Search

Surface current velocity from high-frequency radar data are used to study tidal currents in the Mid-Atlantic Bight, which represent an average 32% of the total kinetic energy of the surface circulation. Average annual and seasonal tidal current characteristics and the associated variance of the semi-major axis are computed. The M2 constituent dominates the tide, representing a maximum of 72.26% and an average of 51.63% of the total studied tidal signal. Its semi-major axis reaches a maximum of 10 cm s−1 around mid-shelf and its phase sweeps from north to south. Local maxima of the same order of magnitude are found near the mouths of estuaries (Long Island Sound, Hudson River, Delaware Bay, Chesapeake Bay) and an absolute maximum of 50 cm s−1 is found in Nantucket Shoals. These regions of localized elevated tidal amplitude are associated with high interannual and intra-annual variability due to seasonal stratification, internal waves, and sand waves. Seasonal tidal changes are large in some of these regions; thus, should not be neglected in making tidal predictions. Lastly, the authors position this paper as an updated alternative to the Moody tidal atlas as the source for tidal current values in the Mid-Atlantic Bight.

The Arctic Ocean is a challenging region for tidal modelling. The accuracy of the global tidal models decreases by several centimeters in the Polar Regions, which has a large impact on the quality of the satellite altimeter sea surface heights and the altimetry-derived products. NOVELTIS, DTU Space and LEGOS have developed Arctide2017, a regional, high-resolution tidal atlas in the Arctic Ocean, in the framework of an extension of the CryoSat Plus for Ocean (CP4O) ESA STSE (Support to Science Element) project. In particular, this atlas benefits from the assimilation of the most complete satellite altimetry dataset ever used in this region, including Envisat data up to 82°N and CryoSat-2 data between 82°N and 88°N. The combination of these satellite altimetry missions gives the best possible coverage of altimetry-derived tidal constituents. The available tide gauge data were also used for data assimilation and validation. This paper presents the implementation methodology and the performance of this new regional tidal model in the Arctic Ocean, compared to the existing global and regional tidal models.

Previous tidal energy studies in Puget Sound have focused on major deep channels such as Admiralty Inlet that have a larger power potential. This paper focuses on the possibility of extracting tidal energy from minor tidal channels of Puget Sound by using a hydrodynamic model to quantify the power potential and the associated impact on tidal circulation. The study site is a multi-inlet bay system connected by two narrow inlets, Agate Pass and Rich Passage, to the Main Basin of Puget Sound. A three-dimensional hydrodynamic model was applied to the study site and validated for tidal elevations and currents. We examined three energy extraction scenarios in which turbines were deployed in each of the two passages and concurrently in both. Extracted power rates and associated changes in tidal elevation, current, tidal flux, and residence time were examined. Maximum instantaneous power rates reached 250 kW, 1550 kW, and 1800 kW, respectively, for the three energy extraction scenarios. Model results suggest that with the level of energy extraction in the three energy extraction scenarios, the impact on tidal circulation is very small. It is worth investigating the feasibility of harnessing tidal energy from minor tidal channels of Puget Sound.

The tidal stream energy sector is now at the stage of deploying the world's first pre-commercial arrays of multiple turbines. It is time to study the environmental effects of much larger full-size arrays, to scale and site them appropriately. A theoretical array of tidal stream turbines was designed for the Pentland Firth (UK), a strait between Scotland and the Orkney Islands, which has very fast tidal currents. The practical power resource of a large array spanning the Pentland Firth was estimated to be 1.64 GW on average. The ocean response to this amount of energy extraction was simulated by an unstructured grid three-dimensional FVCOM (Finite Volume Community Ocean Model) and analysed on both short-term and seasonal timescales. Tidal elevation mainly increases upstream of the tidal array, while a decrease is observed downstream, along the UK east coast. Tidal and residual flows are also affected: they can slow down due to the turbines action or speed up due to flow diversion and blockage processes, on both a local and regional scale. The strongest signal in tidal velocities is an overall reduction, which can in turn decrease the energy of tidal mixing and perturb the seasonal stratification on the NW European Shelf.

The Taiwan Strait has recently been proposed as a promising site for dynamic tidal power systems because of its shallow depth and strong tides. Dynamic tidal power is a new concept for extracting tidal potential energy in which a coast-perpendicular dike is used to create water head and generate electricity via turbines inserted in the dike. Before starting such a project, the potential power output and hydrodynamic impacts of the dike must be assessed. In this study, a two-dimensional numerical model based on the Delft3D-FLOW module is established to simulate tides in China. A dike module is developed to account for turbine processes and estimate power output by integrating a special algorithm into the model. The domain decomposition technique is used to divide the computational zone into two subdomains with grid refinement near the dike. The hydrodynamic processes predicted by the model, both with and without the proposed construction, are examined in detail, including tidal currents and tidal energy flux. The predicted time-averaged power yields with various opening ratios are presented. The results show that time-averaged power yield peaks at an 8% opening ratio. For semidiurnal tides, the flow velocity increases in front of the head of the dike and decreases on either side. For diurnal tides, these changes are complicated by the oblique incidence of tidal currents with respect to the dike as well as by bathymetric features. The dike itself blocks the propagation of tidal energy flux.

A method of tidal stream energy resource assessment around the Ushant Island in the Iroise Sea, using surface velocity time series from High Frequency radars (HFR) and ADCP measurements, is presented. Remotely sensed velocities provided by the radars allow to augment the industry standard approach of 3D numerical modeling and in-situ ADCP surveying to make a large-scale quantification of tidal stream resource. They capture the real ocean dynamics and thus provide context on the complex spatial variability of tidal currents that are so often feature at potential tidal energy sites. The observations show current velocities of 4 m/s northwest of the Island and in the Fromveur Strait, with 1 m/s value exceeded 60% and 70% of time respectively. Emphasis is given to the peculiarities in tidal flow asymmetry and to the study of the variation of vertical velocity profiles during different tidal stages. Radar derived velocities reveal a pronounced asymmetry between the flood and ebb flow around the Ushant Island, quantified by dimensionless number a - velocity asymmetry. The largest range of asymmetry variation, from 0.5 to 2.5, is observed in the Fromveur Strait. Harmonic analysis demonstrated that a joint variation of phase of the principal semi-diurnal (M2) and quarter-diurnal (M4) tidal velocity component accounts for flow asymmetry variation in the strait. Asymmetry in current direction is also quantified. ADCP measurements show that the vertical velocity profiles follow a 1/α power law with a power law exponent mostly depending on geographic location than on tidal stage. It was demonstrated that, in the Fromveur Strait, the 1/7 power law is appropriate to characterize the velocity profile. The combination of two sources of data enables characterization of the velocity variations in three spatial dimensions and in time thus increasing accuracy of the hydrokinetic resource assessment from HF radar observations. The estimation shows that the mean technical resource is 50% smaller in the lower half than in the upper half of the water column. The theoretical resource on average is three times higher than the technical resource and appears to be more sensitive to variations in the shape of the velocity profile in the lower layer.

The eco-geomorphological development of tidal marshes, from initially low-elevated bare tidal flats up to a high-elevated marsh and its typical network of channels and creeks, induces long-term changes in tidal hydrodynamics in a marsh, which will have feedback effects on the marsh development. We use a two-dimensional hydrodynamic model of the Saeftinghe marsh (Netherlands) to study tidal hydrodynamics, and tidal asymmetry in particular, for model scenarios with different input bathymetries and vegetation coverages that represent different stages of eco-geomorphological marsh development, from a low elevation stage with low vegetation coverage to a high and fully vegetated marsh platform. Tidal asymmetry is quantified along a 4 km marsh channel by (1) the difference in peak flood and peak ebb velocities, (2) the ratio between duration of the rising tide and the falling tide and (3) the time-integrated dimensionless bed shear stress during flood and ebb. Although spatial variations in tidal asymmetry are large and the different indicators for tidal asymmetry do not always respond similarly to eco-geomorphological changes, some general trends can be obtained. Flood-dominance prevails during the initial bare stage of a low-lying tidal flat. Vegetation establishment and platform expansion lead to marsh-scale flow concentration to the bare channels, causing an increase in tidal prism in the channels along with a less flood-dominant asymmetry of the horizontal tide. The decrease in flood-dominance continues as the platform grows vertically and the sediment-demand of the platform decreases. However, when the platform elevation gets sufficiently high in the tidal frame and part of the spring-neap cycle is confined to the channels, the discharge in the channels decreases and tidal asymmetry becomes more flood-dominant again, indicating an infilling of the marsh channels. Furthermore, model results suggest that hydro-morphodynamic feedbacks based on tidal prism to channel cross-sectional area relationships keep the marsh channels from filling in completely by enhancing ebb-dominance as long as the tidal volume and flow velocities remain sufficiently high. Overall, this study increases insight into the hydro-morphodynamic interactions between tidal flow and marsh geomorphology during various stages of eco-geomorphological development of marshes and marsh channels in particular.

In recent years, the application of large-scale beach nourishments has been discussed, with the Sand Motor in the Netherlands as the first real-world example. Such protruding beach nourishments have an impact on tidal currents, potentially leading to tidal flow separation and the generation of tidal eddies of length scales larger than the nourishment itself. The present study examines the characteristics of the tidal flow field around protruding beach nourishments under varying nourishment geometry and tidal conditions, based on extensive field observations and numerical flow simulations. Observations of the flow field around the Sand Motor, obtained with a ship-mounted current profiler and a set of fixed current profilers, show that a tidal eddy develops along the northern edge of the mega-nourishment every flood period. The eddy is generated around peak tidal flow and gradually gains size and strength, growing much larger than the cross-shore dimension of the coastline perturbation. Based on a 3 week measurement period, it is shown that the intensity of the eddy modulates with the spring-neap tidal cycle. Depth-averaged tidal currents around coastline perturbations are simulated and compared to the field observations. The occurrence and behavior of tidal eddies is derived for a large set of simulations with varying nourishment size and shape. Results show that several different types of behavior exist, characterized by different combinations of the nourishment aspect ratio, the size of the nourishment relative to the tidal excursion length, and the influence of bed friction.

The finite volume community ocean model (FVCOM) has been applied to the Ganges-Brahmaputra-Meghna (GBM) delta in the northern part of the Bay of Bengal in order to simulate tidal hydrodynamics and freshwater flow in a complex river system. The delta region is data-poor in observations of both bathymetry and water level; making it a challenge for accurate hydrodynamic models be configured for and validated in this area. This is the first 3D baroclinic model covering the whole GBM delta from deep water beyond the shelf break to 250 km inland, the limit of tidal penetration. This paper examines what controls tidal penetration from the open coast into an intricate system of river channels. A modelling approach is used to improve understanding of the hydrodynamics of the GBM delta system. Tidal penetration is controlled by a combination of bathymetry, channel geometry, bottom friction, and river flow. The simulated tides must be validated before this delta model is used further to investigate baroclinic processes, river salinity and future change in this area. The performance of FVCOM tidal model configuration is evaluated at a range of sites in order to assess its ability to capture water levels which vary over both a tidal and seasonal cycle. FVCOM is seen to capture the leading tidal constituents well at coastal tide gauge stations, with small root-mean-squared errors of 10 cm on average. Inland, the model compares favourably with twice daily observed water levels at thirteen stations where it is able to capture both tidal and annual timescales in the estuarine system. When the river discharge is particularly strong, the tidal range can be reduced as the tide and river are in direct competition. The bathymetry is found to be the most influential control on water levels within the delta, though tidal penetration can be significantly affected by the model's bottom roughness, and the inclusion of large river discharge. We discuss the generic problem of implementing a model in a data-poor region and the challenge of validating a hydrodynamic model from the open coast to narrow river channels.

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 d...

Potential energy extraction from tidal currents is investigated in this work. Recordings on the streams' velocity and the sea level in the Euripus' strait in Evia, Greece are used to calculate the energy yield. Data on sea level measurements were used to extract information for the current velocity profile through harmonic analysis method. Requirements, limitations and possible new designs that will improve the energy extraction from the low velocity tidal current of the area are discussed. Also, exploitation of tidal energy in cooperation with RES microgrid is proposed for areas where the abundance of sun, wind, island communities and coast areas such as the Mediterranean.

National efforts to reduce energy dependency on fossil fuels have prompted examination of macrotidal nearshore sites around the United Kingdom (UK) for potential tidal stream resource development. A number of prospective tidal energy sites have been identified, but the local hydrodynamics of these sites are often poorly understood. Tidal energy developers rely on detailed characterisation of tidal energy sites prior to device installation and field trials. Although first-order appraisals may make macrotidal tidal straits appear attractive for development, detailed, site-specific hydrodynamic and bathymetric surveys are important for determining site suitability for tidal stream turbine (TST) installation. Understanding the ways in which coastal features affect tidal velocities at potential TST development sites will improve identification and analysis of physical constraints on tidal energy development. This paper presents and examines tidal velocity data measured in Ramsey Sound (Pembrokeshire, Wales, UK), an energetic macrotidal strait, which will soon host Wales' first TST demonstration project. While maximum tidal velocities in the strait during peak spring flood exceed 3 m s−1, the northern portion of Ramsey Sound exhibits a marked flood-dominated tidal asymmetry. Furthermore, local bathymetric features affect flow fields that are spatially heterogeneous in three dimensions, patterns that depth-averaged velocity data (measured and modelled) tend to mask. Depth-averaging can therefore have a significant effect on power estimations. Analysis of physical and hydrodynamic characteristics in Ramsey Sound, including tidal velocities across the swept area of the pilot TST, variations in the stream flow with depth, estimated power output, water depth and bed slope, suggests that the spatial and temporal variability in the flow field may render much of Ramsey Sound unsuitable for tidal power extraction. Although the resource potential depends on velocity and bathymetric conditions that are fundamentally local, many prospective tidal energy sites are subject to similar physical and hydrodynamic constraints. Results of this study can help inform site selection in these complicated, highly dynamic macrotidal environments. In order to fully characterise the structure of the tidal currents, these data should be supplemented with 3-D modelling, particularly in areas subject to a highly irregular bathymetry and complicated tidal regime.

The radial tidal current field accounts for the formation of the radial sand ridges in the South Yellow Sea. Understanding the formation and evolution of this radial tidal current field is vital to assessing the morphodynamic features in the area. A semi-enclosed rectangular basin with and without a coastal barrier was schematized from the topography of the Bohai Sea and Yellow Sea. The 2D tidal current field in this basin was simulated using the DELFT3D-FLOW model. The concept of tidal wave refraction, which highlights the effect of the sloped or stepped submarine topography on the propagation of the tidal waves, was introduced to explain the formation of the radial tidal current field. Under the effect of tidal wave refraction, co-phase lines of the counterclockwise rotating tidal wave and incident tidal wave are transformed into clockwise and counterclockwise deflections, respectively, leading to the convergence and divergence of the flow field. Regardless of whether a coastal barrier exists or not, the outer radial tidal current field might emerge over certain topography. The responses of the radial tidal current field in this basin to the environmental variations such as coastline changes and bottom erosions were discussed. Results show that local protrusion near the focal point of the radial tidal current field will have limited effects on the location of the tidal system. However, a remarkable shift of the amphidromic point toward the entrance and central axis of this basin and a movement of the focal point of the radial tidal current field toward the entrance could be caused by the significant seaward coastline advance and submarine slope erosion.

The formation and dynamics of tidal bores in funnel-shaped estuaries is investigated from both a global tidal wave scaling analysis and new quantitative field observations. We show that tidal bore occurrence in convergent estuaries can be estimated from a dimensionless scaling parameter characterizing the relative intensity of nonlinear friction versus local inertia in the momentum equation. A detailed analysis of tidal bore formation and secondary wave structure is presented from a unique long-term database (observations of more than 200 tides) acquired during four campaigns in the two main French tidal-bore estuaries: the Seine and Gironde/Garonne estuaries. We describe the effect of freshwater discharge on the global tidal wave transformation at the estuarine scale and on local tidal bore occurrence in the upper estuary. Our field data suggest that the tidal bore intensity is mainly governed by the dimensionless tidal range, which characterizes the local tidal wave nonlinearity. We also show that the secondary wavefield associated with tidal bore propagating in natural estuaries differs significantly from those associated to undular bores in rectangular channels. In particular, we observe an abrupt decrease of the whelp steepness when the Froude number goes below 1.1. This secondary field transition can explain why tidal bore occurrence in worldwide estuaries is certainly underestimated.

At least 19 remarkable dikes and land reclamations have been constructed since 1970 along the west coast of Korea, which resulted in a reduction in tidal flat area of almost 50%. Both the reduction in tidal flats and the artificially simplified coastal line have distorted the spatio-temporal tidal hydrodynamics; to quantify this, we analyzed and evaluated tidal asymmetry by phase differences of the principal semi-diurnal lunar constituent M 2 and its first over-tide M 4 . Moreover, we applied the ADCIRC model to quantitatively investigate near- and far-field impacts on tidal variations using the gamma parameter, tidal energy flux, and dissipation rate. Through this study, we found that the tidal regime around the Incheon harbor area in Gyeonggi Bay has changed from ebb- to flood-dominant due to multiple nearby reclamations, in particular to the construction of the Siwha dike. The Saemangeum dike caused near-field de-amplification of M 2 but far-field amplification in the Shandong area of China. In addition to allowing a traditional asymmetry approach using phase difference, analyses based on the gamma parameter and tidal energy variations could distinctly improve spatial understanding of anthropogenic impacts on coastal tidal hydrodynamics.

This study demonstrates a site resource assessment to examine the temporal variation of the current speeds, current directions, turbulence intensities, and power densities for a tidal energy site in the East River tidal strait. These variables were derived from two months of acoustic Doppler velocimeter (ADV) measurements at the design hub height of the Verdant Power Gen5 hydrokinetic turbine. The study site is a tidal strait that exhibits semi-diurnal tidal current characteristics, with a mean horizontal current speed of 1.4 m s−1, and a turbulence intensity of 15% at a reference mean current of 2 m s−1. Flood and ebb flow directions are nearly bi-directional, with a higher current speed during flood tide, which skews the power production towards the flood tide period. The tidal hydrodynamics at the site are highly regular, as indicated by the tidal current time series that resembles a sinusoidal function. This study also shows that the theoretical force and the power densities derived from the current measurements can be significantly influenced by the length of the time window used for averaging the current speed data. Furthermore, the theoretical power density at the site, derived from the current speed measurements, is one order of magnitude greater than that reported in the U.S. national resource assessment. This discrepancy highlights the importance of conducting site resource assessments based on measurements at the tidal energy converter device scale.

In spring 2013, 33 repeat shipboard Acoustic Doppler Current Profile (ADCP) surveys were conducted to measure the tidal current in the Qiongzhou Strait (QS). The major tidal currents and the residual current along a section across the QS were estimated using a modified tidal harmonic analysis method based on the inverse technique. A simple simulation and comparisons with previous observations demonstrated that the tidal currents estimated using the modified tidal harmonic analysis method are reasonable, and this method was able to control the magnitude and deviation of the estimation error. The direction of the major axis of tidal current ellipses is generally along the strait. Diurnal tidal constituents are dominant among the five tidal current constituents (K1, O1, M2, S2, and MSf). The ratio of the amplitudes of O1, K1, M2, S2, and MSf, averaged along the section across the QS is 1:0.79:0.42:0.27:0.29. The residual current along the entire section is all westward; the averaged velocity over the section is 6.0±2.1 cm s−1; the associated volume transport through the section is −0.065 ± 0.046 Sv (Sv = 106 × m3 s−1), in which the second value denotes the uncertainty of first value. Dynamic analysis indicates that tidal current activity is more dominant than mean current and eddy activity, and tidal rectification and sea level difference between two entrances of the QS are important in maintaining the residual current through the strait.

Predicting tides in upstream reaches of rivers is a challenge, because tides are highly nonlinear and nonstationary, and accurate short-time predictions of river flow are hard to obtain. In the St. Lawrence fluvial estuary, tide forecasts are produced using a one-dimensional model (ONE-D), forced downstream with harmonic constituents, and upstream with daily discharges using 30 day flow forecasts from Lake Ontario and the Ottawa River. Although this operational forecast system serves its purpose of predicting water levels, information about nonstationary tidal-fluvial processes that can be gained from it is limited, particularly the temporal changes in mean water level and tidal properties (i.e., constituent amplitudes and phases), which are function of river flow and ocean tidal range. In this paper, a harmonic model adapted to nonstationary tides, NS_TIDE, was applied to the St. Lawrence fluvial estuary, where the time-varying external forcing is directly built into the tidal basis functions. Model coefficients from 13 analysis stations were spatially interpolated to allow tide predictions at arbitrary locations as well as to provide insights into the spatiotemporal evolution of tides. Model hindcasts showed substantial improvements compared to classical harmonic analyses at upstream stations. The model was further validated by comparison with ONE-D predictions at a total of 32 stations. The slightly lower accuracy obtained with NS_TIDE is compensated by model simplicity, efficiency, and capacity to represent stage and tidal variations in a very compact way and thus represents a new means for understanding tidal rivers.

[1] Tidal rivers feature oscillatory and steady gradients in the water surface, controlled by interactions between river flow and tides. The river discharge attenuates the tidal motion, and tidal motion increases tidal-mean friction in the river, which may act as a barrier to the river discharge. Time series of tidal water level amplitudes at five gauge stations along the River Mahakam in Indonesia, and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis. Temporal variations in tidal damping coefficients for quaterdiurnal, semidiurnal, and diurnal tidal species were quantified from the observed amplitude profiles. The analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb. Wavelet cross-correlations between surface levels yielded empirical estimates of wave numbers. An empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the Mahakam. The subtidal friction is decomposed into contributions from the river flow only, from river-tide interaction, and from tidal asymmetry. Even for high river flow and low tidal velocity, river flow enhances friction attributed to river-tide interaction, causing subtidal water level setup. A simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream, with a relatively good agreement between predictions and observations. The explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity, explaining the complex behavior of tidal-mean surface level profiles.

[1] Reliable estimation of river discharge to the ocean from large tidal rivers is vital for water resources management and climate analyses. Due to the difficulties inherent in measuring tidal-river discharge, flow records are often limited in length and/or quality and tidal records often predate discharge records. Tidal theory indicates that tides and river discharge interact through quadratic bed friction, which diminishes and distorts the tidal wave as discharge increases. We use this phenomenon to develop a method of estimating river discharge for time periods with tidal data but no flow record. Employing sequential 32 day harmonic analyses of tidal properties, we calibrate San Francisco (SF), CA tide data to the Sacramento River delta outflow index from 1930 to 1990, and use the resulting relationship to hindcast river flow from 1858 to 1929. The M2 admittance (a ratio of the observed M2 tidal constituent to its astronomical forcing) best reproduces high flows, while low-flow periods are better represented by amplitude ratios based on higher harmonics (e.g., M4/M22). Results show that the annual inflow to SF Bay is now 30% less than before 1900 and confirm that the flood of January 1862 was the largest since 1858.

The aim of this study is to understand the effects of friction and advection in the hydrodynamics of a two-inlet coastal lagoon, Santa Maria La Reforma, in Northwest Mexico. A vertically integrated numerical model is used to describe sea level variations and tidal currents, and to study the dynamics inside the system. Observed sea level and current measurements were used to calibrate the model. Results show a ∼90 min phase lag of the tidal signal in the center of the system with respect to both inlets. Tidal currents greater than 1.0 m s −1 were recorded and modeled at both inlets. The sea level in the lagoon shows one-quarter of period of M 2 out of phase (∼3 h) with respect to the velocity. Bottom friction generated the greatest M 4 harmonic and largest tidal asymmetries at the narrowest section of the lagoon, ∼35 km away from the inlets. The tidal momentum balance along the main axis of the lagoon was dominated by pressure gradient and friction, describing a quasi-standing tidal wave in currents and in amplitude. This behavior resulted from waves traveling in opposite directions from the two tidal inlets, causing constructive interference in elevation but destructive interference inflow.

Bathymetric effects on tidal currents are investigated at Main Pass, which is the primary inlet of Mobile Bay, Alabama. A 12-h ship-mounted ADCP survey, which covered nearly one-half of the diurnal tide during flood conditions, included 24 repetitions. The resulting velocity data demonstrate significant tidal variability in the horizontal and vertical current structure between the ship channel and the shoals. The diurnal tidal flows, the dominant tidal forcing, are 72° (4.8 h) ahead of the water level throughout shallower areas of Main Pass, indicating near-standing wave conditions. Moving across the mouth, a phase lag (5.37° or 20 min) develops with the deep channel tidal currents lagging the shoal region. The vertical tidal structure is also modified across the mouth where near-bottom flows change their direction first in the ship channel, while near-surface flows change their direction first over the western shoal. This may be related to the seaward pressure gradient associated with the relatively large (~1715 m 3 /s) freshwater discharge or the discharge interaction with a nearby opening, Pass-aux-Herons. Current magnitudes over the shoals and in the ship channel vary by as much as 1 m/s. Flows at the east side of Main Pass, close to Mobile Point, behave oppositely to those in the rest of the transect during the survey. This inconsistent flow pattern is caused by an anticyclonic eddy that is triggered by flow separation at Mobile Point.

A methodology for assessment of the potential impacts of extraction of energy associated with astronomical tides is described and applied to a site on the Beaufort River in coastal South Carolina, USA. Despite its name, the site features negligible freshwater inputs; like many in the region, it is a tidal estuary that resembles a river. A three-dimensional, numerical, hydrodynamic model was applied for a period exceeding a lunar month, allowing quantification of harmonic constituents of water level and velocity, and comparison to values derived from measurements, recorded at a location within the model domain. The measurement campaign included surveys of bathymetry and velocity fields during ebb and flood portions of a tidal cycle for model validation. Potential far-field impacts of a generic tidal energy conversion device were simulated by introducing an additional drag force in the model to enhance dissipation, resulting in 10–60% dissipation of the pre-existing kinetic power within a flow cross-section. The model reveals effects of the dissipation on water levels and velocities in adjacent areas, which are relatively small even at the 60% dissipation level. A method is presented to estimate the optimal vertical location for the energy conversion device and the potential power sacrificed by moving to a different altitude.

Holman, R.A. and Stanley, J., 2013. cBathy Estimation in the Mixed Wave-Current Domain of a Tidal Estuary. The last decade has seen considerable progress in the development of algorithms for nearshore bathymetry estimation based on celerity observations of ocean surface waves. This work has evolved into a robust algorithm called cBathy which produces operational results that compared well to 16 CRAB surveys at Duck, NC, collected over two years (bias 0.19 m, rmse 0.51 m over a 1000 by 500 analysis region). However, cBathy is presently based on a wave dispersion implementation that neglects the effects of currents. In May 2012, cBathy was tested in a tidal inlet environment at the RIVET experiment at New River Inlet, NC, a location with a complex ebb tidal delta and strong tidal currents. Initial analyses without Doppler correction to the algorithm show up to 50% overestimation of depth excursions at tidal time scales, presumably associated with wave-current effects. Data from in situ instruments ...

Shelf tidal stream velocities are accelerated by nearshore geographic features, such as headlands and islands. In the search for sustainable forms of electrical energy generation, such locations may become attractive for tidal stream power developments. For some prospective tidal stream energy sites, however, little is known about the intricacies of the local tidal dynamics: knowledge which is crucial to the understanding of the resource and the potential environmental consequences of its extraction. In this paper a two dimensional hydrodynamic model is used to investigate a complex tidal strait, the Pentland Firth (Scotland, UK). This channel, considered one of the most promising tidal stream energy sites in the world, is set for extensive development over the coming decade. We show that the tidal stream velocities that regularly occur within, and up to 20-km beyond the Pentland Firth, are accelerated above that of a free shallow-water wave. The primary mechanism for these accelerations is hydraulic in nature, associated with a large shift in tidal phase. Tidal streaming around headlands and islands further promotes conversion from potential to kinetic energy. We calculate a mean energy flux into the Pentland Firth from the North Atlantic Ocean of 8.97 GW. Changes in tidal amplitude and phase along the strait are associated with a reduction in energy flux, such that the majority (∼60%) of the incoming energy is lost within the Pentland Firth through bed friction. Localised geographical factors complicate the tidal dynamics of the Pentland Firth, therefore detailed modelling is the only means with which to accurately characterise the environmental conditions in this channel. Of more general oceanographic significance, this example shows that high levels of tidal energy dissipation are associated with energetic tidal straits. Energy losses in these straits may contribute significantly to balancing the energy flux onto the continental shelf from the deep seas.

Tidal asymmetry is a key factor in the geomorphology of many coastal lagoons. Whilst tidal asymmetry in semi-diurnal tidal regimes has been extensively studied, its occurrence in mixed tidal regimes is less well understood, and has a number of unique causes and characteristics. Tidal phase duration analysis and least squares harmonic analysis have been used to study the temporal and spatial nature of asymmetry in both offshore and coastal lagoon tides at the Murray Mouth in south-eastern Australia. GIS analysis of bathymetric survey data has been used to study the roles of lagoon bathymetry on tidal distortion. Tidal asymmetry in the Murray Mouth coastal lagoon results from frequency relationships between major astronomical driving tides as well as bathymetry-induced tidal transformations. The frequency difference between the K1 and S2 tides produces an important 6-monthly ebb/flood-dominant asymmetry cycle in the incoming oceanic tides, whilst phase relationships between the K1 and K2 tides contribute to persistent asymmetry. The use of standard relationships between the M2 and M4 tides as asymmetry indicators is shown to be invalid for this mixed tidal regime. In this shallow, microtidal system, the impacts of bathymetry on tidal asymmetry within the lagoon are profound, with inlet and channel configurations identified as the most important controlling factors. The results of this study may inform the strategic management of tidal inlets in mixed tidal regimes, such as the Murray Mouth, that are subject to intermittent or long-term constriction.

The Bay of Fundy in eastern Canada has the highest tides in the world. Harnessing the tidal energy in the region has long been considered. In this study, the effects of tidal in-stream energy extraction in the Minas Passage on the three-dimensional (3D) tidal circulation in the Bay of Fundy (BoF) and the Gulf of Maine (GoM) are examined using a nested-grid coastal ocean circulation model based on the Princeton Ocean Model (POM). The nested-grid model consists of a coarse-resolution (~4.5 km) parent sub-model for the GoM and a high-resolution (~1.5 km) child sub-model for the BoF. The tidal in-stream energy extraction in the model is parameterized in terms of nonlinear Rayleigh friction in the momentum equation. A suite of numerical experiments are conducted to determine the ranges of extractable tidal in-stream energy and resulting effects on the 3D tidal circulation over the Bay of Fundy and the Gulf of Maine (BoF-GoM) in terms of the Rayleigh friction coefficients. The 3D model results suggest that the maximum energy extraction in the Minas Passage increases tidal elevations and tidal currents throughout the GoM and reduces tidal elevations and circulation in the upper BoF, especially in the Minas Basin. The far-field effect of tidal energy extraction in the Passage on the 3D tidal circulation in the BoF-GoM is examined in two cases of harnessing tidal in-stream energy from (a) the entire water column and (b) the lower water column within 20 m above the bottom in the Passage. The 3D model results demonstrate that tidal in-stream energy extraction from the lower water column has less impact on the tidal elevations and circulation in the BoF-GoM than the energy extraction from the whole water column in the Minas Passage.

The nonlinear distortion of the astronomic tide in the Lower St. Johns River is investigated. Computed tidal elevations are analyzed at various locations within the Lower St. Johns River. The modeling approach first evaluates the boundary condition applied at the open ocean with regards to it providing a complete description of the tidal elevation, followed by numerical experimentation and a tidal constituent analysis that examines the effects of finite wave amplitude, advection, and bottom friction towards distorting the tide as it propagates upriver. The distortions caused by each nonlinear source are presented in both the time and frequency domains. Analysis at observation stations reveals a river tide with more coastal characteristics near the mouth and with more considerable distortion upriver. The spectroscopy of the astronomic tide for the Lower St. Johns River is established in terms of a custom set of tidal constituents.

Tidal stream systems make use of the kinetic energy of tidal movement to power turbines, in a similar manner to the way in which windmills extract energy from the wind. This method of renewable energy generation is gaining in popularity because of the high predictability of tides, the lower investment needed for tidal turbines, and the lower ecological impact, as compared with other schemes involving barrages or lagoons. It is generally considered that a mean spring peak tidal current of at least 2 m/s is required for tidal stream power to be worth exploiting. In the Severn Estuary, the peak tidal current exceeds 2 m/s, with a corresponding minimum depth of greater than 20 m, and it is thereby a potential location for tidal stream power. Previous studies cannot provide the detailed and precise distribution of tidal stream power in this estuary, and it has therefore been deemed appropriate to undertake a numerical model assessment of tidal stream energy resources in the Severn Estuary. In the present study, an existing finite volume numerical model has been refined, with the inclusion of an algorithm for computing the power density and its mean value across the estuary. The refined model has also been validated against (a) measured tidal currents at four sites, using the method of harmonic analysis; (b) measured tide level hydrographs at five tide gauging stations, taken over a 15-day period and covering the full spring—neap cycle; and (c) in situ velocity measurements at two sites. Finally, the validated model has been used to assess the potential tidal stream energy resources without and with the Severn Barrage, including the distributions of the mean power density over a spring—neap cycle in the Severn Estuary and a detailed assessment of the tidal stream energy resources at two sites near the coast of South Wales. The model predictions indicate that at two sites, the annual power output with the presence of barrage could be reduced by 70—80 per cent, as compared with the value without any structure.

Tidal stream turbines are exploited in regions of high tidal currents. Such energy extraction will alter the hydrodynamics of a tidal region, analogous to increasing the bed friction in the region of extraction. In addition, this study demonstrates that energy extracted with respect to tidal asymmetries due to interactions between quarter (M4) and semi-diurnal (M2) currents will have important implications for large-scale sediment dynamics. Model simulations show that energy extracted from regions of strong tidal asymmetry will have a much more pronounced effect on sediment dynamics than energy extracted from regions of tidal symmetry. The results show that energy extracted from regions of strong tidal asymmetry led to a 20% increase in the magnitude of bed level change averaged over the length of a large estuarine system, compared with energy extracted from regions of tidal symmetry. However, regardless of the location of a tidal stream farm within a tidal system, energy extraction reduces the overall magnitude of bed level change in comparison with non-extraction cases. This has practical application to many areas surrounding the UK, including the Irish Sea and the Bristol Channel, that exhibit strong tidal currents suitable for exploitation of the tidal stream resource, but where large variations in tidal asymmetry occur.

Tidal circulation and river plume dynamics in shallow-water estuarine systems with large intertidal zones are complex. Strong asymmetries in tidal currents and stratification often occur in the intertidal zones and subtidal channels over a tidal cycle. The Skagit River is the largest estuary with respect to the discharge of a significant amount of freshwater and sediment into Puget Sound, Washington. It consists of a large intertidal zone with multiple tidal channels near the mouth of the estuary. To simulate the tidal circulation and salinity stratification accurately in the intertidal region, an unstructured grid numerical model with wetting–drying capability and the capability to accurately represent the bathymetry of tidal flats and the geometry of shallow distributary channels is necessary. In this paper, a modeling study for the Skagit River estuary using a three-dimensional unstructured grid, finite-volume coastal ocean model (FVCOM) supported by high-resolution LIDAR data is presented. The hydrodynamic model was validated with observed water surface elevation, velocity, and salinity data over spring and neap tidal cycles under low-river-flow and high-river-flow conditions. Wetting and drying processes in the intertidal zone and strong stratification in the estuary were simulated successfully by the model. Model results indicate that the Skagit River estuary is a highly stratified estuary, but destratification can occur during flood tide. Tides and baroclinic motion are the dominant forcing in the Skagit River estuary, but strong wind events can affect the currents in the intertidal zone significantly. Preliminary analysis also indicated that the salinity intrusion length scale is proportional to the river flow to the −¼ power.

Seafloor gravity and pressure measurements for 4D reservoir monitoring require precise models of the time-varying tidal signals. Current seafloor instrumentation can resolve [Formula: see text] in time-lapse gravity differences and [Formula: see text] [Formula: see text] in pressure. To verify model accuracy, a seafloor gravimeter and pressure gauge were operated continuously for [Formula: see text] next to the Troll A gas platform in the North Sea (60.64227° north, 3.72417° east) at a depth of [Formula: see text]. The seafloor gravity and pressure time series were filtered and corrected with estimates from the tidal model, which predicts the solid earth tide, ocean loading, and direct gravitational attraction of the varying water level. The rms difference between the observed tidal gravity signal and the prediction is about [Formula: see text] during periods when there are no surface storms. A slight difference is observed for the direct attraction of the water overhead as computed from the tidal prediction versus that computed from direct seafloor pressure measurements when the entire [Formula: see text] record is analyzed; it shows an rms difference of [Formula: see text], equivalent to [Formula: see text] of water-height variation, yielding a gravity effect of [Formula: see text]. We conclude that existing theoretical tide models in combination with in situ pressure records are sufficiently precise for correcting time-lapse gravity observations.

Tidal currents within many estuaries are stronger than on the adjacent continental shelf. Estuarine tidal influence extends onto the shelf elevating tidal amplitudes above ambient shelf levels over a region outside the estuary. In this paper, a kinematic theory that describes tidal flow in these estuary–shelf tidal interaction zones is derived and tested. Using these results, tidal current amplitudes outside estuaries are estimated and the range and intensity of estuarine tidal influence is characterized. The estimates for the tidal current amplitudes (utide) of the dominant constituent are appropriate for linear or weakly nonlinear systems with predominantly barotropic tides; the ratio of tidal height to water depth is small (η/h≪1) in linear or weakly nonlinear regimes. Within tidal interaction zones, the tidal current amplitude is composed of an ambient shelf part (ua) and an estuary-induced part (ue). The characteristic shelf amplitude far from the estuary is used to set ua. Continuity arguments indicate that ue (averaged over a control volume arc centered on the mouth with radius r and a swath angle of γπ) approximately equals the ratio of the tidal volume flux through the mouth (Vm) and the cross-sectional area of any control volume arc ( u e ≈ V m / γ π r h ¯ ) . This approximation holds where the squared product of the tidal wave number and radial distance is small: (kr)2≪1. For a shelf with constant slope α and small coastal wall depth, the arc-averaged depth is h ¯ ≈ sr (where s=2α/pi for γ=1). For this shelf bathymetry, ue decays with squared radial distance from the estuary mouth. Theoretical predictions are consistent with observed tidal current amplitudes outside the Delaware Bay and Block Island Sound. In both test cases, the estimated and observed amplitudes exhibit an r−2 dependence and decay over a similar distance. The relative importance of estuarine tidal influence is assessed with the tidal interaction index (Ti=ue/ua). The intensity of estuarine influence is characterized by the value of Ti at the mouth (Tim). The extent of an estuary–shelf tidal interaction zone is measured by the interaction radius ri (where Ti=1) and by r∞ (where Ti=0.1). These metrics are used to compare the tidal interaction zone characteristics for the Delaware Bay, Block Island Sound, several other major estuaries, and a small tidal inlet. The kinematic theory can be applied outside other estuaries where only limited tidal information is available or used to interpret observed patterns in tidal amplitudes and characterize the degree of estuarine influence.

The synthetic tidal parameters with high spatial resolution for gravity over China and its neighbor area are constructed with Earth’s tidal model and ocean tide loading calculated using TPXO7 global ocean tide model as well as tidal data over China seas. The comparison between synthetic parameters and ones observed by spring gravimeters at some seismic network stations and Hong Kong station and one observed by super-conducting gravimeter at Wuhan station shows that the average differences in amplitude factors and phases are smaller than 0.005 and 0.5° respectively; and that the discrepancies between observational and synthetic parameters are dependent on gravimetric technique in that the synthetic parameters are in well agreement with the superconducting gravimetric observations. This also indicates that the synthetic result is a good estimation for tidal gravity, and the numerical results in the present paper not only can provide ground and space gravimetry such as absolute gravimetry with correction model of tidal gravity, but also provide effective tidal parameters over areas where no observation is carried out.

This study is based on a series of numerical modeling experiments to understand the tidal circulation in the Kangjin Bay (KB). The tidal circulation in the KB is mostly controlled by the inflow from two channels, Noryang and Daebang which introduce the open ocean water into the northern part of the KB with relatively strong tidal current, while in the southern part of the KB, shallowest region of the entire study area, weak tidal current prevails. The model prediction of the sea level agrees with observed records at skill scores exceeding 90 % in terms of the four major tidal constituents (M2, S2, K1, O1). However, the skill scores for the tidal current show relatively lower values of 87, 99, 59, 23 for the semi-major axes of the constituents, respectively. The tidal ellipse parameters in the KB are such that the semi-major axes of the ellipse for M2 range from 1.7 to 38.5 cm/s and those for S2 range from 0.5 to 14.4 cm/s. The orientations of the major-axes show parallel with the local isobath. The eccentricity values at various grid points of ellipses for M2 and S2 are very low with 0.2 and 0.06 on the average, respectively illustrating that the tidal current in the KB is strongly recti-linear. The magnitude of the tidal residual current speed in the KB is on the order of a few cm/s and its distribution pattern is very complex. One of the most prominent features is found to be the counter-clockwise eddy recirculation cell at the mouth of the Daebang Channel.

The tidal flow into an estuary controls the export of pollutants and determines the net flux and redistribution of sediments. To make an assessment of the accuracy of model simulations, a ship-mounted acoustic Doppler current profiler was used to measure the flow into the Firth of Forth near the Edinburgh road bridge during neap and spring tide conditions. A pressure gauge was used to record the tidal elevation and concurrent meteorological data were obtained from local weather sensors. The maximum tidal flux into the estuary during spring tides reached 30 000 m3/s. The observations were simulated using nested versions of the DIVAST depth-averaged tidal model. Good agreement was obtained between the observed and simulated tidal elevations, and also in the magnitude of the computed tidal fluxes. There were, however, sometimes large instantaneous differences between the observed and computed fluxes. An analysis of low-pass sea-level data, atmospheric pressure and wind forcing, suggests that the errors in the flux estimates were due to meteorologically induced shifts in the phase of the tide at the open boundary of the model. Such shifts limit the accuracy that can be obtained by a tidally forced model when the impact of meteorological forcing is not included at the open boundary.

In this paper, we analyse the contribution of tidally induced drift in the surface layer to the overall dynamics of well-mixed tidal basins undergoing drying and flooding. The study area covers the East Frisian Wadden Sea (German Bight, Southern North Sea), which consists of seven tidal basins. The major interest is focused on the tidal basin behind the islands of Langeoog and Spiekeroog and the inlet connecting it with the North Sea. The comparison between theoretical concepts, results from direct observations, and simulations with a numerical model helps to understand the underlying physics controlling the tidal response. The data were collected during the period 1995–1998 and consist of cross-channel ADCP transects. The identification of the dominant spatial patterns and their temporal variability is facilitated by applying an EOF analysis to the data. The numerical simulations are based on the 3-D primitive equation General Estuarine Transport Model (GETM) with a horizontal resolution of 200 m and terrain-following vertical coordinates. We find distinct differences between the temporal variability of the transports near the surface and those in deeper layers of the tidal inlets. The near surface transport is dominated by the tidally induced drift (similar to the Stokes drift), whereas the deeper layer transport is dominated by asymmetries caused by the hypsometric properties of the intertidal basins. These transports, when averaged over a tidal period, have opposite directions and compensate each other. This explains the establishment of a vertical overturning cell: landward motion in the upper layers and seaward motion in the deeper parts of the tidal channels. This vertical circulation cell is also observable in our numerical simulations and shows a clear dependency of the temporal asymmetry in the transport patterns on the local depth. In deep tidal channels, the overall properties of the tidal signal show a clear ebb dominance, whereas in the shallow extensions of the channels the transports during flood are larger than during ebb. Although, our research area can be characterized as a well mixed estuary, baroclinicity associated with the fresh water flux from the coast can substantially affect vertical overturning.

A three-dimensional, primitive-equation model is used to simulate the barotropically-forced semidiurnal tidal currents in the New York Bight (NYB) and Block Island Sound (BIS). Model tidal velocity ellipses are verified at historical current meter locations and with measurements from acoustic Doppler current profilers (ADCPs) and HF radar (CODAR). The model reproduces well the regional tidal flow pattern as well as the vertical tidal velocity structure. The model misfits typically are 2–4 cm/s in amplitude and 5–7° in orientation. Through comprehensive skill assessment, the model's capacity of simulating the three-dimensional barotropic tidal currents is clearly demonstrated. Moreover, it is shown that the integrity of HF radar measurements can be assured by verifying with model tidal ellipses.

Tidal energy flux and dissipation in the Chesapeake Bay are examined using a three-dimensional baroclinic model. The model currents are validated by a comparison with observed tidal current ellipses collected during previous field surveys. The model elevations are validated against sea-level records collected at tidal gauges. The baroclinic model produces more accurate predictions for sea-level heights and tidal currents than the tidal models which do not consider the effects of stratification. The averaged rms differences between the observed and modeled surface elevations are 3.4 cm for the M2 constituent and 0.7 cm for the K1 constituent. The averaged rms differences between the observed and modeled tidal current ellipses are 2.6, 2.1 cm s−1, 5.1° and 21.7° for the semi-major, semi-minor axes, inclination and phase of the ellipses, respectively. The total amount of tidal energy flux entering the Bay mouth is found to be 188 MW, 88% of which is associated with the M2 component. Dissipation of tidal energy is highly non-uniform in the Chesapeake Bay. 40% of the energy dissipation occurs in four topographic hotspots: the Bay mouth region around the headland of Delmarva Peninsula, the region near the Rappahannock sill, the constriction near the Bay Bridge and the constriction north of Baltimore.

Current measurements obtained from a sparse array of moorings on the Ross Continental Shelf during the 1980 and 90s are analysed for their tidal constituents. Diurnal (K1 and O1) tides are about five times stronger than semi-diurnal tides, and are strongest near the shelf break in agreement with recent model results. At some energetic locations the diurnal tides are significantly weaker at depth, presumably due to bottom friction. Complex demodulation analysis shows that at some locations the tidal response varies significantly in time. This time variability rises markedly above the noise floor expected from the spectral continuum between tidal bands, and does not scale with tidal bandwidth as would be expected of broadband noise. Further its magnitude is generally proportional to the associated tidal constituent, indicating that it is truly a varying tidal response. Space scales of this tidal instability were not resolved but are less than 150 km, while time scales appear mostly seasonal to interannual. The rms magnitude of the unstable response can be 1/3 of a given component’s mean magnitude, placing substantial limits on the ability of prognostic or even data assimilative models to accurately predict these tides for any specific time period.

A s-coordinate three-dimensional model, regional ocean modeling system (ROMS), was implemented in the Western Iberian region ranging from the coast to 11°W aiming high-resolution tidal simulations for an homogeneous ocean. The features for tidal heights and ellipses for the principal constituents, M 2 , S 2 , N 2 , K 2 , K 1 , O 1 , P 1 and Q 1 , were imposed at the boundaries of the model. A tidal analysis for heights and tidal currents was done allowing to calculate two-dimensional distribution of amplitudes and three-dimensional structure of tidal currents. The amplitudes and phases for heights agree with previous results and observations, showing a good precision on the tidal propagation in the interior of the domain. Tidal kinetic energy is dominated by the semi-diurnal components, mainly M 2 , and increases on the shelf. Over the Lisbon Promontory the diurnal component K 1 is however the second more energetic harmonic. Vertical variation of tidal ellipse parameters evidences the different structure of semi-diurnal and diurnal tidal components, as well as differences between the open sea and shelf tidal circulation.

Portland Bill (Dorset, UK) is a promising site for tidal stream energy exploitation; it combines high tidal stream velocities around the headland with a location closer to population centres than other proposed sites. To better estimate available energy resources at the site, a two-dimensional tidally driven hydrodynamic numerical model of Portland Bill was developed using the TELEMAC system, with validation using tidal elevation measurements and tidal stream diamonds from Admiralty charts. The results of the model were used to produce a time series of the tidal stream velocity over the simulation period and may be used in future work to optimize the location of turbine arrays at the site.

The tidal characteristics of Maputo Bay (a bay located in South part of Mozambique) were assessed in this work through the implementation of a numerical model (SIMSYS2D) and exploration of its numerical results, and by the analysis of observed time series of free surface elevations in Maputo Harbor. The calibration of the numerical model was carried out based on time series of tidal currents and free surface elevation, which were collected at Maputo Harbor, Baixo Ribeiro and Portuguese Island. By means of the model results, important harmonic constants of the tidal heights and currents, as well as the form factor, were computed. These results have revealed that there is a phase delay and an increase in amplitude of the major constituents as the tide propagates to the inshore zone. Based on these results, the tidal ellipses in whole Maputo Bay were also computed, which showed the pattern of the tidal currents. The hydrodynamics of the Maputo Bay under extreme tidal conditions were also analyzed (during the largest spring tide and smallest neap tide). The phase difference between tidal heights and currents revealed that there are no maximum fluxes of energy in most of Maputo Bay and that the mean tidal current (residual) may be different from zero in this system.

Observational data, high-resolution numerical modelling results and a simple analytical theory are combined in this paper to demonstrate the dependence of the volume transports through tidal inlets on topographical or morphological parameters of a Wadden Sea system. The area of interest covers the East Frisian Wadden Sea and consists of seven weakly connected tidal basins. The observations include time series of tidal gauge data and surface currents measured at a pile station in the backbarrier basin of the island Langeoog, as well as several ADCP transects in the Accumer Ee tidal inlet. The numerical simulations are based on the 3-D primitive equation General Estuarine Transport Model (GETM) with a horizontal resolution of 200 m and terrain following vertical coordinates. The model is forced at its open boundaries with sea-level data from an operational model for the German Bight (German Hydrographic Office). The simple theoretical concepts presented illustrate the effect of topography (hypsometry) in the tidal basins on the temporal variability of the exchange of water. This topographic control is effectuated through the bottom slope in the areas prone to drying and flooding. For our study area it takes about twice as long from slack water to maximum flood current than from slack water to maximum ebb current. The underlying physics of this signal modulation from a more or less harmonic forcing at the open-sea boundary and the quantification of the contributing physical processes are the major results of this paper. Estimates based simply on volume conservation are consistent with observations and results from numerical modelling, but they do not completely capture the actual non-linear tidal response. Our analysis shows that at least during part of the tidal cycle characteristic topographic parameters of the inlet/bay system have a major impact on the rate of exchange of waters between the Wadden Sea and the open ocean. This impact is especially strong during the transition between flood and ebb conditions. The possible morphodynamic responses are also addressed focusing on some common (“universal”) topographic features in seven tidal basins.

A non-linear hydrodynamic model is used to describe the tidal dynamics of Shark Bay, Western Australia. The model is forced by tidal elevations generated by M 2 , S 2 , K 1 and O 1 constituent data at the open boundaries. The absence of suitable boundary data required a ‘calibration’ of the boundary condition against the known constituent data from within the model domain. The model provides a good match to the available field data, and allows the surface-level and current response to be resolved over the entire domain. Due to a near quarter-wave resonance of the semi-diurnal tide along the eastern Hopeless Reach, which increases the semi-diurnal tide by a factor of 2, the tidal characteristics on each of the Reaches are different: on the eastern Hopeless Reach the tides are mainly semi-diurnal while on the western Freycinet Reach the tides are mainly diurnal. The tidal range is also higher along Hopeless Reach. Tidal harmonics, generated by non-linearity, are important in the shallow regions. The tidal wave is shown to propagate as a progressive wave into the Bay. Substantial phase-lag, attenuation and dissipation occur over the Faure Sill, a major shallow region of the eastern reach of the Bay. Non-linear generation of the M 4 and MS 4 tides is also significant in this region. Depth-averaged residual currents are presented, which show a tidally generated circulation that is enhanced in regions of complex topography. Estimates of tidal dissipation indicate that although the total dissipation is small on a global scale, the areal average is comparable with the Gulf of Carpentaria and approximately one-quarter of the value estimated for the Patagonian Shelf.

(ROMS), which is described in the next section. The model results are given and compared with the existing observations in the results section. Implications of the model results are discussed in the final section of the paper. Abstract: In certain regions of the Southern Ocean, tidal energy is believed to foster the mixing of different water masses, which eventually contribute to the formation of deep and bottom waters. The Ross Sea is one of the major ventilation sites of the global ocean abyss and a region of sparse tidal observations. We investigated M 2 tidal dynamics in the Ross Sea using a three-dimensional sigma coordinate model, the Regional Ocean Model System (ROMS). Realistic topography and hydrography from existing observational data were used with a single tidal constituent, the semi-diurnal M 2 . The model fields faithfully reproduced the major features of the tidal circulation and had reasonable agreement with ten existing tidal elevation observations and forty-two existing tidal current measurements. The differences were attributed primarily to topographic errors. Internal tides were generated at the continental shelf/slope break and other areas of steep topography. Strong vertical shears in the horizontal velocities occurred under and at the edges of the Ross Ice Shelf and along the continental shelf/slope break. Estimates of lead formation based on divergence of baroclinic velocities were significantly higher than those based on barotrophic velocities, reaching over 10% at the continental shelf/slope break.

A 3D finite-element numerical model is applied to the Adriatic Sea to simulate its tidal motions. This fully nonlinear model includes a free surface, very realistic topography, and an advanced turbulence closure. Comparison with available tidal elevations at coastal stations and with tidal ellipses at a few locations in the open sea demonstrates that the model simulations are highly accurate. The results are then used to determine the 3D distribution of the tidal residual currents. D 2002 Published by Elsevier Science B.V.

We examine tidal asymmetry in a 100-km long coastal plain estuary, a 15-km long tidal creek closed at the end, and a small side channel of a coastal plain estuary closed at low water. Current meter and water depth data were harmonically analyzed for M2 and the M4 and M6 overtide. The results are displayed in a plot of tidal current versus water level and the effects of the M2, M2+M4, and M2+M4+M6 are compared in order to show how overtides affect tidal asymmetry in the different systems. The long estuary showed a gradual increase in tidal current asymmetry. The current takes on a more progressive nature as it goes into the estuary, as indicated by increasing lags between high or low water and the corresponding slack water. On the other hand, the tidal creek has its reflection point at the head, a relatively short distance from the observations, which reflects the incident tidal wave more efficiently. The tidal creek has a high salt marsh which is covered only an hour or so before high water. Since its intertidal areas flood and drain near the time of high water, maximum flood and ebb currents occur a short time before and after high water slack throughout the tidal creek. Most of the tidal energy is dissipated at the end of the creek where M6/M2 of the tidal current almost doubles. The small side channel has tidal flats that become covered soon after the time of low water. The relative time of maximum flood and ebb currents occurs much closer to the time of low-water-slack, which contrasts significantly to the timing in the tidal creek channel surrounded by high salt marsh.