A Tidal Flow Model for the Gulf of Kachchh,India

A vertically integrated model has been used to study the tidal circulation and currents in the Gulf of Kachchh along the west coast of India. The model is fully nonlinear and uses a semiexplicit finite difference scheme to solve the basic hydrodynamic equations on a staggered grid. The model is forced by prescribing the tides along the open boundary of the model domain. The flow is simulated both with and without the presence of the proposed tidal barrage across the Hansthal Creek in the Gulf of Kachchh. The results show a considerable change in the behavior of the tidal flow in the presence of the barrage.     

Tidal eddies in a semi-enclosed basin: a model study

A modeling study has been carried out to support a Marine Management Plan for the Gulf of Kachchh, India and here the hydrodynamic part of the programme is described. The hydrodynamic model accurately predicts the tides and tidal currents present in the Gulf and these have been validated with the measured data, albeit at only a few locations. The time averaged residual currents obtained from the model for one lunar cycle clearly reproduce the complex, small-scale, topographically induced flows with several eddies. The existence of a dynamic barrier along Sikka-Mundra section, which divides the Gulf into two distinct dynamic systems, is very evident. The model is further used to predict the movement of surface floating particles launched at different locations in the Gulf, as an aid to determining floating pollutants. The results indicate that industries discharging wastes upstream of the barrier should use extreme caution, as these will remain in the vicinity for at least one lunar cycle.     

新沂河海口控制工程闸下河道冲刷试验研究

新沂河海口控制工程深泓闸闸下泓道长约１．３ｋｍ,河床由淤积历时较长的淤泥质粘性土组成。试验中首先取原状土土样,通过水槽试验确定起动流速,据此选择模型沙和进行模型设计。试验表明,下游河道冲刷主要由过闸水流及河口跌水造成,其中,前者形成的冲刷坑为设计的控制条件。根据试验结果认为,对于新沂河海口控制工程这样流量大、河口潮位低的闸下泓道,冲刷是不可避免的,建议放弃海漫防冲的方法,改设板桩截墙。试验中采用的某些观点和方法,对于淤泥质粘土海岸地区河口段闸下冲刷研究具有一定的参考价值。     

Ocean coast effect on magnetotelluric data: a case study from Kachchh, India

The effects of the ocean coast on magnetotelluric (MT) data have been studied and results are described in this article. MT soundings from various sites along coastal plains of Kachchh were acquired where volcanic rocks overlie Mesozoic sediments having potential resource prospects. The region of our study lies in the proximity of Gulf of Kachchh and Arabian Sea. This article describes the effects the presence of a conductive body on the acquired MT data. With the help of synthetic MT modelling and induction arrows we demonstrate the influence of shallow conductive body on the MT data. The modelling results when compared to the field observations show that much of the high frequencies are unaffected by the coast, however low frequencies of the data do seem to be distorted by onshore–offshore resistivity contrasts. The least affect on high frequencies can be attributed to very shallow water depth as well as to the fact that the onshore–offshore resistivity contrasts are not large enough to influence the high frequency data badly. The results presented here report for the first time the effect of the coast on the analysis on MT data from Kachchh. Due to several academic as well as industrial onshore–offshore MT experiments presently being carried out to explore its hydrocarbon potential, our results have an important bearing on designing and acquisition of future MT surveys in this region.     

Numerical Modeling of Suspended Sediment Transport in the Gulf of Kachchh Including Kandla Creek, West Coast of India

A depth-averaged numerical model has been developed to study tidal circulation and suspended sediment transport in the Gulf of Kachchh including Kandla creek, west coast of India. The resolution of the model is taken as 750 m × 750 m, which is found to be adequate for the gulf region. However, this resolution could not produce the realistic circulation pattern and suspended sediment concentration in the Kandla creek region. There is a major seaport at Kandla which serves as the sea gate to northwest India. Therefore, a 2-D fine resolution (75 m × 75 m) model for Kandla creek has been developed and coupled with the coarser gulf model to compute the flow features in the creek region. The model dynamics and basic formulation remain the same for both the gulf model and the creek model. The models are barotropic, based on shallow water equations, and neglect horizontal diffusion and wind stress terms in the momentum equations. The models are fully nonlinear and use a semiexplicit finite difference scheme to solve mass, momentum, and advection-diffusion equations in a horizontal plane. The tide in the gulf is represented in the model by the semidiurnal M₂ constituent mainly. In this study, no fresh water discharge conditions have been considered so the results are appropriate for the dry season. Numerical experiments are carried out to study the circulation and suspended sediment concentrations in the gulf and the creek regions. The computed results are validated with the available observations.     

Numerical Modeling of Suspended Sediment Transport in the Gulf of Kachchh Including Kandla Creek,West Coast of India

A depth-averaged numerical model has been developed to study tidal circulation and suspended sediment transport in the Gulf of Kachchh including Kandla creek, west coast of India. The resolution of the model is taken as 750 m × 750 m, which is found to be adequate for the gulf region. However, this resolution could not produce the realistic circulation pattern and suspended sediment concentration in the Kandla creek region. There is a major seaport at Kandla which serves as the sea gate to northwest India. Therefore, a 2-D fine resolution (75 m × 75 m) model for Kandla creek has been developed and coupled with the coarser gulf model to compute the flow features in the creek region. The model dynamics and basic formulation remain the same for both the gulf model and the creek model. The models are barotropic, based on shallow water equations, and neglect horizontal diffusion and wind stress terms in the momentum equations. The models are fully nonlinear and use a semiexplicit finite difference scheme to solve mass, momentum, and advection-diffusion equations in a horizontal plane. The tide in the gulf is represented in the model by the semidiurnal M₂ constituent mainly. In this study, no fresh water discharge conditions have been considered so the results are appropriate for the dry season. Numerical experiments are carried out to study the circulation and suspended sediment concentrations in the gulf and the creek regions. The computed results are validated with the available observations.     

The morphology and evolution of tidal sand bodies in the macrotidal Gulf of Khambhat,western India

Tidal sand bars and tidal sand ridges are extensively developed in the macrotidal Gulf of Khambhat, offshore western India. The inner and outer regions of the gulf are characterised by the development distinct tidal sand bodies with discrete geometries and dimensions. The outer gulf ridges are long, narrow, curvilinear and several metres high (∼20 m). They are asymmetric in cross-section and migratory in nature, forming ‘ribbon’ like sand bodies separated by tidal channels. Active dunes on these ridges indicate the presence of sand and their orientation parallel to palaeo-shorelines supports a tidal origin. In contrast to the outer gulf tidal sand ridges, sand bars associated with macrotidal estuaries flanking the Gulf of Khambhat typically have an elongate to diamond shape and are only hundreds of metres in width and a few kilometres length. These tidal sand bars occur in the estuary mouths and within the tidally influenced fluvial reaches of the rivers flowing into the gulf. The height of these sand bars is in the range ∼1–3 m. Due to high tidal ranges and bi-directional flow the sand bars do not develop significant height and are formed between the mutually evasive ebb and flow channels. Their bi-directional foresets and the presence of abundant mud drapes associated with the dunes within in-channel sand bars indicate a tidal origin.The Gulf of Khambhat acquired the present configuration in the last few thousand years since the Pleistocene sea-level lowstand (last glacial maximum, ∼18 ka) when the entire continental shelf was subaerially exposed and rivers down-cut into the coastal plain. With increasing sea-level rise, the exposed shelf was drowned, flooding parts of the Modern western Indian peninsula, and large tidal sand ridges formed in the outer gulf. After the fall of sea-level at 2 ka the gulf acquired the Modern configuration with multiple estuaries on both coastlines, rivers supplied the embayment with sandy sediment, and tidal sand bars formed in the Modern estuaries.Quantitative data gathered from the Modern Gulf of Khambhat indicates that for the P50 case, a vertical drill hole will encounter tidal sand bodies (ridges and bars combined) of approximate dimensions 1700 m long, 470 m wide and 1.5 m high, with a spacing of 400 m. In subsurface hydrocarbon reservoirs, where data is sparse and only limited amount of core is available, this quantitative dataset can be useful to constrain subsurface geocellular models. Also, the overall geometry, distribution and aspect ratio of the tidal sand ridges and tidal sand bars can be used to identify ancient counterparts through seismic geomorphology or in core.     

Morphodynamic responses to the deep water harbor development in the Caofeidian sea area,China's Bohai Bay

Vast bay-type tidal inlets can be found along the coastal zones of China. They are generally suitable for deep water channels and large harbors because of the presence of large water depth and good mooring conditions. The deep channel, in front of the head of Caofeidian Island in Bohai Bay, China, is a typical bay-type tidal inlet system. The tidal current, a type of reverse flow, makes the key contribution to maintain the deep water depth. The co-action of waves and tidal currents is the main dynamic force for sediment motion. Waves have significant influence on the sediment concentration. Based on the characteristics of waves, tidal currents, sediment and seabed evolution in Caofeidian sea area, a 2D mathematical model for sediment transport under influence of waves and tidal currents is developed to study the development schemes of the Caofeidian Harbor. The model has been verified for spring and neap tides, in winter as well as in summer of 2006. The calculated tidal stages, flow velocities, flow directions and sediment concentrations at 15 stations are in good agreement with the observations. Furthermore, the calculated data on pattern and magnitude of sedimentation and erosion in the related area agree well with the observations. This model has been used to study the effects of the reclamation scheme for Caofeidian Harbor on the hydrodynamic environment, sediment transport and morphological changes. Attentions are paid to the project inducing changes of flow velocities and morphology in the deep channel at the south side of Caofeidian foreland, in the Laolonggou channel and in various harbor basins. The conclusions can provide the important foundation for the protection and use of bay-type tidal inlets and the development of harbor industry.     

Cohesive sediment transport in the 3D-hydrodynamic-baroclinic circulation model,: study case for idealized tidal inlet

This work provides a general hydrodynamic circulation model that can be used to understand density driven flows, which may arise in the case of suspension of fine-grained materials. The research is expected to provide a better understanding of the characteristics of spatial and temporal variability of current, which is associated with the period of ebb and flood tidal cycles.The model development includes extending the existing three-dimensional (3D) ADCIRC model with (1) baroclinic forcing term and (2) transport module of suspended and soluble materials. The transport module covers the erosion, material suspension and deposition processes for cohesive type sediment. In the case of an idealized tidal inlet in stratified water, the inclusion of baroclinic term can demonstrate the prevailing longshore sediment transport. It is shown that the model has application to the transport of the cohesive sediments from the mouth of the Mississippi River along the north shore of the Gulf of Mexico towards and along the Texas coast.     

潮汐河口支流建闸闸下淤积研究

潮汐河口建闸的关键问题是闸下淤积。在潮汐河口支流口门上建闸,其闸下淤积面貌主要取决于干流主槽的位置,这与在潮汐河口干流上建闸的闸下淤积问题有着本质上的差异。以钱塘江河口支流曹娥江口门建闸为例,应用河床演变分析、动床实体模型和现场冲淤试验预测了曹娥江大闸闸下淤积面貌和淤积速率,为曹娥江大闸的建设提供了科学依据。     

Numerical study of power production from tidal energy in the Khuran Channel and its feedback on background hydrodynamics

This study focuses on the development of a farm of tidal turbines in the Khuran Channel. The important factors include the location of turbines and their hydrodynamic effects on the environment. A three-dimensional circulation model for the Persian Gulf is employed for the comprehensive evaluation of the tidal energy potential throughout the study area. The model is validated by using in situ observations of water level and current data.The appropriate potential points for extracting the tidal e...     

黄河口区风暴潮及其影响与预防对策的研究

黄河口三角洲位于渤海西南岸,介于渤海湾和菜州湾之间,是我国沿海三大三角洲之一。从其发育史考证,黄河经利津县有效行水时间约千年。自1855年至今,黄河口三角洲平均每年以25k㎡的速度淤积造陆,使其面积增加了2500k㎡以上(书书享,1985；郭永盛,1980)。由陆地等高程图(图1)可知,三角洲等高线大体与海岸平行,但两侧低,中间高,高程1-8m,平行坡降1%-1.5%,是沿海坡度最小的地区。这种地形给洪水内侵创造了有利条件,历史上发生的大量潮灾记载(刘凤树,1984；翟乾祥,1983)充分证明了这一论断。 近几年来,国内不少学者(刘凤树,1984;陈彰容,1983；刘凤岳,1982; Zhang Yanting etc,1982；孙文心等,1979； 北海分局青岛中心站,1978；海洋局预报总台海况组,1978)对渤海风暴潮特性和潮灾作了较深入的研究,进行了数值模拟和统计分析,并获得了一些成果。本文根据从1952-1980年间的历史资料中选择的、对黄河口区影响较显著的90次寒潮和18次台风过程的风暴增水作了概略分析，并对黄河口区沿岸各测站(塘沽堤口、东风港、富国、羊角沟)多年年极值水位作了统计分析,为黄河口三角洲的开发以及港口和防潮堤的建筑提供了安全保证和设计依据。     

Two-dimensional analysis of the semidiurnal tide in some regions of the white sea

An improved method of two-dimensional kinematical structural analysis of tides (the “method of the orbits”) is presented. This method allows us to determine the parameters of the primary tidal waves shaping the observed tidal structure. The construction of the vertical orbits for the individual tidal harmonics is performed along the horizontal coordinate axes; one of them is oriented along the so-called “reactive azimuth,” which coincides with the direction of the tidal current at the instant of the zero tidal level. In this case, the orbit parameters include information on the amplitude-phase relations of the interfering waves and allow us to determine the angle of the waves crossing. The suggested method enables us to quantitatively describe the mechanism of the tidal formation with oblique interference both close to the shore and in the open sea. We tested the new method in two local zones of the White Sea (Morzhovets Island and in the vicinity of the entrance to Kandalaksha Gulf) where the presence of rotating semidiurnal tidal currents evidences the significant role of oblique interference of tidal waves. In these zones, the developed method made it possible to perform a detailed quantitative analysis of the local tide structure caused by the M₂ tidal wave, which plays the dominant role in the White Sea. The result describes the structure of the propagation of the primary tidal waves better than the field of “pure” energy fluxes that was used earlier.     

Assessment of SARAL-ALTIKA Tidal Corrections in the Coastal Oceans Around India

The present tidal correction of sea level records of Satellite with ARgoes and ALtimeter (SARAL) is based on the finite element solution (FES) of global tide model FES2012 tidal solution. In this study, we examined the validity of the tidal corrections in the coastal oceans around India using tide gauge measurements and a regional tidal model. Our regional model is based on the barotropic version of the Princeton Ocean Model that is forced by the time-varying tidal levels at the open ocean end based on the global FES99 tidal solution. Tide charts prepared from the simulated tidal levels are very similar to the FES tidal solutions. Comparison with the tide gauge measurement shows close agreement with the regional tidal solutions. On the other hand, the agreement with the FES tide models differ significantly in the Gulf of Khambhat and the Gulf of Kutch on the northwest, and in the Hooghly estuary on the northeast continental shelf. However, the agreement is exceptional in other parts of the study domain. These tidal solutions are used in the SARAL-ALTIKA X-track data to assess the FES tidal correction and to draw some inferences associated with the coastal processes. It is revealed that these corrections are reasonably accurate for the coastal oceans around India except the aforementioned converging channels.     

Generation mechanisms of tidal residual circulation

Two new types of mechanism for the generation of tidal residual flow are revealed with the use of a hydraulic model experiment. A remarkable anticlockwise tidal residual circulation is formed in a model bay due to the presence of a tidal current, the Coriolis force and a horizontal boundary. A similar circulation is also formed due to the presence of a bottom slope, a horizontal boundary and a tidal current which flows normal to the inclination of the bottom slope. The residual circulation in the Sea of Iyo in the Seto Inland Sea is considered to be due to a combination of the effects of the Coriolis force, a bottom slope, a horizontal boundary and the tidal current. We classified some of the generation mechanisms of tidal residual flow which have been described to date into seven types on the basis of vorticity considerations.     

Vertical two-dimensional mechanism of tidal exchange in a bay with a sill-entrance

For a vertical two-dimensional field with a sill at a bay entrance, the tidal exchange mechanism is discussed.The schematic model is proposed as follows. The tidal trapping effect which is detected at the entrance section,i. e., the material transport due to the phase difference between the tidal periodic constituent of material concentration and tidal current at the entrance section, results because the oscillatory tidal flow at the sill entrance induces a gravitational flow along the sill slope inside the entrance. Accordingly, the tidal trapping effect depends largely upon the difference in water density between the bay and open sea and the density stratification in the bay.This model is supported by the observations at Kabira Cove (Okinawa Pref.) and Lake Hamana (Shizuoka Pref.) in 1976 through 1984. In addition, based on this model, in the case of Lake Hamana, the activity of the tidal exchange is inferred to change seasonally.     

远海航渡式水深测量水位改正方法研究

针对远海航渡式水深测量作业中的潮汐改正难题,基于全球潮汐场DTU10模型及GPS无验潮测深两种改正模式,通过潮汐场预报精度评估、验潮站实测数据比对分析以及GPS大地高计算潮汐值等多种手段,开展了大范围、长时段、单测线情况下水深测量水位改正研究,形成了一套适用性强的航渡水深测量水位改正方法与流程,为面向全球的海洋水深测量资料处理提供了潮汐、垂直基准和水位归算的方法和技术支持。     

Tides and currents in Fury and Hecla Strait

Under-ice current measurements reveal a homogeneous flow of water along Fury and Hecla Strait; it had a westward direction during the passage, over Igloolik, of low pressure cells in the atmosphere and an eastward direction at other times. It is presumed that barometric pressure differences between the Gulf of Boothia and Foxe Basin control partly the direction of the flow. The diurnal and semidiurnal components of the tidal currents also have a simple structure across the section of measurements. The subtidal and tidal components of the current all have the same order of magnitude, namely some 15 cm/s. The vertical tide progresses eastward; the diurnal component diminshhes abruptly once it enters Foxe Basin while the semidiurnal component increases steadily, its mean amplitude rising from 48 to 68 cm between the two extremities of the channel. Convective and frictional effects are evident in the water level records, indicating marked non-linear effects in the tides and currents, an eastward decrease in the diurnal currents and an increase in the semidiurnal ones.     

On flow in Northwestern Gulf of Alaska,May 1972

Southwestward volume transport (referred to 1,500 db) out of the Gulf of Alaska seaward of the continental shelf in May 1972 was 12.5 Sv, and nearly 3/4 of this flow occurred within 50 km of the shelf edge. Mean geostrophic velocities of about 50 cm s^–1 occurred in a band 20 km wide, which extended 500 km along the shelf edge; a maximum velocity of 98 cm s^–1 (nearly 2 knots) was obtained. Bottom flow along the inshore part of the shelf as determined by seabed drifters was generally onshore at 0.5 cm s^–1. Evidence is presented of a large cyclonic gyre on the shelf encompassing the Portlock and Albatross Banks, perturbations in surface flow along the shelf edge, and relations between coastal tidal heights and fluctuations in geopotential topography at the shelf edge.     

一种二维和三维嵌套海洋流体动力学数值模式及其在北部湾潮汐和潮流数值模拟中的应用

研究设计了一种二维和三维嵌套、外模态和内模态分离的水动力学数值模式,既可用于潮汐,也可用于风暴潮的数值计算。该模型对全部海区进行二维计算,对其中重点关心的海区同时进行三维计算。在三维计算区域,采用了内、外模态既分离又耦合的计算技术。数值格式采用全部交错的网格结构,三维模型中垂直方向采用σ-坐标代替通常的z-坐标,垂直涡动粘性系数由混合长度理论确定,垂直粘性项采用隐式差分格式。作为算例,本文对南海北部湾潮波进行了细网格的数值计算。