【作者】 刘锋；

【导师】 陈沈良；

【作者基本信息】 华东师范大学 ， 自然地理学， 2012， 博士

【摘要】 黄河1855年入渤海形成了巨大的扇形堆积体——黄河三角洲,在过去的150多年里,由于人为或者自然原因,黄河在三角洲上频繁决口改道,流路变迁,且每次改道入海泥沙都会在河口处形成大沙嘴,废弃后在海洋动力作用下不断蚀退,黄河三角洲发育演变是陆海相互作用的结果。经过60多年的发育,黄河口及其邻近海域逐渐形成了不同水动力控制的演变体系,即现行河口属于河控型,废弃刁口河口和神仙沟属于波流控制型。不同海域由于动力控制体系不同,其泥沙输运以及沉积动力过程具有明显差异,另外,20世纪80年代以来由于全球变化引起黄河流域降水量减少,流域人类活动增强,导致黄河入海水沙锐减,这些因素导致了该区域动力地貌过程明显的时空变化特征。本文基于2004到2011年黄河口及其邻近海域多次水文泥沙同步观测资料、悬沙、表层沉积物及短柱样等大面积采样数据,系统地研究了黄河口及其邻近海域动力沉积特征、沉积环境、悬沙输移扩散过程及其动力机制,并结合研究区域不同时期岸线、卫星遥感数据以及水下三角洲地形数据分析了该区域动力地貌演变时空变化规律,探讨了入海泥沙扩散、海岸带泥沙输运和沉积动力等过程对海岸冲淤演化的控制效应,揭示了海岸冲淤演变对泥沙输运的响应机制,结果表明：黄河口及其邻近海域表层沉积物以粘土质粉砂为主,还包括砂、粉砂质砂、砂质粉砂、粉砂以及粉砂质粘土等类型,且大致以5m等深线为界,其以浅区域砂组分含量较多,以深区域粉砂和粘土组分含量增多；由于受到波浪和潮流冲刷和分选作用,从近岸向海侧表层沉积物粒径大体呈细化趋势；从该区域表层沉积物时间变化来看,研究区域内表层沉积物中粉砂组分含量增多,粘土、砂组分含量减少,整体来说,近岸表层沉积物粒径变粗,而深水区沉积物粒径变细。运用端元分析模型从动力组分的角度反演了研究区域内的沉积环境,从各海域反演结果来看,三端元模型基本可以反映各海域的沉积动力环境,各海域端元分布大体与表层沉积物中粘土、粉砂、砂组分含量分布基本一致,在不同海域代表了不同动力组分。从研究区域水动力分布来看,在刁口河到神仙沟海域,十八井外海域实测潮流流速较大,刁口河外和五号桩外实测潮流流速相对较小,十八井外和五号桩外海域欧拉余流和拉格朗日余流较大,刁口河外斯托克斯余流较大；在孤东到现行河口海域,河口处潮流流速较大,孤东海域较小；孤东海域欧拉余流和拉格朗日余流较大,而河口区斯托克斯余流较大。各海域余流引起的单宽净输水量分布与其拉格朗日余流分布相对应。从研究区域悬沙分布及其输运过程来看,在刁口河到神仙沟海域,刁口河外水体含沙量最高,五号桩外最低；由于近岸波浪动力作用泥沙运动活跃,近岸水体含沙量高,深水区水体含沙量较底,另外,局部区域在潮流作用下会发生底沙再悬浮现象,但持续时间较短；在孤东到现行河口海域,河口水体含沙量较高,孤东水体含沙量相对较少,由于河口区域潮流流速较大,存在潮流作用下底沙再悬浮现象,而孤东海域再悬浮能力较弱。对比调水调沙期、后河口水动力和悬沙输运特征,调水调沙过程加强了河口落潮动力,抑制了涨潮动力,促进了河口切变锋的发育,并且由于大量淡水入海,加大了河口盐度垂向梯度,分层现象明显；调水调沙期间河口悬沙浓度较大,在输移过程中以沉降作用为主,河口以淤积为主,而调水调沙结束后悬沙浓度降低幅度较大,且与流速大小成正比,泥沙再悬浮作用较强。在黄河三角洲滨海区悬沙输运过程中,平流输沙、潮汐捕集输沙、垂向净环流输沙为主要的输沙因子,且平流输沙起主导作用,但不同区域各种输沙因子作用程度略有不同。黄河三角洲岸线变化主要受行水河口、入海水沙、海洋动力及人类活动的影响,在大部分区域岸线变化受到入海水沙和海洋动力间的制衡作用,而在局部区域由于人工护岸大堤的建设以及围海造田、滩涂养殖、建造虾池鱼池和盐田等人类活动的开展,这些岸段岸线变化缓慢甚至出现土地面积增加。研究区域水下三角洲地貌演变具有明显的时空变化特征,即空间上表现出地域性和转换性,时间上表现出阶段性,总体来讲,研究区域水下三角洲北部侵蚀速率和南部淤积速率均减缓,逐渐向冲淤动态平衡状态发展。黄河三角洲动力地貌演变与入海泥沙、泥沙输运及沉积动力过程息息相关。在废弃的刁口河和神仙沟水下三角洲主要受到波浪、潮流等海洋动力的影响,近岸区域,波浪扰动作用强烈,泥沙运动活跃,造成近岸水下岸坡侵蚀强烈,再悬浮的泥沙在潮流作用下离岸向深水区域输运,使深水区域处于淤积状态；在现行河口,入海泥沙和泥沙输运对河口水下三角洲的演变产生重要影响,入海径流带来大量泥沙在河口处淤积,造成水下三角洲特别是前坡段淤积严重,由于河口存在切变锋的阻挡作用,入海泥沙主要在近岸区域特别是10m等深线以浅区域淤积,部分悬浮泥沙在余流的作用下向西北方向输运；老河口处由于遭到废弃,水下岸坡在波浪作用下不断受到侵蚀。更多还原

【Abstract】 The Yellow River delta was developed by the sediment load delivered by Yellow River into Bohai Sea since1855. Due to the human activities or natural causes, the Yellow River course was shifted frequently in the delta over the past150years. In different distributary course, the Yellow River sediment into the sea built up the large sand spit in the estuary. Once abandoned, the sand spit was eroded by ocean dynamic. It can be inferred that the evolution of the Yellow River delta was the result of interaction between land and ocean. The Yellow River estuary and its adjacent sea are controlled by different water dynamic with development since1953. The present estuary was river-dominated, and the Diaokou and Shenxian promontories are wave-tide-dominated. Therefore, the process of sediment transport and sediment dynamic is different in different sea area, what’s more, the sediment load delivered into the sea decrease dramatically since1980s due to the human activities and decrease in basin precipitation. These factors resulted in the spatial and temporal variability of dynamic morphology evolution.The hydrological and sediment observations were conducted in the Yellow River estuary and its adjacent sea, and the samples of suspended sediment, surface sediment and short length core were collected in the sea area form2004to2011. Base on these data, the dynamic sediment characteristic, sediment environment, transport process of suspended sediment and its dynamic mechanism were studied systematically in the Yellow River estuary and its adjacent sea. Additionally, the spatial and temporal characteristics of morphology evolution in the study area were analyzed based on the satellite remote data of modern Yellow River delta and the bathymetry data in the subaquatic delta. Furthermore, the controlling effects of sediment diffusion into the sea, sediment transport in coastal area and sediment dynamic process on the evolution of coast in the study area. These results can be concluded as follows: The surface sediment type is dominated by clayey silt in the study area. The content of sand is more in the area above～5m isobaths, and the contents of silt and clay are more in the area below～5m isobaths. Because of scouring and sorting by wave and tide, the grain size decreases from shore side to ocean side. As to the temporal change of surface sediment in the study area, the silt fraction increase but both clay and sand fraction decrease with time gonging on. In all, the grain size of surface sediment in the shore side increases, and the grain size in the deep water area decrease with time. The sediment environment was studied by method of End member model in the respective of dynamic component. The results indicate that three end members can reflect the sediment dynamic environment in study area. The distribution of end members in study area corresponds to the distribution of clay, silt and sand faction, and the end member represents different dynamic component in different sea area.From the respective of distribution of water dynamic in the sea area from Diaokouhe to Shenxiangou, the tide velocity is bigger in the sea area off Shibajing, and it is relative small in the sea area off Diaokouhe and Wuhaozhuang. The residual current of Euler and Lagrange is bigger in the sea area off Shibajing and Diaokouhe, and the residual current of Stokes is bigger in the sea area off Diaokouhe. As to the sea area from Gudong to present estuary, the tide velocity and the residual current of Stokes is big in the present estuary, and the tide velocity and residual current of Euler and Lagrange is small in the sea area off Gudong. The distribution of net water flux per width is consistent with the distribution of residual current of Lagrange in the study area.From the respective of the distribution of suspended sediment in the sea area from Diaokouhe to Shenxiangou, the suspended sediment concentration was high in the sea off Diaokouhe and Shibajing, and suspended sediment concentration was low in the sea off Wuhaozhuang. And the suspended sediment concentration was high in the shallow water and low in the depth water because the influence of wave dynamic on surface sediment is strong in the shallow water. Additionally, the surface sediment resuspends under the influence of tide current in this sea area, but the last time of resuspension is short. As to the sea area from Gudong to present estuary, suspended sediment concentration is high in the present estuary and low in the sea area off Gudong. And the sediment resuspension occurs in the present estuary because of big tide velocity, but the capability of sediment resuspension is weak under the influence of tide current. The hydrodynamics and transport process of suspended sediment is analyzed with comparing their characteristics in and after the water-sediment regulation period in July,2009. The results show that the process of water-sediment regulation intensifies the ebb dynamics but weakens the flood dynamics, and facilitates the formation of tidal shear front. And during the period of water-sediment regulation, the vertical salinity gradient increases and the water stratification is evident in the estuary; additionally, the suspended sediment concentration is high, and the sedimentation process is dominant in the transport process of the suspended sediment. After the water-sediment regulation, the suspended sediment concentration decreases greatly and is in direct proportion to current velocity; what’s more, the sediment re-suspension is predominant in the process of suspended sediment transport. Furthermore, during the transport process of suspended sediment in the study area, the sediment transportation by advection current, tidal trapping and net vertical circumfluence is remarkable, and the advection current plays in key role in the sediment transportation, but the influence degree of these factors is different in different sea area.The change of coastline of Yellow River delta was influenced by estuary, water discharge and sediment load into the sea, ocean dynamic and human activities. The change of coastline of most area in the delta is result of interaction between sediment load into the sea and ocean dynamic. Otherwise, the coastline in some area change slowly because the construction of levee protecting the alongshore, and it extend towards sea due to the human activities including the enclosing tideland for cultivation and building shrimp and fish ponds and salt fields. The spatial and temporal changes of evolution of subaqueous delta are clear. The spatial change is characteristic of regional and switching between scouring and silitation, and the temporal change is characteristic of phase nature. In all, both the erosion rate in the north area of subaqueous delta and silitation rate in the south area decrease with time, and the evolution of subaqueous delta have been developing into dynamic equilibrium of scouring and silitation.The evolution of dynamic morphology of the Yellow River delta is influenced by the sediment into sea, sediment transport and sediment dynamic process. In the abandoned Diaokouhe and Shenxiangou area, the evolution of subaqueous delta is mainly shaped by wave and tide current. In the alongshore area, the movement of sediment is actively because of strong disturbance of wave dynamic, resulting in the strong erosion of slope below water; the resuspension sediment is transported by tide current towards depth water, causing the silitation in the depth water. The evolution of subaqueous delta in the present estuary is influenced by the sediment delivered by river into sea and sediment diffusion. Large amount of sediment delivered by Yellow River into the sea is deposited in the estuary, resulting in the strong silitation in the subaqueous delta especially in the front slope. Because the barrier effects of tidal shear front in the present estuary, the sediment delivered into the sea is mainly deposited in the sea area above～10m isobaths, and some suspended sediment diffuses northwestern under influence of residual current; in the abandoned old estuary, the subaqueous delta is eroded by wave dynamic.更多还原