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长江河口北槽水沙过程对航道整治工程的响应 总被引:4,自引:3,他引:1
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。 相似文献
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Evidence for sediment recirculation on an ebb-tidal delta of the East Frisian barrier-island system, southern North Sea 总被引:2,自引:2,他引:0
The Otzum ebb-tidal delta, located between Langeoog and Spiekeroog islands along the East Frisian barrier-island coast, southern
North Sea, was investigated with respect to its morphological evolution, sediment distribution patterns and internal sedimentary
structures. Bathymetric charts reveal that, over the last 50 years, the size of the Otzum ebb-tidal delta has slightly shrunk,
while sediment has accreted on the ebb-delta lobe to the east of the main inlet channel (west of Spiekeroog). Swash bars superimposed
on the eastern ebb-tidal shoal (Robben Plate) have migrated south or south-eastwards, i.e. towards the inlet throat. The main
ebb-delta body is composed of fine quartz sand, whereas the superimposed swash bars and the inlet channel bed consist of medium-grained
quartz sand containing high proportions of coarser bioclastic material. Internal sedimentary structures in short box-cores
(up to 30 cm long) are dominated by flood-oriented cross-beds. Longer vibro-cores (up to 1.5 m long) show that, at depth,
the sediment is dominated by storm-generated parallel (upper plane bed) laminations with intercalated shell layers and dune
cross-bedding. The cross-bedded sands in both box-cores and vibro-cores from the ebb-delta shoal predominantly dip towards
the south or southeast, indicating transport towards the inlet throat by the flood current. The observations demonstrate that,
contrary to previous contentions, the sediments of the highly mobile swash bars do not bypass the inlet but are instead being
continually recirculated by the combined action of tidal currents and waves. In this model, the cycle begins with both fine
and medium sands, including shell hash, being transported seawards in the main ebb channel until they reach the shallow ebb-delta
front. From here, the sediment is pushed onto the eastern ebb-delta shoal by the flood current assisted by waves, becoming
strongly size-sorted in the process. The medium sands together with the shell hash are formed into swash bars which migrate
along arcuate paths over a base of fine sand back to the main ebb channel located south of the ebb delta. By the same token,
the fine sand between the swash bars is transported south-eastwards by the flood current in the form of small dunes until
it cascades into the large flood channel located to the west of Spiekeroog. From here, the fine sand is fed back into the
main ebb channel, thus completing the cycle. No evidence was found on the ebb delta for alongshore sediment bypassing. 相似文献
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弱动力浅海中的悬沙输运机制:以天津港附近海域为例 总被引:3,自引:1,他引:2
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。 相似文献
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Widely applied in maintaining estuarial waterway depth, the spur dike has played an important role in currents and sediment exchange between channel and shoal and sediment back-silting in the channel. Through establishing a generalized physical model at a bifurcated estuary and conducting current tests under the joint action of runoff and tide, the influence of the spur dike length on current exchange between channel and shoal is analyzed. Results show that when the spur dike length reaches a certain value, the direction of the flow velocity shear front between the channel and shoal will change. The longer the spur dike, the larger the transverse fluctuating velocity at the peak of flood in the channel shoal exchange area, while the transport of the transverse hydrodynamics is obvious in the process of flood. There is an optimum length of spur dike when the shear stress in the channel and the longitudinal velocity in flood and ebb reach the maximum, and the flow velocity will decrease when the spur dike length is smaller or larger than the optimum. For a certain length of spur dike, the larger the channel shoal elevation difference, the larger the peak longitudinal flow velocity in the middle of the navigation channel in flood and ebb. However, the transverse flow velocity will first decrease and then increase. The transverse transportation is obvious when the channel shoal elevation difference increases. 相似文献
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胶州湾海域潮流动力特征及其与含沙量的关系 总被引:1,自引:0,他引:1
根据2009年胶州湾海域的悬沙、流速、流向的实测资料,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,对含沙量与潮流之间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性质,半日分潮流的东分量大于北分量,潮流以带有旋转性质的往复流为主,涨潮流流向偏西,落潮流流向偏东。胶州湾内含沙量分布特征与海底沉积物粒径特征基本一致。含沙量在涨落潮的交替和流速的更迭作用下出现明显的周期性变化,含沙量的峰值基本与海域半日潮流特点相对应,几乎每1个流速峰值对应1个含沙量的峰值,含沙量的峰值一般出现在流速峰值之后。胶州湾口处流速和单宽输沙量都为最大,涨潮单宽输沙量大于落潮单宽输沙量,输沙方向为偏西向。 相似文献
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近期长江河口南汇南滩水域水沙变化特征 总被引:1,自引:0,他引:1
基于南汇南滩水域2011年12月和2012年6月洪、枯季大潮的现场水文观测资料及2003年2月枯季大潮、2004年9月洪季大潮的历史观测资料,分析潮流历时、流速、优势流和含沙量等水沙现状和变化特征,探讨近年来该水域水沙变化的主要影响因素。结果表明:(1)目前,南汇南滩水域洪季大潮落潮流占主导优势,枯季大潮涨潮流占主导优势;(2)东海大桥及其周边促淤围垦工程后,洪季大潮落潮优势增强,涨潮垂线平均含沙量减少,落潮垂线平均含沙量增多;枯季大潮落潮优势减弱,涨、落潮垂线平均含沙量均减少;(3)近岸工程建设是南汇南滩水域洪季落潮优势增强、枯季落潮优势减弱的主要影响因素;涨、落潮垂线平均含沙量的变化主要与工程建设、流域来沙量减少、近岸沙体变迁等作用有关。可为河口河槽治理提供理论依据。 相似文献
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崇明岛南岸发育有六滧涨潮槽,研究其演变过程对于崇明世界级生态岛港口建设、通航安全和岸滩稳定具有重要意义。为此,在长江口北港中上段2000、2004、2008、2012和2018年海图水深数据的基础上,分别于2018年7月利用SeaBat 7125、2019年7月利用M80无人艇搭载的SeaBat T50-P多波束测深系统以及ADCP对六滧涨潮槽开展了水下地形和流速的测量工作,分析工程影响下六滧涨潮槽的演变特征。结果表明:六滧涨潮槽淤浅,外侧沙脊冲刷剧烈,槽内落潮优势明显。其原因为流域来沙减少、以青草沙水库为主体工程的南北港分流口整治及长江大桥的修建导致了北港中上段主槽冲刷、主流北移。同时,六滧涨潮槽局部水动力条件增强,槽内的丁坝坝头局部冲刷加剧,并且奚家港东侧岸滩出现侵蚀,需引起重视。 相似文献
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长江口南北槽分流口洪季水沙变化过程研究 总被引:1,自引:0,他引:1
河口分流口的水沙变化过程是影响河口三角洲发育的核心环节,对下游河势的稳定起着关键性的作用。本文通过对北槽二、三期工程前后的南北槽分流口河段洪季大潮期间的同步水沙观测数据进行分析,以探讨长江口深水航道工程整治对分流口水沙过程的影响。结果表明:(1)北槽二期工程到三期工程后,分流口洪季以落潮优势流、优势沙为主的格局基本没有发生改变,但南槽优势流、优势沙出现略有变大,而北槽略有变小现象;(2)分流口洪季的水体输移主要受控于欧拉余流的变化,除北槽入口段水体净输移量一直较小外,其他河段在二、三期工程实施期间均有大幅提升,其中斯托克斯余流变化不大,拉格朗日余流与欧拉余流变化相一致,南槽呈波动状上升,北槽先增后减;(3)在二期到三期工程期间,北槽分流比明显减小,入口段落潮流速减小,含沙量较高,水体输移量降低,输沙强度减弱,由此导致二期工程以来北槽入口河段淤积强度加重。 相似文献
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江苏如东西太阳沙及烂沙洋海域潮流泥沙数值模拟 总被引:10,自引:0,他引:10
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. 相似文献
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潮汐汊口作为河网的重要单元,关系到水沙以及可溶污染物、营养物质的输运和分配,对河口三角洲的水文过程、地貌沉积和生态环境,都有至关重要的影响。本文选取国内最大的珠江河网的分汊顶点-马口、三水分汊,基于一个大潮潮周期内走航ADCP测量,分析潮汐汊口各个支汊的流速过程及三维流速的时空分布特征;结合非稳态的调和分析算法和小波连续变换确定汊口处主要的潮汐组分,利用潮流分离技术,剥离出占主导作用的潮波信号并探讨潮波动力在潮汐汊口处的空间分布形态。研究发现,由于潮波在西江马口和北江三水汊道内传播的不对称性,两汊间的流速过程存在1.5 h左右的相位差。而连接西北江的岗根汊道,由于存在频繁的水体交换和弯道水流的特性,岗根断面的动力作用较为复杂,其最大垂向平均流速在涨落急时刻分别向左、右岸偏移,横向断面均出现了显著的顺时针二次流。 相似文献
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山东庙岛海峡的峡道动力地貌 总被引:7,自引:0,他引:7
在庙岛海峡的动力、沉积、地貌条件比较系统的分析基础上,对庙岛海峡的峡道效应和动力地貌进行了研究,主要包括峡道形成及演变、潮流聚散与侵蚀堆积、涨落潮流歧路与登州浅滩形成、峡道泥沙搬运与沉积效应,结果表明,庙岛海峡具有显著的峡道效应,且峡道东西两段差异明显,对峡道以东的山东半岛北部沿岸海底泥沙运动和沉积具有重要影响。 相似文献
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Process-based modeling of morphodynamics of a tidal inlet system 总被引:1,自引:0,他引:1
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. 相似文献
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黄河口滨海区冲淤演变与潮流不对称 总被引:1,自引:1,他引:0
涨落潮不对称是河口滨海区流场的重要特征,在泥沙输运和地貌演变过程中扮演着重要的角色。本文基于实测水深地形、沉积物粒度、水文泥沙观测等资料,分析了黄河口滨海区的冲淤变化、泥沙输运和沉积物特征。同时,本文利用Delft 3D模型模拟了黄河口滨海区的流场,并计算了不同条件下涨落潮流速的不对称分布,结合上述分析,探讨了黄河口滨海区冲淤演变的动力机制。结果表明:现行黄河口至莱州湾滨海区相间分布多个淤积和侵蚀中心;黄河口滨海区存在显著的涨落潮流速不对称现象,现行河口外为涨潮优势流分布区,并呈舌状向南部莱州湾方向伸展,而近岸和莱州湾则普遍为落潮主导;黄河口滨海区的冲淤变化很大程度上受涨落潮流速不对称空间分布及涨落潮优势流转换所控制;强北风作用增强和扩展涨潮优势,促使莱州湾淤积和沉积物粗化。 相似文献
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A field campaign was conducted to better understand the influence of wave action, in terms of turbulence and bed shear stress, on sediment resuspension and transport processes on a protected tidal flat. An H-frame was deployed in a tidal channel south of Gangwha Island for 6 tidal cycles during November 2006 with instrumentation including an Acoustic Doppler Velocimeter, an Acoustic Backscatter System, and an Optical Backscatter Sensor. During calm conditions, the current-induced shear was dominant and responsible for suspending sediments during the accelerating phases of flood and ebb. During the high-tide slack, both bed shear stress and suspended sediment concentration were reduced. The sediment flux was directed landward due to the scour-lag effect over a tidal cycle. On the other hand, when waves were stronger, the wave-induced turbulence appeared to keep sediments in suspension even during the high-tide slack, while the current-induced shear remained dominant during the accelerating phases of flood and ebb. The sediment flux under strong waves was directed offshore due to the sustained high suspended sediment concentration during the high-tide slack. Although strong waves can induce offshore sediment flux, infrequent events with strong waves are unlikely to alter the long-term accretion of the protected southern Gangwha tidal flats. 相似文献