Waves and Currents in Tide-Dominated Location Off Dahej,Gulf of Khambhat,India

Based on measurements of waves, currents, and tides off Dahej in the Gulf of Khambhat, hydrodynamics are studied. Estimated tidal constituents show that primary lunar semi-diurnal constituent M2 was the strongest constituent, and the amplitude was found to be around 4.5 times stronger than that of the major diurnal constituent K1. Currents were predominantly tide induced with speeds up to 3.3 m/s and were north-northwest during flood tide and south-southeast during ebb tide. Residual cross-shore and along-shore current was found to be varying with the corresponding change in the cross-shore and along-shore wind speed. Influence of tidal current was observed in most of the wave statistical parameters.     

The modern change and evolution tendency of sand coast in the eastern area of Liaodong Gulf

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苏北南黄海潮成沙体的发育条件及演变过程

典型钻孔的层序地层、沉积磁组构、碎屑矿物等的分析资料以及古河谷的地质雷达探测资料等的综合研究表明,苏北南黄海潮成沙体是全新世海退以来形成的,辐聚辐散的潮流和长江、黄河的供沙是其主要发育条件.辐聚辐散的潮流场是南黄海固有的,至少在苏北亚近代潮成沙体发育之初就已存在.大河供沙主要发生在全新世海退期,海退前长江不可能向苏北岸外海域大量供沙,更不可能在港岸外形成三角洲.潮成沙体的演变主要受长江、黄河的供沙率控制,大致经历了雏形发育、高速建设、动态调整等3个阶段.     

The morphodynamic modelling of tidal sand waves on the shoreface

An artificial sand wave on the Dutch shoreface of the North Sea has been studied in conditions with relatively strong tidal currents in the range of 0.5 to 1 m/s and sediments in the medium sand size range of 0.2 to 0.5 mm. The sand wave is perpendicular to the tidal current and has a maximum height and length of the order of 5 m and 1 km, respectively. The sand wave is dynamically active and shows migration rates of the order of a few metres per year. A numerical morphodynamic model (DELFT3D model) has been used to simulate the morphological behaviour of the sand wave in the North Sea. This model approach is based on the numerical solution of the three-dimensional shallow water equations in combination with a surface wave propagation model (wind waves) and the advection–diffusion equation for the sediment particles with online bed updating after each time step. The model results show that the sand wave grows in the case of dominant bed-load transport (weak tidal currents; relatively coarse sediment; small roughness height; low waves) and that the sand wave decays in the case of dominant suspended transport (strong currents, relatively fine sediment, large roughness height; storm waves).     

南黄海太阳沙西侧潮流脊槽的沉积物分布特征和沉积环境演变

对南黄海太阳沙西侧潮流脊槽区进行了底质调查,采用密集站位的振动活塞柱状沉积物采样器取样。根据粒度分析结果,比较精细地研究了厚度约2～3 m浅表层沉积物的空间分布特征。结果表明:表层沉积物中,细砂主要分布在潮流脊和岸滩上,其它较细的沉积类型主要分布于潮流槽内,呈显“脊砂槽泥”的沉积地貌基本特征。同时,沙脊上的表层细砂的分布范围明显与沙脊至海岸的距离有关,除了潮流的影响外,主要与外侧沙脊的消浪作用有关。另外,根据表层沉积物分布的沉积地貌特征,探讨了潮流脊槽的沉积环境演变。     

芬迪湾、缅因湾和圣劳伦斯湾潮汐共振的数值研究

本文采用"初值方法"研究了芬迪湾、缅因湾和圣劳伦斯湾的潮汐共振情况。结果表明,缅因-芬迪湾系统共振是由陆架共振造成的,最强共振周期约为13.0h。芬迪湾次强共振周期约为9.2h,是由该海湾本身的四分之一波长共振引起的。圣劳伦斯湾共振现象主要体现在其东北海区,共振周期约为9.2h,可能是由半波长共振引起的。     

江苏辐射沙洲海区潮流对涌浪能量传播的影响

为研究了江苏辐射沙洲地区潮流场对涌浪能量传播的影响,本文利用双向耦合的Delft3D-FLOW和SWAN模型进行了对江苏辐射沙洲地区风-浪-潮流的整体模拟。时间尺度,是表达波能传播速率的有量纲参数。本文利用时间尺度这一物理概念来描述涌浪的波能在地理空间和谱空间中的传播规律。时间尺度越小,波能的传播速率越快。研究发现,通过计算和对比波能的时间尺度在地理空间、谱空间内的变化规律,发现在辐射沙洲地区,波能时间尺度在谱空间内变化偏大。而在潮流影响下,涌浪的频率运移表现更明显。通过理想实验的对比,发现涌浪能量的时间尺度在有潮流明显较无潮流作用时变小,这反映了潮流对于涌浪能量的传递速率有正向作用。在地理空间上,波能的时间尺度在涨潮时刻减小,落潮时刻增大。     

辐射沙脊主要水道的演变特征及其水动力机制研究

近四十年来的水下地形资料对比显示：南黄海辐射沙洲区水道普遍存在逐渐向南偏移的趋势（西洋主槽冲深、南延,南翼烂沙洋水道、小庙洪水道向南逼进）。有关辐射沙洲整体南移的原因及机理虽有诸多猜想,但至今没有统一可靠的认识,这种趋势性过程的驱动力成为辐射沙洲区海岸冲淤动态研究及港口建设过程中亟待解决的问题。在恢复黄河北归以来苏北黄河三角洲海岸不同发育阶段的岸线位置和水下地形的基础之上,通过所建立的潮波数学模型,研究了在苏北黄河三角洲不同演变阶段南黄海潮波系统的特征及水动力变化。研究表明,随着岸线后退和水下三角洲的夷平,辐射沙洲地区潮差不断增大;水动力不断加强,而且加强的区域逐渐向南偏移,这种大范围区域性水动力主轴的向南偏移就有可能是导致辐射沙洲整体南移的主导因素之一。     

苏北辐射沙洲岸滩沉积物元素地球化学记录的百年尺度环境变化

苏北辐射沙洲是分布于江苏岸外的典型沉积堆积体,受长江、黄河泥沙供给和近岸潮流动力的共同影响,发育了典型的粉砂淤泥质潮滩,沉积物元素可以记录潮滩环境变化的重要信息。在辐射沙洲岸滩采集了3个短柱沉积物岩芯,建立可靠的年代框架,采用高分辨率XRF元素扫描仪进行地球化学元素测试,选用XRF信号强度高的14种元素进行聚类和相关性方法提取环境信息,研究过去百年尺度人类活动和海岸环境变化下的苏北辐射沙洲岸滩沉积环境变化。结果表明,该区典型潮滩剖面岩芯沉积物中Si、Ca、As和Fe元素相对含量较高,且自北向南其含量不断增加,Mn、Ba、Cu和Zn元素含量较低,在所有剖面含量变化不大。在垂向上,Si、Ca和Fe元素变化趋势一致,而Ni、Zn和S元素在不同柱状岩芯中呈现与Si、Ca和Fe相反的变化趋势。相关关系和聚类分析显示,Si、Ca和Fe元素之间具有较高的相关性,即具有近似的地球化学行为和一致的物质来源;与元素Ni、Cu和Zn呈负相关,暗示了这几种元素与前者具有不同的地球化学行为。苏北辐射沙洲潮滩沉积物沉积环境发生了明显变化且在不同区域呈现不同的变化规律,物质来源、水动力环境、人类活动等因素是导致沉积环境变化的主要原因。     

辐射沙脊群潮滩地形遥感遥测构建

潮滩地形是合理开发利用潮间带滩涂最重要的指标之一。滩涂水边线测量法是目前公认的具有可操作性的滩涂地形遥感测量方法。本文以水边线测量方法为基础,提出一种基于水位测站基线的潮滩地形遥感遥测构建方法。以江苏沿海大面积潮滩为研究区,将该区域自建的4座水位测站的连线作为水位测站基线,结合不同潮情下采集的遥感影像提取的滩涂水边线数据,通过水位测站基线计算滩涂水边线高程,从而构建出辐射沙脊群潮滩地形。采用实测地形数据进行检验,结果表明:构建的DEM能够反应当前潮滩的基本形态,平面精度达30 m,垂直精度达20 cm。     

The effect of a tidal cycle on the dynamics of nutrients in a tidal estuary in the Seto Inland Sea, Japan

A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH₄ ⁺−N, (NO₃ ⁻+NO₂ ⁻)−N, PO₄ ³⁻−P and Si (OH)₄−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r ²=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r ²=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.     

基于数值模拟与统计学方法的南黄海近岸沙脊与水道稳定性评价

以南黄海江苏岸外辐射沙脊群为对象,基于已验证的该区域沉积动力学数值模型模拟近30 a(1979~2011年)的水下地形演化,计算辐射沙脊区域海底地形年际变化标准偏差,对沙脊和水道的地貌稳定性进行定量评估。研究发现,地形变化标准偏差愈小,地貌愈稳定;标准偏差愈高,地貌愈不稳定。定量地确定了南黄海辐射沙脊区域内沙脊与水道稳定性系数的时空分布,发现主要淤积区域位于沙脊周围,近岸沙洲有淤高的趋势;主要侵蚀区位于水道,沙脊间水道逐渐冲刷加深,如西洋水道和黄沙洋水道。本研究提出的基于海底地形年际变化标准偏差确定地貌稳定性评估方法,可为海岸陆架地貌稳定性研究、区域资源开发和环境保护等提供参考。     

泰国湾及邻近海域潮汐潮流的数值模拟

本文基于FVCOM(Finite-Volume Coastal Ocean Model)模式,模拟了泰国湾及其周边海域K1、O1、M2和S2四个主要分潮。采用47个验潮站实测调和常数与模拟结果进行比较,所得4个分潮的均方差分别为4.06cm、3.76cm、8.22cm和4.71cm,符合良好。根据计算结果分析了泰国湾及其周边海域的潮汐、潮流的分布特征和潮波的传播特征。数值试验表明,现有的数字水深资料(ETOPO1,ETOPO5,DBDB-V)的准确度不足以合理地模拟泰国湾潮波。     

北部湾地区不同相对密度的海砂力学特性分析

为探究相对密度和有效围压对饱和海砂力学特性的影响,利用GDS动态三轴试验仪,对广西北部湾地区海砂开展了一系列固结排水三轴剪切试验,分析了相对密度、有效围压对饱和海砂强度特征、体变特征、割线模量以及摩擦角的影响规律。结果表明：随着围压的减小或相对密度的增大,试样体积应变不断增大,而相对密度或有效围压的增加均会提高试样的峰值强度,有效围压与峰值强度之间呈现良好的线性增长关系。随着围压的减小或相对密度的增大,应力相对软化系数、剪胀系数均不断增大,且有效围压与应力相对软化系数、剪胀系数分别呈线性和半对数线性相关。割线模量随轴向应变的增加整体呈衰减趋势,各试验工况下轴向应变为5%时试样的割线模量相比于轴向应变0.164%衰减了80%~90%。饱和海砂的峰值摩擦角随相对密度的增加而增大,随有效围压的增大而减小,相对密度D_r为50%时有效围压σ_c为50 kPa对应的峰值摩擦角是σ_c为200 kPa的1.098倍。     

The morphology and migration of transverse bars off the west-central Florida coast

A series of migrating shore-normal sandbars with wavelengths of 75–120 m and heights up to 2 m have been identified off the northern tip of Anna Maria Island, a barrier island on the west-central Florida coast. Similar features have been described elsewhere since the 1930s and termed ‘transverse bars’. The transverse bars identified off Anna Maria Island are found for about 3 km along the coast and extend 4 km offshore, well outside the normal surf-zone width. No cusps or any other associated beach expression is evident despite the fact that the bars come to within about 75 m of the beach. Sediments on the crests of the bars are a well-sorted fine quartz sand, whereas sediments in the troughs are a poorly sorted coarse carbonate shell hash. Historical aerial photographs and repeated high-resolution bathymetric surveys provide a means of quantifying the migration of the transverse bars. Analyses of orthorectified aerial photographs from the early 1940s through the mid 1990s clearly show movement or migration taking place in the bar field. In the 40-yr period from 1951 to 1991, the southern edge of the bar field moved 200–350 m to the south, with an average long-term migration rate of 8 m/yr. Repeated bathymetric surveys over an 8-month period give an average short-term migration rate of 21 m/yr to the south. Wave and current measurements suggest that southerly winds associated with the passage of cold fronts drive near-bed currents to the south that are strong enough to initiate sediment transport and cause the southerly migration of the transverse bars.     

泰国湾西部表层沉积物自生矿物分布及组成

Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the Mn O content in siderite decreases, but Fe_2O_3 and Mg O content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains,which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The K_2O content of glauconite is low or absent, indicating its short formation time.     

Cenozoic evolution of sediment accumulation in deltaic and shore-zone depositional systems, Northern Gulf of Mexico Basin

Paleogeographic and volumetric lithofacies mapping of 18 Cenozoic genetic sequences within the Northern Gulf of Mexico Basin quantifies the proportional sequestering of sediment within wave-dominated shore-zone vs. deltaic systems through time. Three long-term depositional phases are revealed by plots, based on paleogeographic and sediment isochore maps, of total shore-zone system area and volume to total delta system area and volume (SZ/D). (1) SZ/D area and volume ratios are highly variable in Paleocene through Eocene sequences. However, typical volume ratios for major genetic sequences (Upper, Middle, and Lower Wilcox; Queen City (QC), and Yegua) range between 0.2 and 0.6. Minor sequences (Sparta (SP), Jackson (JS)), which record very low rates and volumes of sediment accumulation, have the greatest variability in their ratios. (2) Oligocene and Miocene sequences display consistently high proportions of shore-zone sediment. SZ/D area ratios range from 0.6 to 1.0, and volume ratios cluster between 0.4 and 0.8. (3) A substantial late Neogene decrease in SZ/D ratios is presaged in the late Miocene sequence. Pliocene and Pleistocene sequences are uniformly characterized by very low ratios of <0.2. Consistently high Oligocene–Miocene ratios reflect a post-Eocene period of strong E–W climate gradient across the Northern Gulf margin. Shore-zone volume displays no correlation to overall rate of sediment supply. The late Neogene decrease in proportional shore-zone system importance corresponds to development of the West Antarctic and Northern Hemisphere ice sheets and related increase in amplitude and frequency of glacioeustatic sea level cycling.     

空间互相关方法在分析海底沙波迁移规律中的应用

海底沙波具有显著的活动性并能够对海底工程设施造成潜在威胁,因此对海底沙波活动性的评估一直以来受到广泛关注。目前大多数研究者仍利用平面剖面对比来分析海底沙波的迁移特征。然而,该方法难以全面高效地获取海底沙波二维平面迁移矢量。本文基于2007年和2009年的高分辨率多波束测深数据,详细阐述了空间互相关方法在分析北部湾东南海域海底沙波迁移规律中的应用过程。利用实测数据进行对比分析,获得了研究区海底沙波的活动特征,并进一步讨论了空间互相关算法中不同参数的选取对结果的影响。结果显示,利用空间互相关分析方法能够有效获取海底沙波二维迁移矢量,获得的海底沙波迁移速率和迁移方向与前人研究成果吻合,表明了该方法的可行性和可靠性。但在对实际DTM数据进行空间互相关分析时,需根据海底沙波形态、数据质量等因素选取合适的参数及矢量获取方法。本研究实验了一种确定海底沙波迁移规律的新方法,该方法将有效提升获得海底地形变化规律的效率和准确度,可获得更加精细的海底地形动力过程。     

Response of bedload transport, submarine topography, and dune internal structures to typhoon processes off Dongfang coast in the Beibu Gulf

Bedload sediment transport was estimated by the SEDTRANS96 model based on three-day hydrodynamics data obtained off the Dongfang coast in the Beibu Gulf during Typhoon Ketsana in September 2009. Bedforms on the sea floor off the Dongfang coast and internal structures of a typical dune were interpreted to evaluate storm influences on individual dunes and the dune field. Results indicated that flow forcings and related bedload transport were both strengthened significantly due to Typhoon Ketsana. The measurements and modeling results, which mainly included three different stages, presented noticeable phasic variation. The three stages were dominated by tidal current (Period Ⅰ), tidal current combined with wind-induced waves (Period Ⅱ), and swells combined with tidal current and seaward flows (Period Ⅲ). This phasic variation could be a common trait of hydrodynamics due to typhoons moving westwardly to the south of Hainan Island and Beibu Gulf in South China Sea. Results indicated that the maximum bedload transport rate for every burst in Period Ⅲ was almost 100 times larger than that in Period I and was ten times larger than that in Period II. However, the short-term increase in bedload transport induced by storms like Ketsana did not change the long-term evolution of dune morphology. Evidence was given by the internal structures of a typical dune, which revealed renewed modification under subsequent moderate conditions after storm erosion. Instead, storms may influence at different scales and regional allocation of sand dunes in some large areas because changes of the sea floor in large scales can hardly be recovered. More surveys during and after storm passage are also needed to document the level of positive contribution to forward migration.     

闽江口拦门沙砂体的演变及其沉积年代

本文介绍了闽江口拦门沙砂体的~(14)C年代、沉积速率、堆积趋势及其变化,从历史的演变规律推测现代闽江口拦门沙砂体堆积的可能发展趋势,指出航道整治的重点地段。