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1.
To investigate the influence of asymmetric tidal mixing(ATM) on sediment dynamics in tidal estuaries, we developed a vertically one-dimensional idealized analytical model, in which the M2 tidal flow, residual flow and suspended sediment concentration(SSC) are described. Model solutions are obtained in terms of tidallyaveraged, and tidally-varying components(M2 and M4) of both hydrodynamics and sediment dynamics. The effect of ATM was considered with a time-varyin...  相似文献   

2.
The salinity fluctuations at an STD near the halocline in Southampton Water have been spectrally analysed. Mixing is shown to commence at a layer Richardson number of about 20. The predominant energy inputs have periods of 7–9 and 3·5–4·5 min. These motions arise from lateral internal seiching and it is considered that they are produced by interaction of the surface seiche with the shallow side of the estuary. The wavelengths of the standing wave are calculated to be about 120 and 60 m respectively, and these compare well with echo-sounding surveys of the elevation of the halocline.  相似文献   

3.
Dyer (1982) observed internal oscillations in Southampton Water of predominantly 8 and 4 min periods. These were thought to be lateral standing waves generated by the interaction of the first- and second-order surface seiches, respectively, with estuarine topography. The present paper extends the work of Rattray (1960) to model the cross-sectional topography of Southampton Water, and shows that internal waves of the observed periods, wavelengths and amplitudes could indeed have been generated in the manner envisaged, but only near the times of certain internal resonant conditions. In general, about two or three such resonances occur per half tidal cycle, and this is in qualitative agreement with Dyer's observations.  相似文献   

4.
5.
Field measurements of vertical profiles of velocity and salinity along with turbulence measurements have been used to examine the effect of density gradients on the flow structure in the Great Ouse estuary. During the flood tide shear and longitudinal density gradients cause well mixed conditions in the lower part of the water column. In the upper part of the water column secondary flow effects induced by transverse density gradients, and acceleration effects can contribute to the formation of stable vertical density gradients. On the ebb tide the vertical density gradient appears to be the dominant factor which determines the structure of the flow. The velocity and shear stress data show the evidence of large scale motions which are consistent with the postulated flood and ebb flow structures.  相似文献   

6.
An analytical theory which describes the motion in an oscillatory smooth turbulent boundary layer using a two-layer time invariant eddy viscosity model is presented. The eddy viscosity in the inner layer increases quadratically with the height above the wall. In the outer layer the eddy viscosity is taken as a constant.  相似文献   

7.
Field measurements of the vertical and horizontal components of fluid velocity 0·43 m above the bed have been made with an electromagnetic flowmeter in a partially mixed reach of the Conwy estuary for parts of a flood and an ebb tide. The turbulent mean velocity and density fields showed different effects for flood and ebb tides caused by the interaction of shear and the longitudinal density gradient. The turbulent velocity parameters were generally dominated by bed-generated turbulence effects, but significant longer period contributions attributed to the shear-density interactions were detected. The shear-stress measurements made by two independent methods showed good agreement. The results generally show good agreement with previous less complete data. The use of the Richardson number to quantify vertical stability needs further consideration for partially mixed estuarine flows.  相似文献   

8.
The circulation and salinity distribution in the Hooghly Estuary have been studied by developing a two‐dimensional depth‐averaged numerical model for the lower estuary, where the flow is vertically well mixed. This has been coupled with a one‐dimensional model for the upper estuary, where the flow is assumed to be unidirectional and well mixed over the depth and breadth. The Hooghly River receives high freshwater discharge during the monsoon season (June to September), which has significant effect on the salinity distribution in the estuary. The model‐simulated currents, elevations, and salinities are in good agreement with observations during the dry season. However, during the wet season the computed salinities seem to deviate slightly from the observed values.  相似文献   

9.
钱塘江河口盐度数值模拟   总被引:1,自引:0,他引:1  
强潮河口盐水入侵对饮用水源地危害极大。基于平面二维水动力盐度模型, 对典型强潮河口—钱塘江的水动力及盐水入侵过程进行了数值模拟研究。结果表明枯水径流时盐度变化与潮位过程曲线类似, 潮差对盐度大小影响显著, 径流量的增加将逐渐减小其相似程度。当流量增加到一定程度后, 继续增加的一定径流量所产生的抑咸效果减弱, 水资源有效利用率降低, 此时允许水源地盐度超标并改从蓄淡避咸水库取水可有效节约水资源。盐度平面分布显示, 盐水入侵在强潮河口弯道处受涨潮流主流线影响明显, 靠近主流线一岸的盐度大于对岸, 单从盐水入侵角度考虑, 强潮河口弯道段的取水口应设置在远离涨潮流主流线一岸。钱塘江河口盐度数值模拟对于研究减轻盐水入侵对水源地危害的措施具有指导意义。  相似文献   

10.
The results of an echo-sounding survey of the Tees estuary are presented. Intense mixing periods, characterized by a surface layer of increasing salinity and thickness, were observed on the ebb tide and were preceded by periods of internal wave activity. Previously, it had been conjectured that similar mixing periods were caused by the breaking of upstream-travelling internal waves. The present survey, however, reveals that the observed waves were travelling down-stream and indicates that the mixing was principally due to a series of bridges. The times of the onset of mixed water at various stations in the estuary were consistent with the production of mixing from about the time of high water, with subsequent advection downstream. The mixing produced in this way, and by similar structures in other estuaries, clearly needs to be quantified.  相似文献   

11.
Study of colloidal phosphorus variation in estuary with salinity   总被引:1,自引:0,他引:1  
The variation of colloidal phosphorus with salinity in estuary was studied in this paper, which was compared with those of particle and truly dissolved phosphorus with the purpose of ˉnding out the similarities and di?erences between their behaviors in the estuary. Distribution patterns of phospho- rus in particle, colloidal and truly dissolved phase at di?erent salinities and their relationships with suspended particulate matter were also studied to understand the transformation and transporta- tion of colloidal phosphorus in estuarine area. The result showed that the concentrations of total colloidal phosphorus, organic colloidal phosphorus and inorganic colloidall phosphate all descended from river-end to sea-end, illustrating their terrigenous source. Ratios of organic to total colloidal phosphorus decreased with salinity's increment, indicating that organic phosphorus was in°uenced by scavenging process of colloid more signiˉcantly as compared with inorganic phosphate. Both of the phosphorus variation tendencies and the proportion between organic and inorganic phosphorus in colloidal phase was similar with that in truly dissolved phase while di?erent from that in particle phase.  相似文献   

12.
13.
胶体磷在河口区随盐度变化的研究   总被引:1,自引:0,他引:1  
陈丁  郑爱榕  陈敏 《海洋学报》2009,31(1):71-78
研究了胶体磷在河口海区随盐度变化的趋势,并将其与颗粒态、真溶解态磷随盐度的变化趋势进行对比,分析胶体态磷在河口的行为与颗粒态磷和真溶解态磷二者的异同。探讨磷在颗粒相、胶体相和真溶液相之间的分配及其与悬浮颗粒物浓度的关系,研究胶体磷在河口海区中的迁移转化作用。研究结果表明,胶体相中总磷、有机磷和活性磷浓度由河端向海端降低,表明陆源输入是其主要来源。胶体有机磷占总磷比例随盐度增加而下降,表明有机磷受胶体去除过程的影响较明显,胶体磷在河口海区的浓度变化趋势及胶体中有机磷和活性磷的比例都与真溶解相接近而与颗粒相差别较大。  相似文献   

14.
研究了胶体磷在河口海区随盐度变化的趋势,并将其与颗粒态、真溶解态磷随盐度的变化趋势进行对比,分析胶体态磷在河口的行为与颗粒态磷和真溶解态磷二者的异同.探讨磷在颗粒相,胶体相和真溶液相之间的分配及其与悬浮颗粒物浓度的关系,研究胶体磷在河口海区中的迁移转化作用.研究结果表明,胶体相中总磷、有机磷和活性磷浓度由河端向海端降低,表明陆源输入是其主要来源.胶体有机磷占总磷比例随盐度增加而下降,表明有机磷受胶体去除过程的影响较明显,胶体磷在河口海区的浓度变化趋势及胶体中有机磷和活性磷的比例都与真溶解相接近而与颗粒相差别较大.  相似文献   

15.
Observations of lateral residual circulation patterns are presented for three sections in the upper reaches of the Tamar Estuary. The data include measurements over spring and neap tidal cycles, and are compared with predictions from a depth-averaged, numerical model of the lateral circulation.The model shows features of the lateral structure which also occur in the observed data. The computed mass-transport Stokes drift has a similar lateral structure at spring and neap tides for all sections, and is up-estuary in the deeper, central part of a section, and down-estuary on the intertidal areas near the banks. A distinctive feature of this drift is the reduction in lateral structure when axial density gradients are ignored.The mass-transport residual current has a characteristic lateral structure when the run-off is not too high. The current in the central part of a section is slow (less than a few cm s−1), and may be up- or down-estuary, depending on the magnitude of the run-off. The current over the intertidal areas is faster (∼ 10 cm s−1) and directed down-estuary. This distribution consists of three components: (a) a run-off induced current which has a river-like form, (b) density currents which are up-estuary in the deeper part of a section and down-estuary over the intertidal and shallow areas, and (c) tidally-driven currents which have a similar form to density currents, and whose formation depends strongly on the existence of intertidal areas.Results from this paper are compared with published observations of lateral circulation patterns for several other estuaries.  相似文献   

16.
A three-dimensional semi-implicit finite volume numerical model has been developed and applied to study tidal circulation and salinity stratification in the region of Oujiang River Estuary, China. The model employs horizontally unstructured grids and boundary-fitted coordinate system in the vertical direction. Governing equations consisting of continuity, momentum, and transport equations are all solved in the integral form of the equations, which provides a better representation of the conservative laws for mass, momentum, and transport in the coastal region with complex geometry and bottom bathymetry. The model performance was firstly quantified with skill assessment statistics on the choice of different parameters and validated with observed tidal elevation, current velocity, direction and salinity data over a spring–neap tidal cycle collected in 2006. Numerical results show that the model with wetting–drying capability successfully simulated the tidal currents and salinity fields with a reasonable accuracy and indicate that the Oujiang River Estuary is a macrotidal estuary with strong tidal mixing. In addition, the model results also show that the Oujiang River Estuary is a well-mixed estuary during spring tide. Then, the numerical simulations were performed to compare the hydrodynamic process and salinity distribution before and after a river training, which was conducted by blocking the south branch of the Oujiang River mouth. The results reveal that with the only north access to the sea, the influence of the blocking project on the flood discharge capacity is limited and the incremental velocity is beneficial to the navigation channel maintenance, although it will cause some scour to the embankment. Furthermore, the redistribution of tidal prism passing in or out the north branch makes a little severe salinity intrusion during high tide or low tide. However, the salinity intrusion is still within acceptable range, although it can cause some adverse effect on water intaking of production and life. The variations of salinity levels in Yueqing Bay situated at the north of the river mouth are not obvious, so the blocking project will not bring damage to local aquiculture. However, significant changes of salinity happen inside or outside of the south branch, so enough attention need to be paid to the changes of environment caused by the salinity variation after the blocking project. Overall, by weighing advantages and disadvantages of the blocking project, it is feasible and the model can be considered as a tool for managing and studying estuarine circulation.  相似文献   

17.
Salt intrusion in estuaries is important for ecological reasons as well as water extraction purposes. The distance salt intrudes upstream depends on a number of factors, including river discharge, tidal and wind mixing and gravitational circulation. In this paper, an analytical solution is presented for the salt intrusion in a well mixed, funnel-shaped estuary whose cross sectional area decreases exponentially (with decay coefficient β) with distance, x, inland, and in which longitudinal mixing is constant along the length of the estuary. The solution predicts that a graph of the logarithm of salinity against exp (βx) should be a straight line, with slope proportional to the mixing coefficient Kx. The solution is tested against observations from 15 surveys over a four-year period in the Incomati estuary. Good straight line fits, as predicted, are observed on all surveys, with a mean R2 = 0.97. The average value of Kx for all surveys is 38 m2 s−1. The solution is used to make predictions about the minimum river flow required to prevent salt intruding to an extent where it causes a detrimental effect on water extraction. The minimum recommended river flow required to prevent this is 35 m3 s−1. In recent years, flow has fallen below this level for several months each year.  相似文献   

18.
This 3-year study provides a large-scale perspective of fish assemblage structure across an ocean–estuarine ecotone, given range of salinity encountered (0.1–32) based on sampling at 12 stations along 40 km from the Mullica River (river), Great Bay (bay), and the adjacent inner continental shelf (ocean) in southern New Jersey. Otter trawl (4.9 m, 6 mm mesh) collections were dominated by young-of-the-year of most of the 49 species encountered. Species richness and abundance appeared greatest in the ocean, decreased (with an increase in inter-station variability) in the bay, and appeared to increase again towards the uppermost river stations. The same areas contained three non-discrete, but identifiable, fish assemblages based on Detrended Correspondence Analysis. Members of the Triglidae and Stromateidae characterized the ocean and bay, whereas representatives of the Percichthyidae and Ictaluridae characterized the river. Several species, including Anchoa mitchilli and Cynoscion regalis, exhibited a ubiquitous distribution across the sampling area. Further analyses with Canonical Correspondence Analysis identified salinity and geographic distance, among the variables examined, as the most important determinants in shaping the assemblages. Other contributors included habitat heterogeneity and water depth. In summary, these observations indicate that large-scale patterns in the structure of this estuarine fish assemblage are primarily a result of individual species' responses to dominate environmental gradients, as well as ontogenetic migrations, whereas smaller-scale patterns appear to be the result of habitat associations that are most likely driven by foraging, competition, and/or predator avoidance.  相似文献   

19.
An investigation was made into the fate of freshwater algae in the Tamar estuary, south-west England, to examine the hypothesis that oxygen minima, observed at the freshwater-brackish water interface, were a consequence of mass mortality of freshwater algae and the subsequent oxidative degradation of the lysed cells by bacteria. The quantity and species composition of algae in the river and estuary were determined by measurements of chlorophyll and cell numbers. Phytoplankton numbers were transformed into biomass by measuring the volume of the cells and calculating the carbon content. Salinity, dissolved oxygen, turbidity, pH and temperature were also recorded. The size of the upper estuarine community was inversely related to freshwater input. During the summer months, very large populations of freshwater algae (up to 8 mg carbon l−1) were observed between 0 and 8‰ salinity, after long periods of low freshwater input. This population was completely dominated by the diatom Cyclotella atomus and was very stable with respect to changing tides, remaining in the estuary until river flow increased. Death of these algae only occurred at salinities greater than 8‰ and oxygen minima were not observed. The oxygen minima were more closely associated with the turbidity maxima than with algal mortality. There is some evidence that the oxygen depletion may be due to decreased photosynthesis as a result of the reduced light availability at the turbidity maxima.  相似文献   

20.
河控型河口盐度混合和层化是控制悬沙输移扩散的重要动力机制。以珠江磨刀门河口为研究对象,基于2017年洪季三船同步大、小潮水文泥沙观测数据,分析河控型河口水体盐度层化结构的时空变化对悬沙分布的影响机制。结果表明:受径潮动力耦合时空变化影响,河口盐度垂向分布表现出时空差异,即受径流主导的M1站(挂锭角),河口盐度在涨落潮周期内垂向混合均匀,受径潮控制的M2站(口门)在整个潮周期内盐度层化结构明显,口门外侧的M3站,潮动力作用较强,盐度垂向分布随涨落潮变化而变化;悬沙空间分布与盐度分布关系密切,盐度混合均匀利于悬沙垂向均匀分布,而盐度层化则使悬沙倾向于滞留在底层水体中,且在盐度层结界面之下出现高悬沙浓度,悬沙浓度垂向分布曲线呈L字型或抛线型,纵向上表现为高浓度悬沙团抑制在盐水楔前端,盐度层化对悬沙的捕集效应明显。通过对比水体标准化分层系数与水流垂向扩散强度系数发现,两者呈现负相关关系,即标准化分层系数愈大,垂向扩散强度愈小,表明水体层化抑制悬沙垂向扩散强度,而且水体层化程度越高,悬沙垂向扩散抑制程度越大,进而促进了河口水体盐度层化对悬沙捕集作用。本研究有助于揭示河口细颗粒泥沙运动机制及河口拦门沙演变机制,并为磨刀门河口拦门沙治理提供科学依据。  相似文献   

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