Seston transport and deposition in Pelorus sound,south Island,New Zealand

Transport of seston (suspended sediment) in Pelorus Sound is controlled by tides and freshwater inflow. During high freshwater inflow, a moderately stratified estuarine circulation may be superimposed on the tidal circulation, but the latter dominates and transports seston seawards and landwards with the ebb and flood phases respectively. With extreme freshwater inflow, the estuarine circulation gains impetus and most seston is rapidly transported seaward in the low saline surface layer.

Irrespective of circulation there is a persistent trend in seston concentrations. Highest values occur at the sound's head because of the influence of nearby Pelorus and Kaituna Rivers and because of resuspension of bottom sediment by strong tidal currents. Seston concentrations wane along the sound until near the entrance, where values increase as a result of greater production of biogenic seston and because additional seston is brought in from Cook Strait with the flood tide. This trend parallels variability in the thicknesses of muddy bottom sediments. Muds are thick at the head where an extensive delta extends from the river mouths; muds gradually thin seaward and then thicken markedly in the vicinity of the sound entrance.

Seston weight and composition patterns and 3.5 kHz seismic profiles indicate Pelorus Sound acts as a double‐ended sediment trap. The upper reaches receive and retain river‐derived seston, whereas the sound entrance traps seston derived from Cook Strait. This situation appears to hold for both high and extremely high influxes of sediment.     

基于原位观测的胶州湾沉积物侵蚀再悬浮过程研究

海洋动力作用下,河口海岸地区海床通常处于动态变化之中。作为地质环境的控制因素,海床沉积物侵蚀再悬浮过程的研究具有重要意义。为阐明胶州湾海域水动力条件对海床侵蚀再悬浮的作用,本文利用海底原位观测三脚架进行了现场观测。观测结果显示：通常条件下,潮流导致的最大海床剪应力可达0.35 N/m²,高于波浪引起的剪应力。涨潮期间,海床发生侵蚀;退潮期间,海床发生淤积。风速达到5 m/s时,波浪引起的剪应力近似等于流致剪应力。风速达到7 m/s时,有效波高为26 cm,波浪对海床侵蚀再悬浮过程起主要作用;此时也会导致海水浊度显著上升,高于通常条件下的2-8倍。分析表明：通常条件下,周期性海流影响海床侵蚀再悬浮过程;而大幅度沉积物再悬浮过程由偶发的波浪事件控制。针对胶州湾沉积物动力学机制的深入研究仍待进一步开展。     

苏北中部滨海平原成陆机制研究

苏北中部滨海平原位于废黄河三角洲和长江三角洲之间，其形成与全新世最大海侵之后长江、古黄河的供沙历史和供沙状况密切相关，并且现今海域南黄海辐射沙洲的辐聚点也位于这段海岸，故探讨其成陆机制具有重要意义。本文数值模拟了公元８世纪时该区的Ｍ２潮汐、潮流，在此基础上，计算了７种粒径泥沙在当时潮流场中的净输运状况，划分了海底冲淤区。计算结果表明，公元８世纪时苏北岸外存在大致以东台为顶点的辐射状古潮流场，其分布格局与现今苏北岸外大致以京港为顶点的辐射关潮流场基本一致，该辐射状潮流场的存在是由当时台东岸外的独特驻潮波波腹所决定的。进入苏北岸外古辐射状潮流场中的泥沙，在辐聚、辐散的潮流作用下，每一个潮周期均自ＮＥ、ＳＥ方向向东台附近海域净输运泥沙，在东台附近海域发生淤积。由此认为，苏北中部滨海平原是大致以东台为顶点的辐聚、辐散潮     

Observed fluxes of water,salt and suspended sediment in a partly mixed estuary

Observations of the residual fluxes of water, salt and suspended sediment are presented for seven stations along the Tamar Estuary. The data include measurements over single spring and neap tidal cycles, and are generally applicable to medium or high run-off conditions.Surface to bed differences in salinity are typically of the order of several parts per thousand. Gravitational circulation is an important component of residual flow in the deep, lower reaches of the estuary. Here, Stokes drift is insignificant. In the shallow upper reaches, the major residual currents are generated by Stokes drift and freshwater inputs. Data are compared with predictions from Hansen and Rattray's (1966) model of estuarine circulation.Salt fluxes due to tidal pumping and vertical shear are directed up-estuary at spring tides, tidal pumping being dominant. Tidal pumping of salt is also directed up-estuary at neap tides, although it is insignificant in the lower reaches, where vertical shear dominates.Tidal pumping of suspended sediment is directed up-estuary near the head at spring tides, and probably contributes to the formation of the turbidity maximum. The existence of the turbidity maximum is predicted using a simplified model of the transport of water and sediment. The model shows that an additional mechanism for the existence of the turbidity maximum is an up-estuary maximum in the tidal current speeds (and thus resuspension). In the lower reaches, transport of suspended sediment is directed down-estuary at both spring and neap tides, and sediment is essentially flushed to sea with the fresh water.     

桐花树红树林潮滩近底层悬沙浓度垂向剖面变化特征分析*

观测红树林潮滩在波浪和潮流作用下的近底层垂向剖面悬沙浓度变化过程, 对理解海岸带植被的消能促淤机制和滨海湿地生态修复工程有着重要作用。本文以北部湾七星岛岛尾桐花树红树林潮滩为例, 基于剖面流速仪HR、声学多普勒单点流速仪ADV、浪潮仪T-wave及剖面浊度仪ASM, 获取了研究区域2019年夏季大潮连续3天的水文数据, 同时结合桐花树典型植株实测参数, 分析了潮周期内红树林潮滩近底层垂向剖面悬沙响应波浪、潮流作用及桐花树空间结构的运动过程。结果表明: 1) 桐花树潮滩近底层悬沙浓度和悬沙通量具有涨潮明显大于落潮的潮汐不对称现象, 剖面垂向高悬沙浓度区域在涨潮初期—涨急由距底部0.1~0.37m转变为距底部0.5~0.67m, 落急—落潮末期则由上部转变为下部; 2) 潮周期内悬沙起动和再悬浮阶段发生在以波浪作用主导的涨潮初期和落潮末期, 平流和沉降发生在以潮流作用为主的涨急至落急整个阶段; 3) 涨潮阶段桐花树冠层的茂密枝叶通过减缓流速拦截多于冠层上部40%以上的悬沙, 落潮水体则挟沙自陆向海经过桐花树群落, 使得悬沙浓度下降超过71%。该不对称涨、落潮动力沉积机制有利于悬沙向岸输运, 促进潮滩扩张过程。     

试论植物在潮滩发育演变中的作用

根据１９８５－１９９１年对长江三角洲和苏北潮滩－潮沼系统中潮流和波浪观察、滩面高程量算、沉积物分析和人工海草试验，研究植物对潮滩动力和沉积的影响。结果表明，（１）植物可使底层流速降低２０％－６０％，使波浪能量大部分被吸收。（２）沼泽前缘存在侵蚀机制，而沼泽的主体则有明显的促淤现象；沼泽中的沉积速率可达光滩的９倍以上。（３）沼泽前缘沉积物有粗化现象，沼泽主体则是细化环境；沼泽是孢粉相对富集的场所；沼     

杭州湾枯季水沙若干特征分析

根据2014年1月及2017年2月杭州湾大、小潮水沙资料,计算了流速、含沙量、单宽潮量、单宽输沙量,进而分析了潮周期断面净潮量、净输沙量和区域冲淤分布。研究发现杭州湾涨、落潮平均流速比值整体较20世纪八九十年代增大,绝大部分区域大于1.0,涨潮流相对增强,澉浦南岸和金山北岸尤为显著。含沙量平面上分布澉浦、杭州湾南岸两个高值区(大潮大于3 kg/m³,小潮大于1.3 kg/m³)以及北岸湾口至乍浦之间的低值区(大潮小于2 kg/m³,小潮小于0.9 kg/m³),随潮汛变化显著,最大含沙量浓度通常滞后于急流时刻。各测站涨、落潮量和输沙量呈现“大涨大落”和“大进大出”的特征,造成杭州湾短时间尺度内的“大冲大淤”。大潮两涨两落金山与乍浦、乍浦与澉浦之间区域净输沙量可达几千万吨,净冲淤则在几百万吨。     

伶仃洋河口泥沙絮凝特征及影响因素研究

泥沙絮凝对河口细颗粒泥沙运动过程起着极其重要的作用。本文通过LISST-100激光粒度仪等仪器实测伶仃洋河口2013年洪季悬浮泥沙絮凝体现场粒径及水动力、泥沙条件,结合实验室悬沙粒径分析,研究大小潮期间伶仃洋河口泥沙絮凝特征,探讨紊动剪切强度、含沙量、盐度分层及波浪等因素对伶仃洋河口泥沙絮凝的影响。结果表明:伶仃洋河口水体中现场粒径平均值为148.53 μm,大于实验室悬沙分散粒径36.74 μm,河口絮凝现象明显;沉速与有效密度、粒径呈正相关,絮团平均有效密度为153.49 kg/m3,平均沉速达1.13 mm/s;小潮时絮团平均粒径大于大潮,垂向上表底层絮团粒径小、中层大,中底层絮团沉速大于表层。伶仃洋河口水动力、泥沙条件是影响其泥沙絮凝的重要因素,低剪切强度（小于5 s-1）、低含沙量（小于50 mg/L）及高体积浓度有利于细颗粒泥沙之间的相互碰撞,促进絮凝作用;当剪切强度与颗粒间碰撞强度高于絮团所能承受的强度时,絮团易破碎分解成小絮团或更细的泥沙颗粒;伶仃洋河口盐度层化引起的泥沙捕获现象增大中层泥沙体积浓度,有利于中层絮凝体的发育;观测期相对较大的波浪增强水体紊动,增大了水体细颗粒泥沙的碰撞几率,表层絮团粒径随波高峰值的出现而增大。     

天津塘沽驴驹河-独流减河潮间带沉积物特征研究

通过对研究区潮间带36个表层沉积物的定位采样,采用综合法对样品进行粒度分析。结果表明,研究区潮间带表层沉积物由-粉砂质极细砂、极细砂-粉砂-粘土、粉砂-粘土-极细砂、极细砂质粉砂、极细砂-粉砂、粉砂和极细砂组成,从岸边向潮下带方向表层沉积物由细变粗;由于修建海滨浴场,改变了岸线的轮廓使水流发生变化,从驴驹河-独流减河潮间带表层沉积物粒度由粗变细;垂向上,由于修建海防公路造成岸线后退,沉积物表现为下粗上细,这些特征与本地区的人类活动和水动力条件变化密切相关。     

舟山本岛南部附近海域潮汐潮流特征分析

文章基于沈家门长期潮位站、长峙岛临时潮位站的观测资料和对舟山本岛南部海域多个站位实测的潮流基础数据,采用调和分析法对潮汐潮流进行特征分析。舟山本岛南部附近海域潮汐类型属于规则半日潮,潮差变化和日不等现象明显,有一定的潮汐浅海作用。潮流类型属于以往复流为主的规则半日浅海潮流,实测潮流中涨落潮流速不等、历时不等现象显著,最大流速、平均流速均是大潮大于小潮,涨潮流历时长于落潮流历时,潮流变化主要受协振波所控制,流向在涨落潮方向波动。     

南海东沙岛西南大陆坡内潮特征

2008年4月-10月,在南海东沙岛西南大陆坡底部布放了1套全剖面锚系,同时沿大陆坡底部布放了3套近底锚系,应用谱分析和调和分析方法分析温度和海流连续观测资料,进而研究该海域的内潮特征.结果表明,东沙岛西南大陆坡存在强内潮现象,大陆坡底部温度变化受到内潮波的影响,上层海洋存在强日潮周期的内潮波振动;正压潮和斜压潮均以O...     

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).     

弱动力浅海中的悬沙输运机制:以天津港附近海域为例

根据在天津港附近海域获取的水动力和浊度数据,分析了悬沙输运特征和输运机制,结果表明:天津港附近海域受不规则半日潮控制呈低流态往复流特征,但涨潮流强于落潮流;涨潮期间底部悬沙浓度与垂线平均流速呈显著线性相关,存在显著的再悬浮作用;潮周期内的悬沙输运呈典型的不对称特征,形成向岸的净输运趋势。输运机制分析结果显示:潮泵效应(尤其是潮汐捕捉效应)是天津港附近海域悬沙输运的主要贡献项,其次是拉格朗日平流输运项,前者比后者高一个量级;垂向剪切作用最小。涨落潮期间流速与悬沙浓度的显著不对称是造成潮汐捕捉效应占主导的基本条件。在潮下带这种悬沙输运格局可能和潮间带发生的细颗粒沉积物捕集(堆积)作用有关。     

废黄河口海域潮流动力与悬沙输运特征

根据2006年废黄河口海域的悬沙、流速、流向的观测资料,应用短期资料的潮流准调和分析方法,对连续海流资料进行了分析,并结合悬沙资料,对悬沙质量浓度与潮流之间的动力关系进行了探讨.研究结果表明:该海域潮流属于正规半日潮流,潮流以往复流为主,离岸越远,旋转性越强;涨潮流流向以SSE为主,落潮流流向以NNW为主.悬沙质量浓度...     

成山头海域潮流能资源可开发量评估

针对潮流能资源较丰富的成山头外海域,利用FVCOM数值模式,在良好模拟该海域潮流场的基础上,运用能量耗散原理,对该海域的潮流能资源可开发量进行了评估。结果表明,在转换装置的拖拽系数为0.07时,面积为27km2的成山头近岸海域的可开发潮流能资源约为17.9MW,其中大潮期间的可开发量高达37.7MW,而小潮期间则为7.3MW。在此条件下,该海域大潮期间涨急和落急时刻的流速分别减小了40%和38%,但发电装置对潮汐的影响较小,在成山头顶端的高潮潮位仅下降了4cm。     

磨刀门拦门沙区域枯季波流共同作用近底切应力和泥沙运动研究

On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.     

Modelling 3D hydrodynamics governing island-associated sandbanks in a proposed tidal stream energy site

A 3D numerical modelling study to investigate the existing hydrodynamic regime of the Pentland Firth Inner Sound Channel, Scotland, UK is presented. Hydrodynamics that govern some sensitive sedimentary deposits in the Inner Sound Channel are discussed. A 3D hydrodynamic model Delft3D is set up for Pentland Firth, located between Orkney Islands and mainland Scotland and a full sensitivity analysis of the numerical model is carried out. The current model set up sufficiently captures the existing hydrodynamics during a full spring-neap tidal cycle inside Pentland Firth. Using model results, the 3D structure of the dynamics of the tidal flows in the Inner Sound Channel is investigated. The temporal variability of tidal flows, the residual tidal flows in the channel and local flow interactions with the Island of Stroma are described. It is proved that the tidally dominant flows drive the sediment transport gradient model to explain the principle maintenance mechanisms of two island-associated sandbanks present in the Inner Sound. The present study provides detailed information on the physics of the tidal regime in the Inner Sound and explains the presence of sandbanks in an area of high tidal flows. Due to extremely high tidal flows, Inner Sound is considered as one of the most favourable sites for tidal energy extraction in the UK. The findings of this study will be very useful in assessing the significance of impacts of future tidal energy extraction on natural hydrodynamics and sediment dynamics of the area.     

对应分析方法在粤西水东湾动力沉积环境分析的应用

本文以粤西水东湾表层沉积物样品的粒度分布为基本数据,使用对应分析方法并结合地形与波流特征,分析了海湾动力沉积环境。分析结果表明,海湾现代沉积环境可划分为4个动力沉积区。     

Very small waves and associated sediment resuspension on an estuarine intertidal flat

Field data from a microtidal estuarine intertidal flat (Tamaki estuary, New Zealand) are used to analyse very small waves (height <10 cm; period 1.0–1.8 s) and associated sediment resuspension under light winds. Mean spectral period at the bed varied over the tidal cycle, driven by changes in surface-wave spectrum and depth-attenuation of orbital motions. Wave-orbital currents exceeded 30 cm/s, disturbing the fine-sand (100–200 μm) matrix of the seabed and resulting in the release of fine silt (particle size <20 μm) at concentrations >120 mg/L. Resuspension was initiated when ∼40% of the maximum zero-downcrossing orbital speeds in a burst exceeded the critical speed for initiation of sediment motion. Sediment concentrations were highest around low tide, when waves were smaller compared to high tide because of a reduced fetch but depth-attenuation of orbital motions was less because the water was shallower. Wave period exerted a control on sediment resuspension through the wave friction factor. There was a hysteresis in the wave Reynolds number such that it was greater on the ebbing tide compared to on the flooding tide: since it did not exceed 3 × 10⁵ the bed was hydraulically smooth, and the wave friction factor therefore is inversely proportional to wave period. Hence, the tidal-cycle hysteresis in wave Reynolds number translated into a smaller wave friction factor on the ebbing tide, and accounting for this caused the ebb and flood sediment concentration data to collapse onto one curve when plotted against wave-induced skin friction. A simple model is presented to evaluate the relative contribution to sediment resuspension of waves associated with weak and strong winds. At the base of the flat (waves competent to resuspend sediment for 5% of the inundation time), waves associated with stronger, infrequent winds dominate resuspension. At the top of the flat (waves competent to resuspend sediment for 30% of the inundation time), waves associated with lighter, frequent winds dominate resuspension. Moderate winds – neither the strongest nor most frequently occurring – dominate resuspension integrated across the profile. The mass of sediment resuspended by waves is greatest towards the top of the flat: shoreward of this, resuspension is smaller because of wave dissipation; seaward of this, resuspension is smaller because of greater depth-attenuation of orbital motions. The location of maximum sediment mass resuspended by waves and the location of maximum duration of resuspension are not necessarily the same.     

台湾海峡M_2分潮的三维数值模拟

本文利用普林斯顿海洋模式对台湾海峡 Ｍ ２ 分潮作了分辨率较高的三维数值模拟。在较准确地模拟了潮汐分布的基础上,研究了 Ｍ ２ 分潮流椭圆分析、最大流同时线分布、潮流场的水平及垂直结构,最后还给出了 Ｍ ２ 分潮余流、余水位的分布。结果表明, Ｍ ２ 分潮最大流同时线在海峡中部同时形成密集区和一个圆流点;构成海峡潮波系统的两股潮波中,南支潮波的影响似超出了以往所认为的范围;最大潮流仅在近海底处急剧减小,最大流方向随深度增加右转,到近底层又向左转;潮汐余流和余水位均较弱,仅在澎湖水道、台湾浅滩附近余流较大。