具有“冬强夏弱”的特点,冬季水动力环境较强,海底表层泥沙在冬季强海浪的作用下容易发生再悬浮,使冬季成为渤海泥沙的输送的重要时段。本文以2006年冬季和2007年夏季实测黄河三角洲3船同步连续站及毗邻渤海海域24个大面站的水文泥沙资料和对冬季黄河三角洲近岸泥沙再悬浮过程分析的基础上,以2004年黄河三角洲滨海水深数据和2000年渤海湾水深数据及岸线等较新的资料为依据,建立了渤海高分辨率(水平1’)三维斜压水动力泥沙数学模型,并将浅海波浪模式SWAN计算结果耦合入模型中,将近岸再悬浮泥沙作为冬季主要物源进行考虑,讨论分析了渤海泥沙输运的季节性变化特征和输运机制。在大体恢复古地形的基础上,应用数值模拟的手段,对最大海侵以来(距今约7ka)古渤海及古黄河三角洲发育的沉积作用进行了探讨。本文主要结论如下：1.实测资料表明,冬季泥沙再悬浮是非常重要的泥沙动力过程。冬季高悬浮泥沙浓度带(>100mg/l)分布在离岸约35km的近岸区域,悬浮泥沙浓度更高、范围更大的区域出现在底层,充分表明了泥沙再悬浮的机制。三个高浓度中心分别位于废弃钓口河口、现行河口和废弃清水口河口,是冬季泥沙的主要物源区,和波流共同作用导致的底部剪切应力的三个高值中心具有很好的对应关系,河口附近地形因素及强向浪NNE-NE-ENE是产生三个高浓度中心的基本因素。在整个研究区域,除了现行河口外冬季悬浮泥沙浓度都要高于夏季的,悬浮泥沙单宽通量除河口外的各连续站冬季约为夏季的2-122.5倍,表明冬季泥沙输运强度远高于夏季,冬季是近岸泥沙向外海输送的主要季节；2.对模型中波流共同作用下的底部切应力的计算进行了改进,改进后恢复了潮流导致的底部切应力。对渤海泥沙输运的季节性变化研究结果显示,受冬季较强风浪作用的影响,冬季平均状况下底部切应力和悬浮泥沙浓度明显高于夏季,尤其是近岸大约15m等深线以内的区域,高值区位于等深线4-10m之间。在渤海其值较大的区域主要分布在现代黄河三角洲沿岸和辽东湾沿岸。近岸区域底部切应力和悬浮泥沙浓度冬季约是夏季的10倍,符合近岸再悬浮的高浓度泥沙区域是冬季泥沙主要物源的结论。冬季大风条件下,其值进一步增加,可以达到冬季平均状况的2倍以上。前人的工作没有考虑冬季泥沙再悬浮产生的物源中心作用,也没有冬季实测资料的验证,而本论文数值模拟结果(流速和流向、悬浮泥沙浓度)与冬季渤海近岸大范围实测水文泥沙资料对应较好,基本反映了冬季渤海的泥沙输运特征。3.本文采用的网格分辨率较高,地形较新,通过模拟发现了莱州湾废弃清水沟河口外侧存在潮流切变锋,与实测结果相符,说明本文的模拟较好地反映了近岸区域的动力状况。模拟结果显示此切变锋除了与近岸与离岸由于底摩擦作用而导致转流时刻存在相位差外,还与莱州湾的清水沟河嘴向外凸出的地形相关。此切变锋对黄海入海泥沙向莱州湾扩散具有阻隔作用。4.7kaBP的古渤海较现在渤海水深大,区域较宽广。模拟结果表明,传入古渤海的潮波没有现在强,古渤海的潮流较现在的弱很多,尤其是渤海西部黄河入海区域。在这种较弱的潮流动力环境下,黄河入海泥沙更容易沉降,更容易快速堆积并向外海推进,更有利于黄河物质在近岸堆积和形成黄河三角洲。由于渤海古水动力较弱,输出渤海的泥沙较现在的比例要少。辽东湾内整体潮流动力较强,细颗粒泥沙不易沉降,是导致辽东湾内底质颗粒较粗的主要原因之一;更多还原

【Abstract】 The Bohai Sea is a shallow semi-enclosed inner shelf sea in China, which receives many terrestrial materials every year. Due to seasonal changes in wind strength, hydrodynamics are weak in the summer season and strong in the winter season, as characteristic for most of the Bohai Sea. The seabed surface sediment can be resuspended easily and transported by storm waves. So the winter season is a major period for sediment transport in the Bohai Sea. Hydrographic and suspended sediment data were collected in winter 2006 and summer 2007 along three survey transects at three time-series, ship-based stations off the Huanghe (Yellow River) delta, and at twenty-four grid survey stations in the adjacent Bohai Sea. Based on the verification of these data, using newer bathymetric and coastline data of 36 survey transects along the Huanghe delta in 2004 and the Bohai Bay in 2000, a 3-D high resolution (horizontal resolution of 1’×1’) hydrodynamic and sediment transport numerical model, coupled with shallow sea wave model (SWAN), was used to study the seasonal variation characteristic of sediment transport in the whole Bohai Sea. Especially, the coastal areas were considered to be very important sediment sources in the winter season. The paleotopography of the Bohai Sea during the period of the maximum transgression (7 ka B.P.) was grossly recovered, and then the numerical simulation method was first applied to study the sedimentation of the ancient Bohai Sea and the ancient Huanghe delta.The major contents in this dissertation are shown as following:1. Based on the analysis of in-situ data, the results show that the sediment resuspension and its effects are the most important dynamic sediment processes in winter. Without considering the effect of sediment resuspension in winter, it would be hard to discern the sediment transport process. A zone of high SSC (>100 mg /l) with a width of about 35 km was formed along the delta coast. A much larger area of high SSC and higher SSC occurred in the bottom layer, indicating resuspension origins. The coincident locations of the three highest SSC centers around the abandoned Diaokou river mouth, present river mouth and the abandoned Qingshuigou river mouth, coupled with the distribution of three centers of high bottom shear stress zone caused by wave effects, offer convincing evidence that wave-induced resuspension caused the high SSC that we observed in the study area. The protuberant topography of all three areas and the strong NNE-NE-ENE wave direction in winter led to high bottom shear stress around the three river mouths, resulting in the creation of the three highest SSC centers, and they were the major sediment source areas in winter. The SSC in winter was much higher in the entire study area than that in summer except for the area around the present river mouth. The SSF at all the time-series stations were 2-122.5 times higher in winter than in summer except one station near to the present river mouth. This indicates that the intensity of sediment transport in winter is much stronger than in summer.2. The calculation of bottom shear stress under co-existing wave currents was modified in our model, and the bottom shear stress caused by currents was recovered after modification. According to the results of the seasonal variation characteristic of sediment transport, there were some obvious differences of the distribution of bottom shear stress and SSC in the Bohai Sea between winter and summer, especially in the coast area. As a result of strong waves in winter, a zone of high values was mainly alone the coast with water depth less than 15 meters and the highest centers lied in depths of approximately 4 to 10 meters in the winter season. The regions with highest values were mainly along the coast of the Huanghe delta and the Liaodong Bay. The values of bottom shear stress and SSC in those regions were about 10 times higher in winter than in summer. During the winter storm events, the values were further increased to more than 2 times higher than average conditions in winter. Most previous studies have no considering the main sources of sediment resuspension and no verification of measured data in winter, but in this paper the model can give a reasonable agreement between simulated results (velocity and suspended sediment concentration) and measured data.3. High resolution grids and newer topography were used in this study. According to the result of simulation, the shear front outside the abandoned Qingshuigou river mouth in the Laizhou Bay was found which is consistent with the measured data. The forming mechanism of this shear front was caused not only by a tidal phase gradient along the delta slope, but also by the topography of the protrusion of the abandoned Qingshuigou river mouth. This shear front played an important role in obstructing the sediment dispersion from Huanghe into the Laizhou Bay.4. Because of the greater water depth, the wider coastline and the weaker tidal waves from the Huanghai Sea, the tidal currents of the ancient Bohai Sea during the period of the maximum transgression (7 ka B.P.) were much weaker than the present Bohai Sea, especially around the west area of the ancient Bohai Sea. Therefore, under this weak tidal hydrodynamic environment, the sediment of the ancient Huanghe discharge into the sea deposited more easily and accumulated more rapidly around the river mouth, and it was beneficial to form the Huanghe delta. In addition, there was less sediment being transported from the Bohai Sea to other seas in China. The hydrodynamic in the Liaodong Bay is stronger than other places, which is the important reason for the surface sediment of the seabed with coarser particles than other places.更多还原