Effect of Development of Caofeidian Harbor Area in Bohai Bay on Hydrodynamic Sediment Environment

Based on the characteristics of waves, tidal currents, sediment and seabed evolution in the Caofeidian sea area in the Bohai Bay, a 2D sediment mathematical model of waves and tidal currents is employed to study the development schemes of the harbor. Verification of spring and neap tidal currents and sediment in the winter and summer of 2006 shows that the calculated values of tidal stages as well as flow velocities, flow directions and sediment concentration of 15 synchronous vertical lines are in good agreement with the measured data. Also, deposition and erosion of the sea area in front of Caofeidian ore terminal induced by suspended load under tidal currents and waves are verified; it shows that the calculated values of depth of deposition and erosion as well as their distribution are close to the measured data. Furthermore, effects of reclamation scheme of island in front of the land behind Caofeidian harbor on the hydrodynamic environment are studied, including changes of flow velocities in the deep channels at the south side of Caofeidian foreland and Laolonggou and in various harbor basins, as well as changes of deposition and erosion of seabed induced by the project.     

A two-dimensional morphological model based on next generation circulation solver II: Application to Caofeidian, Bohai Bay, China

This paper is a companion of a two-part papers on the development of a two-dimensional morphological model—CurWaC2D-Sed, based on next generation circulation solver. In this paper, the model developed in paper I is applied to the large-scale construction of near-harbor industrial zone with deep water harbor by reclamation in Caofeidian, Bohai Bay, which is a typical sandbar-lagoon bay-type tidal inlet system. Characteristics of tides, currents, waves and sediments in Caofeidian are firstly analyzed with field data from comprehensive field observations carried out in 2008. These data are then used for model calibration and validation, showing a good agreement between simulated results and field measurements for tides, currents and suspended sediments. The verified model is applied to study the effects of the construction of Caofeidian embankment and the on-going engineering scheme on hydrodynamics and sediment transports as compared with no constructions under three representative tide conditions and their combinations with normal and strong waves as well as on morphology evolution. The simulated results indicate that the present scheme leads to morphological changes in Caofeidian with acceptable rates of erosion and sedimentation. However, some attentions should be paid to erosion at offshore wharf in front of Caofedian foreland which may lead to potentially increasing landslide risks due to steep slope and sedimentation in Laogonggou creek.     

A 2D Mathematical Model for Sediment Transport by Waves and Tidal Currents

In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orthogonal curvilinear coordinates. Non-equilibrium transport equations of suspended load and bed load are used in the model. The concept of background concentration is introduced, and the formula of sediment transport capacity of tidal currents for the Oujiang River estuary is obtained. The Dou Guoren formula is employed for the sediment transport capacity of waves. Sediment transport capacity in the form of mud and the intensity of back silting are calculated by use of Luo Zaosen＇ s formula. The calculated tidal stages are in good agreement with the field data, and the calculated velocities and flow directions of 46 vertical lines for 8 cross sections are also in good agreement with the measured data. On such a basis, simulations of back silting after excavation of the waterway with a sand bar under complicated boundary conditions in the navigation channel induced by suspended load, bed load and mud by waves and tidal currents are discussed.     

曹妃甸粉沙质海岸围垦后港内泥沙研究

粉沙质海岸离岸围垦后港内淤积引人关注。基于平面二维潮流数学模型,采用网格嵌套技术,模拟了渤海、曹妃甸海域潮流场;该海域泥沙为粘性沙,且围垦后港内流速很小,采用悬沙运动数学模型模拟了潮流和波浪作用下正常天气和大风天的含沙量场,分析了大风后含沙量衰减过程,计算了正常天气年淤积强度和大风天泥沙淤积厚度。计算表明,外海泥沙主要通过甸头东侧老龙沟进入港池水域。正常天气下,港内流速小,基本处于淤积环境,但由于外海含沙量小,港池水域年淤积厚度小于10 cm。大风浪作用下,曹妃甸海域含沙量明显增大,由老龙沟进入三港池的泥沙沿程落淤,港内普遍淤积,泥沙淤积厚度在5 cm以内。     

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.     

长江河口北槽水沙过程对航道整治工程的响应

北槽大型航道整治工程确定了南北槽分汊口分流界线, 阻碍了北槽和邻近滩槽的水沙自由交换过程, 使北槽水沙动力过程发生调整。基于工程前后北槽主槽纵向同步水沙观测数据的统计分析表明:入口段落潮优势显著减弱;上段枯季时落潮优势显著减弱, 而洪季时落潮优势有所增强;中段(弯曲段拐点附近)落潮优势略有减弱;下段落潮优势明显加强。北槽主槽水沙纵向输移机制分析表明:欧拉余流、潮泵作用、斯托克斯效应和垂向环流为悬沙输移的主要驱动力, 其中欧拉余流输沙指向海, 斯托克斯输沙和垂向环流输沙指向陆, 而潮泵输沙随着季节而变化。洪季, 欧拉余流输沙和潮泵输沙在工程前后的变化使大潮期河床冲淤由中段和下段普遍落淤转化为中上段集中落淤。枯季, 工程前后稳定的潮流辐散输沙作用使大潮期河床以冲刷为主, 但工程后在入口段和上段潮泵的向上游输沙占优势, 使悬沙在入口段落淤。     

潮汐汊道及其沙滩的安全风险和动力机制

为提高海水浴场的安全性,避免发生溺水事故,文章以潮汐汊道及其沙滩的动力地貌结构和发育演变为基础,研究青岛市灵山湾城市阳台海水浴场沙滩的安全风险和动力机制,并提出风险防范建议。研究结果表明:河口潮汐汊道落潮流三角洲的潮汐水道延伸至沙滩滩面,高潮时淹没,落急时水流集中,形成流向外海的高速水流,极易引发海水浴场安全事故;区域落潮流与汊道落潮流相叠加、落潮流三角洲阻挡沿岸输沙造成下游局部岸段侵蚀以及沿岸输沙变化导致水道迁移摆动等因素进一步加大潮汐汊道附近沙滩的安全风险;安全风险最大的地点位于沿岸输沙下游与区域落潮流流向一致的潮汐水道末端附近沙滩,且该位置不稳定,随波浪场发生年际和季节变化;在潮汐汊道沙滩岸段设置海水浴场前应研究其动力地貌和发育演变,划分危险区和安全区,浴场设置后定期监测并确定危险区的位置,并在沙滩安全维护和质量评价等方面将潮汐汊道作为重要判定指标。     

江苏如东西太阳沙及烂沙洋海域潮流泥沙数值模拟

基于不规则三角形网格有限差分法并考虑波浪及其破碎作用,建立了平面二维潮流场和泥沙场数学模型.该模型对有望建设成深水码头和深水航道的江苏如东西太阳沙和烂沙洋海域的潮流场和泥沙场进行了细化数值模拟.数值模拟结果表明：（1）本海区潮流基本上是顺深槽流动的往复流,潮流流速大,烂沙洋北水道和西太阳沙附近大潮涨落潮最大流速分别在2 m/s和1 m/s以上;（2）本海区的潮平均水体含沙量在0.5 kg/m^3以下,落潮含沙量大于涨潮含沙量;（3）小浪对水体含沙量影响很小,大浪作用下水体含沙量明显增加.     

山东荣成月湖潮汐汊道的时间-流速不对称特征

月湖是山东半岛东端的一个小型潮汐汊道.在月湖进行了潮位、潮汐观测及地形测量,运用两种方法从潮位记录推算出口门落潮主干道垂线平均流速和断面平均流速.发现除涨潮优势型和落潮优势型外,月湖还表现出另外两种时间-流速不对称,即涨潮历时大于落潮历时且涨潮流速大于落潮流速、涨潮历时小于落潮历时且涨潮流速小于落潮流速.月湖的时间-流速不对称特征与不规则潮汐、涨(落)潮的流速跟潮位的匹配关系、汊道口门的断面形态、口门特殊的水流结构及循环过程等因素有关.时间-流速不对称类型的研究,对于理解潮汐汊道系统的沉积动力行为及进行人工整治有一定意义.     

淤泥质潮流深槽最大冲刷深度的一个概念模型

以概念模式方法计算了淤泥质潮流深槽的最大深度,探讨了涨落潮流速、涨落潮历时、深槽淤泥质物质粒径、深槽顶底部原始深度、水道长度等因素对潮流深槽最大深度的影响。概念模式的假设条件是:(1)深槽形态为长方体,底部纵向坡度为0;(2)沉积物粒径无垂向变化;(3)只考虑潮流作用的影响,涨、落潮流速在时间序列上呈正弦分布;(4)不考虑细颗粒物质的粘性和絮凝作用。模拟结果显示:(1)涨、落潮历时对深槽最大深度的影响很小。(2)优势潮流流速与最大深槽深度之间存在着幂函数关系。(3)深槽的底质粒径、深槽的长度均与最大冲刷深度呈正相关关系。(4)深槽顶部水深与最大深度呈负相关关系。(5)由于潮汐水道深度与潮流流速和沉积物侵蚀强度之间具有负反馈关系,因此水道冲刷存在着一个极限,即最终可以达到均衡状态。潮流深槽的均衡态特征和达到均衡态所需的时间可运用沉积动力学方法来确定;同时,若应用深槽的真实参数,进一步减少模型的假设条件,可望使该模型具有实际的应用价值。     

Bed load transport on the shoreface by currents and waves

Tide-driven bed load transport is an important portion of the net annual sediment transport rate in many shoreface and shelf environments. However, bed load transport under waves cannot be measured in the field and bed load transport by currents without waves is barely measurable, even in spring tidal conditions. There is, consequently, a strong lack of field data and validated models. The present field site was on the shoreface and inner shelf at 2 to 8.5 km offshore the central Dutch coast (far outside the surfzone), where tidal currents flow parallel to the coast. Bed load transports were carefully measured with a calibrated sampler in spring tidal conditions without waves at a water depth of 13–18 m with fine and medium sands. The near-bed flow was measured over nearly a year and used for integration to annual transport rates. An empirical bed load model was derived, which predicts bed load transports that are a factor of > 5 smaller than predicted by existing models. However, they agree with laboratory data of sand and gravel transport in currents near incipient motion. The damped transport rates may have been caused by cohesion of sediment or turbulence damping due to mud or biological activity. The annual bed load transport rate was calculated using a probability density function (pdf) derived from the near-bed current and orbital velocity data which represented the current and wave climate well when compared to 30 years of data from a nearby wave station. The effect of wave stirring was included in the transport calculations. The net bed load transport rate is a few m²/year. This is much less than predicted in an earlier model study, which is partly due to different bed load models but also due to the difference in velocity pdf. The annual transport rate is very sensitive to the probability of the largest current velocities.     

Sediment and hydrodynamics of the Tauranga entrance to Tauranga harbour

To relate the textural characteristics of the bottom sediments of a tidal inlet to hydrodynamics, 45 sediment samples from the Tauranga Entrance to Tauranga Harbour were analysed for textural parameters, and tidal currents and waves were monitored. Tidal currents dominate sediment transport processes near the Tauranga Entrance although swell waves are significant on the ebb tidal delta, and wind waves may influence intertidal sediments within the harbour. The bulk of the sediment is probably derived from marine sand from the Bay of Plenty continental shelf, but tidal currents and waves have changed its textural character. In areas of swift tidal currents, particularly in the inlet channel itself, sediment is coarser, more poorly sorted, and more coarsely skewed than that in areas of slower currents.     

江苏海岸中部近岸冬季潮汐和潮流特征

南黄海西侧的江苏海岸近岸区域,素以地形复杂、潮流强劲、悬沙输运剧烈著称,但是较长期的同步潮位和潮流观测数据仍然缺乏,尤其是在近岸(20 km)浅水(20 m)区域。2014年1月在大丰港附近开展了连续潮位和潮流观测,获得的数据揭示了一系列特征。此地潮汐潮流为正规半日潮,浅水分潮显著。平均潮差为3.05 m,最显著的两个分潮为M2和S2分潮,振幅分别为1.45 m和0.52 m。潮流最显著的半日分潮M2分潮和最显著的浅水分潮M4分潮在沿岸方向上振幅分别为0.84m/s和0.12m/s,在跨岸方向上振幅分别为0.24 m/s和0.01 m/s,沿岸方向占绝对优势。潮波的沿岸传播介于前进波和驻波之间,驻波的特征稍强。M2分潮潮流椭圆最大流(长轴)方向为南偏东7.4°。存在冬季沿岸向北的余流,垂向平均值的大小为2.2 cm/s。以上潮汐潮流特征为该区域海洋物质输运研究提供了基础资料。     

The influence of wind waves and tidal currents on sediment resuspension in Middle Chesapeake Bay

Resuspension of bottom sediments by waves and tidal currents was investigated in three characteristic environments of middle Chesapeake Bay (shallow platform, deep platform, and main channel). In the shallow near shore platform wind waves frequently resuspended significant amounts of sediment, some of which was transported offshore. In both the shallow and adjacent deep platform regions, tidal currents were too weak (<20 cm cm/sec) to resuspend bottom sediments. In the main channel, peak current velocities were substantially stronger (40 cm/sec), but were still not competent to erode the bottom. The stability of the bottom in this area is related to the activities of the benthic organisms which are influenced by seasonal anoxia. University of Maryland Center for Environmental and Estuarine Studies (CEES) Contribution No. 1572.     

Contribution of hydrodynamic conditions during shallow water stages to the sediment balance on a tidal flat: Mont-Saint-Michel Bay, Normandy, France

Field measurements were conducted in Mont-Saint-Michel Bay, a megatidal embayment (spring tidal range of 15 m), in order to monitor, over the course of a tidal cycle, sediment transport variability due to waves and tides on the upper part of a tidal flat characterised by shallow water depths. Sensors used to measure currents, water depth and turbidity were installed just above the bed (0.04 m). Two experiments were conducted under contrasting hydrodynamic conditions. The results highlight wave activity over the tidal flat even though observed wind waves were largely dissipated due to the very shallow water depths. Very high suspended sediment concentrations (up to 6 kg/m³) were recorded in the presence of wave activity at the beginning of the local flood, when significant sediment transport occurred, up to 7 times as much as under conditions of no wave activity. This influence may be attributed to the direct action of waves on bed sediments, to wave-induced liquefaction, and to the erosive action of waves on tidal channel banks. The sediment composition, comprising a clay fraction of 2-5%, may also enhance sediment transport by reducing critical shear stress through the sand lubrication effect. The results also show that antecedent meteorological conditions play an important role in suspended sediment transport on the tidal flat. Total sediment flux directions show a net transport towards the inner part of the bay that contributes to deposition over the adjacent salt marshes, and this tendency also prevails during strong wave conditions. Such sediment transport is characterised by significant variability over the course of the tidal cycle. During fair and moderate weather conditions, 83% and 71% of the total flux was observed, respectively, over only 11% and 28% of the duration of the local tidal cycle and with water depths between 0.04 and 0.3 m. These results suggest that in order to improve our understanding of sediment budgets in this type of coastal environment, it is essential to record data just at the beginning and at the end of tidal submergence close to the bed.     

莱州湾东部外航道回淤预测及影响因素

为探讨外航道回淤特征,采用二维波浪潮流泥沙数学模型,模拟研究了莱州湾东部航道回淤情况并探讨了其影响因素,以期对航道泥沙输运研究提供借鉴。研究表明,正常天气下,水流跨越航道,流速减小、挟沙能力下降导致的悬沙落淤是航道淤积的主要原因,但淤积量有限。大风浪是造成航道淤积的主要动力因素,其淤积泥沙主要来源于海底侵蚀来沙,河流来沙和沿岸输沙对航道淤积的贡献不大。从水深地形、泥沙来源、底质类型、水文动力条件等方面分析,航道发生骤淤的可能性较小。     

Sediment transport near the Tauranga entrance to Tauranga Harbour

Abstract

Sediment transport at the Tauranga Entrance was studied in relation to tidal currents and waves. Bedforms resulting from tidal flow were investigated with scuba divers and echo‐soundings. The alignment and scale of bedforms indicated the direction and approximate rate of sediment transport. Sediment transport was measured directly using sediment traps, and results were compared with rates calculated by another method. Maximum sediment transport rates of 20 000–30 000 g.m^?1 per half tidal cycle occur near the inlet gorge, but rates vary considerably in time and space, depending mainly upon power of tidal currents. A model of sediment transport for this inlet has been evolved based on tidal flow streamlines, bedform features, and the measured and calculated rates of sediment transport.     

葫芦岛港柳条沟港区规划潮流泥沙数模研究

建立了基于不规则三角形网格的考虑波浪作用的潮流泥沙数学模型，在对模型进行充分验证的基础上，对葫芦岛海域的潮流、泥沙场的进行了数值模拟，对该海区的潮流扬、泥沙场特征进行了分析；对萌芦岛港柳条沟港区规划方案进行了潮流、泥沙场模拟研究。详细分析了工程前后港池和航道的流扬变化，计算了航道的横流，预报了规划港区港池和航道的泥沙年淤积量，为港区的规划设计提供了科学依据。     

Ephemeral sand waves in the hurricane surf zone

Airborne bathymetric LIDAR observations along the Florida panhandle after Hurricane Dennis (2005) show the first unequivocal observations of surf-zone sand wave trains.

These are found in depths of 5m along the trough of the hurricane bar, where hindcasts show strong longshore currents only during severe storms. The waves extend over tens of kilometers of coast after Dennis but are absent from the same area in four other datasets. Observed wavelength to water depth ratios are comparable to river dunes and tidal sand waves but height to depth ratios are smaller, with the largest wave heights around 0.1 times the water depth. The sand wave generation mechanism is hypothesized to be from wind-and-wave-induced longshore currents, which were hindcast to be large during Dennis, with destruction from water wave orbital velocities.     

Process-based modeling of morphodynamics of a tidal inlet system

The morphodynamic evolution of an idealized inlet system is investigated using a 2-D depthaveraged process-based model,incorporating the hydrodynamic equations,Englund-Hansen’s sediment transport formula and the mass conservation equation.The model has a fixed geometry,impermeable boundaries and uniform sediment grain size,and driven by shore-parallel tidal elevations.The results show that the model reproduces major elements of the inlet system,i.e.,flood and ebb tidal deltas,inlet channel.Equilibrium is reached after several years when the residual transport gradually decreases and eventually diminishes.At equilibrium,the flow field characteristics and morphological patterns agree with the schematized models proposed by O’Brien (1969) and Hayes (1980).The modeled minimum cross-sectional entrance area of the tidal inlet system is comparable with that calculated with the statistical P-A relationship for tidal inlets along the East China Sea coast.The morphological evolution of the inlet system is controlled by a negative feedback between hydrodynamics,sediment transport and bathymetric changes.The evolution rates decrease exponentially with time,i.e.,the system develops rapidly at an early stage while it slows down at later stages.Temporal changes in hydrodynamics occur in the system;for example,the flood velocity decreases while its duration increases,which weakens the flood domination patterns.The formation of the multi-channel system in the tidal basin can be divided into two stages;at the first stage the flood delta is formed and the water depth is reduced,and at the second stage the flood is dissected by a number of tidal channels in which the water depth increases in response to tidal scour.