【作者】 陈小英；

【导师】 陈沈良；

【作者基本信息】 华东师范大学 ， 自然地理学， 2008， 博士

【摘要】 随着近年来黄河来水来沙迅速减少,黄河三角洲滨海区地形发生了很大的变化,海岸演变由河流作用为主转变为海洋作用为主,部分岸段出现了不同程度的侵蚀后退,给海岸防护带来很大挑战。本文基于三角洲滨海区多年剖面地形实测数据、沉积物以及波浪、潮流数据,从动力地貌、沉积学的角度出发,运用回归分析、EOF方法、麦夸特方法(Levenberg-Marquardt)以及Mapinfo等GIS技术手段,定性研究和定量计算相结合,系统地对黄河三角洲河口来水来沙特征、三角洲岸线变迁、海岸剖面冲淤变化规律、三角洲滨海区沉积特征和沿岸潮滩沉积特征等相关问题进行了研究,并对潮滩沉积环境进行沉积相的划分,建立废弃三角洲海岸剖面的长时间尺度演变模式,结论如下:(1)黄河入海水沙的变化大致可分为三个阶段:丰水丰沙期(1976～1985年);中水中沙期(1986～1996年);枯水小沙期(1997～2006年)。1997年以来,海岸剖面除口门附近轻微淤积外,其余岸段均出现了不同程度的侵蚀。(2)在不同的区域,海岸剖面表现出不同的时空演变规律:北部废弃三角洲海岸,1976～1980年表现为整体迅速蚀退,1981～1998年进入冲淤调整期,并在剖面上出现一冲淤平衡带,其深度主要与潮流流速有关:潮流流速越大,平衡带深度也越大。1999年以后剖面蚀退速率增加,表现为均衡蚀退。清水沟河口附近,剖面表现为不断淤进。在1976～1985年快速向海淤进,1986～1995年淤积速率减缓,1996年后,淤积速率又逐渐增大。空间上整体向海推进,推进的范围与入海泥沙的堆积过程和海洋动力作用对泥沙侵蚀过程之间的对比有关。而清水沟老河口附近1996年后则表现为快速蚀退。莱州湾滨海区,水下地形基本稳定,不随时间发生明显的淤积或蚀退,这与该区潮流场有关。(3)运用麦夸特法(Levenberg-Marquardt)拟合废弃三角洲剖面演变公式,预测了三角洲废弃0、10、20、40、60、80、100和150年的剖面地形。表明随着废弃时间变长,海岸剖面侵蚀速率逐渐变小,海岸剖面演变类型由典型的破坏型转变为稳定型,最大侵蚀深度约15m。(4)滨海区沉积环境表现不同的特点,通过Fleming(2000)的三角图式,按水动力强度,结合泥沙来源及水动力特征,将滨海区分为三个沉积环境:废弃三角洲滨海区,现行河口区,莱州湾滨海区。在早期废弃的湾湾沟海域,主要受风浪作用,岸坡经历了长期冲刷分选,底部沉积物显著粗化和均匀化。废弃不久的飞雁滩海域,在5～6m水深以浅存在一明显粗化带,该区内砂含量较高;而该区正是波浪发生破碎的主要部位,破碎频率达到98.2%。5～6m以深的水域,沉积物砂含量显著降低,以粉砂和粘土为主。对于现行河口区,由于沙嘴前方强潮流带的影响,沉积物粒径由岸向海表现为粗-细-粗的分布特征,且河口三角洲向海最大淤积范围大致为15m水深。对于莱州湾海区,由于潮流场的影响,阻止了河口泥沙大量向南运移,细颗粒泥沙主要淤积在广利河河口以北的滨海区,在广利河口以南由于没有大量的泥沙供应,滨海区海洋动力占优势,表层沉积物粗化。(5)黄河三角洲潮滩沉积环境特点:根据潮滩柱状样粒度参数以及磁学参数垂向变化特征,清水沟流路潮滩Q1柱状样沉积相自上而下划分为潮滩沉积相(0～298.5cm)、河口砂坝沉积相(298.5～412.5cm)和前三角洲沉积相(412.5～667cm);刁口河流路潮滩D1柱状样依次划分为潮滩沉积相(0～435cm)和河口砂坝沉积相(435～687cm)。两个地区沉积相特点有明显差异,这与黄河河口来水来沙及海洋动力条件密切相关。更多还原

【Abstract】 With the sharp decrease of.sediment supply from the Yellow River,marine dynamics have become more dominant in reshaping coastal topography along the subaerial Delta of the Yellow River.During recent years,some parts of coasts have undergone notable erosion.It leads to a great challenge for coastal protection and has become a hot subject for the scientific study.This paper presents a data-based study of waves,currents,sediments and subaqueous bedforms by applying Regression,Empirical Orthogonal Function (EOF),Levenberg-Marquardt methods and GIS techniques to the measured coastal profiles in order to understand the evolution of topography and sedimentary. environments of the subaerial Delta of the Yellow River.The results are shown as follows:(1) Since 1997,the coasts along the Yellow River Delta have shown extensive erosion except that there is slight accretion at the current river mouth.(2) The coast of the Yellow River Delta can be divided into three areas: abandoned estuary area,current estuary area and Laizhou Bay.For abandoned estuary area,the coasts of Wanwangou were relative stable because it has been abandoned for a long time and the geomorphology of the coast had already adjusted itself to resist further erosion.But Diaokou estuary and Shenxiangou estuary,which are abandoned in 1976 and 1964 respectively,have shown continuous erosion since 1976.The erosion processes can be divided into three stages:rapid erosion stage (1976-1980),accretion-erosion adjustment stage(1981-1998) and slow erosion stage (1999-2004).During the accretion-erosion adjustment stage,there was an erosion-accretion balance zone(EABZ) on every profile,whose depth mostly depended on the local tidal current velocity.The higher the tidal current velocity,the deeper the depth of EABZ.The coastal profiles near the Qingshuigou estuary showed continuous progradation.The evolution process exhibited three distinct stages:rapid progradaion phase(1976-1985),stable phase(1986-1995) and slow accretion phase(i996-2004).All the profiles have been prograded seawards generally.The distance of the seaward movement was controlled by the relative strength of riverine and marine dynamics.The coast of Laizhou Bay was generally stable.Due to the influence of the tidal current field,little suspended sediment from the Yellow River was transported to Laizhou.Bay.Erosion and accretion tended to occur in the.shallow area while slow deposition prevailed in deep.water area alternatively.(3) From the forecast of coast topography at abandoned subaerial delta after they have been abandoned 0,10,20,40,60,80,100 and 150 years,respectively,we find that the longer time the subaerial delta have been abandoned,the more slowly the erosion velocity of coastal profile.The coastal types also switch from destructive type to stable type slowly.Furthermore,the maximum erosion,depth is about -15m.(4) Based on measured data of bottom sediment samples,combined with sediment texture,topography and hydrodynamics,a new triangular diagram advanced by Fleming is applied to reveal the sedimentary environments and their hydrodynamic processes.The results indicate that nearshore zone of the Yellow River delta can be divided into three sedimentary environments:abandoned estuary area,current estuary area,and Laizhou Bay.At the abandoned estuary area,there are two parts,Wanwan’gou and Feiyantan,which were abandoned respectively in 1953 and 1976.Due to long term scouring of wind wave,the grain composition of the majority bottom sediment near Wanwan’gou is relatively coarse with strong erosion-resisting characteristics.For Feiyantan,because of the combined effect of wave and tidal current,the bed sediment contained a high proportion of sands at the water area shallower than 5-6m.The distribution of various sediment fractions did not seem to change noticeably with the water depth,which probably indicates the strong mixing effects of wave breaking on the bed sediments in this area.In contrast, the,bottom sediment was finer with low percent of sand and high percent silt and clay at the deeper water area seaward of 5m to 6m contours.For current estuary area, the grain size had a changing tendency of coarse-fine-coarse which resulted from the effect of strong tidal current zone in front of sand spit.For the area near Laizhou Bay, because of the influence of tidal current field,grain size of bottom sediment.particles was coarser in the area south of Guangli River estuary than the area north of that. (5) According to the variations of grain size and magnetic parameters of Core Q1 at Qingshuigou estuary and Core D1 at Diaokou estuary,their sedimentary facies have.been established.The difference between their facies was the result of the sediment and water discharge from the Yellow River and the marine dynamics.更多还原