往复潮流作用下推移质粒径趋势形成模拟初探

粒径趋势分析是一种用于判断海洋环境中沉积物净输运方向的方法，但是至今粒径趋势形成的物理机制尚不够清楚，因而影响了粒径趋势分析适用条件的确定。针对这个问题，本文通过建立一维、推移质、往复流（近岸潮流）条件下的数值模型，采用正演方法模拟粒度参数在输运方向上的分布．以评价沉积动力过程的影响，初步探讨粒径趋势形成的物理机制。数值模型实验的初步结果显示，水动力条件的空间差异导致的沉积物粒度参数的空间分布符合粒径趋势分析的假设，粒径趋势分析中定义的两种粒径趋势可由沉积物输运强度的空间梯度而形成，并且在沉积物净输运方向上出现的频率最高。     

基于“动力组分”思想的沉积物粒径趋势模型

“粒径趋势分析”的基本思想是利用沉积物粒度参数的空间变化(粒径趋势)来反推沉积物输运路径.依据“动力组分”思想,通过建立一个一维的悬浮沉积物输运模型来正演沉积物输运方向上的表层沉积物粒度分布和粒径趋势,探讨水动力能量沿程衰减和沿程增强两种不同情形下的粒径趋势特征.研究表明:粒径趋势形成的直接原因是沉积物中不同“动力组分...     

北黄海西部海底沉积物的粒度特征和净输运趋势

根据对北黄西部海底沉积物的粒度测试,运用“粒度趋势分析”方法,分析探讨了北黄海西部（渤海海峡区）海底表层底质的粒度分布特征和净输运趋势,结果表明,本区的细颗粒沉积物主要位于北黄海中部和山东半岛沿岸,大连湾附近,粗颗粒沉积物则主要分布于庙岛群岛以东和大连湾东南侧海区,沉积物的平均粒径、分选系数、偏态系数闰度参数的分布特征有一定的对应性,除庙岛群东侧的砂质沉积,分选较好之外,其它海区的沉积物总体特征是,粒径越粗,分选越差,偏态更正偏;而粒径越细,分选越好,偏态系数也较低。山 岛北侧的沉积物具有向东和向东北的输运趋势,西中沉积物的输运趋势向东南并转向东,北部喾物的输运趋势向南,形成了向北黄海中部汇聚的趋势,本碛研究还表明“粒度趋势分析”方法在大范围的陆架区域具有较好的适用性,在操作中,使用规则的正方形网格可以较全面判     

Group Settling Velocity of Non-Cohesive Sediment Mixtures

Settling velocity is a fundamental parameter in sediment transport dynamics.For uniform Par-ticles,there are abundant formulas for calculation of their settling velocities.But in natural fields,sedi-ment consists of non-uniform particles.The interaction among particles is complex and should not be neg-lected.In this paper,based on the analysis of settling mechanism of non-cohesive and non-uniform parti-cles,a theoretical model to describe settling mechanism is proposed.Besides suspension concentration andupward turbulent flow caused by other particles,collision among particles is another main factor influ-encing settling velocity.By introducing the collision theory,equations of fall velocity before collision,colli-sion probability,and fall velocity after collision are established.Finally,a formula used to calculate the set-tling velocity of non-cohesive particles with wide grain gradation is presented,which agrees well with theexperimental data.     

珠江磨刀门河口底质沉积特征及其泥沙运移趋势

根据珠江磨刀门河口的表层沉积物粒度分析结果,运用Gao-Collins粒径趋势分析方法(GSTA模型),计算河口的沉积物净输运趋势,并分析河口底质沉积特征。结果表明:河口较粗的沉积物分布在交杯沙浅滩和拦门沙顶部,受波浪作用影响分选较好;磨刀门主槽、龙屎窟和口外海滨的沉积物则较细,以粉砂和粘土为主,分选稍差。沉积物在纵向和横向上都表现出细-粗-细的变化趋势。磨刀门主槽泥沙受强径流影响,具有向南的输运趋势;龙屎窟在涨潮流作用下,泥沙净向北输运;在西向沿岸流和东南向浪作用下,拦门沙东侧浅滩泥沙向西侧搬运,口外海滨的泥沙输运趋势则向北。     

The role of bore collapse and local shear stresses on the spatial distribution of sediment load in the uprush of an intermediate-state beach

Spatial variations in sediment load in the swash uprush and textural properties of sediment in transport were evaluated to investigate the mechanisms responsible for sediment transport during wave uprush. Four streamer traps were deployed at 2.0-m intervals across the swash zone of a sheltered, microtidal sandy beach at Port Beach, Western Australia, over a 4-day period. During these trapping experiments, offshore significant wave heights were 0.3–0.5 m and wave periods were about 10 s. The average width of the uprush zone was 6.9 m and the average uprush duration was 5.9 s. Cross-shore distributions of sediment load for 70 uprush events reveal a maximum in sediment load landward of the base of the swash (at about 20% of swash width) during single events and a maximum closer to mid-swash (at about 40% of swash width) during multiple events characterized by swash interactions. Settling velocity distributions of trap samples during individual uprush events are similar to distributions found on the beach surface, with the lowest settling velocities (finest sediments) near the base of the swash zone and maximum settling velocities (coarsest sediments) around the mid-swash position. It was found that sediment transport during wave uprush occurs through two distinct mechanisms: (1) sediment entrainment during bore collapse seaward of the base of the swash zone and subsequent advection of this bore-entrained sediment up the beach by wave uprush; and (2) in situ sediment entrainment and transport induced by local shear stresses during wave uprush. Both mechanisms are considered important, but the first mechanism is considered most significant during the early stages of wave uprush when sediment is transported mainly in suspension, while the second mechanism is likely to dominate the mid- to later stages of wave uprush when sediment is transported mainly by sheet flow. The relative importance of the two mechanisms will vary between different beaches with the morphodynamic state of the beach (reflective versus dissipative) expected to play a major role.     

长江河口三角洲区有孔虫沉降速度试验

作者对有孔虫壳体沉降速度进行了测试和研究,提出了不同属种有孔虫的壳径与沉降速度相关方程,引进了“当量直径”的概念,并用于长江口三角洲地层中的化石群,提出了解释潮汐河口有孔虫埋葬群的形成机理,从而定量的研究和辨别三角洲地层中的原地埋葬和异地埋葬化石群。     

Sediment grain size measurements are affected by site-specific sediment characteristics and analysis methods: implications for environmental monitoring

Sediment grain size, and specifically changes in the percent mud content (i.e. the fraction <63?µm) over time is often used as an indicator of estuarine environmental health. Using sediment samples from three distinct estuarine systems, we determined that different analytical methods (laser diffraction and wet sieving) gave significantly different results in terms of percent mud content. These differences are also ecologically meaningful when considering the influence of mud on estuarine macrofauna. We propose an approach to measuring sediment grain size termed Environmentally Available Sediment (EAS), which advocates for the measurement of the sediment that biota are directly exposed to. For the purposes of environmental monitoring, it is also essential to monitor sediment grain size in a repeatable way which is likely to be achieved using consistent (or no) pre-treatment and the use of a measurement technique that is unlikely to change over time, e.g. wet sieving.     

Origin of grain size spectra of suspension deposited sediment

Hydronamic modification by settling from a turbulent suspension of an originally unsorted sediment produces grain size distributions that correspond to the size characteristics of many natural suspended and bottom sediments. Evaluation of the resulting equations allows parameterization of sediments in terms of three constants describing the source material, transport energy, and reworking history, respectively.     

废黄河口海域的悬沙输运机制研究

废黄河三角洲是南黄海内陆架的重要物源。为深入探索废黄河口海域沉积物输运机制,利用2015~2016年夏季与冬季在废黄河口外海域10个站位获取的现场沉积动力数据,计算潮不对称参数、余流、悬沙输运量等。分析结果表明,废黄河口海域沉积物输运模式存在显著的空间差异,大部分海域悬沙沿等深线向南输运,仅在近岸侧局部悬沙向岸或向北输运、离岸最远处站位向北输运但输运率较小;近岸浅水海域以平流输沙为主,其他离岸区域以再悬浮作用为主。由于流速和悬沙浓度之间的相位差,导致余流(净水输运)方向与净悬沙输运方向存在差异。研究沉降速度与悬沙输运涨落潮不对称的关系,发现沉降速度越大,悬沙输运的不对称性就越显著;沉降速度是造成近底部流速与悬沙浓度相位差的主要原因,导致废黄河口外净悬沙输运存在显著的垂向差异。     

互花米草对泉州湾盐沼表层沉积物输运的影响

海岸盐沼是海岸湿地系统的重要组成部分，具有很强的环境调节功能．互花米草（Spartina alterniflora）的引种对海岸盐沼的沉积动力产生很大影响．粒度分析结果表明，互花米草盐沼边缘与沉积物平均粒径为6．7φ的等值线分布一致．现场观测表明，互花米草对流速具有明显的阻滞作用，使得光滩流速明显大于互花米草内的流速；在互花米草滩内，随着离盐沼边缘距离、植被高度、植株直径的不同，涨落潮流速也表现出不同的变化趋势．粒径趋势分析结果显示，互花米草盐沼边缘的表层沉积物由光滩向盐沼内输运，潮水沟的存在对沉积物的输运格局具有显著影响．对比分析表明落潮后期的水动力条件控制着研究区内表层沉积物的净输运方向．     

九龙江河口区现代沉积环境及其物质输运趋势

对九龙江河口区58个表层沉积物样品进行了激光粒度分析,并分别应用系统聚类分析和GSTA模型分析,探讨了研究区的沉积特征、沉积环境和表层沉积物输运趋势。结果表明,九龙江河口区表层沉积物由10种沉积物类型组成,与20世纪80年代相比,该海区底质沉积物在类型分布和粒径粗细上发生了一定的变化;将研究区划分为3种与沉积动力特征相对应的主要沉积环境区;表层沉积物输运趋势因受该区特殊的地形和复杂的水动力条件影响而表现为北进南出,海门岛西北海域形成逆时针方向输运趋势,而海门岛以东海域形成三向汇聚的输运趋势。     

The effect of suspended sediment concentration on the settling velocity of cohesive sediment in quiescent water

A laboratory study was carried to qualitatively investigate the effect of suspended sediment concentration C on the settling velocity w_s of cohesive sediment in quiescent water. A bay mud sample was mixed with water in a cylindrical container, and three optical back scatterance sensors were then used to measure suspended sediment concentrations of the mud–water mixture at three levels every 15 s for 5 h while sediments were settling in the quiescent water. Based on the measured sediment concentrations, the settling velocities at different concentrations were derived from the depth-integrated mass balance equation. This study has found that the settling velocity w_s is independent of C in the free settling regime of C<0.3 g/l, and then increases nonlinearly with C in the enhanced settling regime of 0.3<C<4.3 g/l, and finally decreases sharply with C in the hindered settling regime of C>4.3 g/l. The maximum settling velocity occurs at C≈4.3 g/l and is about nine times faster than the settling velocity in the free settling regime. A single empirical formula is also proposed to calculate the settling velocities at different sediment concentrations.     

陇西盆地晚更新世风成堆积物粒度参数的对比

计算了末次冰期旋回陇西盆地的黄土古土壤和风成砂的粒度参数，并对图解法与矩值法粒度参数进行了对比。结果表明，对黄土古土壤来说两种方法所获得的平均粒径基本相同，分选系数、偏度和偏态的相关性逐渐降低，对风成砂和砂黄土来说，除了平均粒径呈较好的线性相关外，其他参数则差别很大。造成这种差异的主要原因是由于它们粒度组分的分布不同所致。图解法主要反映了样品总体中主要粒度组分的粒度特征，而矩值法则反映了样品的总体特征。在沉积环境的分析和比较中，应充分考虑这两种方法的差异，并建立不同的标准。激光粒度仪和吸管法对平行样品测试的图解计算结果表明，粒度参数的变化趋势比较接近。     

Along channel flow and sediment dynamics at North Inlet, South Carolina

In May of 2005, an observational program was carried out to investigate the along channel hydrodynamics and suspended sediment transport patterns at North Inlet, South Carolina. Along channel variability, which is important in establishing sediment transport pathways, has not been characterized for this system. Measurements of water column currents, salinity, bed sediment, suspended sediment concentration, and particle size distribution were obtained over a complete tidal cycle along the thalweg of the inlet entrance. Along channel currents, shear stress and bed sediment distributions vary significantly in space and time along a 3 km section bracketing the inlet throat. Most of the variability is consistent with geomorphic controls such as bed elevation variability and channel width. The highest velocities, shear stresses, suspended sediment concentration and bed sediment grain size are observed in the narrowest section of the inlet throat. Magnitudes systematically decrease along the channel toward the marsh as changes in channel geometry and branching reduces flow energy. Due to tidal asymmetry, the ebb phase contains significantly higher currents and associated sediment transport. Over the complete tidal cycle, depth integrated transport is directed towards the marsh landward of the intersection of Town and Debidue Creek. In contrast, net transport is out of the inlet seaward of this intersection. Sediment grain size distributions show 35% more material less than 63 μm on flood, suggesting net landward transport of fines.     

Grain-size distribution patterns of suspended sediment in response to hydrodynamics on the Dafeng intertidal flat, Jiangsu, China

1Introduction The sediment dynamics of intertidal flats in-volves erosion, transport, and settling processes. A-mong these, the mechanisms of sediment transportare a key question. Progress has been made in awide range of associated areas, including sedime…     

Investigation of the effects of offshore breakwater parameters on sediment accumulation

Littoral sediment transport is the main reason for coastal erosion and accretion. Therefore, various types of structures are used in shore protection and littoral sediment trapping studies. Offshore breakwaters are one of these structures. Construction of offshore breakwaters is one of the main countermeasures against beach erosion. In this paper, offshore protection process is studied on the effect of offshore breakwater parameters (length, distance and gap), wave parameters (height, period and angle) and on sediment accumulation ratio, one researched in a physical model. In addition to the experimental studies, numerical model in which the formulae of the sediment discharge (i.e. the formulae of CERC and Kamphuis), was used was developed and employed. The results of the experimental and numerical studies were compared with each other.     

A textural analysis of Wellington Harbour sediments

Grain‐size and carbonate analyses have been carried out on bottom sediment samples of Wellington Harbour. From grain‐size parameters it was possible to establish a number of facies types and to outline sediment sources and directions of transport.     

Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain

An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cádiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higher-energy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management.