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1.
根据磨刀门2003年12月9~15日的大、中潮同步水文观测资料,分析了磨刀门枯季的潮汐、潮流、余流、悬移质含沙量、盐度等水文特征,并对枯季河口动力过程,如咸淡水混合、河口射流等进行了初步研究。在枯季由于径流较弱,潮流成为主要动力。表层由于受径流和风的影响余流基本上沿河道走向向下游,中层以下有稳定的向上的余流存在。枯季磨刀门含沙量较小(<1 kg/m3),盐度在平面上和垂向上均有一定变化。磨刀门枯季咸淡水混合类型为缓混合型,各站盐度分层参数均在0.01~1.0。从实测流速的分布情况来看,河口下层有反向的水流,存在明显的因密度差而形成的密度环流。根据枯季实测资料计算所得的密度弗劳德数,磨刀门枯季以浮力射流为主。 相似文献
2.
为研究磨刀门盐水混合层化特征,基于SCHISM模型,建立了三维盐度数值模型,根据实测资料对其进行验证。结合水体势能异常理论,对枯季磨刀门河口混合层化的时空变化特征及深槽与浅滩的层化机制差异进行分析。结果表明:磨刀门河口小潮时水体层化最强,中潮时水体层化最弱,且拦门沙至挂定角段水体层化始终较强。磨刀门深槽水体层化主要受纵向平流、纵向水深平均应变和垂向混合影响,而浅滩水体层化则受横向平流、横向水深平均应变和垂向混合影响;磨刀门河口表、底层水体湍动能耗散率较高,而中间水层存在低耗散区,且涨潮时湍动能耗散率比落潮时大。 相似文献
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周期性潮积岩及其研究意义 总被引：2，自引：0，他引：2
回顾了最近十余年来国外对周期性潮汐沉积物，特别是潮汐韵律层的研究进展，系统介绍了几种从古代沉积物中识别出来的潮汐周期，包括基本潮汐（半日潮，全日潮和混合潮），大一小潮周期以及一些长周期波动等。最后，对潮汐韵律层在推测地史时期地－月系的演化历史及计算短期沉积速率中的意义作了评述。 相似文献
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浅析重金属在潮汐河段的变化规律 总被引：3，自引：0，他引：3
大辽河营口段系感潮河段,是河流和海洋两种动力因素共同作用的区域,河川径流有丰、平、枯及年内、年际变化,而潮汐则有涨、落潮和大、中、小潮的周期变化,这些变化使污染物质的迁移转化、稀释扩散及自净的机理变得更加复杂。对潮汐河段特性、重金属在潮汐河段中的变化及回荡时间的演变规律进行研究探讨,得出重金属在潮汐河段中的转化与氯离子浓度、有机络合物、碳酸盐等物质有关,向海水排泄速度与上游来水量大小及涨落潮有关,认识这些规律,对治理和净化大辽河河水水质有一定的促进作用。 相似文献
7.
珠江河口区枯季咸潮入侵与盐度输运机理分析 总被引：3，自引：0，他引：3
以河口区物质平衡原理为基础,应用物质输运机理对珠江三角洲河口区盐度净输运进行分析,对比各动力因子对盐度净输运贡献的大小.结果表明:珠江三角洲各河口盐淡水混合以缓混合型为主,分层系数均在0.01～1.0之间:盐度净输运主要是由斯托克斯输运和平均流输运控制,潮抽吸作用也不容忽视,其中,斯托克斯输运是导致咸潮上溯的最主要动力因素;珠江三角洲各口门径潮流情况及动力条件各有不同,除黄金站和挂定角V6站外,盐度输运以向上游为主,咸潮上溯明显. 相似文献
8.
《地球科学进展》2016,(8)
通过2015年1月、4月、7月、10月水温、电导率、溶解氧、pH及叶绿素a监测数据对水体温度的季节动态及其垂直分层结构进行分析,探讨了泸沽湖水体水化学性质的季节性分层特征。结果表明:泸沽湖水体在春、夏、秋季出现明显的热力分层现象,冬季水温在垂向上接近同温状态,夏季温跃层位于10~25 m水深处,而秋季温跃层下移至20~30 m处。均温层水温维持在9.5~10℃与泸沽湖年均温一致,说明均温层水体稳定且处于相对恒温状态,是湖区年均温的反映。热力分层结构对电导率、溶解氧、pH及叶绿素a变化有一定影响,致使水体电导率、溶解氧、pH出现明显的分层现象,尤其在夏季,气温升高,热力分层现象显著,溶解氧和pH在温跃层内出现峰值,自峰值处向上、向下均呈递减趋势,均温层处于缺氧状态且p H值较小。虽然叶绿素a在温跃层以下维持较低水平,整体不高,但在表层有突然增高的现象,应予以高度警示,防止泸沽湖出现大面积藻类繁殖甚至局部性爆发。电导率垂向上呈递减变化,在温跃层内降低幅度较大。泸沽湖水体盐度基本保持恒定(约0.10‰),在不考虑盐度效应的情况下,无论是在垂直断面上还是在变温层、温跃层及均温层中,电导率与水温之间存在一简单线性函数关系,证明泸沽湖仍受自然气候影响,保持自然水体状态。 相似文献
9.
为研究磨刀门水道咸潮上溯的动力特性,基于非结构网格海洋模型（Finite Volume Coastal Ocean Model,FVCOM）,构建了覆盖珠江河口及其上游网河区的高分辨率三维斜压数值模型,采用实测资料对其进行率定和验证,并开展了咸潮上溯的数值模拟计算。根据计算结果和实测资料,对磨刀门水道大、中、小潮期间的盐淡水分层与混合特征、盐分物质的分层输移机制进行分析,探讨其咸潮上溯强度时空分布差异的原因。结果表明:小潮期,底层累积盐通量明显大于表层,净输移方向为陆向;大潮期,表层累积盐通量明显大于底层,净输移方向为海向;而平衡点一般出现于中潮期,这就是磨刀门水道咸潮上溯最强和最弱时刻分别出现于小潮和大潮后的中潮期的原因所在。 相似文献
10.
珠江磨刀门水道地处亚热带季风气候区,直面南海,容易受到热带风暴的袭击。选取台风"纳沙",采用SCHISM模型建立磨刀门水道三维水流盐度数值模型,通过数值试验对比,结合势能异常分析法,探究了台风期间波浪和局地风对磨刀门水道混合与层化的影响。结果显示:由于近岸及河道内水深较浅,波高整体较小,波浪对水体层化过程影响不大,对流速分布有一定的调整作用,使其分布更为均匀,并在一定程度上加强水体掺混,利于外海高浓度盐水向河口和海岸扩散。而台风期间强劲的局地风对垂向水体状态以及势能异常变化率各项均有显著作用,影响着盐淡水的层化混合过程。 相似文献
11.
P. Lindsay 《Environmental Geology》1996,28(4):201-212
Spatial variations in the density and velocity fields have been observed in the Gareloch (Scotland) during surveys in 1987–1988
and 1993–1994. The variation of the density field has been analyzed on a variety of time scales from semidiurnal to seasonal
in order to quantify effects caused by the forcing factors of tidal mixing, freshwater input, and wind. Initial results indicate
that water density in the loch is controlled (to a major degree) by the freshwater input from runoff from the local catchment
area and from freshwater entering on the flood tide from the Clyde Estuary. It is estimated that during winter periods the
high freshwater flows from the rivers Leven and Clyde into the Clyde Estuary account for up to 75% of the freshwater creating
the density structure in the loch. Analysis of long-term dissolved oxygen data reveals that major bottom water renewals occurred
between July and January in the years 1987–1994. Major bottom water dissolved oxygen renewals have a general trend but during
the year sporadic renewals can take place due to abnormal dry spells increasing the density of the water entering from the
Clyde, or consistently strong winds from the north reducing stratification in the loch and producing better mixed conditions.
Velocities vary spatially, with the highest velocities of up to 0.6 m s–1 being associated with the velocity jet effect at the constriction at the sill of the loch. Observed near-surface mid-loch
velocities increased as the vertical density gradients in the upper layers increased. This indicates for the observed conditions
that increased stratification in the upper layers inhibits the entrainment rate and hence rate of gain of thickness of the
wind-driven surface layer, resulting in increased surface velocities for a given wind speed and direction. The main flow is
concentrated in the upper 10 m and velocities below 10 m are low. Observed mean spring tide surface velocities are on average
30% greater than mean neap tide surface velocities.
Received: 22 May 1995 · Accepted: 23 August 1995 相似文献
12.
The short-term variability observed in the near surface meteorological parameters and in the vertical thermal structure of
the upper layers of the northern Bay of Bengal during a weak monsoonal regime is examined with the aid of time series measurements.
The variability of the mixed layer depth is interpreted in terms of forced mixing caused by the surface wind stress and free
mixing by buoyancy flux, Ekman pumping controlled by the curl of the surface wind stress, convergence associated with a clockwise
gyral circulation and stratification caused by freshwater discharges from rivers. The daily-averaged current vectors in the
upper layers indicate the presence of clockwise gyral circulation in the polygon area. 相似文献
13.
We describe the tidal circulation and salinity regime of a coastal plain estuary that connects to the ocean through a flood
tide delta. The delta acts as a sill, and we examine the mechanisms through which the sill affects exchange of estuarine water
with the ocean. Given enough buoyancy, the dynamics of tidal intrusion fronts across the sill and selective withdrawal (aspiration)
in the deeper channel landward appear to control the exchange of seawater with estuarine water. Comparison of currents on
the sill and stratification in the channel reveals aspiration depths smaller than channel depth during neap tide. During neap
tide and strong vertical stratification, seawater plunges beneath the less dense estuarine water somewhere on the sill. Turbulence
in the intruding bottom layer on the sill promotes entrainment of fluid from the surface layer, and the seawater along the
sill bottom is diluted with estuarine water. During ebb flow, salt is effectively trapped landward of the sill in a stagnant
zone between the aspiration depth and the bottom where it can be advected farther upstream by flood currents. During spring
tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during
ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with
high salinity water far inland. The neapspring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb
interacts with the sill to play an important role in the transport and retention of salt within the estuary. 相似文献
14.
Data are presented from several experiments in the freshwater-saltwater interface (FSI) region of the Tamar Estuary. Longitudinal surveys of salinity and suspended particulate matter (SPM) at high water showed that the location of the FSI could be predicted in terms of a power-law regression with freshwater runoff. Longitudinal transects also were surveyed over periods of several hours. The FSI was observed to advect into the region on the flood with strong vertical mixing. After high water, stratification became intense as fresher water ebbed in the surface layers. The near-bed water in the stratified region began to ebb between 2 h and 3 h before low water. A model of the vertical structure of longitudinal currents showed that the enhanced stratification on the ebb, coupled with the longitudinal density gradient, partly produced this long period of slack, near-bed currents following high water. A strong turbidity maximum (TM) occurred during spring tides and was located slightly up-estuary of the FSI at high water. Longitudinal transects during a period of low freshwater runoff and large neap tide showed that at the start of the flood the TM was associated with the FSI region. As the FSI advected up-estuary on the flood there was considerable resuspension of sediment at the FSI. Some of this SPM moved with the FSI and reached the limit of saline intrusion, where it formed a slowly-eroding TM as particles settled during the long, high-water slack period. As the near-bed currents increased on the ebb and the FSI moved down-estuary, strong vertical mixing and resuspension of recently deposited sediment occurred in the unstratified water behind the FSI and the associated TM advected down-estuary. Additional effects were present with stronger tides and increased runoff. 相似文献
15.
River discharge, tide, wind, topography and other factors all have great impacts on the saltwater intrusion of Modaomen Waterway (MW), a major outlet of the Pearl River Estuary. A coupled 1D–3D numerical model was applied in this study to account for the dynamic characteristics of saltwater intrusion in the MW, and the impacts of tide and river discharge on the length of saltwater intrusion were uncovered. Results are as the followings: (1) River discharge from upstream induces an obvious dilution of salinity along the MW, whereas tide can exert a positive force that pushes salt water landward. The effects of river discharge and tide on the length of saltwater intrusion can be well described by a regression function; (2) the saltwater intrusion along the MW is generally aggravated by increases in tidal range from the South China Sea. The length of saltwater intrusion usually reaches a maximum 2 or 3 days before spring tide, and the hourly length of saltwater intrusion along the MW usually slows the tidal process for approximately 4 h, which can provide important information that the pumping operation along the MW to store freshwater in the backup storages needs to be at least 3 days ahead of the spring tide so as to avoid serious impact from saltwater intrusion; (3) the length of saltwater intrusion generally decreases with increasing river discharge. In 2005, 2009 and 2010, the average river discharge from upstream was 2680, 2630 and 3160 m3/s, respectively, with corresponding average lengths of saltwater intrusion of 32.7, 42.3 and 21.4 km. The inverse correlation between the water flow and the length of saltwater intrusion may provide some guidance for operations to maintain enough upstream flow to dilute the salinity and therefore satisfy the domestic water supply. 相似文献
16.
Periodic frontogenesis in a region of freshwater influence 总被引：1，自引：0，他引：1
Observations are presented from a series of three conductivity-temperature-depth (CTD) surveys of the salinity and temperature structure of Liverpool Bay, a region that is strongly influenced by the input of fresh water from the rivers of northwest England. The surveys demonstrate the development, seaward movement, and eventual decay of a haline front. The frontogenesis is driven by the relaxation of a freshwater-induced horizontal density gradient following the decrease in tidal range at neap tides. It results in the area of Liverpool Bay being stratified for a period of 8 d before the increase in tidal mixing as the spring tide approaches returns the region to its initial vertically mixed state. In Liverpool Bay this process usually repeats on the spring-neap cycle, though strong wind-mixing may prevent the frontogenesis and subsequent stratification. Analysis with a 1-dimensional numerical model suggests that relaxation of an initially nonlinear horizontal density field, creating the front, is triggered by the stability produced by tidal straining of the water column during the ebb half-cycle. The reduction in tidal mixing energy approaching neap tide does not lead to frontogenesis without this initial stability. Such a regular stratification signal will have a marked effect on the local environment. The periodic frontogenesis will act as a tidal pump, moving buoyant substances in the water column offshore, while the onshore residual currents lower in the water column will more deeper dissolved substances inshore. The cycling of stability on the springneap time scale is considerably faster than the seasonal cycle of thermal stratification in the shelf seas, but is similar in creating the conditions required for phytoplankton blooms. Conditions favorable for enhanced primary production may therefore occur frequently in such regions of freshwater influence. 相似文献
17.
Loïc Guézennec Robert Lafite Jean-Paul Dupont Robert Meyer Dominique Boust 《Estuaries and Coasts》1999,22(3):717-727
The effects of fortnightly, semidiurnal, and quaterdiurnal lunar tidal cycles on suspended particle concentrations in the tidal freshwater zone of the Seine macrotidal estuary were studied during periods of medium to low freshwater flow. Long-term records of turbidity show semidiurnal and spring-neap erosion-sedimentation cycles. During spring tide, the rise in low tide levels in the upper estuary leads to storage of water in the upper estuary. This increases residence time of water and suspended particulate matter (SPM). During spring tide periods, significant tidal pumping, measured by flux calculations, prevents SPM transit to the middle estuary which is characterized by the turbidity maximum zone. On a long-term basis, this tidal pumping allows marine particles to move upstream for several tens of kilometers into the upper estuary. At the end of the spring tide period, when the concentrations of suspended particulate matter are at their peak values and the low-tide level drops, the transport of suspended particulate matter to the middle estuary reaches its highest point. This period of maximum turbidity is of short duration because a significant amount of the SPM settles during neap tide. The particles, which settle under these conditions, are trapped in the upper estuary and cannot be moved to the zone of maximum turbidity until the next spring tide. From the upper estuary to the zone of maximum turbidity, particulate transport is generated by pulses at the start of the spring-neap tide transition period. 相似文献