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1.
Kaushik Sasmal Eiji Masunaga Adrean Webb Oliver B. Fringer Edward S. Gross Matthew D. Rayson Hidekatsu Yamazaki 《Journal of Oceanography》2018,74(2):169-186
The three-dimensional numerical model SUNTANS is applied to investigate river plume mixing in Otsuchi Bay, an estuary located along the Sanriku Coast of Iwate, Japan. Results from numerical simulations with different idealized forcing scenarios (barotropic tide, baroclinic tide, and diurnal wind) are compared with field observations to diagnose dominant mixing mechanisms. Under the influence of combined barotropic, baroclinic and wind forcing, the model reproduces observed salinity profiles well and achieves a skill score of 0.94. In addition, the model forced by baroclinic internal tides reproduces observed cold-water intrusions in the bay, and barotropic tidal forcing reproduces observed salt wedge dynamics near the river mouths. Near these river mouths, vertically sheared flows are generated due to the interaction of river discharge and tidal elevations. River plume mixing is quantified using vertical salt flux and reveals that mixing near the vicinity of the river mouth, is primarily generated by the barotropic tidal forcing. A 10 ms?1 strong diurnal breeze compared to a 5 ms?1 weak breeze generates higher mixing in the bay. In contrast to the barotropic forcing, internal tidal (baroclinic) effects are the dominant mixing mechanisms away from the river mouths, particularly in the middle of the bay, where a narrow channel strengthens the flow speed. The mixing structure is horizontally asymmetric, with the middle and northern parts exhibiting stronger mixing than the southern part of the bay. This study identifies several mixing hot-spots within the bay and is of great importance for the coastal aquaculture system. 相似文献
2.
通过分析2016年枯季在珠江三角洲8个口门测站的现场同步观测盐度资料,总结了枯季八大口门同步盐度垂向分布和盐淡水混合特征。结果表明:由于八大口门的水动力条件、河口走向等不同,各口门的盐水入侵强度、盐淡水混合程度存在时空差异。其中,在盐度分布上表现为以横门为中心,向东西两侧口门,盐度逐渐递增;在层化参数分布上,总体上由横门向东分布的洪奇沥、蕉门、虎门的层化参数依次递减,横门向西分布的磨刀门、鸡啼门、虎跳门、崖门的层化参数依次递减;在一个潮周期内,盐水入侵程度、盐淡水混合强度随着潮涨潮落表现出周期性特点。盐度垂向上从上往下逐渐增大,并存在盐度拐点。一般潮汐动力越强,盐度拐点的位置越高。八大口门中,一般虎门、崖门的垂向盐度拐点位置最高;蕉门、洪奇沥、横门的垂向盐度拐点位置最低。 相似文献
3.
椒江河口高混浊水混合过程分析 总被引：4，自引：0，他引：4
根据１９９１年洪季的实测资料分析了高度浑浊的椒江河口的混合过程,并探讨了水动力学和沉积动力学因素对河口混合的重要作用,调查研究表明,椒江河口最大浑浊带下的高浑浊水－浮泥层厚达１ｍ,高浑浊水－浮泥层与上覆水之间是泥跃层,泥跃层与高混浊水－浮泥层对水体稳定的作用比同期观测到的盐跃层大１７倍以上,当高浑浊水－浮泥层被侵蚀时,在高浑浊水－浮泥层中的低盐水体又增加了水体的垂向混合能力。 相似文献
4.
5.
The design and operation of mathematical models of solute mixing and sediment transport in estuaries rely heavily on the provision of good-quality field data. We present some observations of salinity, suspended sediment concentration and velocity at one of the tidal limits of a semi-enclosed tidal lagoon in Southern England (Pagham Harbour, West Sussex, UK) where the natural processes of tidal incursion and solute mixing have been heavily modified as a result of the construction of sea walls dating back to the 18th Century. These observations, made immediately downstream of two parallel tidal flap gates by conductivity-temperature-depth (CTD) profiler, and also using bed-mounted sensor frames to measure velocity at 2 fixed depths, have yielded a set of results covering 11 tidal cycles over the period 2002–04. It is clear from the results obtained that over a typical tidal cycle, the greatest vertical salinity gradients occur in the 1–2 h immediately after the onset of the flood tide, and that subsequently, energetic mixing acts to rapidly break down this stratification. Under moderate-to-high fresh water flows (>0.5 m3/s), the break-down in vertical salinity gradient is more gradual, while under low fresh water flows (<0.2 m3/s), the vertical salinity gradient is generally less pronounced. Estimates of Richardson number during the early flood-tide period reveal values that vary rapidly between <1 and about 20, with lower values occurring after around 1.5–2 h after low water. Observations of suspended sediment concentration vary widely even for similar tidal and fresh water flow conditions, revealing the possible influence of wind speed, the storage effects of the water in the lagoon downstream of the observation site, and the complexity of the hydrodynamics downstream of tidal flap gates. The data also show that most of the sediment transport is landward, and occurs during flood tides, with estimated total tidal landward flood tide flux of fine sediment of the order of 50–120 kg under low fresh water flow conditions. These observations, which reinforce the results presented in Warner et al. (2004) and elsewhere, can help to provide information about the appropriate techniques for managing sediments and pollutants, including nutrients from sewage effluent waters, in estuaries where hydraulic flap gates are used to control the entry of fresh water over the tidal cycle. 相似文献
6.
近海潮锋的分布与温度、盐度乃至海洋生产力的分布都存在紧密联系。基于北部湾东北部的实测数据,对比分析2016—2017年北部湾东北部海域的温度、盐度、密度等分布,并利用ROMS(Regional Ocean Model System)正压与斜压模式,计算Simpson-Hunter (S-H)参数,阐述了潮锋出现位置及其与温度、盐度和密度的关系。结果表明:北部湾东北部潮锋发生的主要区域位于雷州半岛附近,潮混合区温盐密混合较为均匀。利用ROMS模式计算所得的最大垂直平均流速来计算S-H参数,认为潮锋出现位置位于S-H参数值为2处,与实测结果较为一致,且认为正压模式比斜压模式更能准确模拟潮混合区。另外,分析观测数据发现,温度、盐度、密度锋终年存在。近岸处密度锋主要受盐度锋控制,而潮混合产生的盐度锋又容易被径流掩盖。风力较大时三种锋都易向水深更深处推进,潮混合区终年垂向混合较好。 相似文献
7.
Anh Duc Nguyen Hubert H.G. Savenije Duc Nghia Pham Duc Thang Tang 《Estuarine, Coastal and Shelf Science》2008
The fresh water discharge is an important parameter for modelling salt intrusion in an estuary. In alluvial converging estuaries during periods of low flow, when salinity is highest, the river discharge is generally small compared to the tidal flow. This makes the determination of the fresh water discharge a challenging task. Even if discharge observations are available during a full tidal cycle, the fresh water discharge is seldom much larger than the measurement error in the tidal discharge. Observations further upstream, outside the tidal region, do not always reflect the actual flow in the saline area due to withdrawals or additional drainage. Discharge computation is even more difficult in a complex system such as the Mekong Delta, which is a multi-channel estuary consisting of many branches, over which the freshwater discharge distribution cannot be measured directly. This paper presents a new approach to determine the freshwater discharge distribution over the branches of the Mekong Delta by means of an analytical salt intrusion model, based on measurements made during the dry season of 2005 and 2006. It appears that the analytical model agrees well with observations and with a hydraulic model. This paper demonstrates that with relatively simple and appropriate salinity measurements and making use of the analytical salt intrusion model, it is possible to obtain an accurate discharge distribution over the branches of a complex estuary system. This makes the analytical model a powerful tool to analyze the water resources in tidal regions. 相似文献
8.
Dong Lixian 《海洋学报(英文版)》1998,17(4):469-482
ThisstudywassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49276274,theZhejiangProvinceNaturalScienceFoundationundercontractNo.490013,theChina-Australiabilateralscienceandtechnologyprogram,theAustralianInstituteofMarineScience,theModellingLaboratoryoftheMarineScienceintheSecondInstituteofOceanographyoftheStateOceanicAdministration.INTRODUCTIONTheJiaojiangEstuaryis1ocatedintheeasterncoastofChina,2OokmfromthesouthoftheChangjiangRiver(YangtzeRiver),linkedin… 相似文献
9.
针对杭州湾独特的喇叭型强潮河口湾的特点,基于Blumberg等(1996)的ECOMSED模式,引入动边界技术,建立杭州湾三维动边界的潮流模型.模型以正交曲线坐标下三维非线性水动力方程为基本方程,应用Mellor和Yamada的2.5阶湍流闭合模型计算紊动黏滞系数,嵌入Grant和Madsen的底边界层模型考虑波浪对底部应力的作用,采用干湿网格法模拟潮流漫滩过程;综合考虑径流,风应力,密度流和M2,S2,K1,O1四个主要分潮和M4,S4,MS4三个浅水分潮的作用,从而提高杭州湾潮流模拟的精度.通过验潮站调和常数和多次海流连续观测资料的验证,表明该文建立的模型可以更好的用于杭州湾流场的预报模拟. 相似文献
10.
河口区斜压梯度对余水位的累积影响及其机制探讨 总被引：1，自引：1，他引：0
余水位（即潮平均水位）是河口区径潮相互作用的典型结果，研究其形成演变机制对探讨河口区的水资源高效开发利用具有重要科学意义。本文基于不同径潮边界条件下的三维斜压水动力数值模拟及切比雪夫机制分解，初步探讨了概化地形条件下斜压梯度对余水位沿程变化的影响。数值模拟结果表明:河口区余水位的沿程变化明显受径流量、潮波振幅、辐聚地形及斜压梯度等因素的共同影响，斜压梯度对余水位的影响是一种累积效应且影响区域集中在回水区，同时其影响强度具有明显的大小潮变化、洪枯季变化。利用数值模型提供的水位及流速场信息，通过切比雪夫分解非线性摩擦项分离出控制余水位变化的3个主要因素，即径流、潮流和径潮相互作用因子，并与斜压梯度产生的余水位进行对比分析，结果表明:回水区域余水位主要以径潮相互作用因子为主导；斜压梯度对余水位影响主要体现在小潮期间，有可能成为影响余水位变化的主控因子。 相似文献
11.
A. Mantovanelli E. Marone E. T. da Silva L. F. Lautert M. S. Klingenfuss V. P. Prata Jr. M. A. Noernberg B. A. Knoppers R. J. Angulo 《Estuarine, Coastal and Shelf Science》2004,59(4):523-537
Net transports of water, salt and suspended particulate matter (SPM) for a cross-section in front of the Paranaguá Harbour (Paranaguá Bay, Brazil) are presented for eight distinct tidal cycles. Data include measurements over single spring and neap tidal cycles, during both wet and dry seasons. The main drive forces of circulation and SPM dynamics are identified. Advective transport dominated under moderate to high vertical salinity stratification and weak currents, while mixing processes dominated under well-mixed conditions generated by high currents and low freshwater input. Under partially mixed conditions, both advective and mixing processes were important. The tide-induced residual circulation dictated the magnitude and direction of residual currents and net transports of water and salt, but not of SPM transport. The SPM dynamics was intrinsically related to cyclical processes of erosion, resuspension and deposition driven by tidal currents. The turbulent mixing intensity conditioned the vertical mixing of SPM. Resuspension and vertical mixing were conspicuous in spring cycles, while the horizontal advection preponderated in the neaps. Lags between maximum currents and SPM peak concentrations occurred, with more pronounced hysteresis during ebb periods. 相似文献
12.
潮致余流和潮混合对长江口外东北海域低盐水团的作用 总被引：1，自引：0，他引：1
长江冲淡水对黄海、东海水文环境有重要影响,它主要以羽状形态向外海扩展,在某些年份的特殊时间段也存在孤立的低盐水团现象。在低盐水团的动力机制研究中,风、径流量、台湾暖流、天文潮和斜压不稳定的作用已得到讨论。天文潮对冲淡水及低盐水团的影响主要包括潮致余流和潮混合,潮致余流作用仍缺乏讨论。本文对1983年8月低盐水团的动力机制进行数值模拟分析,重点讨论了潮致余流和潮混合的影响。结果表明:潮致Lagrange余流促使一部分冲淡水从口门向北输运,在32°N附近呈舌状转向东,有利于在口外东北海域形成低盐水团;小潮转大潮的垂向混合作用加强,浅水区表层盐度升高的速度快于较深水区,也有利于在口外东北海域形成低盐水团。 相似文献
13.
A 3D,time-dependent,baroclinic,hydrodynamic and salinity model was implemented and applied to the Oujiang River estuarine system in the East China Sea.The model was driven by the forcing of tidal elevations along the open boundaries and freshwater inflows from the Oujiang River.The bottom friction coefficient and vertical eddy viscosity were adjusted to complete model calibration and verification in simulations.It is demonstrated that the model is capable of reproducing observed temporal variability in the water surface elevation and longitudinal velocity,presenting skill coefficient higher than 0.82.This model was then used to investigate the influence of freshwater discharge on residual current and salinity intrusion under different freshwater inflow conditions in the Oujiang River estuary.The model results reveal that the river channel presents a two-layer structure with flood currents near the bottom and ebb currents at the top layer in the region of seawater influenced on north shore under high river flow condition.The river discharge is a major factor affecting the salinity stratification in the estuarine system.The water exchange is mainly driven by the tidal forcing at the estuary mouth,except under high river flow conditions when the freshwater extends its influence from the river’s head to its mouth. 相似文献
14.
Baroclinic terms have been implemented in a three-dimensional fully hydrodynamic model developed by Badiei et al. [2008. A three-dimensional non-hydrostatic boundary fitted model for free surface flows. International Journal for Numerical Methods in Fluids, 56(6), 607-627] modifying its momentum equations to account for density gradients and utilizing the scalar (salinity, temperature, etc.) conservation equation (SCE) and a state equation for the calculation of density. In the solution of advection-diffusion terms of the governing Navier-Stokes equations (NSE) and SCE, a symmetric splitting method was applied to ensure the long-term stability of simulations. Correction terms proposed by Ruddic et al. (1995) were applied to SCE to ensure the conservation of the scalar quantity. In the presence of baroclinic terms, the zero gradient pressure in the vertical direction in the vicinity of surface and bottom boundaries assumed by Badiei et al. [2008. A three-dimensional non-hydrostatic boundary fitted model for free surface flows. International Journal for Numerical Methods in Fluids, 56(6), 607-627] created spurious currents. This problem was solved by assuming a hydrostatic pressure variation at those boundaries. The ability of extended model was validated by comparing its results with an experimental test case. The simulation of hydrodynamic and salt intrusion at Anzali Port located at the southern coasts of Caspian Sea in Iran was carried out by the model with both barotropic and baroclinic modes. The simulated results with baroclinic mode show a better agreement with measured data as compared to the results of barotropic mode that clearly demonstrate the significance of baroclinic terms in the simulation of cyclic intrusion of salt wedge into the Port Basin. 相似文献
15.
长江河口北槽弯道横向次生流、混合与层化 总被引：1，自引：0，他引：1
2013年2月25至26日(枯季/大潮)、7月23至24日(洪季/大潮)分别在长江河口北槽弯道沿着3条横向测线CS6、CSW和CS3(每条测线上有北、中、南3个站位)测得水位、流速、盐度和含沙量的时间序列资料。通过这些资料的定量计算、分析,理解弯道横向次生流、混合与层化的时、空变化和各种物理机制及其相对重要性。3条横向测线均存在横向次生流,且横向测线CS3还出现横向次生环流。枯、洪季,仅在横向测线CS6、CS3出现环状欧拉余流。枯、洪季,沿着横向测线CS3,3个站位的横向斜压梯度比离心加速度和科氏加速度都大1~2个数量级,而后两项大小接近且数量级都是10-4,罗斯贝数在1左右。这些表明:横向次生流受横向斜压梯度、离心加速度和科氏加速度共同驱动,前一项相对于后两项更加重要。沿着3条横向测线:1)枯、洪季大潮,平均势能差异分别约为54.23、66.56 J/m3,表明洪季层化强于枯季;2)枯季涨潮,平均的势能差异普遍小于落潮,而洪季涨潮,平均的势能差异普遍大于落潮,表明枯、洪季湍流混合均存在潮汐不对称性;3)枯季,由横向、纵向水深平均应变(ΦS-y、ΦS-x)引起的势能差异变化率的范围分别是-67×10~(-3)~37×10~(-3)、-7×10~(-3)~11×10~(-3)W/m~3,而洪季,相应的范围分别是-45×10~(-3)~30×10~(-3)、-14×10~(-3)~13×10~(-3)W/m~3,表明枯、洪季差异不明显,横向水深平均应变(ΦS-y)均大于纵向水深平均应变(ΦS-x),前项对水体混合与层化的影响更大;4)枯季大潮,纵向平流(ΦA-x)、横向平流(ΦA-y)、纵向水深平均应变(ΦS-x)和横向水深平均应变(ΦS-y)的潮汐平均绝对值占四项总和之比例分别为26%、33%、18%和23%,而洪季大潮,相应的值的比例分别为13%、9%、22%和56%,表明枯季,平流项(ΦA-y最大)对混合与层化的控制可能占主导地位;洪季,应变项(ΦS-y最大)可能占主导地位。无量纲数(m)被用于判别横向平流(ΦA-y)、横向水深-平均应变(ΦS-y)的相对重要性。一个概念性模式被用于显示层化与横向次生流/环流的相互关系。 相似文献
16.
The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events. 相似文献
17.
引潮力对海洋环流模式的影响 总被引：2，自引：1，他引：1
The eight main tidal constituents have been implemented in the global ocean general circulation model with approximate 1° horizontal resolution.Compared with the observation data,the patterns of the tidal amplitudes and phases had been simulated fairly well.The responses of mean circulation,temperature and salinity are further investigated in the global sense.When implementing the tidal forcing,wind-driven circulations are reduced,especially those in coastal regions.It is also found that the upper cell transport of the Atlantic meridional overturning circulation(AMOC) reduces significantly,while its deep cell transport is slightly enhanced from 9×106m3/s to 10×106 m3/s.The changes of circulations are all related to the increase of a bottom friction and a vertical viscosity due to the tidal forcing.The temperature and salinity of the model are also significantly affected by the tidal forcing through the enhanced bottom friction,mixing and the changes in mean circulation.The largest changes occur in the coastal regions,where the water is cooled and freshened.In the open ocean,the changes are divided into three layers:cooled and freshened on the surface and below 3 000 m,and warmed and salted in the middle in the open ocean.In the upper two layers,the changes are mainly caused by the enhanced mixing,as warm and salty water sinks and cold and fresh water rises;whereas in the deep layer,the enhancement of the deep overturning circulation accounts for the cold and fresh changes in the deep ocean. 相似文献
18.
长江口拦门沙地区的泥沙运动规律 总被引：12，自引：0，他引：12
依据１９８８年７月和１２月水文观测资料，通过流，盐，沙的综合分析，认识到长江口拦门沙地区的泥沙运动有与河口其他地区不同的特点，泥沙输移在水平面上和垂直面上存在着多种循环，潮流和盐水截留大量泥沙积聚的拦门沙地区，河口在盐淡水交锋地带，除了涨，落急时段外，发现在转流时期泥沙也可能产生再悬浮，从而形成一个潮周期中出现３次或４次再悬浮的特殊规律。 相似文献
19.
长江河口北支上口不规则周期潮流的动力机制 总被引：1，自引：1，他引：0
数值模拟和动量分析长江河口北支上口枯季大潮期间 1 d内出现"四涨四落"不规则周期涨落潮流现象。长江河口北支上口 1日内两次涨潮流和两次落潮流为常规涨落潮流,受外海半日潮流控制,两次涨潮流和落潮流为非常规涨落潮流。北支上口非常规的涨潮流处于南支落潮的末期,范围小,流速弱,历时约2 h;表层主要是垂向黏滞项和水平扩散项与正压项间的作用,南向的垂向黏滞项起着决定的作用,底层则是斜压项与正压项间的作用;北支上口非常规涨潮流是北风、盐度锋面产生的南向斜压压强梯度力和南支末期落潮流的牵引作用共同造成的;径流抑制非常规涨潮流的产生,持续时间随径流量的增加呈指数递减,当径流量达到22 300 m3/s时,非常规涨潮流现象消失。北支上口非常规落潮流处于南支涨潮流的初期,由于在北支上口南支的涨潮流早于北支涨潮流,导致南支水体进入北支,形成北支上口第二次落潮流,范围较大,流速较强,历时约2.5 h,从表层至底层主要是垂向黏滞项与非线性平流项和正压项之间的作用。本文揭示了北支上口 1 d内出现"四涨四落"不规则周期涨落潮流的动力过程和机制。 相似文献